Prof. Dr.-Ing. Dieter Brillert

Turbomachinery
University of Duisburg-Essen

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  • Experimental investigation of centrifugal flow in rotor–stator cavities at high reynolds numbers > 108
    Schröder, T.R. and Schuster, S. and Brillert, D.
    International Journal of Turbomachinery, Propulsion and Power 6 (2021)
    The designers of radial turbomachinery need detailed information on the impact of the side chamber flow on axial thrust and torque. A previous paper investigated centripetal flow through narrow rotor–stator cavities and compared axial thrust, rotor torque and radial pressure distribution to the case without through-flow. Consequently, this paper extends the investigated range to centrifugal through-flow as it may occur in the hub side chamber of radial turbomachinery. The chosen operating conditions are representative of high-pressure centrifugal compressors used in, for example, carbon capture and storage applications as well as hydrogen compression. To date, only the Reynolds number range up to Re = 2 · 107 has been investigated for centrifugal through-flow. This paper extends the range to Reynolds numbers of Re = 2 · 108 and reports results of experimental and numerical investigations. It focuses on the radial pressure distribution in the rotor–stator cavity and shows the influence of the Reynolds number, cavity width and centrifugal mass flow rate. It therefore extends the range of available valid data that can be used to design radial turbomachinery. Additionally, this analysis compares the results to data and models from scientific literature, showing that in the higher Reynolds number range, a new correlation is required. Finally, the analysis of velocity profiles and wall shear delineates the switch from purely radial outflow in the cavity to outflow on the rotor and inflow on the stator at high Reynolds numbers in comparison to the results reported by others for Reynolds numbers up to Re = 2 · 107. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstract10.3390/ijtpp6020013
  • Experimental investigations on the pressure fluctuations in the sealing gap of Dry gas seals with embedded pressure sensors
    Luo, J. and Brillert, D.
    Journal of Engineering for Gas Turbines and Power 143 (2021)
    Dry gas-lubricated noncontacting mechanical seals (DGSs), most commonly found in centrifugal compressors, prevent the process of gas flow into the atmosphere. Especially when high speed is combined with high pressure, DGS is the preferred choice over other sealing alternatives. Even though the noncontacting seal is proved reliable, the ultrathin gas film can still lead to a host of potential problems due to possible contact. In order to investigate the flow field in the sealing gap and to facilitate the numerical prediction of the seal performance, a dedicated test facility is developed to carry out the measurement of key parameters in the gas film. Gas in the sealing film varies according to the seal inlet pressure, and the thickness of gas film depends on this fluctuated pressure. In this paper, the test facility, measurement methods, and the first results of static pressure measurements in the sealing gap of the DGS obtained in the described test facility are presented. An industry DGS with three-dimensional grooves on the surface of the rotating ring, where experimental investigations take place, is used. The static pressure in the gas film is measured, up to 20 bar and 8100 rpm, by several high-frequency ultraminiature pressure transducers embedded into the stationary ring. The experimental results are discussed and compared with the numerical model programed in MATLAB (Luo, J., Dohmen, H. J., and Benra, F. K., 2018, "Coupled Thermal-Structural-Fluid Numerical Analysis of Gas Lubricated Mechanical Seals,"ASME Paper No. GT2018-75458), the characteristic and magnitude of which have a good agreement with the numerical simulations. It suggests the feasibility of measuring pressure profiles of the standard industry DGS under pressurized dynamic operating conditions without altering the key components of the seal, and thereby affecting the seal performance. Copyright © 2021 by ASME.
    view abstract10.1115/1.4049662
  • Proof of concept for a novel interstage injection design in axial compressors
    Doerr, T. and Braun, S. and Schuster, S. and Brillert, D.
    Journal of Engineering for Gas Turbines and Power 143 (2021)
    A common technique to increase the thermal efficiency and the power output of gas turbines is to inject water upstream of the compressor section. Through the evaporation of the water throughout the compressor, an isothermal process is approached. A recently developed technology for this enhanced process is interstage injection in which water is injected directly between the stages. One advantage of this over wet compression is the avoidance of icing, since the local temperatures at the injection positions are already above melting point. Moreover, stage characteristics and load distribution can be rearranged within the compressor by individually adjusting the injection amount in different stages. However, there is little practical understanding of this process, and suitable injection methods have still to be found. This paper therefore demonstrates the implementation of a novel technology of interstage injection in an axial compressor test rig whereby twin jet nozzles are integrated directly into the trailing edge of the first stator row to deliver a homogenous spray over the entire radial span. Due to the resultant blade complexity, blades are manufactured by selective laser melting (SLM) and subsequently installed in an enhanced four-stage axial compressor. The installed control and measurement principles of the test rig are presented and results demonstrate the functionality of the innovative design. Copyright © 2021 by ASME.
    view abstract10.1115/1.4049306
  • A design tool for supercritical CO2 radial compressors based on the two-zone model
    El Hussein, I.A. and Hacks, A.J. and Schuster, S. and Brillert, D.
    Proceedings of the ASME Turbo Expo 11 (2020)
    In supercritical Carbon Dioxide (sCO2) cycles, the compressor inlet conditions are selected near the critical point where compressibility factor reaches values as low as 0.2. Consequently, conventional compressor design approaches formulated for fluids obeying the ideal gas law are not verified. Therefore, this paper proposes a design approach for sCO2 radial compressors that consists of a performance prediction model in addition to a set of geometry parameters suitable for radial compressors. The compressor model is based on the two-zone modeling approach, in which the Span and Wagner equation of state for CO2 is integrated. At first, the compressor model is presented in addition to the required correlations. Afterwards, a sensitivity analysis is performed on the model main parameters. Thereafter, a plausibility check is performed against experimentally obtained data. Finally, an overall design approach is proposed and its capability to deliver new geometries is assessed by comparing the tool predictions against the results from a verified CFD code for several test cases. The Comparison shows a maximum deviation of less than 2 percent for the pressure ratio and less than 3.5 percentage points for the efficiency. The results indicate the ability of the proposed approach to predict the performance of sCO2 compressor from correlations that originate from experience with conventional fluids. Additionally, the adopted geometric relations proved its applicability to sCO2 compressors. Copyright © 2020 by ASME; reuse license CC-BY 4.0
    view abstract10.1115/GT2020-15248
  • Experimental investigations on the pressure fluctuations in the sealing gap of dry gas seals with embedded pressure sensors
    Luo, J. and Brillert, D.
    Proceedings of the ASME Turbo Expo 10A-2020 (2020)
    Dry gas lubricated non-contacting mechanical seals (DGS), most commonly found in centrifugal compressors, prevent the process gas flow into the atmosphere. Especially when high speed is combined with high pressure, DGS is the preferred choice over other sealing alternatives. Even though the non-contacting seal is proved reliable; the ultra-thin gas film can still lead to a host of potential problems due to possible contact. In order to investigate the flow field in the sealing gap and to facilitate the numerical prediction of the seal performance, a dedicated test facility is developed to carry out the measurement of key parameters in the gas film. Gas in the sealing film varies according to the seal inlet pressure, and the thickness of gas film depends on this fluctuated pressure. In this paper, the test facility, measurement methods and the first results of static pressure measurements in the sealing gap of the DGS obtained in the described test facility are presented. An industry DGS with three-dimensional grooves on the surface of the rotating ring, where experimental investigations take place, is used. The static pressure in the gas film is measured, up to 20 bar and 8,100 rpm, by several high frequency ultraminiature pressure transducers embedded into the stationary ring. The experimental results are discussed and compared with the numerical model programmed in MATLAB [1], the characteristic and magnitude of which have a good agreement with the numerical simulations. It suggests the feasibility of measuring pressure profiles of the standard industry DGS under pressurized dynamic operating conditions without altering the key components of the seal and thereby affecting the seal performance. Copyright © 2020 ASME
    view abstract10.1115/GT2020-14464
  • Impact of leakage inlet swirl angle in a rotor-stator cavity on flow pattern, radial pressure distribution and frictional torque in a wide circumferential reynolds number range
    Schröder, T.R. and Dohmen, H.-J. and Brillert, D. and Benra, F.-K.
    International Journal of Turbomachinery, Propulsion and Power 5 (2020)
    In the side-chambers of radial turbomachinery, which are rotor-stator cavities, complex flow patterns develop that contribute substantially to axial thrust on the shaft and frictional torque on the rotor. Moreover, leakage flow through the side-chambers may occur in both centripetal and centrifugal directions which significantly influences rotor-stator cavity flow and has to be carefully taken into account in the design process: precise correlations quantifying the effects of rotor-stator cavity flow are needed to design reliable, highly efficient turbomachines. This paper presents an experimental investigation of centripetal leakage flow with and without pre-swirl in rotor-stator cavities through combining the experimental results of two test rigs: a hydraulic test rig covering the Reynolds number range of 4 × 105 ≤ Re ≤ 3 × 106 and a test rig for gaseous rotor-stator cavity flow operating at 2 × 107 ≤ Re ≤ 2 × 108. This covers the operating ranges of hydraulic and thermal turbomachinery. In rotor-stator cavities, the Reynolds number Re is defined as Re = Ωb2/ν with angular rotor velocity Ω, rotor outer radius b and kinematic viscosity ν. The influence of circumferential Reynolds number, axial gap width and centripetal through-flow on the radial pressure distribution, axial thrust and frictional torque is presented, with the through-flow being characterised by its mass flow rate and swirl angle at the inlet. The results present a comprehensive insight into the flow in rotor-stator cavities with superposed centripetal through-flow and provide an extended database to aid the turbomachinery design process. © 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution NonCommercial NoDerivatives (CC BY-NC-ND) license (https://creativecommons.org/licenses/by-nc-nd/4.0/).
    view abstract10.3390/IJTPP5020007
  • Model validation of an euler-based 2D-throughflow approach for multistage axial turbine analysis
    Follner, S. and Amedick, V. and Bonhoff, B. and Brillert, D. and Benra, F.-K.
    Proceedings of the ASME Turbo Expo 2C-2020 (2020)
    In this paper the development and validation of a new meridional throughflow solver for the analysis of multistage axial turbines is presented. The quasi-three-dimensional finite-volume solver named tFlow is based on the inviscid Euler equations. To treat transonic flows with shocks the approximate Riemann solver of Roe for the computation of the inviscid fluxes in combination with the MUSCL approach are used. In the meridional plane turbine blades are numerically modeled by introducing two volume source terms for blade blockage and blade deviation effects. In this contribution four different validation test-cases are discussed. The general fluid solver is validated by analytical solutions of the established Ringleb flow and the simulation of a two-dimensional transonic nozzle flow. In contrast to prior publications [1-3] tFlow uses a different formulation of the blockage effect which is tested using the blockage data of a general convergent-divergent nozzle. Blade deviation effects are validated by comparison with three-dimensional results obtained from the commercial flow solver CFX. The results of tFlow are consistent with the analytical solutions and in case of the blade deviation test-case in good agreement to the three-dimensional results. Compared to fully three-dimensional simulations the developed solver enables faster analyses of multistage axial turbines to evaluate the performance characteristic. © 2020 ASME.
    view abstract10.1115/GT2020-16229
  • Prediction in rotor–stator cavities at high reynolds numbers up to Re ≈ 2 ∙ 108: Towards a new parametric model
    Schröder, T.R. and Schuster, S. and Brillert, D.
    Proceedings of the ASME Turbo Expo 2E-2020 (2020)
    Side chambers of centrifugal turbomachinery resemble rotor–stator cavities. The flow in these cavities develops complex patterns which substantially influence the axial thrust on the shaft and the frictional torque on the rotor. Axial thrust caused by the flow pattern in side chambers accumulates in multistage single shaft radial compressors where it is often balanced by a single axial bearing. Miscalculation of axial thrust may lead to axial loads significantly higher than predicted or even undefined load situations which may cause early bearing failure. Likewise, a wrong prediction of friction losses may lead to lower efficiency than originally intended. Current models for axial thrust and friction torque are limited to circumferential Reynolds numbers of Re ≤ 107. New models are needed for modern high-pressure centrifugal compressors which reach circumferential Reynolds numbers up to Re = 109. The rotor–stator cavity flow model by Kurokawa and Sakuma [16] for merged boundary layers is analysed. It is based on the assumptions of axisymmetric and time invariant flow. Functional forms of the mean tangential and radial velocity and the surface stress vectors on the rotor and stator are assumed. Reynolds averaging is applied to consider turbulence effects in the model. The modelling assumptions are compared with detailed RANS CFD analyses at Reynolds numbers of 4 ∙ 106 ≤ Re ≤ 2 ∙ 108 to investigate their accuracy. Based on these CFD results, a way towards a high Reynolds number model is presented, providing prediction of disc torque, radial pressure distribution and axial thrust in rotor–stator cavities. Copyright © 2020 ASME.
    view abstract10.1115/GT2020-14010
  • Proof of concept for a novel interstage injection design in axial compressors
    Doerr, T. and Braun, S. and Schuster, S. and Brillert, D.
    Proceedings of the ASME Turbo Expo 8 (2020)
    A common technique to increase the thermal efficiency and the power output of gas turbines is to inject water upstream of the compressor section. Through the evaporation of the water throughout the compressor, an isothermal process is approached. A recently-developed technology for this enhanced process is Interstage Injection in which water is injected directly between the stages. One advantage of this over wet compression is the avoidance of icing, since the local temperatures at the injection positions are already above melting point. Moreover, stage characteristics and load distribution can be rearranged within the compressor by individually adjusting the injection amount in different stages. However, there is little practical understanding of this process, and suitable injection methods have still to be found. This paper therefore demonstrates the implementation of a novel technology of Interstage Injection in an axial compressor test rig whereby twin jet nozzles are integrated directly into the trailing edge of the first stator row to deliver a homogenous spray over the entire radial span. Due to the resultant blade complexity, blades are manufactured by selective laser melting and subsequently installed in an enhanced four-stage axial compressor. The installed control and measurement principles of the test rig are presented and results demonstrate the functionality of the innovative design. Copyright © 2020 ASME.
    view abstract10.1115/GT2020-15807
  • The multi-phase flow test facility ⇜emma⇝ to investigate local heat transfer coefficients and liquid water films at wet steam conditions
    Lapp, F.F. and Hecker, S. and Schuster, S. and Brillert, D.
    Proceedings of the ASME Turbo Expo 9 (2020)
    Conventional power plants are obliged to compensate for the fluctuations in power generation, due to the rising amount of renewable energies, to ensure grid stability. Consequently, steam turbines are more frequently facing load variation and start-up/shut-down cycles leading to an increase of thermal stress induced by phase change phenomena. The review of existing test facilities providing measurement data of heat transfer coefficients influenced by multiphase phenomena, such as surface wettability and dry-out, revealed the necessity for a new measurement application. This paper presents the design of the Experimental Multi-phase Measurement Application”EMMA” to generate the required conditions in combination with an academic turbine housing geometry. The performed investigations are focused on the local distribution of heat transfer coefficients (HTC) and the surface wettability affected by phase change phenomena. Two main film formation mechanisms can be observed, depending on the thermal gradient between the fluid and the wall. These are a) saturated/superheated steam in contact with a sub-cooled wall leading to film-wise/drop-wise condensation and b) primary condensed wet steam droplets depositing on a superheated wall, leading to evaporation. Both, the liquid film and the local heat transfer are measured simultaneously. An overview of applicable thickness measurement methods for transparent liquid films is given and the applied optical measurement system is further described. Moreover the HTC measurement methods are presented considering the occurring case of phase change. © 2020 ASME
    view abstract10.1115/GT2020-16307
  • Cycle calculations of a small-scale heat removal system with supercritical CO2 as working fluid
    Straetz, M. and Starflinger, J. and Mertz, R. and Brillert, D.
    Journal of Nuclear Engineering and Radiation Science 5 (2019)
    In the case of an accident in a nuclear power plant with combined initiating events (loss of ultimate heat sink and station blackout), an additional heat removal system could transfer the decay heat from the core to an ultimate heat sink (UHS). One specific additional heat removal system, based upon a Brayton cycle with supercritical carbon dioxide (CO2) as working fluid, is currently investigated within the European Union-funded project "sCO2-HeRo" (supercritical carbon dioxide heat removal system). It serves as a self-launching, self-propelling, and self-sustaining decay heat removal system used in severe accident scenarios. Since this Brayton cycle produces more electric power than it consumes, the excess electric power can be used inside the power plant, e.g., for recharging batteries. A small-scale demonstrator is attached to the pressurized water reactor (PWR) glass model at Gesellschaft für Simulatorschulung (GfS), Essen, Germany. In order to design and build this small-scale model, cycle calculations are performed to determine the design parameters from which a layout can be derived. © 2019 by ASME.
    view abstract10.1115/1.4039884
  • Effect of interstage injection on compressor flow characteristic
    Von Deschwanden, I. and Braun, S. and Brillert, D.
    ASME-JSME-KSME 2019 8th Joint Fluids Engineering Conference, AJKFluids 2019 5 (2019)
    Wet compression is a widely used approach to enhance the compressor performance of gas turbine units. For wet compression, a water-spray consisting of tiny droplets is injected into the air inlet duct of the compressor. A multi-phase flow of humid air and water droplets enters the compressor. The continued water evaporation inside the compressor stages causes further cooling during the compression process. Water injection between the compressor stages is called interstage injection. An advantage of interstage injection compared to wet compression is the optimized injection of water at specific positions inside the compressor. The amount of injected water can be adopted to the specific operating conditions of the different injection positions with the ideal of isothermal compression. Interstage injection can be realized by several techniques. This paper focuses on interstage injection of water from the trailing edge of stator blades. The water spray is generated in the complex wake flow of the airfoil. This leads to strong interaction between the water spray and the carrier gas flow. In this paper, especially the impact of water injection on the air flow and the spread of the spray is investigated. Phase Doppler Anemometry (PDA) measurements enable two dimensional velocity measurements linked with the droplet size. The comparison of PDA measurements and Computational Fluid Dynamic (CFD) calculations of the dry gas flow allows for the identification of flow instabilities due to interstage injection. Within this publication, a significant influence of the water injection from the trailing edge on the carrier flow is identified. Furthermore, the ability of the spray to spread widely into the flow demonstrates that water injection from the trailing edge is a promising technique for interstage injection. Copyright © 2019 ASME.
    view abstract10.1115/AJKFluids2019-4959
  • Experimental and numerical investigation on the flow in a return channel of multistage centrifugal compressors
    Dolle, B. and Brillert, D. and Dohmen, H.J. and Benra, F.-K.
    Proceedings of the ASME Turbo Expo 2B-2019 (2019)
    Multistage radial compressors are major components in plenty of industrial applications. Today, compressor downsizing for CAPEX reduction is of utmost importance. Accordingly, the pressure ratio must be increased, accommodated in a most compact design, accepting nearly no penalties in the performance level achieved so far. In order to investigate the complex flow in stator parts of multistage centrifugal compressors and to increase the confidence level of numerical methods a new test rig is developed and taken into operation. This test rig allows to separate stationary flow effects from time variant effects leading to an in depth insight into the physical flow features. The aim is to investigate the flow in different stator designs in detail for varying flow coefficients. Additive manufacturing techniques are applied to achieve low costs simultaneously with short production time for the tested parts. In this publucation, the measured flow field in the stator parts is discussed. The experimental results comprise velocity and pressure data from five-hole-probes and unsteady velocity data from single-film hot-film-probes. Using unsteady velocity data, turbulent statistics such as turbulence intensity and the turbulent kinetic energy will be determined. Subsequently, the experimental results are compared to numerical results. Therefore, (U)RANS simulations are performed using a commercial CFD-code. The simulation results are evaluated at planes appropriate to the measuring planes in the test rig to guarantee a directly comparable data base. Copyright © 2019 ASME.
    view abstract10.1115/GT2019-90455
  • Flow-Induced Steam Valve Vibrations - A Literature Review of Excitation Mechanisms, Preventive Measures, and Design Improvements
    Domnick, C.B. and Brillert, D.
    Journal of Engineering for Gas Turbines and Power 141 (2019)
    Steam turbine inlet valves are used to control the power output of steam turbines for power generation. These valves may be subject to vibration under certain operating conditions, especially in part-load operation. Several research papers and reports show that elevated valve vibrations can result in damage to parts of a steam turbine installation. A comprehensive literature review considering 43 different valves investigated in 51 studies reveals the effects causing vibrations. The physics of these effects are explained and methods for reducing flow-induced dynamic forces are presented based on the findings published in the literature. A classification scheme for typical valve designs is developed and the design features are evaluated in terms of valve vibration. Numerical methods for analyzing the fluid dynamics of valves are also presented. Copyright © 2019 by ASME.
    view abstract10.1115/1.4041253
  • Stabilizing effects of supercritical CO2 fluid properties on compressor operationy
    Hacks, A.J. and Schuster, S. and Brillert, D.
    International Journal of Turbomachinery, Propulsion and Power 4 (2019)
    This paper aims to give an understanding of an effect which stabilizes the inlet conditions of compressors for supercritical CO2 (sCO2) operating close to the critical point. The effect was observed during testing of the turbomachine within the sCO2-HeRo project, and is caused by the sCO2 real gas properties close to the pseudocritical line. Under theoretical consideration, strong gradients in the fluid properties around this line-dependent on the static temperature and pressure of sCO2-can result in strong variation of compressor performance and finally lead to unstable cycle behavior. However, this paper demonstrates reduced gradients in density at the compressor inlet when varying the cooling power and taking advantage of a stabilizing effect. The applicable range and the significance of this stabilizing effect depended on the cooler inlet temperature and pressure, and was used to evaluate the relevance for individual cycles. Controlling the cooling power and the measurement of the inlet density allowed control of the compressor inlet conditions equally well, independent of the operating point, even close to the critical point. © 2019 by the authors.
    view abstract10.3390/ijtpp4030020
  • A test rig concept to study fluid structure interactions in a steam turbine valve
    Wallat, S. and Domnick, C.B. and Musch, C. and Brillert, D.
    Proceedings of the ASME Turbo Expo 8 (2018)
    The power output of steam turbines is controlled by steam turbine inlet valves. These valves have a large flow capacity and dissipate a huge amount of energy in throttled operation mode. The dissipation process generates strong pressure fluctuations and leads to high dynamic forces potentially causing valve vibrations. A brief survey of the literature dealing with valve vibrations reveals that vibrational problems and damages mostly occur in throttled operation when jets, shocks and shear layers are present. Previous investigations of the authors reveal a feedback mechanism between the dynamic flow field and the vibrating valve plug. Depending on the flow topologies either axial or lateral forces will dominate the force spectrum. In this paper the design of a test rig including a scaled model of a steam valve is described. As it is difficult to analyse lateral forces in conventional experiments the model is designed not only to study the flow conditions but also the lateral and axial movement of the valve plug. To investigate and model the dynamic characteristic of the valve the entire periphery including the mechanical drive, sealing etc. needs to be considered. To ensure that fluid-structure-interactions are correctly scaled, dimensionless numbers derived with the Buckingham Pi Theorem are used as design criteria. Positions of the transmitters are selected based on results of numerical simulations. Copyright © 2018 Siemens Energy, Inc.
    view abstract10.1115/GT201875094
  • Condensation in radial turbines-Part I: Mathematical modeling
    Schuster, S. and Brillert, D. and Benra, F.-K.
    Journal of Turbomachinery 140 (2018)
    In this two-part paper, the investigation of condensation in the impeller of radial turbines is discussed. In Paper I, a solution strategy for the investigation of condensation in radial turbines using computational fluid dynamics (CFD) methods is presented. In Paper II, the investigation methodology is applied to a radial turbine type series that is used for waste heat recovery. First, the basic CFD approach for the calculation of the gas-droplet- liquid-film flow is introduced. Thereafter, the equations connecting the subparts are explained and a validation of the models is performed. Finally, in Paper I, condensation phenomena for a selected radial turbine impeller are discussed on a qualitative basis. Paper II continues with a detailed quantitative analyses. The aim of Paper I is to explain the models that are necessary to study condensation in radial turbines and to validate the implementation against available experiments conducted on isolated effects. This study aims to develop a procedure that is applicable for investigation of condensation in radial turbines. Furthermore, the main processes occurring in a radial turbine once the steam temperature is below the saturation temperature are explained and analyzed. © 2018 by ASME.
    view abstract10.1115/1.4040934
  • Condensation in radial turbines-Part II: Application of the mathematical model to a radial turbine series
    Schuster, S. and Brillert, D. and Benra, F.-K.
    Journal of Turbomachinery 140 (2018)
    In the second part of this two part paper, the condensation process and the movement of the liquid phase near the impeller blades of a radial turbine are studied. The investigation methodology presented in part 1 is applied to a radial turbine type series used for waste heat recovery. First, the subcooling necessary for the beginning of the condensation process is examined and a relationship between the location of maximum subcooling and the onset of droplet deposition at the surfaces of the turbine impeller is determined. Thereafter, the movement of liquid films on the impeller blades is analysed and characterized. Correlations determining the movement of droplets originating from liquid film atomization on the edge of the impeller blade along the casing are derived. Finally, conclusions are drawn depicting the most important findings of condensing flows in radial turbines. © 2018 by ASME.
    view abstract10.1115/1.4040935
  • Damping behavior of acoustic dominant modes in an aeroacoustic test rig representing a simplified geometry of a high pressure radial compressor
    Barabas, B. and Brillert, D. and Dohmen, H.J. and Benra, F.-K.
    Proceedings of the ASME Turbo Expo 7C (2018)
    Pressure ratios of modern high pressure radial compressors tend to increase along with pressure fluctuations and the excitation potential on the impellers. The vibrational interactions between side cavities, filled with high pressure fluid, and the impeller structure play an important role in designing a machine for reliable operation. However, they are not yet fully understood. Vibrations at frequencies that have been uncritical at lower pressure levels could become critical at a higher pressure level. Additionally, coupling effects between fluid and structure are becoming stronger at higher fluid densities. For a safe and reliable design, the excitation and the damping mechanism of coupled modes has to be better understood. To understand the interaction, especially regarding the damping behavior, of coupled structure and acoustic modes, a comprehension of the behavior of the uncoupled or weakly coupled modes is required. The structural damping ratio is very small and it has been analyzed in existing literature extensively. The damping behavior of uncoupled acoustic modes, however, is not yet well investigated. This paper focuses on the damping behavior of acoustic modes that are weakly coupled to structure modes. Measurement results gathered at the aeroacoustic test rig at the University of Duisburg-Essen are presented. The results show the influence of fluid pressure variations on the damping behavior of acoustic modes. Therefore, the response functions of some selected acoustic modes are evaluated with the Peak-to-Peak method. In general, the damping decreases with increasing fluid pressure. Furthermore, a relationship of the damping ratio, the kinematic viscosity, and the natural frequency of the acoustic modes has been detected. Copyright © 2018 ASME.
    view abstract10.1115/GT201876629
  • Thermodynamic modelling aspects of wet compression in radial compressors
    Schuster, S. and Brillert, D. and Hermes, V. and Yildiz, A. and Benra, F.-K.
    Proceedings of the ASME Turbo Expo 9 (2018)
    Wet compression or evaporative cooling is used during thecompression of gases. Evaporative cooling reduces the powerdemand and keeps the discharge temperature in a suitablerange. The cooling effect can be used before the impeller aswell as within the impeller. The latter is more challenging andthe focus of this research is on it. This paper looks intoevaporative cooling in radial impellers from a generalperspective in order not to limit the scope. Therefore, a meanline calculation program is applied. The program takes intoaccount the entropy production due to the irreversible heatexchange between gas and liquid. This paper focuses on thethermodynamic aspects and shows how to analyse them. Thepaper highlights the necessity to consider the additional entropyproduction during the design and analysis process. © 2018 Solar Turbines Incorporated.
    view abstract10.1115/GT2018-76429
  • Turbomachine Design for Supercritical Carbon Dioxide Within the sCO2-HeRo.eu Project
    Hacks, A. and Schuster, S. and Dohmen, H.J. and Benra, F.-K. and Brillert, D.
    Journal of Engineering for Gas Turbines and Power 140 (2018)
    The paper aims to give an overview over the keystones of design of the turbomachine for a supercritical CO2 (sCO2) Brayton cycle. The described turbomachine is developed as part of a demonstration cycle on a laboratory scale with a low through flow. Therefore, the turbomachine is small and operates at high rotational speed. To give an overview on the development, the paper is divided into two parts regarding the aerodynamic and mechanical design. The aerodynamic design includes a detailed description on the steps from choosing an appropriate rotational speed to the design of the compressor impeller. For setting the rotational speed, the expected high windage losses are evaluated considering the reachable efficiencies of the compressor. The final impeller design includes a description of the blading development together with the final geometry parameters and calculated performance. The mechanical analysis shows the important considerations for building a turbomachine with integrated design of the three major components: turbine, alternator, and compressor (TAC). It includes different manufacturing techniques of the impellers, the bearing strategy, the sealing components, and the cooling of the generator utilizing the compressor leakage. Concluding the final design of the TAC is shown and future work on the machine is introduced. © Copyright 2019 by ASME.
    view abstract10.1115/1.4040861
  • Turbomachine design for supercritical carbon dioxide within the SCO2-hero.EU project
    Hacks, A. and Schuster, S. and Dohmen, H.J. and Benra, F.-K. and Brillert, D.
    Proceedings of the ASME Turbo Expo 9 (2018)
    The paper aims to give an overview over the keystones ofdesign of the turbomachine for a supercritical CO2 (sCO2)Brayton cycle. The described turbomachine is developed aspart of a demonstration cycle on a laboratory scale with a lowthrough flow. Therefore the turbomachine is small and operatesat high rotational speed. To give an overview on thedevelopment the paper is divided into two parts regarding theaerodynamic and mechanical design. The aerodynamic designincludes a detailed description on the steps from choosing anappropriate rotational speed to the design of the compressorimpeller. For setting the rotational speed the expected highwindage losses are evaluated considering the reachableefficiencies of the compressor. The final impeller designincludes a description of the blading development together withthe final geometry parameters and calculated performance. Themechanical analysis shows the important considerations forbuilding a turbomachine with integrated design of the threemajor components turbine, alternator and compressor (TAC). Itincludes different manufacturing techniques of the impellers,the bearing strategy, the sealing components and the cooling ofthe generator utilising the compressor leakage. Concluding thefinal design of the TAC is shown and future work on themachine is introduced. © 2018 Solar Turbines Incorporated.
    view abstract10.1115/GT2018-75154
  • Clarifying the Physics of Flow Separations in Steam Turbine Inlet Valves at Part Load Operation and Improved Design Considerations
    Domnick, C.B. and Brillert, D. and Musch, C. and Benra, F.-K.
    Journal of Fluids Engineering, Transactions of the ASME 139 (2017)
    In steam turbine inlet valves used to adjust the power output of large steam turbines, the through-flow is reduced by lowering the valve plug and hence reducing the cross-sectional area between the plug and the seat. At throttled operation, a supersonic jet is formed between the plug and the seat. This jet bearing tremendous kinetic energy flows into the valve diffuser where it is dissipated. Depending on the dissipation process, a certain portion of the kinetic energy is converted to sound and subsequently to structural vibration, which can be harmful to the valve plug. The flow topology in the valve diffuser has a strong influence on the conversion of kinetic energy to sound and hence vibrations. Several studies show that an annular flow attached to the wall of the valve diffuser causes significantly less noise and vibrations than a detached flow in the core of the diffuser. The relation between the flow topology and the vibrations is already known, but the physics causing the transition from the undesired core flow to the desired annular flow and the dependency on the design are not fully understood. The paper presented here reveals the relation between the flow topology in the steam valve and the separation of underexpanded Coand? wall jets. The physics of the jet separations are clarified and a method to predict the flow separations with a low numerical effort is shown. Based on this, safe operational ranges free of separations can be predicted and improved design considerations can be made. © 2017 by Siemens AG.
    view abstract10.1115/1.4036263
  • Droplet deposition in radial turbines
    Schuster, S. and Benra, F.-K. and Brillert, D.
    European Journal of Mechanics, B/Fluids 61 (2017)
    In this paper droplet deposition in radial turbines used for waste heat recovery in the chemical industry is investigated. During expansion, the water vapour in the working fluid undergoes sub-cooling, at a certain point a cloud of fine droplets begins to form and a fraction of these droplets is deposited on the blade surfaces. In this paper, droplet deposition is calculated by incorporating turbulent fluctuations and Brownian motion into a Lagrange particle tracking algorithm. After introducing the calculation approach, a validation of the enhanced CFD code by means of deposition experiments in a straight tube is presented. For a radial turbine, the functional relation between the location of maximum sub-cooling and the onset of droplet deposition is pointed out. Even though the validation of the numerical code is quite satisfactory, some uncertainties arise from the nucleation modelling. This uncertainty will be addressed in the publication as well. The paper concludes with suggestions on how to increase the reliability of the calculations. © 2016 Elsevier Masson SAS
    view abstract10.1016/j.euromechflu.2016.09.002
  • Introduction of an integrated turbo-electrical machine
    Schuster, S. and Kreischer, C. and Brillert, D.
    Proceedings of the ASME Turbo Expo 8 (2017)
    Turbomachines are commonly designed for a high mass flow rate. However, because of new cycle concepts, turbomachines are also required to compress or expand at small mass flow rates. One example is the supercritical carbon dioxide Brayton cycle. The mass flow rate can be in the range of one kg/s at an almost high fluid density at the inlet to the compressor. This results in a small through flow area. In this paper, a turbomachine concept is presented that integrates the turbomachine parts into an electrical machine. Specifically, the turbomachine is located in the gap between the rotor and the stator of the electrical machine. In that way, a very compact design can be achieved. This paper aims to explain the basic concept. An aerodynamic design study is performed that demonstrates the important parameters for machine performance. Additionally, the design of the electrical machine is discussed based on a realistic application. Finally, conclusions for further development are drawn. Copyright © 2017 ASME.
    view abstract10.1115/GT2017-63526
  • Investigation on flow-induced vibrations of a steam turbine inlet valve considering fluid-structure interaction effects
    Domnick, C.B. and Benra, F.-K. and Brillert, D. and Dohmen, H.J. and Musch, C.
    Journal of Engineering for Gas Turbines and Power 139 (2017)
    The power output of steam turbines is controlled by steam turbine inlet valves. These valves have a large flow capacity and dissipate a huge amount of energy in throttled operation. The dissipation process generates strong pressure fluctuations resulting in high dynamic forces causing valve vibrations. A brief survey of the literature dealing with valve vibrations reveals that the vibrational problems and damages mostly occur in throttled operation when high speed jets, shocks, and shear layers are present. As previous investigations reveal that a feedback mechanism between the dynamic flow field and the vibrating valve plug exists, the vibrations are investigated with two-way coupled simulations. The fluid dynamics are solved with a scale-adaptive approach to resolve the pressure fluctuations generated by the turbulent flow. The finite element model (FEM) solving the structural dynamics considers both frictional effects at the valve packing and contact effects caused by the plug impacting on the valve bushing. As different flow topologies causing diverse dynamic loads exist, the fluid flow and the structural dynamics are simulated at different operating points. The simulations show that differences to the one-way-coupled approach exist leading to a change of the vibrational behavior. The physics behind the feedback mechanisms causing this change are analyzed and conclusions regarding the accuracy of the one-way-coupled approach are drawn. © 2017 by ASME.
    view abstract10.1115/1.4034352
  • Investigation on the influence of surface roughness on the moment coefficient in a rotor-stator cavity with centripet al through-flow
    Hu, B. and Brillert, D. and Dohmen, H.J. and Benra, F.-K.
    American Society of Mechanical Engineers, Fluids Engineering Division (Publication) FEDSM 1A-2017 (2017)
    In radial pumps and turbines, the leakage flow (centripet al through-flow) is quite common from the outer radius of the impeller to the impeller eye, which has major impact on frictional torque. There is still an uncertainty on the impact of surface roughness on the moment coefficient. Part of the 2D Daily&Nece diagram where the flow is categorized into four regimes is extended into 3D with the third axis of through-flow coefficient by distinguishing the profiles of tangential velocity. After classifying the flow regimes with respect to the centripet al through-flow, two correlations are developed to predict the impact of the axial gap, the global Reynolds number, the through-flow coefficient and the surface roughness on the moment coefficient according to the experimental results for both regime III and regime IV. Using the proposed equations for the moment coefficient, the influence of the centripet al throughflow and surface roughness can be better considered when designing radial pumps and turbines. © Copyright 2017 ASME.
    view abstract10.1115/FEDSM2017-69018
  • PDA measurements in spray generated by twin-jet-nozzles
    Von Deschwanden, I. and Benra, F.-K. and Dohmen, H.J. and Brillert, D.
    American Society of Mechanical Engineers, Fluids Engineering Division (Publication) FEDSM 1B-2017 (2017)
    Generating fine widely dispersed sprays is the current focus of research. For this purpose, different types of nozzles are available. In the present paper, the continuous spray formation generated by the collision of two individual water jets is examined. All measurements are conducted in steady-state at ambient temperature and pressure. A non-invasive Phase-Doppler-Anemometry (PDA) laser measurement system enables the spray characteristics to be determined, the droplet distribution and the droplet velocity. Twin-jet-nozzles generate a fine but dense spray. The PDA measurement technique is an optical measurement application. The intensity of the light scattered by the droplets is proportional to the droplets squared diameter. Especially, in dense sprays, a high intensity of light signals is required for high quality data acquisition. Furthermore, the outcome of PDA measurement depends mainly on three aspects: One aspect is the influence of the laser power on the signal intensity. The second important parameter is the voltage of the Photo-Multiplier-Tubes. The third aspect is the orientation of transmitter and receiver of the measurement equipment relative to the spray. In this paper, the precision of PDA measurements in dense sprays influenced by the PMT voltage is analyzed and discussed. © Copyright 2017 ASME.
    view abstract10.1115/FEDSM2017-69003
  • Comparison of different numerical approaches for determination of compressible fluid flow in narrow gaps
    Kefalas, A. and Benra, F.-K. and Brillert, D. and Dohmen, H.J.
    Proceedings of the ASME Turbo Expo 2C-2016 (2016)
    The prediction of fluid flow through a narrow gap is a characteristic problem in fluid mechanics. In today's turbomachinery, several applications in bearing and sealing technology are based on the phenomena of two surfaces being separated by a thin fluid film of only a few micrometers. The common method for analyzing the non-contact application's performance usually applies the lubrication theory based on the Reynolds equation. This two-dimensional model is based on the assumption of a laminar viscous flow field, isothermal conditions and it takes aerostatic as well as aerodynamic effects into account. In cases of a complex geometry and challenging flow conditions this approach has its limitations. The usage of commercial state of the art computational fluid dynamics (CFD) software allows the circumvention of these restrictions. As a matter of fact CFD simulations take up high effort in terms of preparation and calculation time. The present contribution compares the numerical approaches with regard to the application's performance accuracy and calculation effort, using the example of a dry gas seal. To extend the Reynolds equation's applicability to a wide variety of geometries, a method for implementing the topography design with high fidelity is depicted. The numerical methods are performed for various dry gas seal designs at different operating conditions and are compared with reference data. Copyright © 2016 by ASME
    view abstract10.1115/GT2016-57898
  • Modification of a steam valve diffuser for enhanced full load and part load operation using numerical methods
    Domnick, C.B. and Bera, F.-K. and Brillert, D. and Musch, C.
    Periodica Polytechnica, Mechanical Engineering 60 (2016)
    The flow in a steam turbine inlet valve is investigated and improved by numerical methods. From the fluid dynamic point of view two requirements exist: Low pressure losses are desired at the fully opened valve position and dynamic fluid forces acting on the valve plug should be minimized to reduce valve vibration. Usually these undesired dynamic fluid forces occur when the flow is throttled at part load. It is found that these fluid forces are generated by separated jets in the diffuser. The attachment and the separation of the jet are related to the Coanda effect. By understanding the flow physics a way is found to modify the diffuser design in such a way that the flow separations are reduced. Bell-shaped diffusers are able to reduce the flow losses at full load operation. A diffuser contour that fulfils both requirements is developed.
    view abstract10.3311/PPme.9041
  • Numerical Investigation on the Time-Variant Flow Field and Dynamic Forces Acting in Steam Turbine Inlet Valves
    Domnick, C. B. and Benra, F. K. and Brillert, D. and Dohmen, H. J. and Musch, C.
    Journal of Engineering for Gas Turbines and Power-transactions of the Asme 137 (2015)
    The unsteady flow in inlet valves for large steam turbines used in power stations was investigated using the method of computational fluid dynamics (CFD). As the topology of the flow depends on the stroke and the pressure ratio of the valve, the flow was investigated at several positions. Various turbulence models were applied to the valve to capture the unsteady flow field. Basic Reynolds-averaged Navier-Stokes (RANS) models, the scale adaptive simulation (SAS), and the scale adaptive simulation with zonal forcing (SAS-F, also called ZFLES) were evaluated. To clarify the cause of flow-induced valve vibrations, the investigation focused on the pressure field acting on the valve plug. It can be shown that acoustic modes are excited by the flow field. These modes cause unsteady forces that act on the valve plug. The influence of valve geometry on the acoustic eigenmodes was investigated to determine how to reduce the dynamic forces. Three major flow topologies that create different dynamic forces were identified.
    view abstract10.1115/1.4029309
  • Numerical investigation on the vibration of steam turbine inlet valves and the feedback to the dynamic flow field
    Domnick, C.B. and Benra, F.-K. and Brillert, D. and Dohmen, H.J. and Musch, C.
    Proceedings of the ASME Turbo Expo 8 (2015)
    The power output of steam turbines is controlled by steam turbine inlet valves. These valves have a large flow capacity and dissipate in throttled operation a huge amount of energy. Due to that, high dynamic forces occur in the valve which can cause undesired valve vibrations. In this paper, the structural dynamics of a valve are analysed. The dynamic steam forces obtained by previous computational fluid dynamic (CFD) calculations at different operating points are impressed on the structural dynamic finite element model (FEM) of the valve. Due to frictional forces at the piston rings and contact effects at the bushings of the valve plug and the valve stem the structural dynamic FEM is highly nonlinear and has to be solved in the time domain. Prior to the actual investigation grid and time step studies are carried out. Also the effect of the temperature distribution within the valve stem is discussed and the influence of the valve actuator on the vibrations is analysed. In the first step, the vibrations generated by the fluid forces are investigated. The effects of the piston rings on the structural dynamics are discussed. It is found, that the piston rings are able to reduce the vibration significantly by frictional damping. In the second step, the effect of the moving valve plug on the dynamic flow in the valve is analysed. The time dependent displacement of the valve is transferred to CFD calculations using deformable meshes. With this one way coupling method the response of the flow to the vibrations is analysed. Copyright © 2015 by Siemens Energy Inc.
    view abstract10.1115/GT2015-42182
  • fluid dynamics

  • gas dynamics

  • numerical methods

  • steam turbines

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