scholarly journals Assessing Rotation/Curvature Corrections to Eddy-Viscosity Models in the Calculations of Centrifugal-Compressor Flows

2008 ◽  
Vol 130 (9) ◽  
Author(s):  
G. Dufour ◽  
J.-B. Cazalbou ◽  
X. Carbonneau ◽  
P. Chassaing
Keyword(s):  
Centrifugal Compressor ◽  
Eddy Viscosity ◽  
Turbulence Modeling ◽  
Turbulence Models ◽  
Equation Modeling ◽  
Test Case ◽  
Consistency Analysis ◽  
Perfect Agreement ◽  
Local Flow ◽  
The Impact

Rotation and curvature (RC) effects on turbulence are expected to impact losses and flow structure in turbomachines. This paper examines two recent eddy-viscosity-model corrections devised to account for these effects: the Spalart and Shur (1997, “On the Sensitization of Turbulence Models to Rotation and Curvature,” Aerosp. Sci. Technol., 1(5), pp. 297–302) correction to the model of Spalart and Allmaras (1994, “A One-Equation Turbulence Model for Aerodynamic Flows,” Rech. Aerosp., 1, pp. 5–21) and the correction of Cazalbou et al. (2005, “Two-Equation Modeling of Turbulent Rotating Flows,” Phys. Fluids., 17, p. 055110) to the (k,ϵ) model. The method of verification and validation is applied to assess the impact of these corrections on the computation of a centrifugal-compressor test case. First, a review of RC effects on turbulence as they apply to centrifugal compressors is made. The two corrected models are then presented. Second, the Radiver open test case (Ziegler K. U., Gallus, H. E., and Niehuis R., 2003, “A Study on Impeller Diffuser Interaction Part 1: Influence on the Performance,” ASME J. Turbomach, 125, pp. 173–182) is used as a basis for the assessment of the two corrections. After a physical-consistency analysis, the Richardson extrapolation is applied to quantify the numerical errors involved in all the calculations. Finally, experimental data are used to perform validation for both global and local predictions. The consistency analysis shows that both corrections lead to significant changes in the turbulent field, in perfect agreement with the underlying theoretical considerations. The uncertainty analysis shows that the predictions of the global performances are more sensitive to grid refinement than they are to RC turbulence modeling. However, the opposite conclusion is drawn with regard to the prediction of some local flow properties: Improvements are obtained with the RC corrections, the best results being observed for the RC-corrected (k,ϵ) model.

Improved Two-Dimensional Dynamic Stall Prediction with Structured and Hybrid Numerical Methods

2011 ◽  
Vol 56 (4) ◽  
pp. 1-12 ◽  
Author(s):  
K. Richter ◽  
A. Le Pape ◽  
T. Knopp ◽  
M. Costes ◽  
V. Gleize ◽  
...  
Keyword(s):  
Numerical Methods ◽  
Numerical Method ◽  
High Speed ◽  
Turbulence Modeling ◽  
Turbulence Models ◽  
Boundary Layer Transition ◽  
Dynamic Stall ◽  
Two Dimensional ◽  
Layer Transition ◽  
The Impact

A joint comprehensive validation activity on the structured numerical method elsA and the hybrid numerical method TAU was conducted with respect to dynamic stall applications. To improve two-dimensional prediction, the influence of several factors on the dynamic stall prediction was investigated. The validation was performed for three deep dynamic stall test cases of the rotor blade airfoil OA209 against experimental data from two-dimensional pitching airfoil experiments, covering low-speed and high-speed conditions. The requirements for spatial discretization and for temporal resolution in elsA and TAU are shown. The impact of turbulence modeling is discussed for a variety of turbulence models ranging from one-equation Spalart–Allmaras-type models to state-of-the-art, seven-equation Reynolds stress models. The influence of the prediction of laminar/turbulent boundary layer transition on the numerical dynamic stall simulation is described. Results of both numerical methods are compared to allow conclusions to be drawn with respect to an improved prediction of dynamic stall.

Experimental and Numerical Investigation of Tip Clearance and Bleed Effects in a Centrifugal Compressor Stage With Pipe Diffuser

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
Robert Kunte ◽  
Philipp Schwarz ◽  
Benjamin Wilkosz ◽  
Peter Jeschke ◽  
Caitlin Smythe
Keyword(s):  
Numerical Investigation ◽  
Centrifugal Compressor ◽  
Tip Clearance ◽  
Compressor Stage ◽  
Local Flow ◽  
Centrifugal Compressor Stage ◽  
Centrifugal Stage ◽  
Flow Phenomena ◽  
Fundamental Insight ◽  
The Impact

The subject of this paper is the experimental and numerical investigation of a state-of-the-art high pressure centrifugal compressor stage with pipe diffuser for a jet engine application. This study shows the impact of impeller tip clearance- and bleed-variation on the centrifugal stage. The purpose of this paper is threefold. In the first place, it investigates the effects on the stage performance. Secondly, it seeks to explain local flow-phenomena, especially in the diffuser. Finally, it shows that steady CFD simulations are capable of predicting these phenomena. Experimental data were gathered using conventional pitot and three-hole-probes as well as particle-image-velocimetry. Numerical simulations with the CFD solver TRACE were conducted to get fundamental insight into the flow. Thus, this study contributes greatly towards understanding the principle of the flow phenomena in the pipe diffuser of a centrifugal compressor.

scholarly journals THE IMPACT OF VARIOUS MODELLING DECISIONS ON FLOW FIELD PREDICTIONS IN A CENTRIFUGAL COMPRESSOR

2021 ◽  
pp. 1-13
Author(s):  
William Gooding ◽  
Matthew Meier ◽  
Nicole L. Key
Keyword(s):  
Flow Field ◽  
Centrifugal Compressor ◽  
Computational Models ◽  
Turbulence Models ◽  
Numerical Results ◽  
Computational Tools ◽  
Performance Trends ◽  
Sst Turbulence Model ◽  
Overall Performance ◽  
The Impact

Abstract Computational tools have become increasingly important in design and research applications in recent years due to increasing computational resources. In most cases, model geometry and flow-physics are simplified to reduce the complexity of the computational model. While this was necessary historically, modern computational tools are capable of including realistic features such as fillets, surface roughness, and heat transfer. This work presents extensive and systematic numerical results from a simulation of a centrifugal compressor stage for an aero-engine application. Numerical results are compared to detailed experimental data to investigate the effect of various modelling decisions, including turbulence models, on the predicted aerodynamics developing through the diffuser passage. Roughness and the inclusion of fillets significantly impact the flow development, especially with the SST turbulence model. This approach leads to the conclusion that the BSL-EARSM model is best able to predict the experimentally determined diffuser flow profiles and overall performance trends with the inclusion of the previously mentioned model features. Additionally, the misleading conclusions can be reached if modelling decisions are based on merely matching overall performance values. Finally, frozen rotor simulations are used to roughly approximate the impact of unsteadiness on the flow field. The results show a significant impact and also that the inclusion of approximate unsteady effects tends to further improve the predictive capability of the computational models that were considered.

A Methodology for Simulating Compressible Turbulent Flows

2005 ◽  
Vol 73 (3) ◽  
pp. 405-412 ◽  
Author(s):  
Hermann F. Fasel ◽  
Dominic A. von Terzi ◽  
Richard D. Sandberg
Keyword(s):  
Turbulent Flows ◽  
Compressible Flows ◽  
Bluff Body ◽  
Turbulence Modeling ◽  
Flow Behavior ◽  
Flow Simulation ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Fine Grid ◽  
Local Flow

A flow simulation Methodology (FSM) is presented for computing the time-dependent behavior of complex compressible turbulent flows. The development of FSM was initiated in close collaboration with C. Speziale (then at Boston University). The objective of FSM is to provide the proper amount of turbulence modeling for the unresolved scales while directly computing the largest scales. The strategy is implemented by using state-of-the-art turbulence models (as developed for Reynolds averaged Navier-Stokes (RANS)) and scaling of the model terms with a “contribution function.” The contribution function is dependent on the local and instantaneous “physical” resolution in the computation. This physical resolution is determined during the actual simulation by comparing the size of the smallest relevant scales to the local grid size used in the computation. The contribution function is designed such that it provides no modeling if the computation is locally well resolved so that it approaches direct numerical simulations (DNS) in the fine-grid limit and such that it provides modeling of all scales in the coarse-grid limit and thus approaches a RANS calculation. In between these resolution limits, the contribution function adjusts the necessary modeling for the unresolved scales while the larger (resolved) scales are computed as in large eddy simulation (LES). However, FSM is distinctly different from LES in that it allows for a consistent transition between RANS, LES, and DNS within the same simulation depending on the local flow behavior and “physical” resolution. As a consequence, FSM should require considerably fewer grid points for a given calculation than would be necessary for a LES. This conjecture is substantiated by employing FSM to calculate the flow over a backward-facing step and a plane wake behind a bluff body, both at low Mach number, and supersonic axisymmetric wakes. These examples were chosen such that they expose, on the one hand, the inherent difficulties of simulating (physically) complex flows, and, on the other hand, demonstrate the potential of the FSM approach for simulations of turbulent compressible flows for complex geometries.

Turbulence Modeling in a Model Combustor

2005 ◽  
Author(s):  
Lei-Yong Jiang ◽  
Ian Campbell
Keyword(s):  
Reynolds Stress ◽  
Eddy Viscosity ◽  
Turbulence Modeling ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Moment Closure ◽  
Superior Performance ◽  
Combustion Model ◽  
Discrete Ordinates ◽  
Viscosity Models

The flow field of a propane-air diffusion flame combustor with interior and exterior conjugate heat transfers was numerically investigated. Solutions obtained from four turbulence models together with a laminar flamelet combustion model, discrete ordinates radiation model and enhanced wall treatment are presented and discussed. The numerical results are compared, in detail, with a comprehensive database obtained from a series of experimental measurements. It is found that the Reynolds stress model (RSM), a second moment closure, illustrates superior performance over three popular two-equation eddy-viscosity models. Although the main flow features are captured by all four turbulence models, only the RSM is able to successfully predict the lengths of both recirculation zones and the turbulence kinetic energy distribution in the combustor chamber. In addition, it provides fairly good predictions for all Reynolds stress components, except for the circumferential normal stress at downstream sections. However, the superiority of the RSM is not so obvious for the temperature and species predictions in comparison with eddy-viscosity models, except for the standard k-ε model. This suggests that coupling between the RSM and combustion models needs to be further improved in order to enhance its applications in practical combustion systems.

Experimental Investigation of a Truncated Pipe Diffuser With a Tandem Deswirler in a Centrifugal Compressor Stage

2012 ◽  
Author(s):  
Robert Kunte ◽  
Peter Jeschke ◽  
Caitlin Smythe
Keyword(s):  
Experimental Investigation ◽  
Centrifugal Compressor ◽  
Pressure Rise ◽  
Compressor Stage ◽  
Local Flow ◽  
Centrifugal Compressor Stage ◽  
Geometric Configurations ◽  
Flow Phenomena ◽  
Fundamental Insight ◽  
The Impact

The subject of this paper is the experimental investigation of three different geometric configurations of the diffusing system in a high pressure centrifugal compressor stage for a jet engine application. The objective of this study is twofold. On the one hand, it seeks to explain the impact of truncating a diffuser and a redesigned tandem deswirler on the global stage performance; on the other hand, it aims to correlate the performance differences with local flow phenomena. For this purpose, a state-of-the-art centrifugal compressor test rig was used. Particle image velocimetry measurements visualize the separation behavior in the pipe diffuser passage. Thereby it is shown that the truncation of the diffuser changed the boundary conditions for the downstream deswirler including a high incidence. Thus, a new tandem deswirler design was implemented and measured. Moreover, the relative position of the two tandem rows is investigated. An optimal relative circumferential position for the stage efficiency and static pressure rise was found. This paper gives fundamental insight into the physical mechanisms of the influence of three geometric configurations in a centrifugal compressor stage, especially in the pipe diffuser and the deswirler. Hence, this study contributes in furthering knowledge of the fundamental principles of flow phenomena in the diffusing system of a centrifugal compressor.

Evaluation of Turbulence Closure Models for Large-Eddy Simulation over Complex Terrain: Flow over Askervein Hill

2009 ◽  
Vol 48 (5) ◽  
pp. 1050-1065 ◽  
Author(s):  
Fotini Katopodes Chow ◽  
Robert L. Street
Keyword(s):  
Eddy Viscosity ◽  
Mixed Model ◽  
Turbulence Models ◽  
Test Case ◽  
Closure Models ◽  
Eddy Simulation ◽  
Eddy Viscosity Model ◽  
Scale Similarity ◽  
Askervein Hill ◽  
The Hill

Abstract The evaluation of turbulence closure models for large-eddy simulation (LES) has primarily been performed over flat terrain, where comparisons with theory and observations are simplified. The authors have previously developed improved closure models using explicit filtering and reconstruction, together with a dynamic eddy-viscosity model and a near-wall stress term. This dynamic reconstruction model (DRM) is a mixed model, combining scale-similarity and eddy-viscosity components. The DRM gave improved results over standard eddy-viscosity models for neutral boundary layer flow over flat but rough terrain, yielding the expected logarithmic velocity profiles near the wall. The results from the studies over flat terrain are now extended to flow over full-scale topography. The test case is flow over Askervein Hill, an isolated hill in western Scotland, where a field campaign was conducted in 1983 with the purpose of capturing wind data representing atmospheric episodes under near-neutral stratification and steady wind conditions. This widely studied flow provides a more challenging test case for the new turbulence models because of the sloping terrain and separation in the lee of the hill. Since an LES formulation is used, a number of simulation features are different than those typically used in the Askervein literature. The simulations are inherently unsteady, the inflow conditions are provided by a separate turbulent flow database, and (uniquely herein) ensemble averages of the turbulent flow results are used in comparisons with field data. Results indicate that the DRM can improve the predictions of flow speedup and especially turbulent kinetic energy (TKE) over the hill when compared with the standard TKE-1.5 model. This is the first study, to the authors’ knowledge, in which explicit filtering and reconstruction (scale similarity) and dynamic turbulence models have been applied to full-scale simulations of the atmospheric boundary layer over terrain. Simulations with the lowest level of reconstruction are straightforward. Increased levels of reconstruction, however, present difficulties when used with a dynamic eddy-viscosity model. An alternative mixed model is proposed to avoid the complexities associated with the dynamic procedure and to allow higher levels of reconstruction; this mixed model combines a standard TKE-1.5 eddy-viscosity closure with velocity reconstruction to form a simple and efficient turbulence model that gives good results for both mean flow and turbulence over Askervein Hill. The results indicate that significant improvements in LES over complex terrain can be obtained by the use of mixed models that combine scale-similarity and eddy-viscosity components.

Assessment of Turbulence Model Predictions for an Aero-Engine Centrifugal Compressor

2010 ◽  
Vol 133 (1) ◽  
Author(s):  
Jason A. Bourgeois ◽  
Robert J. Martinuzzi ◽  
Eric Savory ◽  
Chao Zhang ◽  
Douglas A. Roberts
Keyword(s):  
Centrifugal Compressor ◽  
Turbulence Modeling ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Flow Fields ◽  
Reynolds Stress Model ◽  
Tip Clearance ◽  
Mean Flow ◽  
Tip Clearance Flow ◽  
Sst Model

The accurate prediction of mean flow fields with high degrees of curvature, adverse pressure gradients, and three-dimensional turbulent boundary layers typically present in centrifugal compressor stages is a significant challenge when applying Reynolds averaged Navier–Stokes turbulence modeling techniques. The current study compares the steady-state mixing plane predictions using four turbulence models for a centrifugal compressor stage with a tandem impeller and a “fish-tail” style discrete passage diffuser. The models analyzed are the k-ε model (an industry standard for many years), the shear stress transport (SST) model, a proposed modification to the SST model denoted as the SST-reattachment modification (RM), and the Speziale, Sarkar, and Gatski Reynolds stress model (RSM-SSG). Comparisons with measured performance parameters—the stage total-to-static pressure and total-to-total temperature ratios—indicate more accurate performance predictions from the RSM-SSG and SST models as compared to the k-ε and SST-RM models. Details of the different predicted flow fields are presented. Estimates of blockage, aerodynamic slip factor, and impeller exit velocity profiles indicate significant physical differences in the predictions at the impeller-diffuser interface. Topological flow field differences are observed: the separated tip clearance flow is found to reattach with the SST, SST-RM, and RSM-SSG models, while it does not with the k-ε model, a larger shroud separation at the impeller exit seen with the SST and SST-RM models, and core flow differences are in the complex curved diffuser geometry. The results are discussed in terms of the production and dissipation of k predicted by the various models due to their intrinsic modeling assumptions. These comparisons will assist aerodynamic designers in choosing appropriate turbulence models, and may benefit future modeling research.

scholarly journals The Impact of Various Modelling Decisions on Flow Field Predictions in a Centrifugal Compressor

2020 ◽  
Author(s):  
William J. Gooding ◽  
Matthew A. Meier ◽  
Nicole L. Key
Keyword(s):  
Flow Field ◽  
Centrifugal Compressor ◽  
Computational Models ◽  
Turbulence Models ◽  
Numerical Results ◽  
Computational Tools ◽  
Performance Trends ◽  
Sst Turbulence Model ◽  
Overall Performance ◽  
The Impact

Abstract Computational tools have become increasingly important in design and research applications in recent years due to increasing computational resources. In most cases, model geometry and flow-physics are simplified to reduce the complexity of the computational model. While this was necessary historically, modern computational tools are capable of including realistic features such as fillets, surface roughness, and heat transfer. This work presents extensive and systematic numerical results from a simulation of a centrifugal compressor stage for an aero-engine application. Numerical results are compared to detailed experimental data to investigate the effect of various modelling decisions, including turbulence models, on the predicted aerodynamics developing through the diffuser passage. Roughness and the inclusion of fillets significantly impact the flow development, especially with the SST turbulence model. This approach leads to the conclusion that the BSL-EARSM model is best able to predict the experimentally determined diffuser flow profiles and overall performance trends with the inclusion of the previously mentioned model features. Additionally, the misleading conclusions can be reached if modelling decisions are based on merely matching overall performance values. Finally, frozen rotor simulations are used to roughly approximate the impact of unsteadiness on the flow field. The results show a significant impact and also that the inclusion of approximate unsteady effects tends to further improve the predictive capability of the computational models that were considered.

Experimental and Numerical Investigation of Tip Clearance and Bleed Effects in a Centrifugal Compressor Stage With Pipe Diffuser

2011 ◽  
Author(s):  
Robert Kunte ◽  
Philipp Schwarz ◽  
Benjamin Wilkosz ◽  
Peter Jeschke ◽  
Caitlin Smythe
Keyword(s):  
Numerical Investigation ◽  
Centrifugal Compressor ◽  
Tip Clearance ◽  
Compressor Stage ◽  
Local Flow ◽  
Centrifugal Compressor Stage ◽  
Centrifugal Stage ◽  
Flow Phenomena ◽  
Fundamental Insight ◽  
The Impact

The subject of this paper is the experimental and numerical investigation of a state-of-the-art high pressure centrifugal compressor stage with pipe diffuser for a jet engine application. This study shows the impact of impeller tip clearance- and bleed-variation on the centrifugal stage. The purpose of this paper is threefold. In the first place, it investigates the effects on the stage performance. Secondly, it seeks to explain local flow-phenomena, especially in the diffuser. Finally, it shows that steady CFD simulations are capable of predicting these phenomena. Experimental data were gathered using conventional pitot and three-hole-probes as well as Particle-Image-Velocimetry. Numerical simulations with the CFD solver TRACE were conducted to get fundamental insight into the flow. Thus, this study contributes greatly towards understanding the principle of the flow phenomena in the pipe diffuser of a centrifugal compressor.

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