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.

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.

Comparative Study of Vaneless and Vaned Diffusers in a Transonic Centrifugal Compressor With Real Gas

2000 ◽  
Author(s):  
Michael M. Cui
Keyword(s):  
Flow Field ◽  
Centrifugal Compressor ◽  
Three Dimensional ◽  
Power Laws ◽  
Navier Stokes ◽  
Local Flow ◽  
Design And Optimization ◽  
Transonic Centrifugal Compressor ◽  
Overall Performance ◽  
The Impact

Vaneless and vaned diffusers in a transonic centrifugal compressor with the refrigerant HFC-134a were studied experimentally and numerically. The compressor was tested on a closed-loop stand instrumented to obtain both overall performance data and local flow field quantities. In numerical studies, the thermodynamic and transport properties of the refrigerant gas were modeled by the Martin-Hou equation of state and power laws, respectively. To include the interaction of the compressor components in these analyses, a unified three-dimensional numerical model was built for the complete compressor stage. The flow field was calculated with a Navier-Stokes solver using the k-ε turbulent model. The impact of the different diffusers on both local flow field and overall performance is analyzed comparatively for each component. The experimental and numerical results agree well. The correlation between the overall compressor performance and local flow field quantities is defined. The methodology developed and data obtained in these studies can be applied to centrifugal compressor design and optimization.

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.

Application of a Multi-Block CFD Code to Investigate the Impact of Geometry Modeling on Centrifugal Compressor Flow Field Predictions

1996 ◽  
Author(s):  
Michael D. Hathaway ◽  
Jerry R. Wood
Keyword(s):  
Flow Field ◽  
Centrifugal Compressor ◽  
Block Code ◽  
Tip Clearance ◽  
Trailing Edge ◽  
Flow Angle ◽  
Significant Difference ◽  
Single Block ◽  
The Impact ◽  
Actual Geometry

CFD codes capable of utilizing multi-block grids provide capability to analyze the complete geometry of centrifugal compressors including, among others, multiple splitter rows, tip clearance, blunt trailing edges, fillets, and slots between moving and stationary surfaces. Attendant with this increased capability is potentially increased grid setup time and more computational overhead — CPU time and memory requirements — with the resultant increase in “wall clock” time to obtain a solution. If the increase in “difficulty” of obtaining a solution significantly improves the solution from that obtained by modeling the features of the tip clearance flow or the typical bluntness of a centrifugal compressor’s trailing edge, then the additional burden is worthwhile. However, if the additional information obtained is of marginal use then modeling of certain features of the geometry may provide reasonable solutions for designers to make comparative choices when pursuing a new design. In this spirit a sequence of grids were generated to study the relative importance of modeling versus detailed gridding of the tip gap and blunt trailing edge regions of the NASA large low speed centrifugal compressor for which there is considerable detailed internal laser anemometry data available for comparison. The results indicate: 1) There is no significant difference in predicted tip clearance mass flow rate whether the tip gap is gridded or modeled. 2) Gridding rather than modeling the trailing edge results in better predictions of some flow details downstream of the impeller, but otherwise appears to offer no great benefits. 3) The pitchwise variation of absolute flow angle decreases rapidly up to 8% impeller radius ratio and much more slowly thereafter. Although some improvements in prediction of flow field details are realized as a result of analyzing the actual geometry there is no clear consensus that any of the grids investigated produced superior results in every case when compared to the measurements. However, if a multi-block code is available it should be used as it has the propensity for enabling better predictions than a single block code which requires modeling of certain geometry features. If a single block code must be used some guidance is offered for modeling those geometry features which can’t be directly gridded.

Investigation of Fan Rotor Interaction With Pressure Disturbance Produced by Downstream Pylon

2013 ◽  
Author(s):  
Tomonori Enoki ◽  
Hidekazu Kodama ◽  
Shinya Kusuda
Keyword(s):  
Flow Field ◽  
Three Dimensional ◽  
Numerical Results ◽  
Rotor Blades ◽  
Flow Structures ◽  
Coupled Analysis ◽  
Unsteady Forces ◽  
Rotor Stator Interaction ◽  
The Impact ◽  
Potential Pressure

This paper presents an investigation of fan rotor interaction with potential pressure disturbances produced by a downstream pylon. Three-dimensional unsteady viscous analyses are performed for two fan rotor-stator-pylon configurations with different axial gaps between the stator and the pylon, and compared with the experimental results. To clarify the impact of the rotor-pylon interaction on the potential pressure flow field, a numerical analysis for the configuration in which a fan rotor is removed is also performed and compared with the numerical results with fan rotor. Actuator disk analyses are also performed to interpret the flow structures observed in the experiments and the numerical results. It is found that a fan rotor-stator interaction also exists in the fan flow field, and this may impact on the upstream propagating potential flow that dominates the unsteady forces acting on the rotor blades. A coupled analysis between fan rotor and stator is essential to accurately predict the unsteady blade force.

scholarly journals Comparative Study of Unsteady Flows in a Transonic Centrifugal Compressor With Vaneless and Vaned Diffusers

2001 ◽  
Author(s):  
Michael M. Cui
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Centrifugal Compressor ◽  
Three Dimensional ◽  
Power Laws ◽  
Working Fluid ◽  
Local Flow ◽  
Transonic Centrifugal Compressor ◽  
Compressor Performance ◽  
Overall Performance

To reduce vibration and noise level, the impeller and diffuser blade numbers inside an industrial compressor are typically chosen without common divisors. The shapes of volutes or collectors in these compressors are also not axis-symmetric. When impeller blades pass these asymmetric structures, the flow field in the compressor is time-dependent and three-dimensional. To obtain a fundamental physical understanding of these three-dimensional unsteady flow fields and assess their impact on the compressor performance, the flow field inside the compressors needs to be studied as a whole to include asymmetric and unsteady interaction between the compressor components. In current study, a unified three-dimensional numerical model was built for a transonic centrifugal compressor including impeller, diffusers, and volute. HFC 134a was used as the working fluid. The thermodynamic and transport properties of the refrigerant gas were modeled by the Martin-Hou equation of state and power laws, respectively. The three-dimensional unsteady flow field was simulated with a Navier-Stokes solver using the k-ε turbulent model. The overall performance parameters are obtained by integrating the field quantities. Both unsteady flow field and overall performance are analyzed comparatively for each component. The compressor was tested in a water chiller system instrumented to obtain both overall performance data and local flow field quantities. The experimental and numerical results agree well. The correlation between the overall compressor performance and local flow field quantities is defined. The methodology developed and data obtained in these studies can be applied to centrifugal compressor design and optimization.

Aerodynamic Analysis of a Multistage Centrifugal Compressor

2003 ◽  
Author(s):  
Duccio Bonaiuti ◽  
Andrea Arnone ◽  
Alberto Milani ◽  
Leonardo Baldassarre
Keyword(s):  
Flow Field ◽  
Centrifugal Compressor ◽  
Three Dimensional ◽  
Operating Range ◽  
Aerodynamic Analysis ◽  
Critical Elements ◽  
Multi Stage ◽  
The One ◽  
Multistage Centrifugal Compressor ◽  
The Impact

The aerodynamic analysis of a four–stage centrifugal compressor was performed by means of a three–dimensional multi stage CFD code. The whole operating range of the compressor was investigated and the critical elements affecting the choke and stall limit were identified. The isolated impellers were also analyzed separately and the flow field was compared to the one coming from the multistage analysis. This allowed us to study the effect of the interactions between components and quantify the impact of the multistage environment on the impellers’ performance.

Experimental and Numerical Investigation of a Centrifugal Compressor and Numerical Study of the Area Ratio and Tip Clearance Effects on the Performance Characteristic

2008 ◽  
Author(s):  
Mahdi Nili-Ahmadabadi ◽  
Ali Hajilouy-Benisi ◽  
Mohammad Durali ◽  
Sayyed Mostafa Motavalli
Keyword(s):  
Flow Field ◽  
Centrifugal Compressor ◽  
Numerical Study ◽  
Pressure Ratio ◽  
Three Dimensional ◽  
Area Ratio ◽  
Tip Clearance ◽  
Performance Characteristics ◽  
Navier Stokes ◽  
Sst Turbulence Model

In this research, the centrifugal compressor of a turbocharger is investigated experimentally and numerically. Performance characteristics of the compressor were obtained experimentally by measurements of rotor speed and flow parameters at the inlet and outlet of the compressor. Three dimensional flow field in the impeller and diffuser was analyzed numerically using a full Navier-Stokes program with SST turbulence model. The performance characteristics of the compressor were obtained numerically, which were then compared with the experimental results. The comparison shows good agreement. Furthermore, the effect of area ratio and tip clearance on the performance parameters and flow field was studied numerically. The impeller area ratio was changed by cutting the impeller exit axial width from an initial value of 4.1 mm to a final value of 5.1 mm, resulting in an area ratio from 0.792 to 0.965. For the rotor with exit axial width of 4.6 mm, performance was investigated for tip clearance of 0.0, 0.5 and 1.0 mm. Results of this simulation at design point showed that the compressor pressure ratio peaked at an area ratio of 0.792 while the efficiency peaked at a higher value of area ratio of 0.878. Also the increment of the tip clearance from 0 to 1 mm resulted in 20 percent efficiency decrease.

Flow Analysis of a High Flowrate Centrifugal Compressor Stage and Comparison With Test Rig Data

2016 ◽  
Author(s):  
Anton Weber ◽  
Christian Morsbach ◽  
Edmund Kügeler ◽  
Christoph Rube ◽  
Matthias Wedeking
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Centrifugal Compressor ◽  
Total Pressure ◽  
Pressure Ratio ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Stress Model ◽  
Test Rig ◽  
Total Pressure Ratio

The flow field inside a single-stage centrifugal compressor characterized by a high flowrate of Φ = 0.15 and a design total pressure ratio of approximately 1.4 is analysed numerically. The stage geometry consists of a radially oriented inlet duct with uniform inflow without swirl, a 90 deg inlet bend in front of the impeller, the shrouded impeller itself followed by a large radial vaneless diffuser, a 180 deg U-turn, a radially oriented turning vane, a subsequent 90 deg bend, and as the last item a long axial exit duct. The impeller blades have large fillets at hub and tip and thick blunt trailing edges. Due to the rotating shroud, a labyrinth seal is placed above the impeller with 5 seal tips. The complete leakage region is also included in the CFD analysis. The blade numbers for the impeller and vane are 15 and 14, respectively. The test rig has recently been built at the Institute of Propulsion and Turbomachinery at RWTH Aachen University (Germany). The first part of the CFD work presented was carried out before the first experimental data were available. Using the k-ω turbulence model of Wilcox (1988), a number of principal steady RANS calculations were performed to investigate the following: Impact of near wall grid resolution and turbulence model wall boundary condition treatment, impact of impeller fillets, and the influence of leakage flow. This part is completed by a comparison of steady RANS simulations with the time-mean results of unsteady RANS analyses of one blade passage. For the calculations presented in the second part, experimental data are available at the inflow and outflow planes. At these planes overall mean values were deduced. Additionally, 3- and 5-hole probe data are available at spanwise traverse planes located at the zenith of the U-turn and in the exit plane. For part two a finer grid with y+ values of approximately unity for all solid walls was used. In addition to the Wilcox k-ω model and the Menter SST k-ω model, two higher level turbulence models — the explicit algebraic Reynolds stress model Hellsten EARSM k-ω and the differential Reynolds stress model SSG/LRR-ω — have been tested and compared with the experiments. The agreement in terms of overall performance (total pressure ratio, isentropic efficiency) is satisfactory for all turbulence models used, but there are some differences: the k-ω model is shown to be the most stable one towards stall. On the other hand, it is shown that details of the flow field in terms of the two spanwise traverses can be better represented by the more advanced turbulence models. All CFD simulations have been performed at 100% shaft speed.

Numerical Investigation of a Transonic Centrifugal Compressor

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
Michele Marconcini ◽  
Filippo Rubechini ◽  
Andrea Arnone ◽  
Seiichi Ibaraki
Keyword(s):  
Shock Waves ◽  
Flow Field ◽  
Centrifugal Compressor ◽  
Pressure Ratio ◽  
Turbulence Models ◽  
Tip Clearance ◽  
Complex Flow ◽  
Low Velocity ◽  
Flow Measurements ◽  
Vaned Diffuser

A three-dimensional Navier-Stokes solver is used to investigate the flow field of a high-pressure ratio centrifugal compressor for turbocharger applications. Such a compressor consists of a double-splitter impeller followed by a vaned diffuser. The inlet flow to the open shrouded impeller is transonic, thus giving rise to interactions between shock waves and boundary layers and between shock waves and tip leakage vortices. These interactions generate complex flow structures which are convected and distorted through the impeller blades. Detailed laser Doppler velocimetry flow measurements are available at various cross sections inside the impeller blades highlighting the presence of low-velocity flow regions near the shroud. Particular attention is focused on understanding the physical mechanisms which govern the flow phenomena in the near shroud region. To this end numerical investigations are performed using different tip clearance modelizations and various turbulence models, and their impact on the computed flow field is discussed.

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