Investigation of Turbulence Modeling and Harmonic Balance Methods Towards Accurately Predicting Compressor Flow Fields

2020 ◽  
Author(s):  
Liam McManus ◽  
Justin Hodges ◽  
Ilyas Beary
Keyword(s):  
Harmonic Balance ◽  
Cfd Simulation ◽  
Turbulence Modeling ◽  
Fluid Dynamic ◽  
Computational Cost ◽  
Sensitivity Study ◽  
Peak Efficiency ◽  
Transonic Compressor ◽  
Unsteady Effects ◽  
Operating Points

Abstract Numerical investigations of the NASA stage 37 compressor case are presented. Simcenter STAR-CCM+ is used for RANS based aerodynamic quantifications of the transonic compressor, with specific attention to the near stall and the peak efficiency operating points. In these axial turbomachines, the unsteady effects are non-trivial, and need to be accounted for in the design methods. Typically, transient simulation of fully realistic engine hardware is unrealistic in terms of the computational expense. However, using a harmonic balance approach in computational fluid dynamic (CFD) simulation has been shown to have a proficiency in capturing the dominant unsteady behaviors at a relatively lower computational cost. As such, the performance of the NASA stage 37 compressor is characterized with both steady and harmonic balance approaches. Furthermore, a thorough exploration and sensitivity study on the turbulence modeling is conducted. The lag elliptic blending k-ε turbulence model is considered, due to its capability for improved predictions in highly separated turbomachinery flows, as compared to the k-O SST and k-O BSL model results.

Prediction of the Acoustic Reflection in a Realistic Aeroengine Intake With Three Numerical Methods to Analyze Fan Flutter

2020 ◽  
Author(s):  
Thomas Bontemps ◽  
Stéphane Aubert ◽  
Maxime de Pret
Keyword(s):  
Analytical Model ◽  
Design Process ◽  
Cfd Simulation ◽  
Computational Cost ◽  
Fidelity Level ◽  
Acoustic Reflection ◽  
Acoustic Coupling ◽  
Air Intake ◽  
Operating Points ◽  
Do So

Abstract For a particular range of frequencies, an acoustic coupling between the fan and the air intake can modify fan stability regarding flutter. Previous works have shown that characterizing the reflection on the intake opening might be a crucial element to target operating points for which the risk of acoustic driven flutter is high. To do so, three methodologies are compared in this paper: an aeroelastic CFD simulation, an acoustic potential simulation and an analytical model. Each of them has a different fidelity level and computational cost, what makes their usage more beneficial at some step in the design process. It is shown that results of aeroelastic CFD and acoustic potential simulations are in excellent agreement. Fast acoustic simulations are then a good option in the early design process. The analytical model presents an important error mainly on the phase, and should be adapted before usage.

scholarly journals A Closed-Loop Optimized System with CFD Data for Liquid Maldistribution Model

Processes ◽  
2020 ◽  
Vol 8 (11) ◽  
pp. 1332
Author(s):  
Wei Zhang ◽  
Liyi Li ◽  
Baoping Zhang ◽  
Xin Xu ◽  
Jian Zhai ◽  
...  
Keyword(s):  
Closed Loop ◽  
Cfd Simulation ◽  
Fluid Dynamic ◽  
Structural Parameters ◽  
Computational Cost ◽  
Pso Algorithm ◽  
Oil Refining ◽  
Support Vector ◽  
Cfd Validation ◽  
Liquid Distributor

For the simulation of a trickle-bed reactor (TBR) in coal and oil refining, modeling the liquid maldistribution of the gas-liquid distributor incurs enormous pre-processing work and bears a huge computational cost. A closed-loop optimized system with computational fluid dynamic (CFD) data is therefore proposed for the first time in this paper. A fast prediction model based on support vector regression (SVR) is developed to simplify the modeling of the liquid flow rate in TBRs. The model uses CFD simulation results to determine an optimized set of structural parameters for the gas-liquid distributor in TBRs. In order to obtain an accurate SVR model quickly, the particle swarm optimization (PSO) algorithm is employed to optimize the SVR parameters. Then, the structural parameters corresponding to the minimum liquid maldistribution factor are calculated using the response surface methodology (RSM) based on the hybrid PSO-SVR model. The CFD validation results show a good agreement with the values predicted by RSM, with liquid maldistribution factors of 0.159 and 0.162, respectively.

An Adjoint-Based Multi-Point Optimization Method for Robust Turbomachinery Design

2015 ◽  
Author(s):  
Benjamin Walther ◽  
Siva Nadarajah
Keyword(s):  
Computational Cost ◽  
Optimization Method ◽  
Finite Difference Approximation ◽  
Operating Point ◽  
Difference Approximation ◽  
Transonic Compressor ◽  
Multi Stage ◽  
Design Variables ◽  
Turbomachinery Design ◽  
Operating Points

This paper introduces a multi-point design capability to discrete adjoint-based aerodynamic shape optimization for multi-stage turbomachines. The developed optimization framework allows to improve a compressor or turbine design not only for a certain operating point, but enables the inclusion of additional off-design operation points, therefore guaranteeing a robust design and annihilating the risk of improving the configuration for a specific design point while deteriorating the overall operability of the turbomachine. To keep the computational cost to a minimum, at every design cycle the flow and adjoint solutions are first calculated and stored for each operating point. This approach ensures that the subsequent finite-difference approximation of the residual sensitivity with respect to the design variables is obtained at a cost nearly independent of the number of investigated operating points. The objective function gradient is then assembled as a weighted sum of the sensitivities calculated for the different operating points. The developed multi-point optimization method is applied to a single-stage transonic compressor and both the back pressure and the rotor wheel speed are varied to investigate the use of adjoint-based design methods to efficiently explore robust turbomachinery designs.

A Theoretical Model for Flow Instability Inception in Transonic Fan/Compressors

2013 ◽  
Author(s):  
Xiaofeng Sun ◽  
Xiaohua Liu ◽  
Dakun Sun
Keyword(s):  
Theoretical Model ◽  
Flow Field ◽  
High Speed ◽  
Cfd Simulation ◽  
Flow Instability ◽  
Computational Cost ◽  
Mean Flow ◽  
Transonic Compressor ◽  
Onset Point ◽  
Transonic Fan

This paper applies a theoretical model, which has been developed recently, to calculate the flow instability inception of axial transonic fan/compressors system. After the mean flow field is computed by steady CFD simulation, a body force approach, which is a function of flow field data, is taken to represent the effects of discrete blades on the flow field and duplicate the physical sources of flow turning and loss. Further by applying appropriate boundary conditions and spectral collocation method, a group of homogeneous equations will yield from which the stability equation can be derived. The singular value decomposition method is adopted over a series of fine grids in frequency domain to solve the resultant eigenvalue problem, and the onset point of flow instability can be judged by the imaginary part of the resultant eigenvalue. The present investigation is to validate the feasibility of calculating the stall onset point for single stage transonic compressor. It is shown that this model is capable of predicting instability inception point of transonic flow with reasonable accuracy, and it is sustainable in terms of computational cost for industrial application. It is shown that this model can provide an unambiguous judgment on stall inception without numerous requirements of empirical relations of loss and deviation angle. It provides a possibility to check over-predicted stall margin during the design phase of new high speed fan/compressors. In addition, the effect of flow compressibility on the stall onset point calculation for transonic rotor is studied.

scholarly journals Conjugate Heat Transfer Predictions for Subcooled Boiling Flow in a Horizontal Channel Using a Volume-of-Fluid Framework

2018 ◽  
Vol 140 (10) ◽  
Author(s):  
M. Langari ◽  
Z. Yang ◽  
J. F. Dunne ◽  
S. Jafari ◽  
J.-P. Pirault ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Turbulence Modeling ◽  
Fluid Dynamic ◽  
Computational Cost ◽  
Thermal Conditions ◽  
Nucleate Boiling ◽  
Volume Of Fluid ◽  
Navier Stokes ◽  
Mass Generation

Abstract The accuracy of computational fluid dynamic (CFD)-based heat transfer predictions have been examined of relevance to liquid cooling of IC engines at high engine loads where some nucleate boiling occurs. Predictions based on (i) the Reynolds Averaged Navier-Stokes (RANS) solution and (ii) large eddy simulation (LES) have been generated. The purpose of these simulations is to establish the role of turbulence modeling on the accuracy and efficiency of heat transfer predictions for engine-like thermal conditions where published experimental data are available. A multiphase mixture modeling approach, with a volume-of-fluid interface-capturing method, has been employed. To predict heat transfer in the boiling regime, the empirical boiling correlation of Rohsenow is used for both RANS and LES. The rate of vapor-mass generation at the wall surface is determined from the heat flux associated with the evaporation phase change. Predictions via CFD are compared with published experimental data showing that LES gives only slightly more accurate temperature predictions compared to RANS but at substantially higher computational cost.

Unsteady Simulation of a 1.5 Stage Turbine Using an Implicitly Coupled Nonlinear Harmonic Balance Method

2012 ◽  
Author(s):  
Chad H. Custer ◽  
Jonathan M. Weiss ◽  
Venkataramanan Subramanian ◽  
William S. Clark ◽  
Kenneth C. Hall
Keyword(s):  
Unsteady Flow ◽  
Time Domain ◽  
Harmonic Balance ◽  
Fourier Coefficients ◽  
Fluid Dynamic ◽  
Time Derivative ◽  
Computational Cost ◽  
Harmonic Balance Method ◽  
Balance Method ◽  
Computational Domain

The harmonic balance method implemented within STAR-CCM+ is a mixed frequency/time domain computational fluid dynamic technique, which enables the efficient calculation of time-periodic flows. The unsteady solution is stored at a small number of fixed time levels over one temporal period of the unsteady flow in a single blade passage in each blade row; thus the solution is periodic by construction. The individual time levels are coupled to one another through a spectral operator representing the time derivative term in the Navier-Stokes equation, and at the boundaries of the computational domain through the application of periodic and nonreflecting boundary conditions. The blade rows are connected to one another via a small number of fluid dynamic spinning modes characterized by nodal diameter and frequency. This periodic solution is driven to the correct solution using conventional (steady) CFD acceleration techniques, and thus is computationally efficient. Upon convergence, the time level solutions are Fourier transformed to obtain spatially varying Fourier coefficients of the flow variables. We find that a small number of time levels (or, equivalently, Fourier coefficients) are adequate to model even strongly nonlinear flows. Consequently, the method provides an unsteady solution at a computational cost significantly lower than traditional unsteady time marching methods. The implementation of this nonlinear harmonic balance method within STAR-CCM+ allows for the simulation of multiple blade rows. This capability is demonstrated and validated using a 1.5 stage cold flow axial turbine developed by the University of Aachen. Results produced using the harmonic balance method are compared to conventional time domain simulations using STAR-CCM+, and are also compared to published experimental data. It is shown that the harmonic balance method is able to accurately model the unsteady flow structures at a computational cost significantly lower than unsteady time domain simulation.

An Implicit Harmonic Balance Method in Graphics Processing Units for Vibrating Blades

2015 ◽  
Author(s):  
Javier Crespo ◽  
Roque Corral ◽  
Jesus Pueblas
Keyword(s):  
Finite Difference ◽  
Harmonic Balance ◽  
Graphics Processing Units ◽  
Stokes Equations ◽  
Computational Cost ◽  
Harmonic Balance Method ◽  
Balance Method ◽  
Transonic Compressor ◽  
Speed Up ◽  
Graphics Processing

An implicit harmonic balance method for modeling the unsteady non-linear periodic flow about vibrating airfoils in turbomachinery is presented. As departing point, an implicit edge-based three-dimensional Reynolds Averaged Navier-Stokes equations solver for unstructured grids that runs both on central processing units (CPUs) and graphics processing units (GPUs) is used. The harmonic balance method performs a spectral discretization of the time derivatives and marches in pseudo-time a new system of equations where the unknowns are the variables at different time samples. The application of the method to vibrating airfoils is discussed. It is shown that a time spectral scheme may achieve the same temporal accuracy at a much lower computational cost than a Backward Finite Difference method at the expense of using more memory. The performance of the implicit solver has been assessed with several application examples. A speed-up factor of 10 is obtained between the spectral and finite difference version of the code whereas and an additional speed-up factor of 10 is obtained when the code is ported to GPUs, totalizing a speed factor of 100. The performance of the solver in GPUs has been assessed using the 10th standard aeroelastic configuration and a transonic compressor.

Modeling Capability for Cavity Flows in an Axial Compressor

2017 ◽  
Author(s):  
Syed Moez Hussain Mahmood ◽  
Mark G. Turner
Keyword(s):  
Coming Out ◽  
Parametric Design ◽  
Early Stage ◽  
Fluid Dynamic ◽  
Axial Compressor ◽  
Sensitivity Study ◽  
Vortical Flow ◽  
Cavity Flows ◽  
Definition Of ◽  
Unsteady Effects

Seal-teeth cavity leakage in a shrouded stator blade deteriorates the performance of an axial compressor. This impact of shrouded stator seal-teeth cavity flows on compressor performance is demonstrated by presenting a sensitivity study with different seal-teeth clearances. A parametric definition of the cavity geometry (including the seal teeth) is created for an axial compressor, which allows for variation in seal teeth design, clearance and cavity shape. One and a half subsonic stages (rotor-stator-rotor) of a 10 stage axial compressor derived from the EEE design is considered to perform a computational fluid dynamic study. A NLH calculation is performed to account for the unsteady effects across the rotor-stator interface. Accuracy of the NLH calculations is determined by a comparison with time-marching results. For mixing plane calculations the location of the rotor-stator interface relative to the upstream and down-stream cavity connections is crucial. Comparison for mixing plane calculation at different rotor-stator interface is made with NLH results. For this configuration the low momentum leakage flow through the cavities gets entrained in the power stream upstream of the stator which increases the near hub blockage for the stator. Excessive near hub blockage alters the outlet flow conditions for the stator which changes the incoming flow for the down-stream rotor. A vortical flow structure exists at the upstream and downstream cavity connections which changes with the increase in clearance and defines the flow going into and coming out of the cavity. An increase in seal-teeth cavity clearance is shown to deteriorate compressor efficiency up to 0.86% for the largest clearance analyzed. The parametric design and simulation process presented represents the first step in a design optimization process that accounts for cavity flows and seal leakage. The seal-teeth cavity should be modeled correctly to account for the correct blockage and loss distribution. It should also be integrated into the airfoil design at an early stage.

An Implicit Harmonic Balance Method in Graphics Processing Units for Oscillating Blades

2015 ◽  
Vol 138 (3) ◽  
Author(s):  
Javier Crespo ◽  
Roque Corral ◽  
Jesus Pueblas
Keyword(s):  
Finite Difference ◽  
Harmonic Balance ◽  
Graphics Processing Units ◽  
Stokes Equations ◽  
Computational Cost ◽  
Harmonic Balance Method ◽  
Transonic Compressor ◽  
Central Processing ◽  
Speed Up ◽  
Graphics Processing

An implicit harmonic balance (HB) method for modeling the unsteady nonlinear periodic flow about vibrating airfoils in turbomachinery is presented. An implicit edge-based three-dimensional Reynolds-averaged Navier–Stokes equations (RANS) solver for unstructured grids, which runs both on central processing units (CPUs) and graphics processing units (GPUs), is used. The HB method performs a spectral discretization of the time derivatives and marches in pseudotime, a new system of equations where the unknowns are the variables at different time samples. The application of the method to vibrating airfoils is discussed. It is shown that a time-spectral scheme may achieve the same temporal accuracy at a much lower computational cost than a backward finite-difference method at the expense of using more memory. The performance of the implicit solver has been assessed with several application examples. A speed-up factor of 10 is obtained between the spectral and finite-difference version of the code, whereas an additional speed-up factor of 10 is obtained when the code is ported to GPUs, totalizing a speed factor of 100. The performance of the solver in GPUs has been assessed using the tenth standard aeroelastic configuration and a transonic compressor.

Experimental Investigation on the Effects of Unsteady Excitation Frequency of Casing Treatment on Transonic Compressor Performance

2010 ◽  
Vol 133 (2) ◽  
Author(s):  
Wei Tuo ◽  
Yajun Lu ◽  
Wei Yuan ◽  
Sheng Zhou ◽  
Qiushi Li
Keyword(s):  
Excitation Frequency ◽  
Maximum Flow ◽  
Peak Efficiency ◽  
Stall Margin ◽  
Rotating Speed ◽  
Casing Treatment ◽  
Transonic Compressor ◽  
Compressor Performance ◽  
Design Speed ◽  
Unsteady Effects

The importance of the unsteady effects between the casing treatment and rotor is still not clear. Experiments are conducted in a transonic compressor with arc skewed slot casing treatment configurations. The experimental results indicate that the unsteady excitation frequency due to the slot number of casing treatment is one of the most important factors influencing compressor performance. Also, compressor performance can be overall enhanced through optimizing this unsteady excitation frequency. For the transonic compressor herein, peak efficiency, stall margin, and maximum flow mass can be improved by 0.17%, 19.86%, and 0.81%, respectively, at near design rotating speed, which can reach up to 1.13%, 57.84%, and 1.57%, respectively, at part design speed.

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