Assessment of Wall Modelling for Large Eddy Simulations of Turbomachinery

2018 ◽  
Author(s):  
Jagadeesh Movva ◽  
Dimitrios Papadogiannis ◽  
Stéphane Hiernaux
Keyword(s):  
Computational Cost ◽  
Large Eddy Simulations ◽  
Compressor Cascade ◽  
Potential Cost ◽  
Wall Model ◽  
Model Interaction ◽  
Large Eddy ◽  
Rans Simulations ◽  
The Impact ◽  
Near Wall

The design process of turbomachinery components relies heavily on Reynods Averaged Navier Stokes (RANS) simulations. This approach is well suited for steady simulations and comes with a low computational cost. However, turbomachinery flows are complex and difficult to predict accurately with RANS computations. Large Eddy Simulations (LES), capable of resolving the larger scales of turbulence, are a promising way to improve the predictive capability of numerical simulations. The main drawback of LES for wall bounded flows is its high computational cost, scaling with Re1.86 [1]. Turbomachinery components are characterized by Re ≈ 105–6, implying simulations with several billions of cells, with most allocated to resolve the turbulent scales inside the boundary layers. A potential cost-reducing approach is to introduce wall modelling. However, several questions remain, notably the wall model interaction with the laminar-to-turbulent transition and the impact of grid resolution. To clarify these points we investigate the flow across a linear compressor cascade with Wall Resolved LES (WRLES) and Wall Modelled LES (WMLES) simulations. Various near-wall resolutions are tested at on and off-design conditions to characterize the impact of the wall model on the flow field and the aerodynamic losses. RANS simulations complement the analysis. The results indicate that the WRLES agree the closest with experimental measurements. WMLES with relatively high near-wall resolution capture most of the flow physics while allowing a significant speed-up. However, reducing the resolution further leads to unphysical flow separations, despite staying well in the range of wall model validity.

Corner Stall Prediction in a Compressor Linear Cascade Using Very Large Eddy Simulation Lattice-Boltzmann Method

2020 ◽  
Vol 142 (7) ◽  
Author(s):  
Antoine Maros ◽  
Benoît Bonnal ◽  
Ignacio Gonzalez-Martino ◽  
James Kopriva ◽  
Francesco Polidoro
Keyword(s):  
Lattice Boltzmann Method ◽  
Lattice Boltzmann ◽  
Computational Cost ◽  
Large Eddy Simulations ◽  
Navier Stokes ◽  
Compressor Cascade ◽  
Numerical Work ◽  
Large Eddy ◽  
Boltzmann Method ◽  
Linear Compressor Cascade

Abstract Compressor corner stall is a phenomenon difficult to predict with numerical tools but essential to the design of axial compressors. Predictive methods are beneficial early in the design process to understand design and off-design limitations. Prior numerical work using Navier–Stokes computational methods has assessed the prediction capability for corner stall. Reynolds-averaged Navier–Stokes (RANS) simulations using several turbulence models have shown to over-predict the region of corner hub stall where large eddy simulations (LES) and detached eddy simulations (DES) approaches improved the airfoil surface and wake pressure loss prediction. A linear compressor cascade designed and tested at Ecole Centrale de Lyon provides a good benchmark for the evaluation of the accuracy of numerical methods for corner stall. This paper presents results obtained with Lattice-Boltzmann method (LBM) coupled with very large-eddy simulations (VLES) approach of PowerFLOW and compares them with the experimental and numerical work from Ecole Centrale de Lyon. The ability to achieve equivalent accuracy at a lower computational cost compared to LES scale resolving methods can enable multi-stage design and off-design compressor predictions. A methodical approach is taken by first accurately simulating the upstream flow conditions. Geometric trips are modeled upstream on the endwalls to match both the mean and fluctuating inflow boundary layer conditions. These conditions were then applied to the simulation of the linear compressor cascade. The benchline experimental study includes trips on both the pressure and suction of the airfoil. These trips are also included for the current simulation. The significance of capturing both inflow conditions and including trips on the airfoil is assessed. Detailed comparisons are then made to airfoil loading and downstream losses between experiment and previous RANS and LES simulations. LBM-VLES corner stall results of pitchwise averaged total pressure match LES agreement relative to experimental data at 50 times lower computational cost.

Corner Stall Prediction in a Compressor Linear Cascade Using Very Large Eddy Simulation (VLES) Lattice-Boltzmann Method

2019 ◽  
Author(s):  
Antoine Maros ◽  
Benoît Bonnal ◽  
Ignacio Gonzalez-Martino ◽  
James Kopriva ◽  
Francesco Polidoro
Keyword(s):  
Lattice Boltzmann Method ◽  
Lattice Boltzmann ◽  
Computational Cost ◽  
Large Eddy Simulations ◽  
Navier Stokes ◽  
Compressor Cascade ◽  
Numerical Work ◽  
Large Eddy ◽  
Boltzmann Method ◽  
Linear Compressor Cascade

Abstract Compressor corner stall is a phenomenon difficult to predict with numerical tools but essential to the design of axial compressors. Predictive methods are beneficial early in the design process to understand design and off-design limitations. Prior numerical work using Navier-Stokes computational methods have assessed the prediction capability for corner stall. Reynolds Averaged Navier-Stokes (RANS) simulations using several turbulence models [1] have shown to over-predict the region of corner hub stall where Large Eddy Simulations (LES) and Detached Eddy Simulations (DES) approaches improved the airfoil surface and wake pressure loss prediction [2, 3]. A linear compressor cascade designed and tested at Ecole Centrale de Lyon [3,4] provides a good benchmark for the evaluation of the accuracy of numerical methods for corner stall. This paper presents results obtained with Lattice-Boltzmann Method (LBM) coupled with Very Large-Eddy Simulations (VLES) approach of PowerFLOW and compares them with the experimental and numerical work from Ecole Centrale de Lyon. The ability to achieve equivalent accuracy at a lower computational cost compared to LES scale resolving methods can enable multi-stage design and off-design compressor predictions. A methodical approach is taken by first accurately simulating the upstream flow conditions. Geometric trips are modeled upstream on the endwalls to match both the mean and fluctuating inflow boundary layer conditions. These conditions were then applied to the simulation of the linear compressor cascade. The benchline experimental study includes trips on both the pressure and suction of the airfoil. These trips are also included for the current simulation. The significance of capturing both inflow conditions and including trips on the airfoil are assessed. Detailed comparisons are then made to airfoil loading and downstream losses between experiment and previous RANS and LES simulations. LBM-VLES corner stall results of pitchwise averaged total pressure match LES agreement relative to experimental data at 50 times lower computational cost.

scholarly journals Turbomachinery Noise Predictions: Present and Future

Acoustics ◽  
2019 ◽  
Vol 1 (1) ◽  
pp. 92-116 ◽  
Author(s):  
Stéphane Moreau
Keyword(s):  
Hybrid Methods ◽  
Free Field ◽  
Broadband Noise ◽  
Large Eddy Simulations ◽  
Analytical Models ◽  
Flat Plates ◽  
Tonal Noise ◽  
Noise Sources ◽  
Large Eddy ◽  
Rans Simulations

In future Ultra-High By-Pass Ratio turboengines, the turbomachinery noise (fan and turbine stages mainly) is expected to increase significantly. A review of analytical models and numerical methods to yield both tonal and broadband contributions of such noise sources is presented. The former rely on hybrid methods coupling gust response over very thin flat plates of finite chord length, either isolated or in cascade, and acoustic analogies in free-field and in a duct. The latter yields tonal noise with unsteady Reynolds-Averaged Navier–Stokes (u-RANS) simulations, and broadband noise with Large Eddy Simulations (LES). The analytical models are shown to provide good and fast first sound estimates at pre-design stages, and to easily separate the different noise sources. The u-RANS simulations are now able to give accurate estimates of tonal noise of the most complex asymmetric, heterogeneous fan-Outlet Guiding Vane (OGV) configurations. Wall-modeled LES on rescaled stage configurations have now been achieved on all components: a low-pressure compressor stage, a transonic high-pressure turbine stage and a fan-OGV configuration with good overall sound power level predictions for the latter. In this case, hybrid Lattice–Boltzmann/very large-eddy simulations also appear to be an excellent alternative to yield both contributions accurately at once.

Prediction of liquid-liquid flow in an SMX static mixer using large eddy simulations

2010 ◽  
Vol 64 (2) ◽  
Author(s):  
Paulina Pianko-Oprych ◽  
Zdzisław Jaworski
Keyword(s):  
Centrifugal Force ◽  
Liquid Flow ◽  
Concentration Distribution ◽  
Large Eddy Simulations ◽  
Dispersed Phase ◽  
Static Mixer ◽  
Phase Concentration ◽  
Large Eddy ◽  
Smx Static Mixer ◽  
The Impact

AbstractThe main purpose of the paper is to apply the large eddy simulations (LES) technique and to verify its use as a predicting tool for turbulent liquid-liquid flow in an SMX static mixer. LES modeling was carried out using the Smagorinsky-Lilly model of the turbulent subgrid viscosity for the Reynolds number of 5000 and 10000. The continuous phase was water and the dispersed phase was silicon oil. The investigation covers the effects of the density ratio between the phases. Three different cases of liquid densities were considered. The dispersed phase concentration distribution in the mixer cross-sections was compared with the corresponding time averaged results obtained formerly for the same configuration in a steady-state simulation using the standard RANS approach with the k-ɛ model. The dependency of the standard deviation of the dispersed phase concentration on the distance from the mixer inlet and the impact of the centrifugal force on the phase concentration distribution were investigated. The presented results for the SMX static mixer confirm conclusions of previous studies by Jaworski et al. (2006) obtained for a Kenics static mixer and show less a pronounced influence of the centrifugal force on the phase concentration distribution of the LES results in comparison to the RANS case.

Wall-model integrated computational framework for large-eddy simulations of wall-bounded flows

2021 ◽  
Vol 33 (12) ◽  
pp. 125120
Author(s):  
Yu Lv ◽  
Xinyi L. D. Huang ◽  
Xiaolei Yang ◽  
Xiang I. A. Yang
Keyword(s):  
Large Eddy Simulations ◽  
Wall Model ◽  
Computational Framework ◽  
Large Eddy ◽  
Wall Bounded Flows

Large-Eddy Simulation of Roughened NACA65 Compressor Cascade

2017 ◽  
Author(s):  
Jongwook Joo ◽  
Gorazd Medic ◽  
Om Sharma
Keyword(s):  
Surface Roughness ◽  
Large Eddy Simulations ◽  
Surface Imaging ◽  
Potential Solution ◽  
Discrete Elements ◽  
Compressor Cascade ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Rans Modeling ◽  
The One

Large eddy simulations over a NACA65 compressor cascade with roughness were performed for multiple roughness heights. The experiments show flow separation as airfoil roughness is increased. In LES computations, surface roughness was represented by regularly arranged discrete elements using guidelines from Schlichting. Results from wall-resolved LES indicate that specifying an equivalent sandgrain roughness height larger than the one in experiments is required to reproduce the same effects observed in experiments. This highlights the persisting uncertainty with matching the experimental roughness geometry in LES computations, pointing towards surface imaging and digitization as a potential solution. Some initial analysis of flow physics has been conducted with the aim of guiding the RANS modeling for roughness.

scholarly journals High-resolution large-eddy simulations of sub-kilometer-scale turbulence in the upper troposphere lower stratosphere

2013 ◽  
Vol 13 (12) ◽  
pp. 31891-31932 ◽  
Author(s):  
R. Paoli ◽  
O. Thouron ◽  
J. Escobar ◽  
J. Picot ◽  
D. Cariolle
Keyword(s):  
Large Scale ◽  
Lower Stratosphere ◽  
Atmospheric Model ◽  
Large Eddy Simulations ◽  
Stratified Flows ◽  
Flow Topology ◽  
Upper Troposphere ◽  
Large Eddy ◽  
Scale Turbulence ◽  
The Impact

Abstract. Large-eddy simulations of sub-kilometer-scale turbulence in the upper troposphere lower stratosphere (UTLS) are carried out and analyzed using the mesoscale atmospheric model Méso-NH. Different levels of turbulence are generated using a large-scale stochastic forcing technique that was especially devised to treat atmospheric stratified flows. The study focuses on the analysis of turbulence statistics, including mean quantities and energy spectra, as well as on a detailed description of flow topology. The impact of resolution is also discussed by decreasing the grid spacing to 2 m and increasing the number of grid points to 8×109. Because of atmospheric stratification, turbulence is substantially anisotropic, and large elongated structures form in the horizontal directions, in accordance with theoretical analysis and spectral direct numerical simulations of stably stratified flows. It is also found that the inertial range of horizontal kinetic energy spectrum, generally observed at scales larger than a few kilometers, is prolonged into the sub-kilometric range, down to the Ozmidov scales that obey isotropic Kolmorogov turbulence. The results are in line with observational analysis based on in situ measurements from existing campaigns.

Large-eddy simulations of tip leakage and secondary flows in an axial compressor cascade using a near-wall turbulence model

2009 ◽  
Vol 223 (6) ◽  
pp. 645-655 ◽  
Author(s):  
D Borello ◽  
G Delibra ◽  
K Hanjalić ◽  
F Rispoli
Keyword(s):  
Secondary Flows ◽  
Tip Clearance ◽  
Navier Stokes ◽  
Wall Region ◽  
Compressor Cascade ◽  
Tip Leakage ◽  
Computational Mesh ◽  
Large Eddy ◽  
Reynolds Averaged Navier Stokes ◽  
Near Wall

This paper reports on the application of unsteady Reynolds averaged Navier—Stokes (U-RANS) and hybrid large-eddy simulation (LES)/Reynolds averaged Navier—Stokes (RANS) methods to predict flows in compressor cascades using an affordable computational mesh. Both approaches use the ζ— f elliptic relaxation eddy-viscosity model, which for U-RANS prevails throughout the flow, whereas for the hybrid the U-RANS is active only in the near-wall region, coupled with the dynamic LES in the rest of the flow. In this ‘seamless’ coupling the dissipation rate in the k-equation is multiplied by a grid-detection function in terms of the ratio of the RANS and LES length scales. The potential of both approaches was tested in several benchmark flows showing satisfactory agreement with the available experimental results. The flow pattern through the tip clearance in a low-speed linear cascade shows close similarity with experimental evidence, indicating that both approaches can reproduce qualitatively the tip leakage and tip separation vortices with a relatively coarse computational mesh. The hybrid method, however, showed to be superior in capturing the evolution of vortical structures and related unsteadiness in the hub and wake regions.

High Resolution Large Eddy Simulations to Evaluate Turbulence Properties Within a Real Helicopter Engine Combustor

2018 ◽  
Author(s):  
Charlie Koupper ◽  
Jean Lamouroux ◽  
Stephane Richard ◽  
Gabriel Staffelbach
Keyword(s):  
Gas Turbine ◽  
Turbulence Intensity ◽  
Numerical Scheme ◽  
Mesh Refinement ◽  
Large Eddy Simulations ◽  
Scale Model ◽  
Large Eddy ◽  
Set Up ◽  
High Level ◽  
The Impact

In a gas turbine, the combustor is feeding the turbine with hot gases at a high level of turbulence which in turns strongly enhances the heat transfer in the turbine. It is thus of primary importance to properly characterize the turbulence properties found at the exit of a combustor to design the turbine at its real thermal constraint. This being said, real engine measurements of turbulence are extremely rare if not inexistent because of the harsh environment and difficulty to implement experimental techniques that usually operate at isothermal conditions (e.g. hot wire anemometry). As a counterpart, high fidelity unsteady numerical simulations using Large Eddy Simulations (LES) are now mature enough to simulate combustion processes and turbulence within gas turbine combustors. It is thus proposed here to assess the LES methodology to qualify turbulence within a real helicopter engine combustor operating at take-off conditions. In LES, the development of turbulence is primarily driven by the level of real viscosity in the calculation, which is the sum of three contributions: laminar (temperature linked), turbulent (generated by the sub-grid scale model) and artificial (numerics dependent). In this study, the impact of the two main sources of un-desired viscosity is investigated: the mesh refinement and numerical scheme. To do so, three grids containing 11, 33 and 220 million cells for a periodic sector of the combustor are tested as well as centred second (Lax-Wendroff) and third order (TTGC) in space schemes. The turbulence properties (intensity and integral scales) are evaluated based on highly sampled instantaneous solutions and compared between the available simulations. Results show first that the duration of the simulation is important to properly capture the level of turbulence. If short simulations (a few combustor through-times) may be sufficient to evaluate the turbulence intensity, a bias up to 14% is introduced for the turbulence length scales. In terms of calculation set-up, the mesh refinement is found to have a limited influence on the turbulence properties. The numerical scheme influence on the quantities studied here is small, highlighting that the employed schemes dissipation properties are already sufficient for turbulence characterization. Finally, spatially averaged values of turbulence intensity and lengthscale at the combustor exit are almost identically predicted in all cases. However, significant variations from hub to tip are reported, which questions the pertinence to use 0-D turbulence boundary conditions for turbines. Based on the set of simulations discussed in the paper, guidelines can be derived to adequately set-up (mesh, scheme) and run (duration, acquisition frequency) a LES when turbulence evaluation is concerned. As no experimental counterpart to this study is available, the conclusions mainly aim at knowing the possible numerical bias rather than commenting on the predictivity of the approach.

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