Improving Eddy Viscosity Based Turbulence Models for High Speed, Cold Wall Flows

2022 ◽  
Author(s):  
Tyler R. Hendrickson ◽  
Pramod Subbareddy ◽  
Graham V. Candler
Keyword(s):  
High Speed ◽  
Eddy Viscosity ◽  
Turbulence Models ◽  
Cold Wall ◽  
Wall Flows

Simulation of Multi-Stage Compressor at Off-Design Conditions

2017 ◽  
Author(s):  
Feng Wang ◽  
Mauro Carnevale ◽  
Luca di Mare ◽  
Simon Gallimore
Keyword(s):  
Mass Flow ◽  
High Speed ◽  
Eddy Viscosity ◽  
Turbulence Models ◽  
Viscosity Model ◽  
Eddy Viscosity Model ◽  
Multi Stage ◽  
Pressure Profiles ◽  
Non Linear ◽  
The Right

Computational Fluid Dynamics (CFD) has been widely used for compressor design, yet the prediction of performance and stage matching for multi-stage, high-speed machines remain challenging. This paper presents the authors’ effort to improve the reliability of CFD in multistage compressor simulations. The endwall features (e.g. blade fillet and shape of the platform edge) are meshed with minimal approximations. Turbulence models with linear and non-linear eddy viscosity models are assessed. The non-linear eddy viscosity model predicts a higher production of turbulent kinetic energy in the passages, especially close to the endwall region. This results in a more accurate prediction of the choked mass flow and the shape of total pressure profiles close to the hub. The non-linear viscosity model generally shows an improvement on its linear counterparts based on the comparisons with the rig data. For geometrical details, truncated fillet leads to thicker boundary layer on the fillet and reduced mass flow and efficiency. Shroud cavities are found to be essential to predict the right blockage and the flow details close to the hub. At the part speed the computations without the shroud cavities fail to predict the major flow features in the passage and this leads to inaccurate predictions of massflow and shapes of the compressor characteristic. The paper demonstrates that an accurate representation of the endwall geometry and an effective turbulence model, together with a good quality and sufficiently refined grid result in a credible prediction of compressor matching and performance with steady state mixing planes.

Simulation of Multistage Compressor at Off-Design Conditions

2017 ◽  
Vol 140 (2) ◽  
Author(s):  
Feng Wang ◽  
Mauro Carnevale ◽  
Luca di Mare ◽  
Simon Gallimore
Keyword(s):  
Mass Flow ◽  
High Speed ◽  
Eddy Viscosity ◽  
Turbulence Models ◽  
Viscosity Model ◽  
Eddy Viscosity Model ◽  
Pressure Profiles ◽  
Multistage Compressor ◽  
Stage Matching ◽  
The Right

Computational fluid dynamics (CFD) has been widely used for compressor design, yet the prediction of performance and stage matching for multistage, high-speed machines remains challenging. This paper presents the authors' effort to improve the reliability of CFD in multistage compressor simulations. The endwall features (e.g., blade filet and shape of the platform edge) are meshed with minimal approximations. Turbulence models with linear and nonlinear eddy viscosity models are assessed. The nonlinear eddy viscosity model predicts a higher production of turbulent kinetic energy in the passages, especially close to the endwall region. This results in a more accurate prediction of the choked mass flow and the shape of total pressure profiles close to the hub. The nonlinear viscosity model generally shows an improvement on its linear counterparts based on the comparisons with the rig data. For geometrical details, truncated filet leads to thicker boundary layer on the filet and reduced mass flow and efficiency. Shroud cavities are found to be essential to predict the right blockage and the flow details close to the hub. At the part speed, the computations without the shroud cavities fail to predict the major flow features in the passage, and this leads to inaccurate predictions of mass flow and shapes of the compressor characteristic. The paper demonstrates that an accurate representation of the endwall geometry and an effective turbulence model, together with a good quality and sufficiently refined grid, result in a credible prediction of compressor matching and performance with steady-state mixing planes.

scholarly journals Assessment of Turbulence Models in a Hypersonic Cold-Wall Turbulent Boundary Layer

Fluids ◽  
2019 ◽  
Vol 4 (1) ◽  
pp. 37 ◽  
Author(s):  
Junji Huang ◽  
Jorge-Valentino Bretzke ◽  
Lian Duan
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Shear Stress ◽  
Turbulent Boundary Layer ◽  
Prandtl Number ◽  
Eddy Viscosity ◽  
Turbulence Models ◽  
Turbulent Heat Flux ◽  
Turbulent Heat ◽  
Cold Wall

In this study, the ability of standard one- or two-equation turbulence models to predict mean and turbulence profiles, the Reynolds stress, and the turbulent heat flux in hypersonic cold-wall boundary-layer applications is investigated. The turbulence models under investigation include the one-equation model of Spalart–Allmaras, the baseline k - ω model by Menter, as well as the shear-stress transport k - ω model by Menter. Reynolds-Averaged Navier-Stokes (RANS) simulations with the different turbulence models are conducted for a flat-plate, zero-pressure-gradient turbulent boundary layer with a nominal free-stream Mach number of 8 and wall-to-recovery temperature ratio of 0.48 , and the RANS results are compared with those of direct numerical simulations (DNS) under similar conditions. The study shows that the selected eddy-viscosity turbulence models, in combination with a constant Prandtl number model for turbulent heat flux, give good predictions of the skin friction, wall heat flux, and boundary-layer mean profiles. The Boussinesq assumption leads to essentially correct predictions of the Reynolds shear stress, but gives wrong predictions of the Reynolds normal stresses. The constant Prandtl number model gives an adequate prediction of the normal turbulent heat flux, while it fails to predict transverse turbulent heat fluxes. The discrepancy in model predictions among the three eddy-viscosity models under investigation is small.

Recalibration of Eddy Viscosity Models for Numerical Simulation of Cavitating Flow Patterns in Low Pressure Nozzle Injectors

2020 ◽  
Vol 143 (3) ◽  
Author(s):  
M. Coussirat ◽  
F. Moll
Keyword(s):  
High Speed ◽  
Eddy Viscosity ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Close Relation ◽  
Cavitating Flow ◽  
Cavitating Flows ◽  
Cavitation Inception ◽  
Viscosity Models ◽  
Jet Behavior

Abstract Cavitation in pressure injectors/atomizers affects the liquid/spray jet behavior at its outlet. The type of atomization induced by cavitation allows developing efficient devices if this cavitation state is controlled. Cavitating flow is related to turbulent and multiphase flows with mass transfer between the liquid and its gaseous phase and which is affected by several factors. Due to the high-speed flow and small spatial and time scales involved, the study of cavitating flows using physical experiments is very expensive. By means of numerical simulations using eddy viscosity models, some of the incipient and slight developed cavitating flow characteristics in nozzles are captured, but the level of the vapor fraction is commonly underestimated. It is evident that a suitable calibration of the turbulence models based on the special characteristics of the incipient/slight developed cavitating flows allows obtaining improved results. This special calibration is necessary due to the close relation between the cavitation inception/developing conditions and the turbulence level in the flow leading to a “nonstandard turbulence state.” So, cavitating flows should not be modeled as a simple turbulent one. It is also demonstrated that the results obtained become competitive compared against the ones computed by large eddy simulations, which need a lot of computational resources and an appropriate initial solution for running. The conclusions obtained can be useful to improve injector designs because the suitable simulation of the incipient cavitation or slight developed cavitation flow conditions can be accurately simulated after calibration.

scholarly journals Optimal nonlinear eddy viscosity in Galerkin models of turbulent flows

2015 ◽  
Vol 766 ◽  
pp. 337-367 ◽  
Author(s):  
Bartosz Protas ◽  
Bernd R. Noack ◽  
Jan Östh
Keyword(s):  
Turbulent Flows ◽  
High Speed ◽  
Eddy Viscosity ◽  
Broad Class ◽  
Constitutive Relations ◽  
Body Height ◽  
Mixing Layer ◽  
The Body ◽  
Stream Velocity ◽  
Initial Vorticity

AbstractWe propose a variational approach to the identification of an optimal nonlinear eddy viscosity as a subscale turbulence representation for proper orthogonal decomposition (POD) models. The ansatz for the eddy viscosity is given in terms of an arbitrary function of the resolved fluctuation energy. This function is found as a minimizer of a cost functional measuring the difference between the target data coming from a resolved direct or large-eddy simulation of the flow and its reconstruction based on the POD model. The optimization is performed with a data-assimilation approach generalizing the 4D-VAR method. POD models with optimal eddy viscosities are presented for a 2D incompressible mixing layer at $\mathit{Re}=500$ (based on the initial vorticity thickness and the velocity of the high-speed stream) and a 3D Ahmed body wake at $\mathit{Re}=300\,000$ (based on the body height and the free-stream velocity). The variational optimization formulation elucidates a number of interesting physical insights concerning the eddy-viscosity ansatz used. The 20-dimensional model of the mixing-layer reveals a negative eddy-viscosity regime at low fluctuation levels which improves the transient times towards the attractor. The 100-dimensional wake model yields more accurate energy distributions as compared to the nonlinear modal eddy-viscosity benchmark proposed recently by Östh et al. (J. Fluid Mech., vol. 747, 2014, pp. 518–544). Our methodology can be applied to construct quite arbitrary closure relations and, more generally, constitutive relations optimizing statistical properties of a broad class of reduced-order models.

Improving predictions of heat transfer in indoor environments with eddy viscosity turbulence models

2015 ◽  
Vol 9 (2) ◽  
pp. 213-220 ◽  
Author(s):  
Christian Heschl ◽  
Yao Tao ◽  
Kiao Inthavong ◽  
Jiyuan Tu
Keyword(s):  
Heat Transfer ◽  
Eddy Viscosity ◽  
Turbulence Models ◽  
Indoor Environments

Application of several turbulence models for high speed shear layer flows

1999 ◽  
Author(s):  
Yildirim Suzen ◽  
Klaus Hoffmann ◽  
James Forsythe
Keyword(s):  
Shear Layer ◽  
High Speed ◽  
Turbulence Models

Assessment of turbulence models using DNS data of compressible plane free shear layer flow

2021 ◽  
Vol 931 ◽  
Author(s):  
D. Li ◽  
J. Komperda ◽  
A. Peyvan ◽  
Z. Ghiasi ◽  
F. Mashayek
Keyword(s):  
Shear Layer ◽  
Compressible Flows ◽  
Eddy Viscosity ◽  
Turbulence Models ◽  
Correlation Coefficients ◽  
Free Shear Layer ◽  
Smagorinsky Model ◽  
Reynolds Analogy ◽  
Velocity Fluctuations ◽  
Scale Similarity

The present paper uses the detailed flow data produced by direct numerical simulation (DNS) of a three-dimensional, spatially developing plane free shear layer to assess several commonly used turbulence models in compressible flows. The free shear layer is generated by two parallel streams separated by a splitter plate, with a naturally developing inflow condition. The DNS is conducted using a high-order discontinuous spectral element method (DSEM) for various convective Mach numbers. The DNS results are employed to provide insights into turbulence modelling. The analyses show that with the knowledge of the Reynolds velocity fluctuations and averages, the considered strong Reynolds analogy models can accurately predict temperature fluctuations and Favre velocity averages, while the extended strong Reynolds analogy models can correctly estimate the Favre velocity fluctuations and the Favre shear stress. The pressure–dilatation correlation and dilatational dissipation models overestimate the corresponding DNS results, especially with high compressibility. The pressure–strain correlation models perform excellently for most pressure–strain correlation components, while the compressibility modification model gives poor predictions. The results of an a priori test for subgrid-scale (SGS) models are also reported. The scale similarity and gradient models, which are non-eddy viscosity models, can accurately reproduce SGS stresses in terms of structure and magnitude. The dynamic Smagorinsky model, an eddy viscosity model but based on the scale similarity concept, shows acceptable correlation coefficients between the DNS and modelled SGS stresses. Finally, the Smagorinsky model, a purely dissipative model, yields low correlation coefficients and unacceptable accumulated errors.

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