Turbulent Flows Over a Backward Facing Step Simulated Using a Modified Partially Averaged Navier–Stokes Model

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Renfang Huang ◽  
Xianwu Luo ◽  
Bin Ji ◽  
Qingfeng Ji
Keyword(s):  
Turbulent Flows ◽  
Grid Size ◽  
Navier Stokes ◽  
Reynolds Stresses ◽  
Reattachment Length ◽  
Backward Facing Step ◽  
Local Grid ◽  
Turbulence Length ◽  
Turbulence Length Scale ◽  
Corner Vortex

A modified partially averaged Navier–Stokes model (MPANS) is proposed by treating the standard k–ε model as the parent model and formulating the unresolved-to-total kinetic energy ratio fk as a function of the local grid size and turbulence length scale. Flows over a backward facing step are used to evaluate the performance of MPANS mode. Computations of the standard k–ε model, the constant fk partially averaged Navier–Stokes (PANS) models (fk = 0.6, 0.7), and the two-stage PANS model are carried out for comparisons. Based on the detailed analyses of calculated results and experimental data, the MPANS model performs better to predict the reattachment length together with the corner vortex and provides overall improved statistics of skin frictions, pressures, velocity profiles, and Reynolds stresses, demonstrating its promising applications in industrial turbomachines that often encounter with flow separations.

scholarly journals Self-consistent triple decomposition of the turbulent flow over a backward-facing step under finite amplitude harmonic forcing

2019 ◽  
Vol 475 (2225) ◽  
pp. 20190018
Author(s):  
E. Yim ◽  
P. Meliga ◽  
F. Gallaire
Keyword(s):  
Turbulent Flow ◽  
Finite Amplitude ◽  
Navier Stokes ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Backward Facing Step ◽  
Eddy Viscosity Model ◽  
Coherent Interaction ◽  
Self Consistent ◽  
The Mean

We investigate the saturation of harmonically forced disturbances in the turbulent flow over a backward-facing step subjected to a finite amplitude forcing. The analysis relies on a triple decomposition of the unsteady flow into mean, coherent and incoherent components. The coherent–incoherent interaction is lumped into a Reynolds averaged Navier–Stokes (RANS) eddy viscosity model, and the mean–coherent interaction is analysed via a semi-linear resolvent analysis building on the laminar approach by Mantič-Lugo & Gallaire (2016 J. Fluid Mech. 793 , 777–797. ( doi:10.1017/jfm.2016.109 )). This provides a self-consistent modelling of the interaction between all three components, in the sense that the coherent perturbation structures selected by the resolvent analysis are those whose Reynolds stresses force the mean flow in such a way that the mean flow generates exactly the aforementioned perturbations, while also accounting for the effect of the incoherent scale. The model does not require any input from numerical or experimental data, and accurately predicts the saturation of the forced coherent disturbances, as established from comparison to time-averages of unsteady RANS simulation data.

Development of a Continuous Model for Simulation of Turbulent Flows

2005 ◽  
Vol 73 (3) ◽  
pp. 441-448 ◽  
Author(s):  
M. Yousuff Hussaini ◽  
Siva Thangam ◽  
Stephen L. Woodruff ◽  
Ye Zhou
Keyword(s):  
Turbulent Flows ◽  
Continuous Model ◽  
Wave Number ◽  
Navier Stokes ◽  
Subgrid Scale ◽  
Reynolds Stresses ◽  
Eddy Simulation ◽  
Proposed Model ◽  
Large Eddy ◽  
Kolmogorov Flows

The development of a continuous turbulence model that is suitable for representing both the subgrid scale stresses in large eddy simulation and the Reynolds stresses in the Reynolds averaged Navier-Stokes formulation is described. A recursion approach is used to bridge the length scale disparity from the cutoff wave number to those in the energy-containing range. The proposed model is analyzed in conjunction with direct numerical simulations of Kolmogorov flows.

Development and Validation of Continuous Models for Simulation of Turbulent Flows

2003 ◽  
Author(s):  
M. Yousuff Hussaini ◽  
Siva Thangam ◽  
Stephen L. Woodruff ◽  
Ye Zhou
Keyword(s):  
Turbulent Flows ◽  
Navier Stokes ◽  
Subgrid Scale ◽  
Reynolds Stresses ◽  
Eddy Simulation ◽  
Proposed Model ◽  
Large Eddy ◽  
Continuous Models ◽  
Kolmogorov Flows ◽  
Development And Validation

The development of a continuous turbulence model that is suitable for representing both the subgrid scale stresses in large eddy simulation and the Reynolds stresses in the Reynolds averaged Navier-Stokes formulation is described. A recursion approach is used to bridge the length scale disparity from the cutoff wavenumber to those in the energy-containing range. The proposed model is analyzed in conjunction with direct numerical simulations of Kolmogorov flows.

Viscosity in Seakeeping

2018 ◽  
Vol Vol 160 (A2) ◽  
Author(s):  
M Pawłowski
Keyword(s):  
Turbulent Flows ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Ship Motions ◽  
Hydrodynamic Coefficients ◽  
Reynolds Stresses ◽  
Navier Stokes Equations ◽  
Inviscid Fluids ◽  
Strip Theory ◽  
Linear Problems

Application of strip theory for the prediction of ship motions in waves relies on sectional hydrodynamic coefficients; i.e. the added mass and damping coefficients. These coefficients apply to linearised problems and are normally computed for inviscid fluids. It is possible to account for viscosity but this cannot be done by the RANS equations, as in linear problems there is no room for turbulence. The hydrodynamic coefficients can include the effect of viscosity but this can be done rightly through the classic Navier–Stokes equations for laminar (non-turbulent) flows. For solving these equations commercial RANS software can be used, assuming no Reynolds stresses.

The determination of turbulence-model statistics from the velocity–acceleration correlation

2014 ◽  
Vol 757 ◽  
Author(s):  
Stephen B. Pope
Keyword(s):  
Turbulent Flows ◽  
Turbulence Model ◽  
Stokes Equations ◽  
Turbulence Models ◽  
Variable Density ◽  
Navier Stokes ◽  
Reynolds Stresses ◽  
Constant Property ◽  
Langevin Model ◽  
High Reynolds

AbstractFor inhomogeneous turbulent flows at high Reynolds number, it is shown that the redistribution term in Reynolds-stress turbulence models can be determined from the velocity–acceleration correlation. It is further shown that the drift coefficient in the generalized Langevin model (which is used in probability density function (PDF) methods) can be determined from the Reynolds stresses and the velocity–acceleration correlation. These observations are valuable, since the second moments of velocity and acceleration can be measured in experiments, in direct numerical simulations and in well-resolved large-eddy simulations (LES), and hence these turbulence-model quantities can be determined. The redistribution is closely related to the pressure–rate-of-strain, and the unknown in the PDF equation is closely related to the conditional mean pressure gradient (conditional on velocity). In contrast to the velocity–acceleration moments, these pressure statistics are much more difficult to obtain, and our knowledge of them is quite limited. It is also shown that the generalized Langevin model can be re-expressed to provide a direct connection between the drift term and the fluid acceleration. All of these results are first obtained using the constant-property Navier–Stokes equations, but it is then shown that the results are simply extended to variable-density flows.

Modified partially averaged Navier–Stokes model for turbulent flow in passages with large curvature

2020 ◽  
Vol 34 (23) ◽  
pp. 2050239
Author(s):  
Weixiang Ye ◽  
Xianwu Luo ◽  
Ying Li
Keyword(s):  
Turbulent Flow ◽  
Turbulent Flows ◽  
Turbulence Model ◽  
Navier Stokes ◽  
Small Scale ◽  
Bounded Region ◽  
Rectangular Duct ◽  
Reynolds Stresses ◽  
Curvature Effects ◽  
Text Model

This study presents a partially averaged Navier–Stokes model, MSST PANS, based on a modified SST [Formula: see text] turbulence model to predict turbulent flows with large streamline curvature. The model was validated for turbulent flow in a [Formula: see text] curved rectangular duct (Re = 224,000) to assess the MSST PANS capabilities. The predictions are compared against flow simulations for the same curved rectangular duct using four turbulence models including the standard [Formula: see text] model, SST [Formula: see text] model, [Formula: see text] PANS model and SST [Formula: see text] PANS model. Comparisons among those numerical results and available experimental data show that the MSST PANS model more accurately predicts the velocity components in all three directions, especially in the wall-bounded region than the other models. The study also shows the advantages of the MSST PANS model for predicting the Reynolds stresses, vorticity, and smaller scale turbulent structures in the wall-bounded region not only qualitatively but quantitatively. Furthermore, the MSST PANS model requires fewer computations than the SST PANS model, indicating that this turbulence model, which takes large streamlines curvature effects into consideration, is an effective alternative for capturing the small-scale turbulence flow structures. This turbulence model is expected to be very useful for engineering applications, especially for flows in turbomachinery.

A Periodically Perturbed Backward-Facing Step Flow by Means of LES, DES and T-RANS: An Example of Flow Separation Control

2004 ◽  
Author(s):  
Sanjin Sˇaric´ ◽  
Suad Jakirlic´ ◽  
Cameron Tropea
Keyword(s):  
Navier Stokes ◽  
Reattachment Length ◽  
Backward Facing Step ◽  
Inlet Channel ◽  
Flow Separation Control ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Sst Model ◽  
Perturbation Frequency ◽  
Length Reduction

Turbulent flow over a backward-facing step perturbed periodically by an alternating blowing/suction through a thin slit situated at the step edge was studied computationally using the LES (Large Eddy Simulation), DES (Dettached Eddy Simulation) and T-RANS (Transient Reynolds-Averaged Navier-Stokes) techniques. The flow configuration considered (ReH = UcH/ν = 3700) has been investigated experimentally by Yoshioka et al. (2001). The periodical blowing/suction with zero mass flux is governed by a sinusoidal law: ve = 0.3Ucsin(2πfet), Uc being the centerline velocity in the inlet channel. Perturbation frequencies fe corresponding to the Strouhal numbers St = 0.08, 0.19 and 0.30 were investigated (St = feH/Uc). The experimental observation, that the perturbation frequency St = 0.19 represents the most effective case, that is the case with the minimum reattachment length, was confirmed by all computational methods applied. However, the closest agreement with experiment (the reattachment length reduction of 28.3% compared to the unperturbed case) was obtained with the LES (24.5%) and DES (35%) methods whereas the T-RANS computations show a weak sensitivity to the perturbation: 5.9% when using the Spalart-Allmaras model and 12.9% using the k–ω SST model.

scholarly journals On the influence of turbulent kinetic energy level on accuracy of k − ε and LRR turbulence models

2018 ◽  
Vol 45 (2) ◽  
pp. 139-149
Author(s):  
Djordje Novkovic ◽  
Jela Burazer ◽  
Aleksandar Cocic ◽  
Milan Lecic
Keyword(s):  
Kinetic Energy ◽  
Theoretical Analysis ◽  
Turbulent Kinetic Energy ◽  
Turbulent Flows ◽  
Cross Sections ◽  
Turbulence Models ◽  
Velocity Profiles ◽  
Navier Stokes ◽  
Test Case ◽  
Reynolds Stresses

This paper presents research regarding the influence of turbulent kinetic energy (TKE) level on accuracy of Reynolds averaged Navier?Stokes (RANS) based turbulence models. A theoretical analysis of influence TKE level on accuracy of the RANS turbulence models has been performed according to the Boussinesq hypothesis definition. After that, this theoretical analysis has been investigated by comparison of numerically and experimentally obtained results on the test case of a steady-state incompressible swirl-free flow in a straight conical diffuser named Azad diffuser. Numerical calculations have been performed using the OpenFOAM CFD software and first and secondorder closure turbulence models. TKE level, velocity profiles and Reynolds stresses have been calculated downstream in four different cross sections of the diffuser. Certain conclusions about modeling turbulent flows by ?? ??? and LRR turbulence models have been made by comparing the velocity profiles, TKE distribution and Reynolds stresses on the selected cross sections.

A Periodically Perturbed Backward-Facing Step Flow by Means of LES, DES and T-RANS: An Example of Flow Separation Control

2005 ◽  
Vol 127 (5) ◽  
pp. 879-887 ◽  
Author(s):  
S. Šarić ◽  
S. Jakirlić ◽  
C. Tropea
Keyword(s):  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Reattachment Length ◽  
Backward Facing Step ◽  
Inlet Channel ◽  
Flow Separation Control ◽  
Eddy Simulation ◽  
Sst Model ◽  
Perturbation Frequency ◽  
Zero Net Mass Flux

Turbulent flow over a backward-facing step, perturbed periodically by alternative blowing∕suction through a thin slit (0.05H width) situated at the step edge, was studied computationally using (LES) large eddy simulation, (DES) detached eddy simulation, and (T-RANS) transient Reynolds-averaged Navier–Stokes techniques. The flow configuration considered (ReH=UcH∕ν=3700) has been investigated experimentally by Yoshioka et al. (12). The periodic blowing∕suction with zero net mass flux is governed by a sinusoidal law: ve=0.3Ucsin(2πfet), Uc being the centerline velocity in the inlet channel. Perturbation frequencies fe corresponding to the Strouhal numbers St=0.08, 0.19, and 0.30 were investigated (St=feH∕Uc). The experimental observation that the perturbation frequency St=0.19 represents the most effective case, that is the case with the minimum reattachment length, was confirmed by all computational methods. However, the closest agreement with experiment (the reattachment length reduction of 28.3% compared to the unperturbed case) was obtained with LES (24.5%) and DES (35%), whereas the T-RANS computations showed a weaker sensitivity to the perturbation: 5.9% when using the Spalart–Allmaras model and 12.9% using the k-ω SST model.

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