scholarly journals A Nonlineark-εTurbulence Model Applicable to High Pressure Gradient and Large Curvature Flow

2014 ◽  
Vol 2014 ◽  
pp. 1-9
Author(s):  
Xiyao Gu ◽  
Junlian Yin ◽  
Jintao Liu ◽  
Yulin Wu
Keyword(s):  
High Pressure ◽  
Pressure Gradient ◽  
Turbulence Model ◽  
Turbulence Models ◽  
Wall Region ◽  
Reynolds Stresses ◽  
Wall Functions ◽  
Large Curvature ◽  
Rans Turbulence Models ◽  
Calculation Results

Most of the RANS turbulence models solve the Reynolds stress by linear hypothesis with isotropic model. They can not capture all kinds of vortexes in the turbomachineries. In this paper, an improved nonlineark-εturbulence model is proposed, which is modified from the RNGk-εturbulence model and Wilcox'sk-ωturbulence model. The Reynolds stresses are solved by nonlinear methods. The nonlineark-εturbulence model can calculate the near wall region without the use of wall functions. The improved nonlineark-εturbulence model is used to simulate the flow field in a curved rectangular duct. The results based on the improved nonlineark-εturbulence model agree well with the experimental results. The calculation results prove that the nonlineark-εturbulence model is available for high pressure gradient flows and large curvature flows, and it can be used to capture complex vortexes in a turbomachinery.

Assessment of Various Turbulence Models in a High Pressure Ratio Centrifugal Compressor With an Object Oriented CFD Code

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Luca Mangani ◽  
Ernesto Casartelli ◽  
Sebastiano Mauri
Keyword(s):  
Boundary Layer ◽  
High Pressure ◽  
Pressure Gradient ◽  
Centrifugal Compressor ◽  
Pressure Ratio ◽  
Turbulence Models ◽  
Object Oriented ◽  
Adverse Pressure Gradient ◽  
High Mass ◽  
High Pressure Ratio

The flow field in a high pressure ratio centrifugal compressor with a vaneless diffuser has been investigated numerically. The main goal is to assess the influence of various turbulence models suitable for internal flows with an adverse pressure gradient. The numerical analysis is performed with a 3D RANS in-house modified solver based on an object-oriented open-source library. According to previous studies from varying authors, the turbulence model is believed to be the key parameter for the discrepancy between experimental and numerical results, especially at high pressure ratios and high mass-flow. Particular care has been taken at the wall, where a detailed integration of the boundary layer has been applied. The results present different comparisons between the models and experimental data, showing the influence of using advanced turbulence models. This is done in order to capture the boundary layer behavior, especially in large adverse pressure gradient single stage machinery.

Lateral straining of turbulent boundary layers. Part 2. Streamline convergence

1997 ◽  
Vol 349 ◽  
pp. 1-30 ◽  
Author(s):  
N. R. PANCHAPAKESAN ◽  
T. B. NICKELS ◽  
P. N. JOUBERT ◽  
A. J. SMITS
Keyword(s):  
Pressure Gradient ◽  
Boundary Layers ◽  
Turbulent Transport ◽  
Turbulent Boundary Layers ◽  
Local Effect ◽  
Wall Region ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Dimensional Parameter ◽  
Outer Flow

Experimental measurements are presented showing the effects of streamline convergence on developing turbulent boundary layers. The longitudinal pressure-gradient in these experiments is nominally zero so the only extra rate-of-strain is the lateral convergence. Measurements have been made of mean flow and turbulence quantities at two different Reynolds numbers. The results show that convergence leads to a significant reduction in the skin-friction and an increase in the boundary layer thickness. There are also large changes in the Reynolds stresses with reductions occurring in the inner region and some increase in the outer flow. This is in contrast to the results of Saddoughi & Joubert (1991) for a diverging flow of the same included angle and zero pressure-gradient which show much smaller changes in the stresses and an approach to equilibrium. A new non-dimensional parameter, βD, is proposed to characterize the local effect of the convergence and it is shown how this parameter is related to Clauser's pressure-gradient parameter, βx. It is suggested that this is an equilibrium parameter for turbulent boundary layers with lateral straining. In the present flow case βD increases rapidly with streamwise distance leading to a significant departure from equilibrium. Measurement of terms in the transport equations suggest that streamline convergence leads to a reduction in production and generation and large increases in mean advection. The recovery of the flow after the removal of convergence has been shown to be characterized by a significant increase in the turbulent transport of shear-stress and turbulent kinetic energy from the very near-wall region to the flow further out where the stresses have been depleted by convergence.

Comparison of Two Two-Equation Turbulence Model Used for the Numerical Simulation of Underwater Ammunition Fuze Turbine Flow Field

2012 ◽  
Vol 591-593 ◽  
pp. 1968-1972
Author(s):  
De Zhang Shen ◽  
He Zhang ◽  
Hao Jie Li
Keyword(s):  
Numerical Simulation ◽  
Turbulence Model ◽  
Turbulence Models ◽  
Axial Pressure ◽  
Two Phase ◽  
Speed Increase ◽  
Pressure Coefficients ◽  
Surface Pressure Distribution ◽  
Calculation Results ◽  
Distribution Trends

To figure out the problem of turbulence simulation of underwater ammunition fuze turbine numerical simulation, respectively, realizable k-ε turbulence model and SST k-ω turbulence model are used for two-phase flow numerical simulation of the turbine rotation. The analysis compared the calculation results of the two turbulence models. The results showed that: the cavitation scale obtained from realizable k-ε turbulence model is shorter than that of SST k-ω turbulence model; turbine surface pressure distribution trends are similar of this two model, the results of realizable k-ε turbulence model are bigger than SST k-ω turbulence model; the turbine axial pressure coefficients using realizable k-ε turbulence model are also bigger than that of SST k-ω turbulence model, and the deviation increases with the speed increase.

The law of the wall in turbulent flow

1995 ◽  
Vol 451 (1941) ◽  
pp. 165-188 ◽  
Keyword(s):  
Turbulence Models ◽  
Turbulence Theory ◽  
Turbulent Shear ◽  
Wall Region ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Law Of The Wall ◽  
Logarithmic Law ◽  
The Law ◽  
Simple Flows

The ‘law of the wall’ for the inner part of a turbulent shear flow over a solid surface is one of the cornerstones of fluid dynamics, and one of the very few pieces of turbulence theory whose results include a simple analytic function for the mean velocity distribution, the logarithmic law. Various aspects of the law have recently been questioned, and this paper is a summary of the present position. Although the law of the wall for velocity has apparently been confirmed by experiment well outside its original range, the law of the wall for temperature seems to apply only to very simple flows. Since the two laws are derived by closely analogous arguments this throws suspicion on the law of the wall for velocity. Analysis of simulation data, for all the Reynolds stresses including the shear stress, shows that law-of-the-wall scaling fails spectacularly in the viscous wall region, even when the logarithmic law is relatively well behaved. Virtually all turbulence models are calibrated to reproduce the law of the wall in simple flows, and we discuss whether, in practice or in principle, their range of validity is larger than that of the law of the wall itself: the present answer is that it is not; so that when the law of the wall (or the mixing-length formula) fails, current Reynolds-averaged turbulence models are likely to fail too.

An Implicitly Consistent Formulation of a Dual-Mesh Hybrid LES/RANS Method

2017 ◽  
Vol 21 (2) ◽  
pp. 570-599 ◽  
Author(s):  
Heng Xiao ◽  
Jian-Xun Wang ◽  
Patrick Jenny
Keyword(s):  
Turbulence Modeling ◽  
Plane Channel ◽  
Turbulence Models ◽  
Original Formulation ◽  
Reynolds Stresses ◽  
New Strategy ◽  
Rans Turbulence Models ◽  
New Formulation ◽  
Plane Channel Flow ◽  
Dual Mesh

AbstractA consistent dual-mesh hybrid LES/RANS framework for turbulence modeling has been proposed recently (H. Xiao, P. Jenny, A consistent dual-mesh framework for hybrid LES/RANS modeling, J. Comput. Phys. 231 (4) (2012)). To better enforce componentwise Reynolds stress consistency between the LES and the RANS simulations, in the present work the original hybrid framework is modified to better exploit the advantage of more advanced RANS turbulence models. In the new formulation, the turbulent stresses in the filtered equations in the under-resolved regions are directly corrected based on the Reynolds stresses provided by the RANS simulation. More precisely, the new strategy leads to implicit LES/RANS consistency, where the velocity consistency is achieved indirectly via imposing consistency on the Reynolds stresses. This is in contrast to the explicit consistency enforcement in the original formulation, where forcing terms are added to the filtered momentum equations to achieve directly the desired average velocity and velocity fluctuations. The new formulation keeps the averaging procedure for the filtered quantities and at the same time preserves the ability of the original formulation to conform with the physical differences between LES and RANS quantities. The modified formulation is presented, analyzed, and then evaluated for plane channel flow and flow over periodic hills. Improved predictions are obtained compared with the results obtained using the original formulation.

scholarly journals NEW METHODS FOR STABILIZING RANS TURBULENCE MODELS WITH APPLICATION TO LARGE SCALE BREAKING WAVES

2020 ◽  
pp. 19
Author(s):  
Georgios Azorakos ◽  
Bjarke Eltard Larsen ◽  
David R. Fuhrman
Keyword(s):  
Turbulence Model ◽  
Large Scale ◽  
Eddy Viscosity ◽  
Turbulence Models ◽  
Breaking Waves ◽  
Wide Spread ◽  
Cfd Simulations ◽  
New Methods ◽  
Rans Turbulence Models ◽  
Scale Breaking

Recently, Larsen and Fuhrman (2018) have shown that seemingly all commonly used (both k-omega and k-epsilon variants) two-equation RANS turbulence closure models are unconditionally unstable in the potential flow beneath surface waves, helping to explain the wide-spread over-production of turbulent kinetic energy in CFD simulations, relative to measurements. They devised and tested a new formally stabilized formulation of the widely used k-omega turbulence model, making use of a modified eddy viscosity. In the present work, three new formally-stable k-omega turbulence model formulations are derived and tested in CFD simulations involving the flow and dynamics beneath large-scale plunging breaking waves.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/T2fFRgq3I8E

Turbulence in a separated boundary layer

1991 ◽  
Vol 226 ◽  
pp. 91-123 ◽  
Author(s):  
M. Dianat ◽  
Ian P. Castro
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Low Frequency ◽  
Turbulence Models ◽  
Adverse Pressure Gradient ◽  
Spanwise Direction ◽  
Wall Region ◽  
Thin Wall ◽  
Wall Boundary Layer ◽  
Stress Ratios

This paper presents and discusses the results of an extensive experimental investigation of a flat-plate turbulent boundary subjected to an adverse pressure gradient sufficiently strong to lead to the formation of a large separated region. The pressure gradient was produced by applying strong suction through a porous cylinder fitted with a rear flap and mounted above the boundary layer and with its axis in the spanwise direction. Attention is concentrated on the structure of the turbulent flow within the separated region and it is shown that many features are similar to those that occur in separated regions produced in a very dissimilar manner. These include the fact that structure parameters, like Reynolds stress ratios, respond markedly to the re-entrainment of turbulent fluid transported upstream from the reattachment region, the absence of any logarithmic region in the thin wall boundary layer beneath the recirculation zone and the lack of any effective viscous scaling in this wall region, and the presence of a significant low-frequency motion having timescales much longer than those of the large-eddy structures around reattachment.Similarities with boundary layers separating under the action of much weaker pressure gradients are also found, despite the fact that the nature of the flow around separation is quite different. These similarities and also some noticeable differences are discussed in the paper, which concludes with some inferences concerning the application of turbulence models to separated flows.

Numerical Investigation of the Compressible Flat-Plate Turbulent Boundary Layer with Extended GAO-YONG Turbulence Model

2013 ◽  
Vol 444-445 ◽  
pp. 416-422
Author(s):  
Yang Yang Tang ◽  
Zhi Qiang Li ◽  
Yong Wang ◽  
Ya Chao Di ◽  
Huan Xu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Flat Plate ◽  
Turbulence Model ◽  
Turbulence Models ◽  
Wall Region ◽  
Flow And Heat Transfer ◽  
Empirical Coefficients ◽  
Near Wall

The extended GAO-YONG turbulence model is used to simulate the flow and heat transfer of flat-plate turbulent boundary layer, and the results indicate that GAO-YONG turbulence model may well describe boundary layer flow and heat transfer from near-wall region to far outer area, without using any empirical coefficients and near-wall treatments, such as wall-function or modified low Reynolds number model, which are used widely in all RANS turbulence models.

An Improved Wall-Distance-Free Version of the Baldwin-Barth Turbulence Model

2003 ◽  
Author(s):  
Michel Elkhoury
Keyword(s):  
Pressure Gradient ◽  
Skin Friction ◽  
Turbulence Model ◽  
Eddy Viscosity ◽  
Present Model ◽  
Adverse Pressure Gradient ◽  
Wall Functions ◽  
Friction Prediction ◽  
Naca 0012 ◽  
Good Agreement

This paper presents a modified version of the Baldwin-Barth (BB) turbulence model. This modification accounts for the asymptotic boundary value of the pseudo eddy viscosity as the wall is approached. The BB Model tends to respond strongly to an adverse pressure gradient, in the sense that it always predicts a large decrease in skin friction relative to the measured values. Hence, in the present work, the importance of the modifications for improving the skin friction prediction of flows with adverse pressure gradient is addressed. All of the implemented modifications are free of wall functions and coordinate independent, which renders the model advantageous relative to other wall dependent models. The results are compared with both the original BB and the Spalart-Allmaras (SA) models. The accuracy of these and the present model is assessed against experimental data for transonic flows over NACA-0012 and RAE 2822 airfoils. In general, good agreement with experiments is indicated.

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