Simulating Boundary Layer Transition With Low-Reynolds-Number k–ε Turbulence Models: Part 2—An Approach to Improving the Predictions

1991 ◽  
Vol 113 (1) ◽  
pp. 18-26 ◽  
Author(s):  
R. C. Schmidt ◽  
S. V. Patankar
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Low Reynolds Number ◽  
Turbulence Models ◽  
Boundary Layer Transition ◽  
Turbulent Regime ◽  
Layer Transition ◽  
Production Term ◽  
Free Stream Turbulence ◽  
Low Reynolds

An approach for improving the prediction of boundary layer transition with k–ε type low-Reynolds-number turbulence models is developed and tested. A modification is proposed that limits the production term in the turbulent kinetic energy equation and is based on a simple stability criterion and correlated to the free-stream turbulence level. The modification becomes inactive in the fully turbulent regime, but is shown to improve both the qualitative and quantitative characteristics of the transition predictions. Although the approach is not limited to a particular low-Reynolds-number model, it is implemented herein using the model of Lam and Bremhorst (1981).

Simulating Boundary Layer Transition With Low-Reynolds-Number k–ε Turbulence Models: Part 1—An Evaluation of Prediction Characteristics

1991 ◽  
Vol 113 (1) ◽  
pp. 10-17 ◽  
Author(s):  
R. C. Schmidt ◽  
S. V. Patankar
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Free Stream ◽  
Low Reynolds Number ◽  
Turbulence Models ◽  
Boundary Layer Transition ◽  
External Boundary ◽  
Layer Transition ◽  
Free Stream Turbulence ◽  
Low Reynolds

An analysis and evaluation of the capability of k–ε low-Reynolds-number turbulence models to predict transition in external boundary-layer flows subject to free-stream turbulence is presented. The similarities between the near-wall cross-stream regions in a fully turbulent boundary layer and the progressive stages through which developing boundary layers pass in the streamwise direction are used to describe the mechanisms by which the models simulate the transition process. Two representative models (Jones and Launder, 1972; Lam and Bremhorst, 1981) are employed in a series of computational tests designed to answer some specific practical questions about the ability of these models to yield accurate, reliable answers over a range of free-stream turbulence conditions.

Characterisation of boundary layer transition over a low Reynolds number rotor

2021 ◽  
pp. 110485
Author(s):  
Thomas Jaroslawski ◽  
Maxime Forte ◽  
Jean-Marc Moschetta ◽  
Gregory Delattre ◽  
Erwin R. Gowree
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Low Reynolds Number ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Low Reynolds

Numerical Simulation of Turbine Blade Boundary Layer and Heat Transfer and Assessment of Turbulence Models

1997 ◽  
Vol 119 (4) ◽  
pp. 794-801 ◽  
Author(s):  
J. Luo ◽  
B. Lakshminarayana
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Low Reynolds Number ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Bypass Transition ◽  
Boundary Layer Development ◽  
Low Reynolds ◽  
Layer Development

The boundary layer development and convective heat transfer on transonic turbine nozzle vanes are investigated using a compressible Navier–Stokes code with three low-Reynolds-number k–ε models. The mean-flow and turbulence transport equations are integrated by a four-stage Runge–Kutta scheme. Numerical predictions are compared with the experimental data acquired at Allison Engine Company. An assessment of the performance of various turbulence models is carried out. The two modes of transition, bypass transition and separation-induced transition, are studied comparatively. Effects of blade surface pressure gradients, free-stream turbulence level, and Reynolds number on the blade boundary layer development, particularly transition onset, are examined. Predictions from a parabolic boundary layer code are included for comparison with those from the elliptic Navier–Stokes code. The present study indicates that the turbine external heat transfer, under real engine conditions, can be predicted well by the Navier–Stokes procedure with the low-Reynolds-number k–ε models employed.

Numerical investigation of the role of free-stream turbulence in boundary-layer separation

2016 ◽  
Vol 801 ◽  
pp. 289-321 ◽  
Author(s):  
Wolfgang Balzer ◽  
H. F. Fasel
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Shear Layer ◽  
Free Stream ◽  
Hydrodynamic Instability ◽  
Low Reynolds Number ◽  
Transition To Turbulence ◽  
Laminar Separation ◽  
Free Stream Turbulence ◽  
Low Reynolds

The aerodynamic performance of lifting surfaces operating at low Reynolds number conditions is impaired by laminar separation. In most cases, transition to turbulence occurs in the separated shear layer as a result of a series of strong hydrodynamic instability mechanisms. Although the understanding of these mechanisms has been significantly advanced over the past decades, key questions remain unanswered about the influence of external factors such as free-stream turbulence (FST) and others on transition and separation. The present study is driven by the need for more accurate predictions of separation and transition phenomena in ‘real world’ applications, where elevated levels of FST can play a significant role (e.g. turbomachinery). Numerical investigations have become an integral part in the effort to enhance our understanding of the intricate interactions between separation and transition. Due to the development of advanced numerical methods and the increase in the performance of supercomputers with parallel architecture, it has become feasible for low Reynolds number application ($O(10^{5})$) to carry out direct numerical simulations (DNS) such that all relevant spatial and temporal scales are resolved without the use of turbulence modelling. Because the employed high-order accurate DNS are characterized by very low levels of background noise, they lend themselves to transition research where the amplification of small disturbances, sometimes even growing from numerical round-off, can be examined in great detail. When comparing results from DNS and experiment, however, it is beneficial, if not necessary, to increase the background disturbance levels in the DNS to levels that are typical for the experiment. For the current work, a numerical model that emulates a realistic free-stream turbulent environment was adapted and implemented into an existing Navier–Stokes code based on a vorticity–velocity formulation. The role FST plays in the transition process was then investigated for a laminar separation bubble forming on a flat plate. FST was shown to cause the formation of the well-known Klebanoff mode that is represented by streamwise-elongated streaks inside the boundary layer. Increasing the FST levels led to accelerated transition, a reduction in bubble size and better agreement with the experiments. Moreover, the stage of linear disturbance growth due to the inviscid shear-layer instability was found to not be ‘bypassed’.

A New Model for Boundary-Layer Transition Using a Single-Point RANS Approach

2002 ◽  
Author(s):  
D. Keith Walters ◽  
James H. Leylek
Keyword(s):  
Boundary Layer ◽  
Single Point ◽  
Turbulence Models ◽  
Boundary Layer Transition ◽  
Heated Wall ◽  
Test Cases ◽  
Predictive Tool ◽  
Layer Transition ◽  
New Model ◽  
Free Stream Turbulence

This paper presents the development and implementation of a new model for bypass and natural transition prediction using Reynolds-Averaged Navier-Stokes (RANS) CFD, based on modification of two-equation, linear eddy-viscosity turbulence models. The new model is developed herein based on considerations of the universal character of transitional boundary layers that have recently been documented in the open literature, and implemented into a popular commercial CFD code (Fluent) in order to assess its performance. Two transitional test cases are presented: (1) a boundary layer developing on a flat heated wall, with free-stream turbulence intensity (Tu∞) ranging from 0.2 to 6%; and (2) flow over a turbine stator vane, with chord Reynolds number 2.3×105, and Tu∞ from 0.6 to 20%. Results are presented in terms of Stanton number, and compared to experimental data for both cases. Results show good agreement with the test cases and suggest that the new approach has potential as a predictive tool.

Predicting Separation and Transitional Flow in Turbine Blades at Low Reynolds Numbers—Part I: Development of Prediction Methodology

2010 ◽  
Vol 133 (3) ◽  
Author(s):  
Darius D. Sanders ◽  
Walter F. O’Brien ◽  
Rolf Sondergaard ◽  
Marc D. Polanka ◽  
Douglas C. Rabe
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Flow Model ◽  
Reynolds Numbers ◽  
Boundary Layer Transition ◽  
Transitional Flow ◽  
Layer Transition ◽  
Low Pressure Turbine ◽  
Low Reynolds ◽  
And Performance

There is an increasing interest in design methods and performance prediction for aircraft engine turbines operating at low Reynolds numbers. In this regime, boundary layer separation may be more likely to occur in the turbine flow passages. For accurate computational fluid dynamics (CFD) predictions of the flow, correct modeling of laminar-turbulent boundary layer transition is essential to capture the details of the flow. To investigate possible improvements in model fidelity, CFD models were created for the flow over two low pressure turbine blade designs. A new three-equation eddy-viscosity type turbulent transitional flow model, originally developed by Walters and Leylek (2004, “A New Model for Boundary Layer Transition Using a Single Point RANS Approach,” ASME J. Turbomach., 126(1), pp. 193–202), was employed for the current Reynolds averaged Navier–Stokes (RANS) CFD calculations. Previous studies demonstrated the ability of this model to accurately predict separation and boundary layer transition characteristics of low Reynolds number flows. The present research tested the capability of CFD with the Walters and Leylek turbulent transitional flow model to predict the boundary layer behavior and performance of two different turbine cascade configurations. Flows over low pressure turbine (LPT) blade airfoils with different blade loading characteristics were simulated over a Reynolds number range of 15,000–100,000 and predictions were compared with experimental cascade results. Part I of this paper discusses the prediction methodology that was developed and its validation using a lightly loaded LPT blade airfoil design. The turbulent transitional flow model sensitivity to turbulent flow parameters was investigated and showed a strong dependence on freestream turbulence intensity with a second-order effect of turbulent length scale. Focusing on the calculation of the total pressure loss coefficients to judge performance, the CFD simulation incorporating Walters and Leylek’s turbulent transitional flow model produced adequate prediction of the Reynolds number performance for the lightly loaded LPT blade cascade geometry. Significant improvements in performance were shown over predictions of conventional RANS turbulence models. Historically, these models cannot adequately predict boundary layer transition.

Predicting Separation and Transitional Flow in Turbine Blades at Low Reynolds Numbers

2008 ◽  
Author(s):  
Darius D. Sanders ◽  
Walter F. O’Brien ◽  
Rolf Sondergaard ◽  
Marc D. Polanka ◽  
Douglas C. Rabe
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Flow Model ◽  
Reynolds Numbers ◽  
Boundary Layer Transition ◽  
Transitional Flow ◽  
Layer Transition ◽  
Low Pressure Turbine ◽  
Low Reynolds ◽  
And Performance

There is increasing interest in design methods and performance prediction for aircraft engine turbines operating at low Reynolds numbers. In this regime, boundary layer separation may be more likely to occur in the turbine flow passages. For accurate CFD predictions of the flow, correct modeling of laminar-turbulent boundary layer transition is essential to capture the details of the flow. To investigate possible improvements in model fidelity, CFD models were created for the flow over two low pressure turbine blade designs. A new three-equation eddy-viscosity type turbulent transitional flow model originally developed by Walters and Leylek was employed for the current RANS CFD calculations. Previous studies demonstrated the ability of this model to accurately predict separation and boundary layer transition characteristics of low Reynolds number flows. The present research tested the capability of CFD with the Walters and Leylek turbulent transitional flow model to predict the boundary layer behavior and performance of two different turbine cascade configurations. Flows over the Pack-B turbine blade airfoil and the midspan section of a typical low pressure turbine (TLPT) blade were simulated over a Reynolds number range of 15,000–100,000, and predictions were compared to experimental cascade results. The turbulent transitional flow model sensitivity to turbulent flow parameters was investigated and showed a strong dependence on free-stream turbulence intensity with a second order effect of turbulent length scale. Focusing on the calculation of the total pressure loss coefficients to judge performance, the CFD simulation incorporating Walters and Leylek’s turbulent transitional flow model produced adequate prediction of the Reynolds number performance for the TLPT blade cascade geometry. Furthermore, the correct qualitative flow response to separated shear was observed for the Pack-B blade airfoil. Significant improvements in performance predictions were shown over predictions of conventional RANS turbulence models that cannot adequately model boundary layer transition.

An experimental study of boundary layer transition induced by a cylinder wake

2011 ◽  
Vol 684 ◽  
pp. 60-84 ◽  
Author(s):  
A. C. Mandal ◽  
J. Dey
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Late Stage ◽  
Free Stream ◽  
Experimental Studies ◽  
Boundary Layer Transition ◽  
Bypass Transition ◽  
Mean Flow ◽  
Layer Transition ◽  
Free Stream Turbulence

AbstractBoundary layer transition induced by the wake of a circular cylinder in the free stream has been investigated using the particle image velocimetry technique. Some differences between simulation and experimental studies have been reported in the literature, and these have motivated the present study. The appearance of spanwise vortices in the early stage is further confirmed here. A spanwise vortex appears to evolve into a $ \mrm{\Lambda} $/hairpin vortex; the flow statistics also confirm such vortices. With increasing Reynolds number, based on the cylinder diameter, and with decreasing cylinder height from the plate, the physical size of these hairpin-like structures is found to decrease. Some mean flow characteristics, including the streamwise growth of the disturbance energy, in a wake-induced transition resemble those in bypass transition induced by free stream turbulence. Streamwise velocity streaks that are eventually generated in the late stage often undergo sinuous-type oscillations. Similar to other transitional flows, an inclined shear layer in the wall-normal plane is often seen to oscillate and shed vortices. The normalized shedding frequency of these vortices, estimated from the spatial spacing and the convection velocity of these vortices, is found to be independent of the Reynolds number, similar to that in ribbon-induced transition. Although the nature of free stream disturbance in a wake-induced transition and that in a bypass transition are different, the late-stage features including the flow breakdown characteristics of these two transitions appear to be similar.

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