An Algebraic Turbulence Model for Flow Separation Caused by Forward and Backward Facing Steps

1989 ◽  
Author(s):  
James E. Danberg ◽  
Nisheeth R. Patel
Keyword(s):  
Turbulence Model ◽  
Flow Separation

Coupled Blowing and Suction for Flow Separation Control

2019 ◽  
Author(s):  
M. Tadjfar ◽  
D. J. Kamari
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Flow Field ◽  
Turbulence Model ◽  
Flow Separation ◽  
Active Flow Control ◽  
Suction Side ◽  
Separation Control ◽  
Flow Separation Control ◽  
Active Flow

Abstract The effects of applying a coupled unsteady blowing and suction combination over SD7003 airfoil at Reynolds number of 60,000 at an angle of attack of 13°, where a large separation on the suction side of the airfoil existed, was considered to investigate active flow control (AFC) mechanism. URANS equations were employed to solve the flow field and k–ω SST was used as the turbulence model. The unsteady blowing and suction were implemented at an angle to the surface crossing the boundary layer (CBL). The influence of location and frequency of the blowing/suction jets were examined.

Shock-boundary layer interaction and transition modelling in turbomachinery flows

1997 ◽  
Vol 211 (3) ◽  
pp. 225-234 ◽  
Author(s):  
V Michelassi
Keyword(s):  
Boundary Layer ◽  
Turbine Blade ◽  
Turbulence Model ◽  
Flow Separation ◽  
Good Description ◽  
Suction Side ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Boundary Layer Development ◽  
Layer Development

The transonic turbulent compressible flow in channels and turbine linear cascades is computed by using a Navier-Stokes solver. Turbulence effects are simulated by means of the k-ω turbulence model. A realiability constraint is introduced to improve the turbulence model performances and stability in the presence of stagnation points. In both the flow over the bump and the turbine blade, the shock induces a flow separation that affects the boundary layer development. In both cases the proposed model succeeds in predicting the flow separation. For the flow over the turbine blade a simple transition model based on integral parameters is introduced to mimic the effect of the boundary layer transition across the shock wave on the suction side. Relaminarization is also properly predicted on the pressure side, thereby allowing a good description of the boundary layer development and shock pattern.

Numerical study of the flow field characteristics over a backward facing step using k-kl-ω turbulence model: comparison with different models

2018 ◽  
Vol 15 (1) ◽  
pp. 173-180 ◽  
Author(s):  
Yasser M. Ahmed ◽  
A.H. Elbatran
Keyword(s):  
Experimental Data ◽  
Fluid Mechanics ◽  
Turbulence Model ◽  
Flow Separation ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Numerical Results ◽  
Backward Facing Step ◽  
Content Type ◽  
Case Comparison

Purpose This paper aims to investigate numerically the turbulent flow characteristics over a backward facing step. Different turbulence models with hybrid computational grid have been used to study the detached flow structure in this case. Comparison between the numerical results and the available experiment data is carried out in the present study. The results of the different turbulence models were in a good agreement with the experimental results. The numerical results also concluded that the k-kl-ω turbulence model gave favorable results compared with the experiment. Design/methodology/approach It is very important to study the flow characteristics of detached flows. Therefore, the current study investigates numerically the flow characteristics in backward facing step by using two-, three- and seven-equation turbulence models in the finite volume code ANSYS Fluent. In addition, hybrid grid has been used to improve the capability of the unstructured mesh elements for predicting the flow separation in this case. Comparison between the different turbulence models and the available experimental data was done to find the most suitable turbulence model for simulating such cases of detached flows. Findings The present numerical simulations with the different turbulence models predicted efficiently the flow characteristics over the backward facing step. The transition k-kl-ω gave the best acceptable results compared with experimental data. This is a good concluded remark in the fields of fluid mechanics and hydrodynamics because the phenomenon of flow separation is not easy to be predicted numerically and can affect greatly on the predicted drag of moving bodies in many engineering applications. Originality/value The CFD results of using different turbulence models have been validated with the experimental work, and the results of k-kl-ω proven acceptable with flow characteristics. The results of the current study conclude that the use of k-kl-ω turbulence model will contribute towards a more efficient utilization in the fields of fluid mechanics and hydrodynamics.

Flow Analysis in a Pump Diffuser—Part 2: Validation and Limitations of CFD for Diffuser Flows

1997 ◽  
Vol 119 (4) ◽  
pp. 978-984 ◽  
Author(s):  
F. A. Muggli ◽  
K. Eisele ◽  
M. V. Casey ◽  
J. Gu¨lich ◽  
A. Schachenmann
Keyword(s):  
Turbulence Model ◽  
Flow Separation ◽  
Static Pressure ◽  
Flow Analysis ◽  
Measurement Data ◽  
Pressure Rise ◽  
Pressure Recovery ◽  
Navier Stokes ◽  
Vaned Diffuser ◽  
Highly Loaded

This paper describes an investigation into the use of CFD for highly loaded pump diffuser flows. A reliable commercial Navier-Stokes code with the standard k-ε turbulence model was used for this work. Calculations of a simple planar two-dimensional diffuser demonstrate the ability of the k-ε model to predict the measured effects of blockage and area ratio on the diffuser static pressure recovery at low loading levels. At high loading levels with flow separation the k-ε model underestimates the blockage caused by the recirculation in the flow separation region and overestimates the pressure recovery in the diffuser. Three steady-state calculations of a highly loaded vaned diffuser of a medium specific speed pump have been carried out using different inlet boundary conditions to represent the pump outlet flow. These are compared to LDA measurement data of the flow field and demonstrate that although the Navier-Stokes code with the standard k-ε turbulence model is able to predict the presence of separation in the flow, it is not yet able to accurately predict the static pressure rise of this highly loaded pump diffuser beyond the flow separation point.

URANS Modeling of Three Airfoils With Different Stall Mechanisms

2008 ◽  
Author(s):  
M. Elkhoury ◽  
J. Najem ◽  
Z. Nakad
Keyword(s):  
Turbulence Model ◽  
Flow Separation ◽  
Numerical Scheme ◽  
Predictive Accuracy ◽  
Grid Size ◽  
Test Cases ◽  
Transition Effect ◽  
Time Stepping

Capability of recently developed Menter (ME) and Modified Menter (MME) one-equation models in predicting prestall and poststall characteristics of three airfoils that exhibit different stall onset mechanisms is investigated. The Spalart-Allmaras (SA) turbulence model is also included to form a baseline against which both the ME and the MME models are assessed. The effects of subiteration, grid size, and time stepping on the predictive accuracy of the numerical scheme are addressed. However, transition effect is not accounted for and hence, all test cases are run fully turbulent. Significant differences in the flow predictions of all models are noticed in regions with massively flow separation.

scholarly journals Calibration of Spalart-Allmaras model for simulation of corner flow separation in linear compressor cascade

2021 ◽  
pp. 1-16
Author(s):  
Kotaro Matsui ◽  
Ethan Perez ◽  
Ryan Kelly ◽  
Naoki Tani ◽  
Aleksandar Jemcov
Keyword(s):  
Mach Number ◽  
Numerical Simulations ◽  
Turbulence Model ◽  
Flow Separation ◽  
Model Parameters ◽  
Compressor Cascade ◽  
Linear Compressor ◽  
Calibration Process ◽  
Corner Flow ◽  
Linear Compressor Cascade

This study focuses on the calibration of Spalart--Allmaras turbulence model parameters using the Bayesian inference approach to reproduce experimental measurements of corner flow separation in linear compressor cascade. The quantity of interest selected for the calibration process is the pitchwise distribution of Mach number in the wake of the linear compressor cascade. The model parameters are assumed to be random variables obeying uniform prior probability distributions. Sensitivity analysis is used to rank the importance and select the most influential turbulence model parameters for the calibration process. The sensitivity ranking indicates that two model parameters cb1 and kappa are the most influential random variables resulting in a two--parameter Bayesian calibration process. The likelihood distribution is specified in the form of the Gauss distribution to include the experimental uncertainty. The likelihood distribution is used together with prior distribution to compute posterior probabilities of selected model parameters. The polynomial chaos expansion is employed as a surrogate model to reduce the cost of posterior calculation. Numerical simulations with calibrated turbulence parameters show a significant increase in the accuracy of Mach number profile prediction for separated flows in linear compressor cascade. Numerical simulations also demonstrate that the calibrated set of model coefficients produce accurate predictions of the total pressure and Mach number profiles for the range of incidence angles that were not part of the calibration process.

scholarly journals ISPH Simulation of Solitary Waves Propagating Over a Bottom-Mounted Barrier With k–ε Turbulence Model

2021 ◽  
Vol 9 ◽  
Author(s):  
Dong Wang ◽  
Sheng Yan ◽  
Chen Chen ◽  
JianGuo Lin ◽  
Xupeng Wang ◽  
...  
Keyword(s):  
Numerical Model ◽  
Turbulence Model ◽  
Flow Separation ◽  
Mean Velocity ◽  
Turbulence Characteristics ◽  
Transmission Coefficients ◽  
Particle Hydrodynamics ◽  
Smoothed Particle ◽  
Incompressible Smoothed Particle Hydrodynamics ◽  
Good Agreement

Solitary wave propagating over a bottom-mounted barrier is simulated using the Incompressible Smoothed Particle Hydrodynamics (ISPH) method in order to study the generation and transport of turbulence associated with flow separation around submerged structures. For an accurate capture of turbulence characteristics during the wave propagation, rather than employing the standard sub-particle scale (SPS) model, the k-ε turbulence model is coupled with the numerical scheme. The results of the numerical model are compared with experimental data, and good agreement is observed in terms of mean velocity, free surface elevation, vorticity fields and turbulent kinetic energy. The numerical model is then employed to investigate the effects of wave non-linearity and geometrical size of the submerged barrier on the flow separation; and calculate the reflection, dissipation and transmission coefficients to evaluate the importance of energy dissipation due to the generation of vortices. The results of this study show that the developed ISPH method with the k-ε turbulence closure model is capable of reproducing the velocity fields and the turbulence characteristics accurately, and thus can be used to perform predictions of comprehensive hydrodynamics of flow-structure interactions in the urban hydro-environment systems.

Optimizing Jets for Active Wake Control of Ground Vehicles

2013 ◽  
Author(s):  
Domenic L. Barsotti ◽  
Sandra K. S. Boetcher
Keyword(s):  
Drag Reduction ◽  
Turbulence Model ◽  
Vortex Shedding ◽  
Flow Separation ◽  
Detached Eddy Simulation ◽  
Ground Vehicles ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
Model Flow ◽  
Ahmed Body

The present study investigates the simulation of slot jets on the rear of an Ahmed body to reduce drag. Improved Delayed Detached Eddy Simulation (IDDES) turbulence model is used to model flow separation and vortex shedding on a 25° Ahmed body. Several optimizations are conducted to maximize drag reduction with a net reduction of 16%. This is accomplished by creating a fluid structure in the wake.

The effects of flow separation on a lambda wing aerodynamics

2019 ◽  
Vol 91 (8) ◽  
pp. 1100-1112 ◽  
Author(s):  
Mehdi Dadkhah ◽  
Mehran Masdari ◽  
Mohammad Ali Vaziri ◽  
Mojtaba Tahani
Keyword(s):  
Drag Coefficient ◽  
Turbulence Model ◽  
Flow Separation ◽  
Turbulence Models ◽  
Leading Edge ◽  
Pitching Moment ◽  
Aerodynamic Coefficients ◽  
Content Type ◽  
Leading Edge Vortex ◽  
Edge Vortex

Purpose In this paper, experimental and numerical results of a lambda wing have been compared. The purpose of this paper is to study the behaviour of lambda wings using a CFD tool and to consider different numerical models to obtain the most accurate results. As far as the consideration of numerical methods is concerned, the main focus is on the evaluation of computational methods for an accurate prediction of contingent leading edge vortices’ path and the flow separation occurring because of the burst of these vortices on the wing. Design/methodology/approach Experimental tests are performed in a closed-circuit wind tunnel at the Reynolds number of 6 × 105 and angles of attack (AOA) ranging from 0 to 10 degrees. Investigated turbulence models in this study are Reynolds Averaged Navior–Stokes (RANS) models in a steady state. To compare the accuracy of the turbulence models with respect to experimental results, sensitivity study of these models has been plotted in bar charts. Findings The results illustrate that the leading edge vortex on this lambda wing is unstable and disappears soon. The effect of this disappearance is obvious by an increase in local drag coefficient in the junction of inner and outer wings. Streamlines on the upper surface of the wing show that at AOA higher than 8 degrees, the absence of an intense leading edge vortex leads to a local flow separation on the outer wing and a reverse in the flow. Research limitations/implications Results obtained from the behaviour study of transition (TSS) turbulence model are more compatible with experimental findings. This model predicts the drag coefficient of the wing with the highest accuracy. Of all considered turbulence models, the Spalart model was not able to accurately predict the non-linearity of drag and pitching moment coefficients. Except for the TSS turbulence model, all other models are unable to predict the aerodynamic coefficients corresponding to AOA higher than 10 degrees. Practical implications The presented results in this paper include lift, drag and pitching moment coefficients in various AOA and also the distribution of aerodynamic coefficients along the span. Originality/value The presented results include lift, drag and pitching moment coefficients in various AOA and also aerodynamic coefficients distribution along the span.

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