scholarly journals Assessment of turbulence model performance: Large streamline curvature and integral length scales

2016 ◽  
Vol 126 ◽  
pp. 91-101 ◽  
Author(s):  
Xiaoyu Yang ◽  
Paul G. Tucker
Keyword(s):  
Turbulence Model ◽  
Model Performance ◽  
Length Scales ◽  
Streamline Curvature

scholarly journals Evaluation of Turbulence-Model Performance in Jet Flows

AIAA Journal ◽  
2001 ◽  
Vol 39 (12) ◽  
pp. 2402-2404 ◽  
Author(s):  
S. L. Woodruff ◽  
J. M. Seiner ◽  
M. Y. Hussaini ◽  
G. Erlebacher
Keyword(s):  
Turbulence Model ◽  
Model Performance ◽  
Jet Flows

Assessment of Turbulence Model Performance Adopted Near Wall Treatment for a Sharp 90° 3-D Turning Diffuser

2017 ◽  
pp. 259-273
Author(s):  
Normayati Nordin ◽  
Zainal Ambri Abdul Karim ◽  
Safiah Othman ◽  
Vijay R. Raghavan ◽  
Sharifah Adzila ◽  
...  
Keyword(s):  
Turbulence Model ◽  
Model Performance ◽  
Near Wall

Numerical Investigation of Flow Past a Prolate Spheroid

2002 ◽  
Vol 124 (4) ◽  
pp. 904-910 ◽  
Author(s):  
George S. Constantinescu ◽  
Hugo Pasinato ◽  
You-Qin Wang ◽  
James R. Forsythe ◽  
Kyle D. Squires
Keyword(s):  
Skin Friction ◽  
Turbulence Model ◽  
Pressure Coefficient ◽  
Angle Of Attack ◽  
Prolate Spheroid ◽  
Leeward Side ◽  
Experimental Measurements ◽  
Axial Pressure ◽  
Streamline Curvature ◽  
Axial Pressure Gradient

The flowfield around a 6:1 prolate spheroid at angle of attack is predicted using solutions of the Reynolds-averaged Navier-Stokes (RANS) equations and detached-eddy simulation (DES). The calculations were performed at a Reynolds number of 4.2×106, the flow is tripped at x/L=0.2, and the angle of attack α is varied from 10 to 20 deg. RANS calculations are performed using the Spalart-Allmaras one-equation model. The influence of corrections to the Spalart-Allmaras model accounting for streamline curvature and a nonlinear constitutive relation are also considered. DES predictions are evaluated against experimental measurements, RANS results, as well as calculations performed without an explicit turbulence model. In general, flowfield predictions of the mean properties from the RANS and DES are similar. Predictions of the axial pressure distribution along the symmetry plane agree well with measured values for 10 deg angle of attack. Changes in the separation characteristics in the aft region alter the axial pressure gradient as the angle of attack increases to 20 deg. With downstream evolution, the wall-flow turning angle becomes more positive, an effect also predicted by the models though the peak-to-peak variation is less than that measured. Azimuthal skin friction variations show the same general trend as the measurements, with a weak minima identifying separation. Corrections for streamline curvature improve prediction of the pressure coefficient in the separated region on the leeward side of the spheroid. While initiated further along the spheroid compared to experimental measurements, predictions of primary and secondary separation agree reasonably well with measured values. Calculations without an explicit turbulence model predict pressure and skin-friction distributions in substantial disagreement with measurements.

Capturing S-Shape of Pump-Turbines by CFD Simulations Using an Anisotropic Turbulence Model

2019 ◽  
Author(s):  
Ernesto Casartelli ◽  
Luca Mangani ◽  
Armando Del Rio ◽  
Angelika Schmid
Keyword(s):  
Turbulence Model ◽  
Electricity Market ◽  
Vortex Formation ◽  
Model Performance ◽  
Reynolds Stress Model ◽  
Market Demand ◽  
Operational Flexibility ◽  
Transient Conditions ◽  
Sst Turbulence Model ◽  
The Right

Abstract Pump-turbines cope very well with modern electricity-market demand, having high operational flexibility and storage capabilities. Nevertheless, dynamic operation of these machines can lead to very challenging transient conditions, depending on the shape of the characteristic. Mechanical integrity can be correspondingly affected. Therefore assessment of the characteristic during the design phase, i.e. before model testing, is of crucial importance. In the past years different attempts to accurately compute the characteristic under steady (i.e. fix point) and transient conditions have been undertaken using RANS CFD. While the SST turbulence model has become the reference for machine design, it often fails for conditions close to or around instabilities. Its strength to accurately predict separation close to sound conditions (i.e. mild part- and over-load) is no more helpful. Under unstable conditions, which are characterized by continuous unsteady vortex formation, turbulence isotropy as assumed by linear two equation models is no more the right choice. Accordingly a turbulence model able to capture anisotropy, EARSM (Explicit Algebraic Reynolds Stress Model), has been implemented in an in-house code and used for the computation of the characteristic of various machines, stable and unstable, in order to assess the model performance. In this paper computations of three different machines in turbine mode are presented. Results using steady boundary conditions (BC) in the unstable region as well as transient BC like load-rejection and runaway are computed with EARSM, showing its superiority compared to linear two equation models.

On Turbulent Flows Dominated by Curvature Effects

1992 ◽  
Vol 114 (1) ◽  
pp. 52-57 ◽  
Author(s):  
G. C. Cheng ◽  
S. Farokhi
Keyword(s):  
Turbulent Flows ◽  
Turbulence Model ◽  
Dominant Role ◽  
Longitudinal Velocity ◽  
Turbulence Models ◽  
Separated Flows ◽  
Local Curvature ◽  
Streamline Curvature ◽  
Curvature Effects ◽  
Numerical Predictions

A technique for improving the numerical predictions of turbulent flows with the effect of streamline curvature is developed. Separated flows and the flow in a curved duct are examples of flow fields where streamline curvature plays a dominant role. New algebraic formulations for the eddy viscosity μt incorporating the k–ε turbulence model are proposed to account for various effects of streamline curvature. The loci of flow reversal (where axial velocities change signs) of the separated flows over various backward-facing steps are employed to test the capability of the proposed turbulence model in capturing the effect of local curvature. The inclusion of the effect of longitudinal curvature in the proposed turbulence model is validated by predicting the distributions of the longitudinal velocity and the static pressure in an S-bend duct and in 180 deg turn-around ducts. The numerical predictions of different curvature effects by the proposed turbulence models are also reported.

Calculation of Annular and Twin Parallel Jets Using Various Discretization Schemes and Turbulence-Model Variations

1981 ◽  
Vol 103 (2) ◽  
pp. 352-360 ◽  
Author(s):  
M. A. Leschziner ◽  
W. Rodi
Keyword(s):  
Experimental Data ◽  
Turbulence Model ◽  
Numerical Scheme ◽  
Turbulence Models ◽  
Turbulence Energy ◽  
Normal Stresses ◽  
Numerical Diffusion ◽  
Streamline Curvature ◽  
Recirculating Flow ◽  
Discretization Schemes

The paper examines the performance of three discretization schemes for convection and three turbulence-model variations when used to simulate the recirculating flow in an annular and a plane twin-parallel jet in still air. The discretization schemes considered are: (i) the hybrid central/upwind differencing scheme (CUDS), (ii) the hybrid central/skew-upwind differencing scheme (CSUDS) and (iii) the quadratic, upstream-weighted differencing scheme (QUDS). Of these, the second and third were proposed recently as superior alternatives to the first in respect of numerical diffusion. The turbulence models examined are the standard k-ε model and two variants of this. The first accounts for effects of streamline curvature on turbulence and the second for the preferential influence of normal stresses on the dissipation of turbulence energy. It is shown that numerical scheme (i) results, particularly in conjunction with the turbulence-model modifications, in severe solution errors and in a generally anomalous response to changes in the modelled viscosity field. In contrast, schemes (ii) and (iii) yield, in all cases, similar results and respond in an expected manner to the modifications. The modifications, particularly that accounting for streamline curvature, reduce, in some cases drastically, the discrepancies between computed and experimental data and yield for both jets examined generally satisfactory results.

Development of a Numerical Based Correlation for Performance Losses due to Surface Roughness in Axial Turbines

2014 ◽  
Vol 30 (6) ◽  
pp. 631-642 ◽  
Author(s):  
S. A. Moshizi ◽  
M. H. Nakhaei ◽  
M. J. Kermani ◽  
A. Madadi
Keyword(s):  
Turbulence Model ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Streamline Curvature ◽  
Sst Turbulence Model ◽  
Stator Blade ◽  
Dimensional Models ◽  
Three Dimensional Models ◽  
Axial Turbines

AbstractIn the present work, a recently developed in-house 2D CFD code is used to study the effect of gas turbine stator blade roughness on various performance parameters of a two-dimensional blade cascade. The 2D CFD model is based on a high resolution flux difference splitting scheme of Roe (1981). The Reynolds Averaged Navier-Stokes (RANS) equations are closed using the zero-equation turbulence model of Baldwin-Lomax (1978) and two-equation Shear Stress Transport (SST) turbulence model. For the smooth blade, results are compared with experimental data to validate the model. Finally, a correlation between roughness Reynolds number and loss coefficient for both turbulence models is presented and tested for three other roughness heights. The results of 2D turbine blade cascades can be used for one-dimensional models such as mean line analysis or quasi-three-dimensional models e.g. streamline curvature method.

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