A zero-equation turbulence model for two-dimensional hybrid Hall thruster simulations

2015 ◽  
Vol 22 (11) ◽  
pp. 114505 ◽  
Author(s):  
Mark A. Cappelli ◽  
Christopher V. Young ◽  
Eunsun Cha ◽  
Eduardo Fernandez
Keyword(s):  
Turbulence Model ◽  
Hall Thruster ◽  
Two Dimensional

Computational Fluid Dynamics Study for Improvement of Prediction of Various Thermally Stratified Turbulent Boundary Layers

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Hirofumi Hattori ◽  
Tomoya Houra ◽  
Amane Kono ◽  
Shota Yoshikawa
Keyword(s):  
Boundary Layers ◽  
Turbulence Model ◽  
Turbulence Models ◽  
Eddy Diffusivity ◽  
Turbulent Boundary Layers ◽  
Heat Fluxes ◽  
Shear Stresses ◽  
Turbulent Heat ◽  
Two Dimensional ◽  
Turbulent Statistics

The objectives of this study are to reconstruct a turbulence model of both the large Eddy simulation (LES) and the Reynolds-averaged Navier–Stokes simulation (RANS) which can predict wind synopsis in various thermally stratified turbulent boundary layers over any obstacles. Hence, the direct numerical simulation (DNS) of various thermally stratified turbulent boundary layers with/without forward-step, two-dimensional block, or two-dimensional hill is carried out in order to obtain detailed turbulent statistics for the construction of a database for the evaluation of a turbulence model. Also, DNS clearly reveals the characteristics of various thermally stratified turbulent boundary layers with/without forward-step, two-dimensional block, or two-dimensional hill. The turbulence models employed in LES and RANS are evaluated using the DNS database we obtained. In the LES, an evaluated turbulence model gives proper predictions, but the quantitative agreement of Reynolds shear stress with DNS results is difficult to predict. On the other hand, the nonlinear eddy diffusivity turbulence models for Reynolds stress and turbulent heat flux are also evaluated using DNS results of various thermally stratified turbulent boundary layers over a forward-step in which the turbulence models are evaluated using an a priori method. Although the evaluated models do not make it easy to properly predict the Reynolds shear stresses in all cases, the turbulent heat fluxes can be qualitatively predicted by the nonlinear eddy diffusivity for a heat turbulence model. Therefore, the turbulence models of LES and RANS should be improved in order to adequately predict various thermally stratified turbulent boundary layers over an obstacle.

scholarly journals Numerical simulation of mixing by Rayleigh–Taylor and Richtmyer–Meshkov instabilities

1994 ◽  
Vol 12 (4) ◽  
pp. 725-750 ◽  
Author(s):  
D.L. Youngs
Keyword(s):  
Numerical Simulation ◽  
Turbulence Model ◽  
Turbulent Mixing ◽  
Inertial Confinement Fusion ◽  
Three Dimensional ◽  
Small Scale ◽  
Inertial Confinement ◽  
Two Dimensional ◽  
Confinement Fusion ◽  
Icf Target

Rayleigh-Taylor (RT) and Richtmyer–Meshkov (RM) instabilities at the pusher–fuel interface in inertial confinement fusion (ICF) targets may significantly degrade thermonuclear burn. Present-day supercomputers may be used to understand the fundamental instability mechanisms and to model the effect of the ensuing mixing on the performance of the ICF target. Direct three-dimensional numerical simulation is used to investigate turbulent mixing due to RT and RM instability in simple situations. A two-dimensional turbulence model is used to assess the effect of small-scale turbulent mixing in the axisymmetric implosion of an idealized ICF target.

K-e and Reynolds Stress Turbulence Model Comparisons for Two-Dimensional Injection Flows

AIAA Journal ◽  
10.2514/2.561 ◽  
1998 ◽  
Vol 36 (8) ◽  
pp. 1401-1412 ◽  
Author(s):  
Clarence F. Chenault ◽  
Philip S. Beran
Keyword(s):  
Reynolds Stress ◽  
Turbulence Model ◽  
Two Dimensional ◽  
Model Comparisons

Predicting Roll Damping for Barge-Type FPSO Using CFD

2019 ◽  
Author(s):  
Arjen Koop ◽  
Frédérick Jaouën ◽  
Xavier Wadbled ◽  
Erwan Corbineau
Keyword(s):  
Turbulence Model ◽  
Three Dimensional ◽  
Model Tests ◽  
Vortical Flow ◽  
Damping Coefficient ◽  
Physical Parameters ◽  
Two Dimensional ◽  
Roll Damping ◽  
End Effects ◽  
Hydrodynamic Damping

Abstract An accurate prediction of the non-linear roll damping is required in order to calculate the resonant roll motion of moored FPSO’s. Traditionally, the roll damping is obtained with model tests using decays or forced roll oscillation tests. Calculation methods based on potential flow are not capable of predicting this hydrodynamic damping accurately as it originates from the viscous nature of the fluid and the complex vortical flow structures around a rolling vessel. In recent years Computational Fluid Dynamics (CFD) has advanced such that accurate predictions for the roll damping can be obtained. In this paper CFD is employed to predict the roll damping for a barge-type FPSO. The objectives of the paper are to investigate the capability and accuracy of CFD to determine roll damping of an FPSO and to investigate whether two-dimensional calculations can be used to estimate the roll damping of a three-dimensional FPSO geometry. To meet these objectives, extensive numerical sensitivity studies are carried out for a 2D hull section mimicking the midsection of the FPSO. The numerical uncertainty for the added mass and damping coefficients were found to be 0.5% and 2%, respectively. The influence of the turbulence model was found to be significant for the damping coefficient with differences up to 14%. The 2D CFD results are compared to results from two-dimensional model tests. The calculated roll damping using the k-ω SST 2003 turbulence model matches the value from the experiments within 2%. The influence of various physical parameters on the damping was investigated through additional 2D calculations by changing the scale ratio, the roll amplitude, the roll period, the water depth, the origin of rotation and the bilge keel height. Lastly, three-dimensional calculations are carried out with the complete FPSO geometry. The 3D results agree with the 2D results except for the largest roll amplitude calculated, i.e. for 15 degrees, where the damping coefficient was found to be 7% smaller. For this amplitude end-effects from the ends of the bilge keels seem to have a small influence on the flow field around the bilge keels. This indicates that the 2D approach is a cost-effective method to determine the roll damping of a barge-type FPSO, but for large roll amplitudes or for different vessel geometries the 2D approach may not be valid due to 3D effects.

Sign in / Sign up

Export Citation Format

Share Document