flow over cylinder

pang

Hi All,

i doing a 'CFD simulation of Riser VIV'. i started it with very simple things first just like flow(water)over a cylinder in order to obtain drag coefficient using Fluent 6.1. i have try many time but the solution is not converge!may i know which setting is wrong?

first i used this link to calculated my cell height: http://geolab.larc.nasa.gov/APPS/Yplus/ with Re=500000,Y+=3, charac length=1 so my calculated ds=0.0000875 Meter

then i used the ds value as my first length when doing meshing in Gambit

After that i start to run my fluent with below setting Solverressure based viscous model: Spalart-Allmaras Spalart-Allmaras option=strain/vorticity based production material:water-liquid Operatin pressure=101325

For my velocity Inlet boundary condition: velocity Spec Method= Component (is this option correct?) X velocity= 0.5 Y velocity= 0(because i intend to start with simple flow which only have x direction flow). Turbulence Spec. Method=Modified Turbulence Viscosity (is this correct? or should i choose other?if yes, why) Modified Turbulence Viscosity=0.001 (this is default value,is it correct? or elso how to calculate?)

For my pressure outlet boundary condition: gauge Pressure= 0 Backflow direction Spec. Method:= Normal to boundary Turbulence Spec. Method= Modified Turbulence Viscosity (is this correct? or should i choose other?if yes, why) Modified Turbulence Viscosity=0.001 (this is default value,is it correct? or elso how to calculate?)

Solution Control: Pressure=Standard Pressure-velocity coupling=simple Momentum=Second order upwind Modified Turbulence Viscosity=second order upwind

Residuals Monitor Convergence criterio=1e-06

Force Monitor: Coeefficient=Drag Force vector,X=1 Force vector,Y=0

then i make sure my Report>reference value is same as my previous input before i start the iteration

i run until 10000 iteration n yet it converge Can anybody help me to solve it? i may send you my meshing file if needed. Thank a lot!