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-   -   Problem with pseudo shock simulation! (http://www.cfd-online.com/Forums/fluent/106675-problem-pseudo-shock-simulation.html)

Sridhar thiru September 5, 2012 06:38

Problem with pseudo shock simulation!
 
Hi Guys!! am doing simulation on constant area straight ducts which mimics supersonic inlet isolators, i would like the study the pseudo shock phenomenon that occurs due to shock wave boundary layer interactions.

My problem domain is a cuboid with dimension 80x80x960 all in mm..
owing to computation i reduced the cross section dimension to 40x40 mm, with two long faces of cuboid set to symmetry. n length remained same.

Grid : cuboid with above dimensions;
structured grid with grid fined near the corner region,
1.5 million hexahedral cells, cell squish is around 0.2

Solver settings:
Density based, implicit, absolute velocity formulation.
Material, Air as ideal gas, viscosity :sutherlands formulation.
Turbulence model: standard K - omega model with low re number effect & shear flow corrections enabled,

Boundary conditions are as follows,

Pressure inlet :
momentum- tot pressure 196000pa
supersonic int gauge pressure - 25050 pa
Turbulence parameters
Hydraulic diameter 0.08m
intensity 5 %
Total Temperature : 300k

pressure outlet :
momentum-gauge pressure - 25050 pa
Turbulence parameters
Hydraulic diameter 0.08m
intensity 5 %
Total temperature : 300k

wall : no slip & stationary, heat flux set to zero (adiabatic!)

symmetry : default symmetry

Solver is a STEADY SOLVER ( just to obtain initial conditions for UNSTEADY SOLVER)

discretization:
flux : AUSM
flow : third order MUSCL
Turbulence scalar equations : QUICK
CFL set to default value of 5.

wall y+, i calculated using NASA viscous grid spacing calculator i fixed y+ of 30 which throws cell height of 1e-5m!! Re.no is 3.8*e6 with reference length as hydraulic diameter..

The problem is my solution is not converging beyond 1e-5, residuals fluctuate around 1e-5.. i set the convergence criteria to 1e-6.!!

Is it enough to switch to unsteady solver???
If that the case what value of time step i provide?? also max iterations per time step..I'm stuck with this, Help me..

Also when check with the contour, fluent shows the max wall y+ value of 19 near the wall though i set the cell height for y+ 30.

Thanks in advance.


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