# transient calculation

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 April 20, 2015, 13:32 transient calculation #1 New Member   Ankur Bhatnagar Join Date: Nov 2013 Posts: 18 Rep Power: 4 Sir , I am performing transient calculations over a body using su2. The flow mach number is changing from mach=0.3 to mach=3 .I am working with unstructured gird.As soon as the code reaches Mach =1 it become unstable.So far i have tried using different limiter coeff value ranging from 15 to 0.3 , reducing time step,grid refinement,JST model but problem is still there. can u please suggest me some way to overcome this problem.Thnxx

April 22, 2015, 15:16
#2
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Heather Kline
Join Date: Jun 2013
Posts: 174
Rep Power: 4
Quote:
 Originally Posted by ankur bhatangar Sir , I am performing transient calculations over a body using su2. The flow mach number is changing from mach=0.3 to mach=3 .I am working with unstructured gird.As soon as the code reaches Mach =1 it become unstable.So far i have tried using different limiter coeff value ranging from 15 to 0.3 , reducing time step,grid refinement,JST model but problem is still there. can u please suggest me some way to overcome this problem.Thnxx
I suggest checking your boundary conditions. Specifically, if you are using an inlet boundary condition try switching to the supersonic inlet condition when the simulation passes Mach 1.0. Note also that the presence of shocks may require significantly more refined grids above Mach 1.0 - ideally you want to have the tightest spacing across the thickness of a shock, and not much larger than the thickness of the shock (numerical methods tend to spread shocks over multiple nodes). Also, depending on your geometry and conditions the presence of shocks may be causing separation - that is, the instability could be physical rather than numerical.

 April 22, 2015, 16:03 @ hlk #3 New Member   Ankur Bhatnagar Join Date: Nov 2013 Posts: 18 Rep Power: 4 thnx for your reply sir ...i will surely look into.. I am using unstructured grid all around with riemann boundary conditions.

 Tags su2, transient analysis

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