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timestep for viscous compressible flows

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Old   July 11, 2005, 07:20
Default timestep for viscous compressible flows
  #1
Ravi
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Can anyone suggest a good timestep formula for explicit compressible viscous flow on unstructured grids. On quadrilateral (2D problem), if i stretch cells at wall boundaries solution is diverging after some number of iterations even if i use small cfl number. problem is converging for triangular grids as amount of stretching is less compared to quadrilateral grid.
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Old   July 11, 2005, 11:19
Default Re: timestep for viscous compressible flows
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Salvador
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dt < rho*Pr*L^2/(4*gamma*visc)

where L is a charateristic dimension of the cell

check Turkel et al.(1991), NASA TR.
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Old   July 12, 2005, 13:51
Default Re: timestep for viscous compressible flows
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lavan
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Thank you for your response.

Earlier for inviscid computation i am using fallowing timestep.

dt = sqrt(area of cell)/(sqrt(u^2+v^2)+ c).

u and v are two velocity components, c is wave speed.

the time step which you have suggested is alone sufficient for viscous computation or i need to combine both inviscid, viscous time steps? how can i get the paper which you have suggested.

Thank you.
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