# timestep for viscous compressible flows

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 July 11, 2005, 07:20 timestep for viscous compressible flows #1 Ravi Guest   Posts: n/a 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.

 July 11, 2005, 11:19 Re: timestep for viscous compressible flows #2 Salvador Guest   Posts: n/a dt < rho*Pr*L^2/(4*gamma*visc) where L is a charateristic dimension of the cell check Turkel et al.(1991), NASA TR.

 July 12, 2005, 13:51 Re: timestep for viscous compressible flows #3 lavan Guest   Posts: n/a 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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