GRID ADAPTATION FOR UNSTEADY-FLOW COMPUTATIONS

A grid adaptation procedure suitable for use during unsteady flow comp utations is described. Transfinite interpolation is used to generate s tructured grids for the computation of steady and unsteady Euler flows past aerofoils. This technique is well suited to unsteady flows, sinc e instantaneous grid positions and speeds required by the flow solver are available directly from the algebraic mapping. A different approac h to grid adaptation is described, wherein adaptation is performed by redistributing the interpolation parameters, instead of the physical g rid positions. This results in the adapted grid positions, and hence s peeds, still being available algebraically. Grid adaptation during an unsteady computation is performed continuously by imposing an 'adaptat ion velocity' on grid points, thereby applying the adaptation over sev eral time steps and avoiding the interpolation of the solution from on e grid to another, which is associated with instantaneous adaptation. For both steady and unsteady flows the adapted grid technique is shown to produce sharper shock resolution for a very small increase in CPU (central processing unit) requirements.