for an oscillating airfoil we can use pressure boundary condition on airfoil surface as dp/dn=-(Du/Dt).n. How can we calculate Du/Dt on airfoil surface for an inviscid and viscous fluid flow to set pressure boundary condition on airfoil surface?

If the surface is moving then you should have the kinematic information you need to compute the surface acceleration. The acceleration of the solid is equal to the acceleration of the fluid at the surface. If the surface is moving due to the fluid, then compute the acceleration as a discrete difference, or relate it to the force imposed on the body.

it seems to me that what ag said is right for viscous fluid flow. how can we calculate acceleration of the fluid at the surface if flow is inviscid?