pressure boundary condition for inviscid flow
 

I think in applying boundary condition for pressure on the surface of an oscillating airfoil in an inviscid flow Du/Dt for fluid particle can not be calculated by differentiating u(t)(u(t) is airfoil motion) because of slip condition on airfoil surface.

Re: pressure boundary condition for inviscid flow
 

You have to apply the tangent flow boundary condition along with the boundary condition on the pressure ( dp/dn=-rho*du/dt dot n ) where u is the structural velocity vector and n is the normal vector.