Inviscid flow

Inviscid flow is an idealized flow in which viscosity is neglected, so the fluid carries no shear stress and the governing equations reduce from Navier-Stokes to Euler. If the flow is also irrotational it admits a velocity potential satisfying Laplace’s equation, which is the basis of potential-flow and panel methods. The idealization captures pressure fields, wave-making, and added mass well, but it cannot produce skin-friction drag, boundary-layer growth, or flow separation, and it leads to d’Alembert’s paradox of zero drag on a closed body in steady flow. Naval architects pair an inviscid outer solution with a viscous boundary-layer or RANS treatment near the hull.