= crack width, typically 0.01 in. to 0.1 in. w = wall enthalpy, Btu/lb = stagnation enthalpy, Btu/lb = crack height, in. = ablation rate, lb/ft sec = blowing rate parameter = local heat transfer to crack wall, Btu/ftsec = surface heat transfer, Btu/f t/sec = momentum thickness Reynolds number, p^ujd/^^ = friction Reynolds number, (rw/p)(pb/^} = Stanton number = freestream velocity, ft/sec = boundary-layer displacement thickness, in. = local density = freestream density = wall shear stress, lb/ft