Plane inviscid gas flow is considered in a channel with parallel walls and a small bulge placed on the low wall and modelling an airfoil. Formation of shock waves in uniform deviations of the profile form from the shockless configuration along all the supersonic part of its surface is numerically studied. Different qualitative flow patterns are found as dependences upon the deviation value. Solution of the direct problem of given form airfoil flow is carried out by the method of decomposition of the calculation domain by subsonic and supersonic subdomains with using a fine grid allowing to find the fine flow structure.