Thin body motion in compressible fluid in the presence of free and rigid boundaries

Two-dimensional problems of thin body motion in fluid parallel to the boundary at a distance comparable with the length of the body are regarded. In particular, the resistance and lift forces in motion parallel to free and rigid surfaces are determined. The fluid is assumed to occupy infinite semi-space and gravity is neglected, in comparison with the fluid inertia. The solution is obtained for the problem of plate motion in slightly compressible fluid at a definite depth under a free surface, with constant velocity and inclination angle. The formation of a finite-length cavity behind the body is taken into account. The solution for the linearized problem of a profile motion near a flat, solid surface in a slightly compressible fluid is given. The screen effect becomes essential when the altitude is smaller than the chord. The numerical solution for the incompressible flow about a profile flying over a rigid surface has been obtained by using a panel method. In this way, the numerical lift is compared with the analytical solution. Moreover, streamlines and velocities are discussed by placing the profile at different altitudes and incidences.