Define Horizontal Buoyancy ?

It is well known that the static-pressure-coefficient values obtained from tests of axisymmetric bodies in, for example, a large water tunnel indicate the existence of tunnel wall interference. This interference is due to blockage experienced by the body operating within the boundaries of the test section walls and to the skin friction on both the tunnel walls and the surface of the body, which, in turn, causes finite-thickness boundary layers to develop. These factors result in a decrease in static pressure along the test section, which leads to a spurious horizontal buoyancy on the body.