Calculation of lift by the distribution of pressures on two walls of the test chamber
In wind tunnels with a closed test chamber with a rectangular shape, it would be possible to calculate the lift acting on a model with a constant section supported between two walls of the test chamber (twodimensional plane flow), through integration of the pressure on the other two walls. This method stems from the principle of conservation of momentum: the lift generated by the airfoil induces an uneven distribution of pressure on the walls, which are streamlines.
Since the disturbance induced by the airfoil will propagate at infinity upstream and downstream, it should be necessary to integrate these pressures on a domain much larger than the test chamber. Therefore, a
correction factor has to be introduced to take into account the finiteness of the domain of integration.
In the case of supersonic motion, the field is necessarily limited by the intersection with the walls of the shock waves generated on the leading edge and on the trailing edge.