A V/STOL Wind-Tunnel Wall Interference Study

An integrated theoretical and experimental study of slotted wall tunnels is described. Theoretical calculations based on a modification of the point-matching method with equivalent homogeneous boundary conditions have been used to show the relationship between the lift- and blockage-interference factors and wall porosity. Experimental interference factors are obtained by comparing lift coefficient vs angle of attack data obtained in a 30 X 45 in. tunnel with those from a 7 X 10 ft tunnel. Theoretical results indicate that the lift interference for conventional models is insensitive to the porosity of the vertical walls for a height to width ratio less than 0.8. It is shown that certain combinations of vertical and horizontal wall slots give simultaneous zero lift and blockage interference. The discrepancy between theoretical and experimental results may be caused by nonhomogeneou s slots and viscous effects.