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The effects of unequal porosity factors, ascribed to the floor and ceiling of two-dimensional wind tunnel test sections, are investigated with a simplified mathematical model that utilizes a point vortex and a point doublet placed mid-way between the two walls. Closed form solutions are derived, using the method of images for wall pressure distributions, and corrections to Mach number and model angle of attack.

The analytic solution for the interference velocity potential due to a source and a vortex between perforated wind tunnel walls has been extended to higher-order singularities. This allows a more accurate construction of the primary perturbation potential at the walls produced by the tested airfoil. The solution for the interference velocity at the position of the model is presented in the form of a series expansion, with Bernoulli polynomials of a suitably chosen function of wall porosity as coefficients. The discussion is limited to subsonic flow and a thin airfoil of small camber and incidence, placed midway between the perforated walls.