Further results of an investigation into general applications of wind tunnel wall corrections

Abstract

An experimental study into the rationale of wind tunnel wall correction is under way in an adaptive flexible walled test section. The investigation has initially concentrated on deliberately introducing nominally uniform streamwise gradients of Mach number or wall-induced upwash into the vicinity of a two-dimensional aft cambered aerofoil, in order to reveal the sensitivities of the model's aerodynamic behaviour to such flow imperfections. Previously reported tests at a relatively low transonic Mach number have generated a valuable body of data, which can not only be used to guide the streamlining policy in an adaptive flexible walled test section but can also aid the application of wall corrections in conventional wind tunnels. Recent tests have concentrated on determining the effects of upwash gradients on lift at a higher transonic speed and form the prime subject of this paper. The most notable finding is that the 34 chord appears to apply to the non-linear situations found with transonic flows as well as to flows that satisfy the restrictions of linear theory. The evidence suggests that the theorem can be used as a basis for the correction of model incidence at a given lift in order to account for the effects of gradient in upwash. There is a need in the short term to determine the effects of blockage gradients at a higher transonic speed and in the long term to broaden the scope of the investigation in terms of model incidence, Mach number and later to m