Adaptable wind tunnel for testing V/STOL configurations at high lift

Abstract

It is argued that the adaptable-wall wind tunnel scheme offers a way to solve a persistent problem of V/STOL testing; namely, interference of tunnel boundaries with the powered, vortical wake at large lift coefficients. First, it is shown that the adaptable-wall scheme permits the simulated freestream direction to be chosen independently of wind tunnel architecture. It is also found that the wake can be allowed to pass downstream without encountering the interface defined by the instrument-array of the tunnel. The combination of these two ideas leads to a new type of wind tunnel—the Arizona V/STOL Tunnel—in which the model's orientation and the freestream vector are chosen to put the wake in the desired position and simulation of the correct freestream vector, defining the desired angle of attack, is achieved by means of the adaptable-wall iterative strategy. To facilitate a numerical demonstration of a tunnel of this kind, a simple panel model of a jet-flap wing and wake is constructed, suitable for the nonlinear, high-lift regime and for the inclusion of wind tunnel effects. Convergence is obtained and the final wing/wake properties are close to unconfined-flow values for the same wing model, although starting conditions were grossly different from preselected final conditions.