Convergence schemes for an adaptive-wall wind tunnel

Abstract

A series of experiments was carried out to demonstrate the feasibility of using the side-wall pressure distribution as the flow variable in the wall-interference compatibility assessment, and to exploit a one-step method in a ventilated adaptive-wall wind tunnel. The iterative and one-step convergence methods were applied using different flow variables to investigate their relative merits. It was shown that the number of iterations could be reduced to a minimum with the application of the one-step convergence scheme. The same unconfined conditions obtained with the streamwise and normal velocity components could be achieved using the resultant velocity from side-wall pressure. Side-wall pressure measurements require simple instrumentation and reduce the total testing time, which are some of the major requirements in production testing. The one-step scheme reduces the testing time by eliminating the intermediate experimental iterations. In the present research, wall corrections were determined using measured influence coefficient matrices, which were evaluated at two control levels. The effects of Mach number, model, suction, and blowing on the influence coefficients were investigated along with the superposition and linearity characteristics. Experiments were carried out at velocities from M = 0.5 to 0.75 and at angles of attack from a = 0 to 4 deg. Nomenclature a 0 = speed of sound at standard atmospheric conditions c -airfoil chord GIJ -element of the influence coefficient C p = pressure coefficient M = Mach number N = number of control points p = pressure P t = total pressure u = streamwise disturbance velocity component u r = U, -I/,* U r = resultant velocity £/ ref = longitudinal freestream velocity x = airfoil longitudinal axis, origin at X/c = -0.25 X = longitudinal coordinate Y = normal coordinate a = angle of attack, deg A/? = pressure change in a plenum compartment AV = disturbance velocity change at a control point Subscripts c = calculated i = ith control point j =yth plenum compartment k = number of plenum compartments m = measured Presented in part as