Two-dimensional adaptive-wall tests in the NASA Ames two- by two-foot transonic wind tunnel

This paper describes the first tests conducted in the adaptive-wall test section of the 2- × 2-ft transonic wind tunnel at NASA Ames Research Center. The purpose of the tests was to demonstrate an automatic procedure for minimizing two-dimensional wall interference by actively controlling flow through the slotted upper and lower walls of the test section. Flow through the walls was regulated by adjusting pressures in compartments of a segmented plenum. The procedure for determining the necessary pressure adjustments consisted of the following steps; 1) using a fast-scanning, two-component laser velocimeter to measure flow velocities along axial lines above and below the model; 2) testing the flow measurements for compatibility with free-air, far-field boundary conditions; and 3) using compirical influence coefficients to relate changes in flow velocity to changes in plenum pressures. A NACA 0012 airfoil was tested at Mach numbers between 0.70 and 0.85 and at angles of attack of 0 and 2 deg. In all cases, the procedure substantially reduced wall interference; however, measurable and significant interference persisted after the final plenum-pressure adjustments. The principal reason that interference could not be completely eliminated was that the effects of the plenum-pressure adjustments on the velocity measurements could not be predicted accurately.