Adaptive-wall wind-tunnel development for transonic testing

Abstract

In principle, the adaptive-wall wind tunnel is an attractive alternative to traditional methods of accounting for wind-tunnel wall interference. The concept has been successfully demonstrated for two-dimensional flows at moderately supercritical Mach numbers, but more work needs to be done before the method can be used in production testing. In this paper experimental techniques for rapid assessment and correction of wall interference are described. The procedure is based on laser velocimetry measurements on two control surfaces and on the use of a dedicated computer for rapid data processing. The experimental arrangement and instrumentation are described and typical results from an experiment on a nonlifting NACA 0012 airfoil at M = 0.78 are discussed. Nomenclature c = airfoil chord C p = pressure coefficient: (p -p^) / [ (Yi)p FjJ M = Mach number, subscript p = static pressure u = axial perturbation velocity component v = normal perturbation velocity component x = axial distance y = distance normal to x axis a = angle of attack p = densitySubscripts cl = calculated value at level 1 c2 = calculated value at level 2 ml = measured value at level 1 m2 = measured value at level 2 oo = freestream 1,2 = at levels 1 and 2

Convergence schemes for an adaptive-wall wind tunnel

“…In the iterative method with the two-level compatibility assessment, 5 ' 8 one flow variable is measured at two control levels. The flow variable at the first level is used to evaluate the functional relationships at the second level applying far-field boundary conditions for unconfined flow.…”

Adaptive Wind Tunnels

“…The experiments at NASA-Ames (Satyanarayana et al 1981) were made at somewhat smaller Mach numbers; they also introduced important innovations in instrumentation and control strategy. Here Qi was defined as the vertical (normal to the interface) component of velocity, measured at the interface, while Pi was defined as the same velocity component measured and computed at horizontal planes slightly closer to the walls but still sufficiently removed from them to avoid the fl ow irregularities there.…”