Theoretical and Experimental Analysis of the Siotted-Wall Flow Field in a Transonic Wind Tunnel

The necessity for accurately measuring the performance of aerospace vehicles became paramount with the advent of sustainable, high subsonic-speed flight. However, at these speeds, wind-tunnel test sections with solid-wall boundaries choked and those with open-jet boundaries proved unsteady and inefficient. Noting that wall corrections for solid-wall tunnels were opposite in sign to those applied to open-jet tunnels, research was directed at developing partially open slotted and perforated walls with the hope of eliminating, or at least reducing the magnitude of, the wall-induced error in the data. The success of these endeavors is history as all transonic tunnels today have slotted or perforated walls.

Even though research on these types of walls has continued for over four decades, the existing theory still does not adequately define the flow near the wall. One reason for this is there has been a lack of an experimental data base for analyzing the behavior of the wall flow field adjacent to perforated and slotted-wall geometry configurations. The purpose of this study is to theoretically analyze the slotted-wall flow field to determine the appropriate fundamental form of the boundary condition which exists there, determine the unknown coefficients in the boundary condition using a data base acquired in the Langley Research Center's 6- by 19-inch Transonic Tunnel, and, then, correlate these coefficients with wall-geometry variables and tunnel free-stream conditions.