H.J. Allen

As is well known, the closed throat wind tunnel, which has been the principal tool for aerodynamic research, is incapable of operation at speeds near sonic speed as a result of the phenomenon of "choking". In this paper the development of two types of wind tunnels capable of operation from subsonic to supersonic is discussed. One type, developed at the Langley Aeronautical Laboratory, employs fixed test section walls that are slotted in the direction of airflow. With this "partly open throat" wind tunnel, because of the inability to support a pressure difference within the slot, choking does not occur so that operation at sonic speed is possible. Moreover by proper ducting of the slots into the diffuser, air can be aspirated into slots to bring about further expansion of the airstream to produce supersonic flow jn the test section as well. By proper design, uniform test section velocity distributions can be attained throughout the transonic speed range. With this simple slotted wind tunnel subsonic wall interference is practically eliminated. However, at supersonic speeds shock waves from a model reflect from the walls disturbances which, if they impinge on the model, influence the model aerodynamic characteristics. These influences can be restricted to a narrow range of Mach numbers by employing models that are small relative to test section dimensions. The second type, developed at the Ames Aeronautical Laboratory, employs flexible walls upstream of the ventilated test section which allows the expansion required to attain supersonic speeds. This permits more freedom in the design of the ventilated walls to better perform the function of acting as a "wave trap" at supersonic speeds. Certain perforated walls are found to materially reduce the intensities of the reflected disturbances as compared with those experienced in the fixed-wall, slotted type transonic wind tunnel. Thus, for the flexible-wall, perforated-type transonic tunnel the supersonic wall interference is reduced as compared with that for the fixed-wall, slotted-type but at some sacrifice in simplicity.

WGL-Tagung, Duisburg, 1954

Conference Paper

englisch

21,0 x 29,7 cm, 9 Seiten

Jahrbuch der Wissenschaftlichen Gesellschaft für Luftfahrt, 1954, Band I, ; S.42-50; 1954; Braunschweig : Vieweg

NA

Bestellbar

1955