Pressure Response in Supersonic Wind-Tunnel Pressure Instrumentation

Abstract

In the development of high-speed aircraft, rockets, missles, etc., wind-tunnel pressure measurements at supersonic velocities are necessary to determine certain aerodynamic characteristics. Because of the lack of knowledge concerning the proper choice of parameters in the design of pressure instrumentation, the response time has been known to exceed the running time in the case of the intermittent tunnel. Pressure systems consisting of an orifice, a capillary tube, a length of connecting tubing, and a pressure-sensitive element connected in series are analyzed. The time required for the pressure in the pressure-sensitive element to reach within 1 percent of the equilibrium pressure is defined as the response time of the system. Experiments are conducted to determine the effect of the various geometric and dynamic parameters on the response time. Analytical solutions of the flow equations by numerical integration are carried out for the special case of a length of capillary tubing connected to the pressure-sensitive element for three different inside diameters. The data indicate that the response time can be maintained within acceptable limits for present-day supersonic wind-tunnel installations by proper choice of the geometric and dynamic parameters. The agreement between theory and experiment, being quite satisfactory for the special case solved analytically, indicated that the approximations in the derived flow equations are justified.