Integration Time Required to Extract Accurate Data from Transonic Wind-Tunnel Tests

Abstract

Because the forces and pressures on wind-tunnel models tested at transonic speeds are not steady, even for static aerodynamic tests, integration time is required to obtain data of acceptable accuracy. The integration time required for both static and dynamic tests is evaluated analytically and confirmed by experimental measurements. It is shown that, for static and dynamic tests, the accuracy obtained is a function of integration time, frequency of the signal, and the ratio of the dynamic amplitude to the full signal of interest. In addition, for the dynamic case, the frequency bandwidth used in analysis is important. Results of this study indicate that, for typical data accuracy desired from models in a large transonic wind tunnel (11-by 11-ft), up to the following integration times are required: static force and moment tests, 0.5 s; static pressure tests, 1 s; flutter tests, 30 to 60 s; and random-dynamic tests, 10 s.

An experimental study of buffet detection on supercritical airfoils in transonic regime

“…The separation can be realized from the fluctuations of the high frequency response pressure transducers. Muhlstein and Coe 39 presented a method that can distinguish the difference between the pressure fluctuations due to the shock wave and that caused by the flow separation. Figure 11 schematically shows their method that distinguishes between the attached and the separated boundary layer state due to the existence of the shock wave from recording the surface pressure signature.…”

“…Figure 11. Schematic of pressure fluctuations for three different cases-attached flow, shock wave, and separated flow 39. …”