Dynamic flow quality measurements in a transonic cryogenic wind tunnel

Abstract

Two instruments mounted in a piggyback arrangement were developed for time-resolved measurements of dynamic flow quality in a transonic cryogenic wind tunnel. The first one is a dual hot-wire aspirating probe for measurement of stagnation pressure and temperature. The second is a miniature high-frequency response angle probe consisting of surface mounted pressure sensors.

The aspirating probe was tested in the 0.3-m Transonic Cryogenic Tunnel (TCT) at NASA-Langley Research Center. Stagnation pressure and temperature measurements were taken in the free-stream of the settling chamber and test section. Data were also obtained in the unsteady wake shed from an airfoil oscillating at 5 Hz. The investigation revealed the presence of large stagnation pressure and temperature fluctuations in the settling chamber occurring at the blade passing frequency of the tunnel driving fan. The fluctuations in the test section are of a much more random nature and have amplitudes much lower than those in the test section. The overall results are consistent with previous tunnel disturbance measurements in the 0.3-m TCT. In the unsteady wake shed from the oscillating airfoil, stagnation temperature fluctuations as high as 42 K rms were observed.

The high-frequency angle probe is a four sensor, pyramid type probe capable of simultaneously measuring time resolved stagnation and static pressures and two orthogonal flow angles. Using measurements from both probes, all flow parameters of interest can be deduced. Aerodynamic behavior of a full size model of the probe was established in an open air jet of known conditions.