An Experimental Investigation of Viscous Effects on Static and Impact Pressure Probes in Hypersonic Flow

An experimental investigation of viscous effects on static and impact pressure probes was conducted in the GALCIT Leg 1 hypersonic wind tunnel. This investigation of the impact probes showed viscous effects to be important for free stream Reynolds numbers less than 6000 based on the probe diameter, in the Mach number range 5.4 to 5.7. For 80 < Re < 6000, the results showed the measured impact pressure to be less than the inviscid value. The maximum deviation from the inviscid impact pressure was 2.3 per cent at a Reynolds number of 200. For Re < 80 the measured impact pressure was greater than the inviscid value. The investigation of the static pressure probes for a Mach number 5.8 and a free stream Reynolds number of 16,000 based on the probe diameter showed a very thick and rapidly growing boundary layer over the probe surface. This boundary layer was sufficient to cause the static pressure measured by a 10 degree cone-nosed probe with its orifice 45 diameters aft of the probe tip to be 7.5 per cent greater than the free stream static pressure. The boundary layer thickness on the 10 degree cone-nosed probe was several times that of the probe radius. The boundary layer was surveyed on a hemispherical-nosed and a flat-nosed probe and showed the boundary layer thickness to be several times that of the 10 degree cone-nosed probe.