A quantitative measurement of thermally induced stress waves

Abstract

measured static and pitot pressures farther away from the oblique shock wave. The good correspondence between the predicted and measured pressure rise indicated, establishes confidence in the actual pressure change across the oblique shock wave and allows an appraisal of the region of probe influence. The increase in pitot pressure across the oblique shock wave is also compatible with that calculated using the oblique shock relations, e.g., experimentally p^'/pti = 1.48, while a value of 1.50 is predicted. Of note in this connection is that the turning of the flow through an angle of 8.3° in passing through the oblique shock wave apparently did not influence the pitot tube reading downstream where the flow is inclined to the probe. The slight blip in the pitot pressure below the oblique shock wave is associated with a small disturbance locally in the flow rather than the presence of the oblique shock wave. This view is supported by pitot measurements at axial distances farther upstream and downstream which indicated the disturbance to lie along a streamline and thus was located at different radial distances from the oblique shock wave. Rather large deviations in Mach number are found by using the local static and pitot pressures measured to calculate the Mach number; this occurs because of the fallacious static pressure readings. It should be mentioned that the upstream Mach number of 3.48 is not compatible with the static to total pressure ratio p/pto = 0.0116 for isentropic flow up to the shock wave because the actual stagnation pressure upstream of the wave is less than the upstream reservoir pressure p to = 100 psia that is used to normalize the data. The reduction in stagnation pressure resulted from the flow passing through another oblique shock wave farther upstream. The influence of the size of the static pressure probe on its reading is shown in Fig. 2. These measurements were made 0.5 in. downstream of those shown in Fig. 1 at a location where the static pressure was lower. The small probe is similar to that used upstream, and the larger probe is twice as long. Confidence in the actual pressure changes across the oblique shock wave is provided by the very good check with the predicted oblique shock relation shown as a dashed curve and the coincidence of both probe readings farther away from the oblique shock wave. The probes are shown at various locations to assist in the discussion of the readings. Upstream of the oblique shock wave (Fig. 2) the larger probe readings do not have as pronounced a hump as observed with the small probe. Also there is a more gradual approach to the actual static pressure which is found farther away from the oblique shock wave, although this change is small for a probe that is twice as long. Downstream of the oblique shock wave (Fig. 2) the small