Calibration and study of the contoured nozzle of the T5 free-piston hypervelocity shock tunnel

A pitot pressure survey of the contoured nozzle of the T5 shock tunnel was performed over a wide range of reservoir conditions and in the region of the exit plane of the nozzle. A rake of thirteen pitot probes was used for this purpose. The survey includes an investigation of the repeatability of the facility and an analysis of the accuracy of the measurements. The features of the pitot pressure distribution across the exit plane are a pronounced minimum near but not exactly on the centerline, and a pronounced drop near the nozzle wall. The concave profile may be quantified in terms of the curvature of the pitot pressure distribution, which increases markedly as the enthalpy is decreased and as the area ratio is increased. The normalized value of the minimum pitot pressure is found to be independent of the reservoir enthalpy, in contrast to the behavior obtained by numerical computation of inviscid flows. The results of this survey show clearly, that the use of a contoured nozzle should be restricted to conditions very close to the design condition. Since flexibility in the reservoir enthalpy and pressure, as well as area ratio, is an important feature of a shock tunnel, the results of this survey strongly suggest the use of a conical nozzle.