Experiments on the interaction of a coflowing light gas jet with a weak oblique shock wave

Citation

Moore, Kevin C. (1996) Experiments on the interaction of a coflowing light gas jet with a weak oblique shock wave. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/qgz4-en52. https://resolver.caltech.edu/CaltechTHESIS:02072013-095344022

Abstract

Results of experiments performed in the GALCIT Supersonic Wind Tunnel involving a coflowing helium jet in a Mach 2.4 air freestream are presented. Measurements of the undisturbed jet arc compared with those made after the jet interacts with different weak oblique shock waves. Data collected using stagnation temperature and pitot pressure probes is used to form time averaged cross sectional views of the flow for different downstream stations. These views show that the baroclinic vorticity generated when the jet passes through the shock wave causes the jet to develop into a pair of counter-rotating vortices whose axes are aligned with the flow. Previously proposed models for the circulation deposited on the jet-freestream interface and characteristic time of an analogous unsteady two-dimensional flow are adapted to this flow. Comparison of the jet cross sections for corresponding characteristic times shows agreement with experiments and analysis previously performed on the uustcady two-dimensional analogy. Shear between the jet and the freestream is not seen to materially affect the development of the flow, but the development of the jet is seen to strongly depend on the strength of the oblique shock. Scattering of a laser light sheet off of ice crystals present in the air but absent from the helium provides time-resolved flow visualization pictures which show large departures from the mean as the flow moves downstream. This demonstrates the need to consider turbulence effects which were not considered in previous two-dimensional studies. They also show that the presence of the shock wave increases the apparent randomness of the flow as well as the spreading rate of the jet, likely increasing mixing. A jet cross section extracted from the average of several Rayleigh scattered images agrees well with the general size and shape of the jet cross section taken from the corresponding time averaged temperature data. The design and construction of the active feedback control loop in a gas blending system used to independently control the mass flowrate and temperature of the jet is described.

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