A new method of measuring shock expansion tube test flow velocities

Abstract

[Email address] ii AcknowledgementsThere are several individuals without whom the completion of this body of work would not have been possible. These people should not go without acknowledgement.Firstly, thanks must go to Tim Cullen for being one the people who conducted testing in the University of Queensland's X2 shock Expansion Tube facility on my behalf.Secondly Christopher James, who also conducted experiments and was very generous with his time in helping me to understand the results.Thirdly, The University of Queensland and the department of hypersonics who made their facilities available for experimentation along with a significant manufacturing budget to produce all the required instruments. AbstractShock expansion tubes are an important tool in the field of hypersonic research. However, these facilities possess a major weakness in the fact there is a great deal of uncertainty associated with the properties of the test flows that they produce.In an attempt to better characterise these properties, an instrument which was capable of measuring the velocity of the test flows produced by shock expansion tubes was to be designed and tested. This instrument would consist of two pitot probes which would be mounted in a shock tube at different locations to detect the arrival of the test gas. Based on the time difference between the arrival of this gas at each probe, its velocity could be calculated.Two probes were designed and manufactured for the testing of this concept in the University of Queensland's X2 shock expansion tube. The design, shown in the image to the right, was created with consideration given to the facts that the probe had to; be structurally capable of withstanding the hypersonic flow environment, protect the pressure transducer from this harsh environment, respond rapidly to changes in pitot pressure, be able to take measurements through the thickest boundary layers, create the smallest disturbance to the test flow possible, and record data which was not adversely affected by noise.This design was tested in the X2, which was configured to produce two high enthalpy test flows with velocities of 9468.1m/s and 9656.5m/s.Over the two experiments, the probes measured the velocity of the two test flows to within 3% of the current best estimates, although determining the arrival time of the test gas at each probe was difficult and there was large potential for error. The data recorded by the two probes was also sufficiently noise free and the instruments responded rapidly to any changes in pitot pressure.There was also no evidence that the probes were significantly disrupting the test flow, however further testing was required to confirm this. In summary, the design was a success and further testing was warranted to confirm these results and develop the concept further.iv