The University of Queensland (UQ) Mechanical Engineering Department currently houses three expansion tubes (X1, X2 and X3) that are used to create hypersonic flows. Recently the experimental results of the X3 shock tube section have been found to be inaccurate. The data obtained from these experiments is in the form of pressure output readings, obtained through piezoelectric transducers placed in the X3. The manufacturer of the transducers used by UQ is PCB Piezotronics.
By analysing previous experiments conducted in X3, it was determined that the inaccuracies were clearly noticeable as the pressure graphs contained sinusoidal wave fluctuations, negative pressures, un-characteristic wave fluctuations and a decay difference between simulated results. Extensive research then concluded that the possible causes of these inaccuracies were thermal shock, transverse vibrations, long cables, variable current in cables and the type of manufacturer. Thermal shock was then chosen to be investigated in depth, by means of a flame test and Finite Element Analysis (FEA). The results of the flame test concluded that the PCB transducer could well be affected by thermal shock and this was supported with the results from the FEA. The flame test also proved that the effect of thermal shock could be reduced by the use of one of four forms of protection applied to the transducer’s diaphragm. These protections were nail polish, vacuum grease, sticky tape and cellophane.
These forms of protections were then trialed along with a different manufactured piezoelectric transducer (Kulite) in two X3 shots conducted by Todd Silvester and were found to be ineffective against thermal shock. It was the recommended that other, more advanced forms of protections be investigated, tested and trialed. Such protections are advanced ceramic coatings. It was also recommended that other possible causes of the inaccurate pressure data such as transverse vibrations should be investigated more in-depth.