Measurements of the instabilities which lead to transition are important for the development of improved models for predicting transition. At hypersonic speeds, these measurements are often difficult and have typically required the use of hot wires, which are too fragile to be used in many hypersonic wind tunnels. Recent work has shown that PCB-132 piezoelectric pressure transducers are capable of measuring the second-mode instability. These sensors are robust and could be used in many hypersonic tunnels, but are not yet calibrated for instability measurements.;An attempt was made to calibrate the sensors with an existing shock tube. The sensors were found to have a linear response over the range that was tested, though some indications of nonlinear behavior were observed. Attempts to determine a model for the sensors were unsuccessful. A new shock tube is being designed and built for the purpose of calibrating these sensors.;Measurements on a 7° half-angle cone were made in the AEDC Hypervelocity Wind Tunnel 9, the Langley 15-Inch Mach-6 Hi-Temperature Tunnel, and the Langley 31-Inch Mach-10 Tunnel. Second-mode waves were measured in all of these tunnels for the first time. Growth, saturation, and breakdown were observed in each tunnel, and the saturation amplitude was observed to increase with Mach number. Adding an isolated roughness was seen to reduce the amplitudes observed and cause breakdown to occur sooner. The effects of non-zero angle of attack were also investigated. Measurements of the freestream fluctuations with the PCB-132 sensors showed signal above the electronic noise at the second-mode frequencies. This is the first time that measurements of acoustic noise at the second-mode frequencies have been available.
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