Freestream disturbances can have a significant impact on studies of boundary layer transition in ground tests, including experiments in high-enthalpy hypersonic facilities such as an expansion tube. Freestream noise reduction in expansion tubes can be achieved by increasing the driver-to-driven pressure ratio p_4/p_1, so we seek methods to increase this ratio in Caltech's HFT facility. Towards this end, an in-house modular parametric code has been developed using Python to explore possible modifications to the HET. The effect of increasing the pressure in a passive driver on potential noise reduction is investigated. Optimization of acceleration section length is also explored for conventional drivers.The performance of detonation drivers using H_2 and C_2H_2 fuels with He, Ar, and CO_2 diluents is examined.
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