Investigation of the shock formation process in double-diaphragm shock tubes*

A comprehensive understanding of the shock formation process is crucial for reliable experimental data in shock tubes. Previous research primarily focused on shock tubes equipped with a single diaphragm, where its rupture leads to the formation of compression waves that accelerate and merge, eventually forming a shock wave. To achieve precise control over post-shock conditions, an additional diaphragm is often incorporated between the primary diaphragm and the driven section. Upon sudden release of the gas in the intermediate section between the two diaphragms, the primary diaphragm ruptures first, followed by the secondary diaphragm, leading to a sequence of shock front acceleration and deceleration.

In our double-diaphragm shock formation investigation, experiments covered driver pressures of 15 to 60 bar and driven pressures of 100 to 600 Torr with Ar, N2, and CO2 as driven gases. At low Mach numbers (Mach < 4), shock profiles were non-uniform, suggesting complex wave interactions. Higher Mach numbers revealed a distinctive behavior with two stages of shock deceleration. Analyzing slope differences in shock profiles provided deeper understanding of their individual contributions.

We used an in-house WENO code for 1D simulations with the intermediate section and a delayed opening of the secondary diaphragm. The results provide insights into shock formation in double-diaphragm mode of shock tube operation and help in precisely controlling shock parameters.