Evolution characteristics of pressure pulse in compressed air-driven variable-section shock tube and prediction of reflected shock wave

With the increasing demand for carrying out far-field explosion tests on large-scale structural components, variable-section shock tubes have been gradually developed. To generate a shock wave similar to the air explosion shock wave in the compressed air-driven variable-section shock tube, the evolution process of the pressure pulse in the tube was investigated. First, the classical one-dimensional Sod shock tube problem and compressed air-driven equi-diametric and variable-section shock tube tests were numerically simulated using the commercial computational fluid dynamics software Ansys Fluent. The applicability and reliability of the material model parameters, boundary conditions, and numerical simulation method were validated through the comparisons of simulation results with analytical solutions and test data. Then, the evolution processes of the pressure pulse in the equi-diametric and variable-section shock tubes was compared, indicating that the location where the rarefaction wave catches up with the shock wave is the formation location of the blast wave. The expanded angle of the low-pressure section has little effect on the waveform of the blast wave in variable-section shock tubes. Furthermore, parametric analyses were carried out to investigate the influence of the geometric dimensions of the shock tube and the initial pressure in the high-pressure section on the blast wave's formation location and the corresponding peak reflected overpressure. It was shown that the peak reflected overpressure increases with increasing diameter and initial pressure, as well as with decreasing the length of the high-pressure section and the expanded angle. Finally, using the above-mentioned simulation results as the database, a principal component analysis-backpropagation neural network-based machine learning model for reflected shock wave prediction was established, capable of rapidly predicting the reflected overpressure–time history in compressed air-driven variable-section shock tubes.