USTC develops high-intensity shock tube and reveals high-speed interface flow mechanism

Research teams led by Prof. LUO Xisheng and Prof. SI Ting from the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences (CAS) established a theoretical method for designing smooth curved wall surfaces with variable cross-section shock tubes, and developed an integrated, high-intensity multifunctional shock tube device. The study was published in Review of Scientific Instruments.

Based on the device and techniques, the research team further developed a discontinuous perturbation interface generation technology, pioneering the experimental and mechanistic study of strong shock wave impact on single-mode fluid interface instability in shock tubes. The results were published in Journal of Fluid Mechanics in the form of Rapids.

Shock wave-induced fluid interface instability is a common key scientific issue in aerospace vehicles and inertial confinement nuclear fusion, while the related basic theories are still insufficient. Shock tubes are often employed to carry out basic aerodynamics research. However, the controllable generation of regularly-shape, high-energy utilization converging shock waves and strong shock waves still remains a challenge.

To address it, researchers established a theoretical method for designing smooth curved wall surfaces based on shock wave dynamics theory and inverse design concepts. Consequently, the team proposed an orthogonal layout and multi-stage transformation shock wave enhancement scheme, and developed special experimental equipment for generating converging shock waves and strong shock waves.

Through experiments, the researchers verified that the device could generate a strong shock wave with the Mach number higher than 3.0 under a single-stage conversion, which was conducive to the initial disturbance interface setting and high-speed flow field diagnosis.

Under multi-stage conversion, the research teams effectively overcame the airflow choking problem caused by single-dimensional area contraction, and controllably generated high-intensity converging, planar, and diverging shock waves in one step. This approach opens up a new path for experimental research on strong shock wave impact on fluid interfaces and its induced turbulent mixing.

The research teams further developed a nearly ideal discontinuous interface generation method. The technology enabled an instant decomposition of the initial gases of different densities separated by a 2-μm-thick polyester film. The decomposition occurred in the high-temperature environment formed by the strong shock wave without generating fragments that interfered with the flow field.

For the basic small-amplitude light-heavy single-mode interface configuration, researchers have also used novel methods. They first observed shock tube experiments of shock-induced fluid interface instability with a shock Mach number higher than 3.0 and clearly captured the entire process of shock and interface evolution.

Subsequently, the research team quantitatively analyzed the evolution of interface disturbances under the main control parameters. Through this analysis, the researchers revealed the influence of strong compressibility effects on the evolution of interface morphology and disturbance amplitude.

Furthermore, the researchers clarified the mechanisms behind the effects of transverse wave effects and shock wave proximity effects on the nonlinear evolution of disturbances.

In addition, based on the experimental results, the research teams have established a prediction model for interface amplitude growth that was applicable to strong compressible flows.

The researchers will continue to study key issues such as fluid-solid coupling and competition at the interface, providing fundamental data and scientific support for major national projects.