Shock wave focusing to achieve high energy concentration

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A shock wave is a thin discontinuous region over which fluid properties abruptly change from one state to another. Shock wave focusing occurs frequently both in nature and in a variety of man-made applications. It takes place when a shock wave propagates through a non-uniform or moving media and reflects from curved surfaces or through reflections with other shock waves. Extreme conditions created at the focal region - resulting in very high pressures and temperatures - can be either beneficial as in the case of shock wave lithotripsy to remove kidney stones or in inertial confinement fusion for energy generation, or detrimental as in the case of superbooms (a type of sonic boom). As the shock wave emerges from the focal region, after the shock focusing event, the shape of the shock is often fundamentally altered. Therefore, a deeper understanding of the shock focusing process, and how to control it, is critical to fully understand its consequences and how to best enhance or mitigate it as needed depending on the application at hand. Today, three-dimensional effects of shock wave focusing are not yet fully understood. Therefore, the principal goal of this research project is to develop a deeper understanding of the key factors that govern shock wave focusing in three dimensions using an experimental approach. This project will also provide opportunities to learn about shock wave dynamics for undergraduate students and high school students, particularly from underrepresented minorities.The primary goal of this research is to experimentally study shock wave focusing using an exploding wire setup capable of producing multiple simultaneous shock waves in two or three dimensions. Ultra high-speed photography coupled with visualization techniques will be used to determine the conditions when regular shock wave reflection transitions into irregular shock wave reflection. Another goal is to quantify the amount of energy focusing at the focal region given the competition between the weakening of each individual shock wave as it propagates radially outward from the exploding wire and the strengthening due to Mach shock generation.The proposed research is expected to lead to a much enhanced understanding of the principles of shock wave dynamics, and shock wave focusing, especially for three dimensional shocks with decaying fluid properties behind them ? in addition to providing a wealth of data to help verify numerical frameworks dealing with shock focusing scenarios.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.