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How curved shock waves behave

- Wits University

Brendan Gray’s construction of a versatile and novel experimental rig contributes to the understanding of how curved shock waves behave.

Understanding curved shock wave behaviour could lead to better designs to mitigate the effects of blasting in mines or aid in modelling the impact of volcanic eruptions.

“Curved shock waves are also present in the engine intakes on supersonic aircraft and understanding the flow in these engines could lead to more efficient engine designs,” explains Gray.

Converging shock waves are also used in the formation of artificial diamonds and the production of several rare chemicals and are already used in shock wave lithotripsy – a common medical procedure used to treat severe kidney stones.

Gray’s research is supplemented by detailed experiments and simulations showing for the first time how a curved shock wave segment will reflect off a plain surface.

“Most of the previous literature has focused on straight shock waves but shock waves in the real world are rarely straight. I focus on converging shock waves, which have applications in a wide range of fields, including blast mechanics, aeronautics, manufacturing, chemistry, medicine and astrophysics,” he adds.

The problem with curved shock waves is that they are difficult to produce under experimental conditions.

Gray designed and built a facility which may be used with a conventional shock tube to produce shock waves with arbitrary two-dimensional profiles in a controlled and repeatable manner.

Together with computer simulations, he used the facility to study the propagation of complex shock waves with both concave and convex segments, some with sharp corners and some with rounded corners. This served to demonstrate the capabilities and limits of the facility.

Gray then generated imploding cylindrical shock waves and studied the interaction between these and straight wedges inclined at various angles. The primary point of interest was the geometric configuration of reflected shock waves behind the incident shock wave.

He also developed a simple numerical method for predicting the shape of the reflection and the point at which the reflection transitions from one configuration to another.