030060022 Eray Cavus 10th week Answer

Shock Wave Forming (Forming Process)

Shock Wave Forming

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Shock Wave Forming (new)(better)

A shoch wave generated by the explosion of a 10 mg silver azide pellet was impinged on a 1.5 mm diameter air bubble placed at the standoff distance of 20 mm from the center of explosive. At the final stage of bubble collapse, a micro-water jet was generated. Its terminal velocity was found to be approximately 100 m/s, which resulted in stegnation pressure of 150 Mpa. This effect was found to be very sensitive to the bubble shape and the shock overpressure. A planar shock wave colliding on a plane interface, the local radius of curvature of the interface is critical which determines the jet formation.

Taking various applications into consideration, we have visulized shock/bubble interaction in water, silicone oil, and golden syrup having kinematic viscosity varying from 1 cSt to 10 kSt. The response of shock loaded bubbles was more or less analogous for most of liquids for a wide range of kinematic viscosity. However, in the case of golden syrup of kinematic viscosity exceeding 6 kSt, the detonation product gases did not expand largely but numerous cracks were developed irregularly to the radial direction. A silver azide pellet was ignited by the irradiation of a Q-switched Nd:YAG laser beam of 7 ns pulse duration and 20 mJ pulse energy directly on its surface or through a 0.6 mm diameter optical fiber through which the pulse laser beam was transmitted.

Glass mentioned that a shock tube is a test tube of modern aerodynamic experiments. Shock tubes were designed and constructed by various design concepts. Traditionally shock waves are generated by rupturing a diaphram which is seperating test gases from high-pressure driver gases. However, the diaphram rupture can never be precisely controlled even with keeping identical initial contion. The projected area of ruptured diaphram sections can never be identical for each run so that the mass flow through it varies. The resulting shock Mach number scatters in every shot. This trend becomes more pronounced in higher shock Mach numbers.

In order to overcome this demerit, we have decided to use a reusable rubber membrane as a replacement of rupturing diaphrams. Bulged with auxiliary high-pressure, it seperated test gas from high-pressure driver gas. Then quick release of the auxiliary high-pressure contracted the expanded membrane. The high-pressure driver gas rashed into the test section forming a shock wave. We constructed a diaphram-less shock tube consisting of a 290 mm diameter and 2 m long high high pressure chamber inside which a 600 mm x 150 mm and 4 m long low pressure channel was placed in the coaxial arrangement. A rubber membrane was placed at the end of high-pressure chamber facing to the low pressure channel. The auxiliary high-pressure chamber was connected to this part. Although diaphram-less operation may slightly elongate the shock formation distance but is so simple that the scatter of shock Mach numbers becomes +-0.25% for Ms ranging from 1.1 to 2.0 in air.

(Shock Waves: Proceedings of the 24th International Symposium on Shock Waves, Yazar: Zonglin Jiang, Z. Y. Han,page:6)