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- Gustafsson, Göran
(author)
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Experiments on shock-wave focusing in an elliptical cavity
- 1987
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In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 61:11, s. 5193-5195
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Journal article (peer-reviewed)abstract
- Experimental work on reflection and focusing of weak cylindrical shock waves in a liquid-filled elliptical cavity is presented. The shocks are generated at one focus of the cavity by electrical discharges, and converge at the other focus after reflection in the cavity wall. High-speed photographs of the resulting wave system, which appears to be considerably more complex than the corresponding one in air, are shown and discussed. The results are of interest in the design of a transient water-jet generator, which utilizes the energy in the converging shock wave to produce a fast liquid jet.
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| 2. |
- Gustafsson, Göran
(author)
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Focusing of weak shock waves in a slightly elliptical cavity
- 1987
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In: Journal of Sound and Vibration. - 0022-460X .- 1095-8568. ; 116:1, s. 137-148
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Journal article (peer-reviewed)abstract
- This paper presents theoretical work on the wave motion in an elliptical water jet generator. Such a device consists of a water filled elliptical cavity in which a shock wave is induced at one focus by a spark discharge. The shock converges to the other focus and via a convergent duct is allowed to reflect off a free surface of the liquid at the front of a nozzle, whereby a jet is emitted. The initial value problem of how a weak shock develops and how it is reflected from the walls of a cavity with small eccentricity is studied by using acoustic theory and a perturbation technique. In order to account for the distensibility of the wall material its admittance is introduced as a parameter. The validity of the results is extended to larger eccentricities by use of Padé approximants and by comparison with a geometrical acoustics solution to the same problem. The implications of the results on the design of the water jet generator are indicated.
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| 3. |
- Gustafsson, Göran
(author)
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Propagation of weak shock waves in an elliptical cavity
- 1985
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Doctoral thesis (other academic/artistic)abstract
- The propagation of weak shock waves in a planar elliptical cavity is studied theoretically and experimentally. The results are of interest in the design of an elliptical high-speed water jet generator operating in a transient fashion with electrically generated shocks in the acoustic regime. Perturbation theory and geometrical acoustics are used to find the resulting shock wave from the discharge. From this the reflected wave from the cavity walls is found through a condition incorporating the wall admittance. Padé approximants are employed to extend the validity of the solutions. The reflected wave is shown to be strongly dependent on the elliptical eccentricity, and the energy in its front is found to have a minimum for a particular, high value of this parameter. With the use of high-speed photography and schlieren technique experiments with a water filled cavity reveal a complex wave system in the liquid. A prominent feature is the appearance of a lateral wave. This is caused by wave motion in the wall, and conditions for when it is induced are derived. It will be absent if the product of eccentricity and propagation speed of the mode that causes it is less than the liquid sound speed. Experiments with a simple jet generator show that liquid jet speeds of the order of 100 m/s are easily attained. The long-time development of perturbations on the shock wave structure is derived. Different rates of approach to the asymptotic shock shape is found. The exact behavior appears to depend on certain combinations of parameters.
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