Shock wave

About: Shock wave is a research topic. Over the lifetime, 36184 publications have been published within this topic receiving 635848 citations. The topic is also known as: Shock waves & shockwave.

Shock waves from nonspherical cavitation bubbles

Abstract: We present detailed observations of the shock waves emitted at the collapse of single cavitation bubbles using simultaneous time-resolved shadowgraphy and hydrophone pressure measurements. The geometry of the bubbles is systematically varied from spherical to very nonspherical by decreasing their distance to a free or rigid surface or by modulating the gravity-induced pressure gradient aboard parabolic flights. The nonspherical collapse produces multiple shocks that are clearly associated with different processes, such as the jet impact and the individual collapses of the distinct bubble segments. For bubbles collapsing near a free surface, the energy and timing of each shock are measured separately as a function of the anisotropy parameter zeta, which represents the dimensionless equivalent of the Kelvin impulse. For a given source of bubble deformation (free surface, rigid surface, or gravity), the normalized shock energy depends only on zeta, irrespective of the bubble radius R-0 and driving pressure Delta p. Based on this finding, we develop a predictive framework for the peak pressure and energy of shock waves from nonspherical bubble collapses. Combining statistical analysis of the experimental data with theoretical derivations, we find that the shock peak pressures can be estimated as jet impact-induced hammer pressures, expressed as p(h) = 0.45(rho c(2) Delta p)(1/2) zeta(-1) at zeta > 10(-3). The same approach is found to explain the shock energy decreasing as a function of zeta(-2/3).

Study of Passive Control in a Transonic Shock Wave/Boundary-Layer Interaction

Abstract: Passive control applied to a turbulent shock wave/boundary-layer interaction has been investigated by considering a two-dimensional channel flow. The field has been probed in great detail by using a two-component laser Doppler velocimetry system to execute mean velocity and turbulence measurements. Four different perforated plates have been considered along with the solid wall reference case. These measurements have shown that passive control deeply modifies the inviscid flowfield structure, the single shock being replaced by a lambda shock system. This modified compression induces a substantial reduction of the wave drag associated with the interaction. On the other hand, the combined injection-suction effect taking place in the control region provokes an increase of the viscous drag, which nearly outbalances the reduction in wave drag. It was found that passive control induced a modest decrease of the total drag compared to the solid wall case. Moreover, the experimental wall transpiration velocity distribution in the control region is well represented by the usual laws

Thermoviscous Attenuation of Plane, Periodic, Finite‐Amplitude Sound Waves

Abstract: The propagation of a plane progressive wave of finite amplitude in a thermoviscous fluid is considered. The wave is taken to be purely sinusoidal in shape at its source. The approach is through Burgers equation, which is a very good approximation of the exact equations of fluid motion when effects of nonlinearity and dissipation are relatively small but definitely not negligible. A complicated but exact solution of Burgers' equation is analyzed. The nature of the solution is found to depend strongly on a parameter Γ, which represents the importance of nonlinearity relative to dissipation. Nonlinear effects prove to be significant when Γ>1, a finding in agreement with the criterion proposed by Gol'dberg (Akust. Zh. 2, 325 (1956) [English transl.: Soviet Phys.—Acoust. 2, 346(1956)]) concerning the appearance of shock waves. When Γ>>1, simple asymptotic representations of the exact solution in terms of Fourier series may be obtained. One of these corresponds to Fay's solution [J. Acoust. Soc. Am. 3, 222 (1931)]. An equivalent “time‐domain” representation shows clearly the sawtooth behavior of the wave. The sawtooth region is found to extend approximately to the point x=O.6/α, where α is the dimensional small‐signal attenuation coefficient. Curves of the extra attenuation suffered by the fundamental as a result of nonlinear effects are given for values of Γ in the range 1–100 000. If Γ is large, the extra attenuation in decibels approaches the asymptotic value −12+20 log10Γ as the distance from the source becomes large. A value 1 dB below the asymptote is attained at a distance x=1/α. Application to waves in argon and air is discussed. It is found that nonlinear effects may be employed to increase the efficiency of long‐range sound transmission. A possible application to low‐frequency sound in the ocean is also discussed.

Near acoustic field and shock structure of rectangular supersonic jets

Abstract: An underexpanded supersonic rectangular jet is studied experimentally at a pressure ratio range of 1-15. The shock-cell and shear-layer structure variation with the pressure ratio is shown to be related to the near-field pressure fluctuations. Near the sonic, fully adapted velocity, the jet is fully symmetric. An abrupt change to a flapping mode occurs at a low Mach number, causing a large increase in the spreading rate, which is also related to the appearance of an upstream propagating screech component