We present detailed observations of the shock waves emitted at collapse single cavitation bubbles using simultaneous time-resolved shadowgraphy and hydrophone pressure measurements. The geometry is systematically varied from spherical to very non-spherical by decreasing their distance a free or rigid surface modulating gravity-induced gradient aboard parabolic flights. produces multiple shocks that are clearly associated with different processes, such as jet impact individual collapses...

An experimental investigation of the rotating stall in reduced scale model a low specific speed radial pump-turbine at runaway and turbine brake conditions generating mode is achieved. Measurements wall pressure stator are performed along with high-speed flow visualizations vaneless gap help air bubbles injection. When starting from best efficiency point (BEP) increasing impeller speed, significant increase fluctuations observed mainly wicket gates channels. The spectral analysis shows rise...

The present paper focuses on the numerical simulation of interaction laser-generated bubbles with a free surface, including comparison results instances from high-speed videos experiment. Volume Of Fluid method was employed for tracking liquid and gas phases while compressibility effects were introduced appropriate equations state each phase. Initial conditions bubble pressure estimated through traditional Rayleigh Plesset equation. simulated expands in non-spherically symmetric way due to...

AbstractIn hydraulic turbines, the tip-leakage vortex is responsible for flow instabilities and promoting erosion due to cavitation. To better understand tip flow, Reynolds-averaged Navier–Stokes (RANS) large eddy simulation (LES) computations are carried out simulate around a NACA0009 blade including gap between wall. The main focus of study influence width on development vortex, as instance its trajectory. RANS performed using open source solver OpenFOAM 2.1.0, two incidences five gaps...

Fast liquid jets, called micro-jets, are produced within cavitation bubbles experiencing an aspherical collapse. Here we review micro-jets of different origins, scales and appearances, propose a unified framework to describe their dynamics by using anisotropy parameter $\unicode[STIX]{x1D701}\geqslant 0$ , representing dimensionless measure the momentum at collapse point (Kelvin impulse). This is rigorously defined for various jet drivers, including gravity nearby boundaries. Combining...

In recent years, considerable interest has been devoted to the interactions between cavitation bubbles and tissue-mimicking materials due their promising applications in medicine biomedical sciences. The strong fluid–structure interaction a bubble these elastic surfaces triggers unique collapse dynamics, characterized by splitting subsequent microjetting phenomena that can damage adjacent boundaries. this work, we investigate how elasticity of boundary distance surface affect dynamics...

The composition of the gaseous phase cavitation bubbles and its role on collapse remains to date poorly understood. In this work, experiments single in aqueous ammonia serve as a novel approach investigate effect vapor contained bubble collapse. We find that higher pressure more concentrated acts resistance collapse, reducing total energy dissipation. line with visual observation, acoustic measurements, luminescence recordings, it is also observed pressures contribute spherical likely...

We studied spark-generated cavitation bubbles inside water drops produced in microgravity. High-speed visualizations disclosed unique effects of the spherical and nearly isolated liquid volume. In particular, (1) toroidally collapsing generate two jets escaping from drop, "splash jet" discloses a remarkable broadening. (2) Shock waves induce strong form secondary due to particular shock wave confinement. This feature offers novel way estimate integral energies volumes. (3) Bubble lifetimes...

The present study deals with the shedding process of von Kármán vortices at trailing edge a 2D hydrofoil high Reynolds number Reh=25×103–65×103. This research focuses mainly on effects cavitation and fluid-structure interaction mechanism vortex generation. frequency, derived from flow-induced vibration measurement, is found to follow Strouhal law provided that no resonance frequencies are excited, i.e., lock-off. For such regime, exhibit strong spanwise 3D instabilities inception index...

Cavitation bubbles collapsing and rebounding in a pressure gradient $\mathbf{\ensuremath{\nabla}}p$ form ``microjet'' enveloped by ``vapor jet.'' This Letter presents unprecedented observations of the vapor jets formed uniform gravity-induced $\mathbf{\ensuremath{\nabla}}p$, modulated aboard parabolic flights. The data uncover that normalized jet volume is independent liquid density viscosity proportional to...

Conflicting reports in the literature have raised question whether radial extracorporeal shock wave therapy (rESWT) devices and vibrating massage similar energy signatures and, hence, cause bioeffects treated tissues.We used laser fiber optic probe hydrophone (FOPH) measurements, high-speed imaging x-ray film analysis to compare fundamental elements of two rESWT (Swiss DolorClast; Electro Medical Systems, Nyon, Switzerland; D-Actor 200; Storz Medical, Tägerwillen, Switzerland) a device...

The present paper focuses on the simulation of expansion and aspherical collapse a laser-generated bubble subjected to an acceleration field comparison results with instances from high-speed videos. interaction liquid gas is handled volume fluid method. Compressibility effects have been included for each phase predict propagation pressure waves. Initial conditions were estimated through Rayleigh Plesset equation, based maximum size time. predictions indicate that during shape very close...

Note: FNSFlash and Splash Reference EPFL-ARTICLE-214200doi:10.1063/1.4931098View record in Web of Science Record created on 2015-12-02, modified 2017-05-10