The removal of surface-attached particles with cavitation bubbles is usually attributed to the jetting or shear stresses when collapse. In this Letter, we report an unexpected phenomenon that millimeter-sized spherical made heavy metals (e.g., stainless steel), initially resting on a fixed rigid substrate, are suddenly accelerated like projectiles through production nearby laser-induced similar sizes. We show experimentally and theoretically motion particle radius R_{p} determined by maximum...

We document experimentally four different interactions of a laser-induced bubble and free-settling particle, with combinations the geometric physical parameters system. Our force balance model shows that nondimensional factors involving particle radius a, maximum R_{max}, initial separation distance l_{0} between center center, fluid viscosity μ_{f}, densities ρ_{p} ρ_{f}, respectively, in detail l_{0}/R_{max}, a/R_{max}, ρ_{p}/ρ_{f}, μ^{*}=μ_{f}T_{c}/ρ_{f}R_{max}^{2}, where...

Recently leading-edge protuberances have attracted great attention as a passive method for separation control. In this paper, the effect of multiple on performance two-dimensional airfoil is investigated through experimental measurement aerodynamic forces, surface tuft visualization, and numerical simulation. contrast to sharp stall baseline with large hysteresis during AOA (angle attack) increasing decreasing, process modified gentle stable. Flow visualization revealed that flow past each...

Leading-edge protuberances on airfoils or hydrofoils have been considered as a viable passive method for flow separation control recently. In this article, the hydrodynamic performance of NACA 63 4 -021 (baseline) foil and two modified foils with leading-edge was numerically investigated using Spalart–Allmaras turbulence model. It found that performed worse than baseline at pre-stall angles, while lift coefficients high angles attack were increased. Both deterioration improvement post-stall...

The stability of pump-turbines is great importance to the operation pumped storage power (PSP) stations. Both hydraulic instabilities and operational have been reported in PSP stations China. In order provide a reference engineers scientists working on pump-turbines, this paper summarizes performance characteristics that promote encountered pump-turbine operations Definitions, analytical methods, numerical experimental studies, main results are clarified. Precautions countermeasures also...

The positive slope on the pump performance curve of pump-turbines suggests potential operational instabilities in mode. Previous research has indicated that increase hydraulic loss caused by sudden changes flow patterns is responsible for slope, however its detailed mechanism still unclear. A low specific speed model pump-turbine was numerically investigated against experiments present study, applying unsteady RANS (Reynolds-Averaged Navier–Stokes equations) simulations with a v2-f...

Owing to the complexity of load rejection process, accompanied complex low frequency pressure fluctuations and their sources have not been determined. Herein, transient process a pump-turbine was simulated with three-dimensional (3-D) large eddy simulation method dynamic mesh technology. The results were validated against experimental data. Through joint time-frequency analysis pressure, fluctuation components captured, which are generally lower than rated rotational runner. A comprehensive...

Abstract

We experimentally, numerically, and theoretically investigate the dynamics of cavitation bubbles in viscous liquids a tube during transient process. In experiments, are generated by modified tube-arrest setup, bubble evolution is captured with high-speed imaging. Numerical simulations using OpenFOAM employed to validate our quasi-one-dimensional theoretical model, which effectively characterizes dynamics. find that onset minimally affected liquid viscosity. However, once occurs, various...

Surface-attached micro- and nanobubbles are known for their resistance to external forces. This study experimentally theoretically investigates response strong ultrasonic fields. with contact radii from 2 μm 20 generated in a microchannel exposed ultrasound through vibrating glass substrate. At driving frequency over 200 kHz up MHz tested, no significant the is observed. By contrast, at 100 kHz–200 kHz, cavitation bubbles appear migrate toward surface nanobubbles. Then merge bubbles, detach...

Pump performance characteristics of pump turbines in transient processes are significantly different from those steady processes. In the present paper, a flow rate that increased and decreased mode model turbine were simulated through unsteady simulations using shear stress transport (SST) k–ω turbulence model. The numerical results reveal there is larger hysteresis loop increasing decreasing directions compared with results. Detailed discussions carried out to determine generation mechanism...

Geometrical modification of airfoils by leading-edge protuberances has attracted plenty attention as a passive separation control method. In this research, the effect single protuberance with different amplitudes on performance two-dimensional airfoil (NACA 634-021) is investigated through wind tunnel experiment and theoretical analysis. Force measurement shows that all modified demonstrate special two-step stall performance. When first step occurs, lift coefficient drops to medium value...

In this paper, the thermodynamic effect is systematically studied by Venturi cavitation in a blow-down type tunnel for first time, using water at temperatures up to relatively high levels and controlled dissolved gas contents supply reservoir (measured oxygen, DO). The mean attached cavity length Lcav chosen reveal effect, characteristics are analyzed from experiments. With an increase parameter Σ*, decrease vs pressure recovery number κ observed, which consistent with suppression of but...

Control of cavitation in confining geometries is vital to the safety hydraulic conduits and structures. Here, we investigate bubble dynamics one typical type open-ended tube with varying cross sections, i.e., a funnel-shaped tube, defined as section connected cylindrical section. In our experiments, single bubbles are generated by spark along symmetric axis at different positions, including (regime 1), near throat 2), 3). With high-speed photography, observe that end collapse, produce weak...

Pressure fluctuations are very important characteristics in pump turbine's operation. Many researches have focused on the (amplitude and frequencies) of pressure at specific locations, but little mentioned distribution a turbine. In this paper, 3D numerical simulations using SSTk − ω turbulence model were carried out to predict prototype turbine mode. Three operating points with different mass flow rates guide vanes’ openings simulated. The results show how blade passing frequency (BPF) its...

We systematically investigate the dynamics of a free-settling particle driven by laser-induced bubble near rigid boundary. Two types particle-bubble interaction are identified, in terms intensity influence boundary on dynamics. important phenomena where ends up impacting at relatively high velocity discovered, which provide potential mechanism for enhanced cavitation erosion sand-laden water.

Thermodynamic effects delay the growth of cavitation bubbles and may accumulate to a considerable level in bubbly cloud. Under thermo-sensitive conditions, due thermodynamic effects, cloud is often believed behave similarly single bubble with respect its shape, oscillation, etc. Discrepancies on cavitating flows previous experimental studies result from lack control non-dimensional parameter groups under this special condition. In present paper, we first derive dynamics traveling through...

We investigate experimentally and theoretically the interactions between a cavitation bubble hemispherical pendant oil droplet immersed in water. In experiments, is generated by focused laser pulse right below with well-controlled bubble–wall distances bubble–droplet size ratios. By high-speed imaging, four typical are observed, namely: rupture; water entrapment; large deformation; mild deformation. The jetting at end of collapse migration centroid particularly different each interaction....