Tip Vortex Cavitation Suppression by Active Mass Injection

2011 ◽  
Vol 133 (11) ◽  
Author(s):  
Natasha Chang ◽  
Harish Ganesh ◽  
Ryo Yakushiji ◽  
Steven L Ceccio
Keyword(s):  
Vortex Core ◽  
Polymer Solutions ◽  
Tip Vortex ◽  
Substantial Decrease ◽  
Tip Vortex Cavitation ◽  
Flow Unsteadiness ◽  
The Core ◽  
Aqueous Polymer ◽  
Mass Injection ◽  
Stereo Particle Image Velocimetry

Injection of water and aqueous polymer solutions in to the core of a trailing vortex was found to delay the inception of tip vortex cavitation (TVC). Optimal levels of mass injection reduced the inception cavitation number from 3.5 to 1.9, or a reduction of 45%. At the optimal fluxes, injection of water alone produced a reduction of 35%, and the addition of polymer solution led to a reduction of 45%. Stereo particle image velocimetry was employed to examine the flow fields in the region of TVC inception and infer the average core pressure, and planar PIV was used to examine the flow unsteadiness in this region. The time-averaged pressure coefficients for the vortex core pressure were estimated and compared to the pressure needed for TVC inception and full development. Measurement of flow variability in the TVC inception region indicated that relatively low fluxes of mass injection in the TVC roll-up region led to a substantial decrease in flow unsteadiness in the core region near the observed location of inception, and this corresponded to a substantial decrease in the inception pressure. Increased injection of water or polymer solutions led to a modest increase in the average vortex core radius, which was discernable in the measured pressure needed for developed cavitation.

An Experimental Study on Tip Vortex Cavitation Suppression in a Marine Propeller

2014 ◽  
Vol 58 (03) ◽  
pp. 157-167
Author(s):  
Sang-LL Park ◽  
Seung-Jae Lee ◽  
Geuk-Sang You ◽  
Jung-Chun Suh
Keyword(s):  
Experimental Study ◽  
Active Control ◽  
Vortex Core ◽  
Main Idea ◽  
Tip Vortex ◽  
Scale Model ◽  
Tip Vortex Cavitation ◽  
Cavitation Inception ◽  
Mass Injection ◽  
National University

Normally, tip vortex cavitation (TVC) is first observed at a certain location behind the tips of propeller blades. Therefore, TVC is important for naval ships and research vessels that require raising the cavitation inception speed to maximum possible values. The concepts for alleviating the tip vortex are summarized by Platzer and Souders (1979), who carried out a thorough literature survey. Active control of TVC involves the injection of a polymer or water from the blade tip. The main effect of such mass injection (both water and polymer solutions) into the vortex core is an increase in the core radius, consequently delaying TVC inception. However, the location of the injection port needs to be selected with great care to ensure that the mass injection is effective in delaying TVC inception. In the present study, we propose a semi-active control scheme that is achieved by attaching a thread at the propeller tip. The main idea of a semi-active control is that because of its flexibility, the attached thread can be sucked into the low-pressure region closer to the vortex core center. An experimental study using a scale model was carried out in the cavitation tunnel at the Seoul National University. It was found that a flexible thread can effectively suppress the occurrence of TVC under the design condition for a model propeller.

scholarly journals Tip Vortex Cavitation on an Oscillating Hydrofoil

1997 ◽  
Vol 119 (4) ◽  
pp. 752-758 ◽  
Author(s):  
O. Boulon ◽  
J. P. Franc ◽  
J. M. Michel
Keyword(s):  
Steady State ◽  
Vortex Core ◽  
Oscillation Frequency ◽  
Strong Influence ◽  
Tip Vortex ◽  
Tip Vortex Cavitation ◽  
Cavitation Inception ◽  
Time Required ◽  
Oscillation Frequencies ◽  
The University

This paper discusses tests conducted in the hydrodynamic tunnel of the University of Grenoble on a 3D oscillating hydrofoil. Visualization of unsteady tip vortex cavitation indicates a strong influence of the water nuclei content. The investigation was focused on the influence of the oscillation frequency on tip vortex cavitation inception. For very low nuclei content, cavitation inception is strongly delayed as compared to the steady-state results at very small oscillation frequencies. This delay is significantly reduced by nuclei seeding. The results can be explained by assuming that the time required for the inception of cavitation in the tip vortex corresponds to the time necessary for a cavitation nucleus to be captured by the vortex core.

Tip Vortex Cavitation Inhibition by Drag-Reducing Polymer Solutions

1989 ◽  
Vol 111 (2) ◽  
pp. 211-216 ◽  
Author(s):  
D. H. Fruman ◽  
S. S. Aflalo
Keyword(s):  
Polymer Solutions ◽  
Tangential Velocity ◽  
Hydrodynamic Forces ◽  
Tip Vortex ◽  
Velocity Measurements ◽  
Tip Vortex Cavitation ◽  
Homogeneous Solutions ◽  
Semidilute Solutions ◽  
Semidilute Polymer Solution ◽  
Drag Reducing Polymer

This paper presents previous and recent results obtained by the authors concerning the modification of the tip vortex cavitation of a finite span hydrofoil by drag-reducing polymer solutions. Experiments were conducted with homogeneous solutions and with semidilute solutions ejected at the tip of the wing. Measurements of the onset cavitation number for tip vortex cavitation, hydrodynamic forces on the hydrofoil and tangential velocities in the tip vortex have been conducted. The results show that tip vortex cavitation is inhibited in all cases but for different reasons. In homogeneous polymer solutions the lift of the hydrofoil, and hence the circulation, is considerably reduced leading to a less intense vortex as shown by tangential velocity measurements. With semidilute polymer solution ejections there is no noticeable change of the hydrodynamic forces but a significant modification of the tangential velocities in the core region. The mechanism for tip vortex cavitation inhibition is thus completely different in these two situations.

Vortex Ring Model of Tip Vortex Aperiodicity in a Hovering Helicopter Rotor

2014 ◽  
Vol 136 (7) ◽  
Author(s):  
Anand Karpatne ◽  
Jayant Sirohi ◽  
Swathi Mula ◽  
Charles Tinney
Keyword(s):  
Vortex Core ◽  
Distribution Functions ◽  
Tip Vortex ◽  
Helicopter Rotor ◽  
Time Step ◽  
Tip Vortices ◽  
Ring Model ◽  
Image Velocimetry ◽  
Blade Tip ◽  
Stereo Particle Image Velocimetry

The wandering motion of tip vortices trailed from a hovering helicopter rotor is described. This aperiodicity is known to cause errors in the determination of vortex properties that are crucial inputs for refined aerodynamic analyses of helicopter rotors. Measurements of blade tip vortices up to 260 deg vortex age using stereo particle-image velocimetry (PIV) indicate that this aperiodicity is anisotropic. We describe an analytical model that captures this anisotropic behavior. The analysis approximates the helical wake as a series of vortex rings that are allowed to interact with each other. The vorticity in the rings is a function of the blade loading. Vortex core growth is modeled by accounting for vortex filament strain and by using an empirical model for viscous diffusion. The sensitivity of the analysis to the choice of initial vortex core radius, viscosity parameter, time step, and number of rings shed is explored. Analytical predictions of the orientation of anisotropy correlated with experimental measurements within 10%. The analysis can be used as a computationally inexpensive method to generate probability distribution functions for vortex core positions that can then be used to correct for aperiodicity in measurements.

On the impulsive blocking of a vortex–jet

1998 ◽  
Vol 369 ◽  
pp. 301-331 ◽  
Author(s):  
J. A. LEE ◽  
O. R. BURGGRAF ◽  
A. T. CONLISK
Keyword(s):  
Vortex Core ◽  
Axial Velocity ◽  
Vortical Structure ◽  
Axial Flow ◽  
Inviscid Flow ◽  
Numerical Results ◽  
Tip Vortex ◽  
Final States ◽  
Core Radius ◽  
The Core

In this paper we consider the flow field within and around a vortex as it ‘collides’ with a thin plate at a right angle to its axis of rotation. We show that based solely on inviscid flow theory, vorticity in the core of the vortex is redistributed significantly. The main cause of this redistribution is the presence of axial flow within the vortex; we call this vortical structure which contains axial flow a vortex–jet. In this work we show that when the axial velocity within the vortex is toward the plate, vorticity is redistributed radially outward from the core resulting in a significant reduction in the axial vorticity there; the vortex is said to ‘bulge’ reflecting an increase in the nominal vortex core radius. A by-product of this interaction is that the suction peak amplitude caused by the presence of the vortex rapidly decreases and the pressure soon returns to a quasi-steady distribution. On the other hand, when the axial velocity within the vortex is directed away from the surface, the suction peak persists and the vortex core radius decreases. The numerical results were validated by comparison with an analytical solution for a sinusoidal vortex jet. Analytical solutions were also derived for the initial and final states of a pure jet; the numerical results are strongly supported by the analysis. In addition, all of these results are consistent with experiments, and their relevance to the interaction between a tip vortex and a helicopter airframe is also discussed.

Noise due to extreme bubble deformation near inception of tip vortex cavitation

2004 ◽  
Vol 16 (7) ◽  
pp. 2411-2418 ◽  
Author(s):  
Jin-Keun Choi ◽  
Georges L. Chahine
Keyword(s):  
Tip Vortex ◽  
Tip Vortex Cavitation ◽  
Bubble Deformation

Study of Tip Vortex Cavitation Inception Using Navier-Stokes Computation and Bubble Dynamics Model

1999 ◽  
Vol 121 (1) ◽  
pp. 198-204 ◽  
Author(s):  
Chao-Tsung Hsiao ◽  
Laura L. Pauley
Keyword(s):  
Vortex Core ◽  
Bubble Dynamics ◽  
Three Dimensional ◽  
Window Size ◽  
Tip Vortex ◽  
Navier Stokes ◽  
Cavitation Inception ◽  
Flow Effects ◽  
Bubble Sizes ◽  
Real Flow

The Rayleigh-Plesset bubble dynamics equation coupled with the bubble motion equation developed by Johnson and Hsieh was applied to study the real flow effects on the prediction of cavitation inception in tip vortex flows. A three-dimensional steady-state tip vortex flow obtained from a Reynolds-Averaged Navier-Stokes computation was used as a prescribed flow field through which the bubble was passively convected. A “window of opportunity” through which a candidate bubble must pass in order to be drawn into the tip-vortex core and cavitate was determined for different initial bubble sizes. It was found that bubbles with larger initial size can be entrained into the tip-vortex core from a larger window size and also had a higher cavitation inception number.

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