Studies of Scaling of Tip Vortex Cavitation Inception on Marine Lifting Surfaces

1991 ◽  
Vol 113 (3) ◽  
pp. 504-508 ◽  
Author(s):  
C. C. Hsu
Keyword(s):  
Vortex Flow ◽  
Vortex Sheet ◽  
Tip Vortex ◽  
Tip Vortex Cavitation ◽  
Cavitation Inception ◽  
Early Stages ◽  
Lifting Surface ◽  
Viscous Core ◽  
Lifting Surfaces ◽  
Good Agreement

The roll up of vortex sheet on a lifting surface in early stages is studied. The structures of tip vortex flow, both in the outer inviscid and inner viscous regions, are examined. The velocity in the viscous core is determined and used as basis for the prediction of tip vortex cavitation. Some comparisons between the calculated and measured tip vortex cavitation inception numbers are made, and the results are generally in good agreement.

scholarly journals Numerical Investigation of Tip-Vortex Cavitation Noise of an Elliptic Wing Using Coupled Eulerian-Lagrangian Approaches

2020 ◽  
Vol 10 (17) ◽  
pp. 5897 ◽  
Author(s):  
Garam Ku ◽  
Cheolung Cheong ◽  
Hanshin Seol
Keyword(s):  
Flow Field ◽  
Numerical Method ◽  
Vortex Flow ◽  
Acoustic Pressure ◽  
Tip Vortex ◽  
Experimental Result ◽  
Cavitation Noise ◽  
Navier Stokes Equation ◽  
Tip Vortex Cavitation ◽  
Cavitation Inception

In this study, a numerical methodology is developed to investigate the tip-vortex cavitation of NACA16-020 wings and their flow noise. The numerical method consists of a sequential one-way coupled application of Eulerian and Lagrangian approaches. First, the Eulerian method based on Reynolds-averaged Navier–Stokes equation is applied to predict the single-phase flow field around the wing, with particular emphasis on capturing high-resolution tip-vortex flow structures. Subsequently, the tip-vortex flow field is regenerated by applying the Scully vortex model. Secondly, the Lagrangian approach is applied to predict the tip-vortex cavitation inception and noise of the wing. The initial nuclei are distributed upstream of the wing. The subsequent time-varying size and position of each nucleus are traced by solving spherically symmetric bubble dynamics equations for the nuclei in combination with the flow field predicted from the Eulerian approach. The acoustic pressure at the observer position is computed by modelling each bubble as a point source. The numerical results of the acoustic pressure spectrum are best matched to the measured results when the nuclei number density of freshwater is used. Finally, the current numerical method is applied to the flows of various cavitation numbers. The results reveal that the cavitation inception determined by the predicted acoustic pressure spectrum well matched the experimental result.

Scaling of Tip Vortex Cavitation Inception Noise With a Bubble Dynamics Model Accounting for Nucleus Size Distribution

2003 ◽  
Author(s):  
Chao-Tsung Hsiao ◽  
Georges L. Chahine
Keyword(s):  
Size Distribution ◽  
Vortex Flow ◽  
Bubble Dynamics ◽  
Tip Vortex ◽  
Navier Stokes ◽  
Nucleus Size ◽  
Scaling Effects ◽  
Dynamics Model ◽  
Tip Vortex Cavitation ◽  
Cavitation Inception

A Surface-Averaged Pressure (SAP) spherical bubble dynamics model accounting for a statistical nuclei size distribution was used to model the acoustic signals generated by cavitating bubbles near inception in a tip vortex flow. The flow field generated by finite-span elliptic hydrofoils is obtained by Reynolds-Averaged Navier-Stokes computations. An “acoustic” criterion which defines the cavitation inception by counting the number of acoustical signal peaks that exceed a certain level per unit time was applied to deduce the cavitation inception number for different scales. It was found that the larger scale results in more cavitation inception events per unite time because more nuclei are excited by the tip vortex at the larger scale. The nuclei size was seen to have an important effect on cavitation inception number with scaling effects due to nuclei increasing as nuclei sizes decreases.

Propeller Tip Vortex Cavitation Suppression Using Selective Polymer Injection

1993 ◽  
Vol 115 (3) ◽  
pp. 497-503 ◽  
Author(s):  
G. L. Chahine ◽  
G. F. Frederick ◽  
R. D. Bateman
Keyword(s):  
Water Channel ◽  
Tip Vortex ◽  
Vortex Center ◽  
Polymer Injection ◽  
Tip Vortex Cavitation ◽  
Cavitation Inception ◽  
Critical Phase ◽  
Viscous Core ◽  
Drag Reducing Polymer ◽  
Selection Of

This paper presents results of experiments where selective injection of a drag-reducing polymer solution into the tip vortex region of the blades of an 11.5 in. diameter propeller was effective in significantly delaying tip vortex cavitation. The most critical phase of the investigation was the selection of the position of the injection ports. For well-positioned injection ports, at a fixed water channel speed the propeller cavitation number had to be decreased by as much as 35 percent in order to reestablish cavitation inception. Injections of water and a viscous mixture of water and glycerin for the same conditions did not affect the inception characteristics of the modified blades. Preliminary analysis of the results indicates that the viscoelastic properties of the Polyox solution injected in the vortex core played a significant role in thickening the viscous core of the tip vortex and thus reducing the pressure drop at the vortex center without affecting circulation or lift.

Noise Due to Extreme Bubble Deformation Near Inception of Tip Vortex Cavitation

2003 ◽  
Author(s):  
Jin-Keun Choi ◽  
Georges L. Chahine
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Vortex Flow ◽  
Jet Noise ◽  
Video Camera ◽  
Tip Vortex ◽  
Bubble Behavior ◽  
Tip Vortex Cavitation ◽  
Cavitation Inception ◽  
Bubble Deformation

A study on the tip vortex cavitation inception based on extreme bubble deformation and jet noise is presented. First, two preliminary experiments are performed to provide a correlation between the numerically computed splitting/jet noise and the measured noise. The bubble behavior and pressure signal predicted by the axisymmetric method are compared with those recorded simultaneously by using a high-speed video camera and hydrophone. Then, numerical studies on the bubble behavior in the tip vortex flow field are conducted. The tip vortex flow near a hydrofoil is provided by a viscous flow computation, and the bubble behavior is simulated by an axisymmetric boundary element method based on the provided vortex flow field. The characteristics of the bubble behavior and jet noise over a range of cavitation numbers are investigated. The effect of initial bubble nucleus size and the Reynolds number effect of the tip vortex flow on the tip vortex cavitation inception, the bubble behavior including its splitting, and jet noise are also discussed.

scholarly journals Computation of vortex sheet roll-up in the Trefftz plane

1987 ◽  
Vol 184 ◽  
pp. 123-155 ◽  
Author(s):  
Robert Krasny
Keyword(s):  
Mesh Size ◽  
Vortex Sheet ◽  
Smoothing Parameter ◽  
Tip Vortex ◽  
Tip Vortices ◽  
Time Calculation ◽  
Long Time ◽  
Principal Value ◽  
Different Levels ◽  
Good Agreement

Two vortex-sheet evolution problems arising in aerodynamics are studied numerically. The approach is based on desingularizing the Cauchy principal value integral which defines the sheet's velocity. Numerical evidence is presented which indicates that the approach converges with respect to refinement in the mesh-size and the smoothing parameter. For elliptic loading, the computed roll-up is in good agreement with Kaden's asymptotic spiral at early times. Some aspects of the solution's instability to short-wavelength perturbations, for a small value of the smoothing parameter, are inferred by comparing calculations performed with different levels of computer round-off error. The tip vortices’ deformation, due to their mutual interaction, is shown in a long-time calculation. Computations for a simulated fuselage-flap configuration show a complicated process of roll-up, deformation and interaction involving the tip vortex and the inboard neighbouring vortices.

Tip Vortex Cavitation Inception Scaling for High Reynolds Number Applications

2009 ◽  
Vol 131 (7) ◽  
Author(s):  
Young T. Shen ◽  
Scott Gowing ◽  
Stuart Jessup
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Boundary Layer Thickness ◽  
Reynolds Numbers ◽  
Present Theory ◽  
Full Scale ◽  
Tip Vortex ◽  
Tip Vortex Cavitation ◽  
Cavitation Inception ◽  
High Reynolds

Tip vortices generated by marine lifting surfaces such as propeller blades, ship rudders, hydrofoil wings, and antiroll fins can lead to cavitation. Prediction of the onset of this cavitation depends on model tests at Reynolds numbers much lower than those for the corresponding full-scale flows. The effect of Reynolds number variations on the scaling of tip vortex cavitation inception is investigated using a theoretical flow similarity approach. The ratio of the circulations in the full-scale and model-scale trailing vortices is obtained by assuming that the spanwise distributions of the section lift coefficients are the same between the model-scale and the full-scale. The vortex pressure distributions and core sizes are derived using the Rankine vortex model and McCormick’s assumption about the dependence of the vortex core size on the boundary layer thickness at the tip region. Using a logarithmic law to describe the velocity profile in the boundary layer over a large range of Reynolds number, the boundary layer thickness becomes dependent on the Reynolds number to a varying power. In deriving the scaling of the cavitation inception index as the ratio of Reynolds numbers to an exponent m, the values of m are not constant and are dependent on the values of the model- and full-scale Reynolds numbers themselves. This contrasts traditional scaling for which m is treated as a fixed value that is independent of Reynolds numbers. At very high Reynolds numbers, the present theory predicts the value of m to approach zero, consistent with the trend of these flows to become inviscid. Comparison of the present theory with available experimental data shows promising results, especially with recent results from high Reynolds number tests. Numerical examples of the values of m are given for different model- to full-scale sizes and Reynolds numbers.

A Method of Predicting the Effect of the Dissolved Gas Content of Water on Cavitation Inception

1984 ◽  
Vol 198 (3) ◽  
pp. 163-166 ◽  
Author(s):  
P Naylor ◽  
A Millward
Keyword(s):  
Aspect Ratio ◽  
Free Stream ◽  
Tip Vortex ◽  
Gas Content ◽  
Dissolved Gas ◽  
Cavitation Inception ◽  
Low Aspect Ratio ◽  
Good Agreement

A technique has been developed which allows the effect on the cavitation inception number of the gas content in the water to be predicted in cavitation experiments. The predicted results have been compared with data obtained during experiments to measure cavitation inception in the tip vortex of a low aspect ratio hydrofoil and have shown good agreement. The results showed that the gas content affected the cavitation inception number significantly at low free stream speeds, particularly below about 4 m/s.

Prediction of tip vortex cavitation inception with low-order panel method

2016 ◽  
Vol 125 ◽  
pp. 124-133 ◽  
Author(s):  
Youjiang Wang ◽  
Moustafa Abdel-Maksoud ◽  
Keqi Wang ◽  
Baowei Song
Keyword(s):  
Panel Method ◽  
Tip Vortex ◽  
Tip Vortex Cavitation ◽  
Cavitation Inception ◽  
Low Order

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.

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