Twenty-Fourth Symposium on Naval Hydrodynamics (2003) / Chapter Skim
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Experimental and Numerical Investigation of the Cavitation Pattern on a Marine Propeller
Experimental and Numerical Investigation of the Cavitation Pattern on a Marine Propeller
Pages 852-867
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From page 852... ...
The effect of the trailing wake vorticity on the prediction of the cavitation pattern is analyzed via a wake alignment technique. INTRODUCTION For two-dimensional and three-dimensional isolated hydrofoils, the cavitation literature offers a limited number of works where quantitative information has been successfully obtained from the direct observation of the cavitation pattern (see e.g.
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From page 853... ...
State-of-the-art theoretical analysis of cavitating propellers is based on inviscid-flow models such as lifting surface methods and boundary element methods. Viscous-how modeling by RANSE or LES approaches are still limited to simple geometries as two- and three-dimensional hydrofoils in uniform flow.
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From page 854... ...
Go, the cavitation number (Sn based on the propeller rotation speed, KT and KQ. Cavitation Extension Measurement We introduce a novel methodology to determine the cavity area, designed to be implementable in field situations where the experimental constraints do not always allow the use of standard techniques of image analysis.
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From page 855... ...
In fact, the complex lens system composed of the camera objective, the prism, the test section window and the water medium introduce focusing aberrations and optical distortions, which are the source of non-linear magnification. If the focusing aberrations can not be removed, image distortions can be compensated through calibration procedures (Soloff et al., 1997~.
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From page 856... ...
The thickness is measured on the average image and at the Figure 6: Cavitation extension location of minimum cross-section of the cavitation pattern. The measured dimension is then nondimensionalized by the propeller diameter, for the purpose of comparison with the numerical solution of the thickness.
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From page 857... ...
In the case of supercavitating flows, a similar derivation leads to an expression for the velocity potential on the cavitating portion of the wake surface us O (s, u)
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From page 858... ...
' or aahC +Vshc q = at +v, on 50CB~ (12) where Vs denotes the surface gradient on JAMB- In the case of supercavitating flow conditions, Kinnas and Fine (1992)
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From page 859... ...
As a fundamental step to assess the accuracy of the present methodology to predict non-cavitating and cavitating flow features, the effects of surface discretization on the numerical results have been investigated and are briefly addressed here. A family of grids characterized by a constant ratio between the number of blade elements in chordwise direction MB' in spanwise direction NB' and the number of wake elements in streamwise direction per turn, MW is used.
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From page 860... ...
0.50 0.48 FLOW FIELD INVESTIGATIONS 0.46 First, the non cavitating flow features of the model propeller E779A are considered. The experimental data have been taken from previous works performed at the CEIMM facility.
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From page 861... ...
rfR=O.9 Wet. r/R=O.9 -1 .0 0.0 0.2 0.4 0.6 0.8 1.0 xlC the inner part of the blade where the Cp distribution ical predictions using a non-cavitating flow model tends to flatten.
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From page 862... ...
The experimental data are represented with the corresponding standard deviation. The cavitation area fluctuations are in general very small, in the range of l to 3%, except for the cases at the lowest values of the cav6n = 1.00 :7 On = 1.51 On = 2.02 Figure 13: Planform view of the cavitating blade and predicted cavitation area at J=0.71: prescribed wake model (_)
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From page 863... ...
, free wake model (_) Figure 15: Planform view of the cavitating blade and predicted cavitation area at J=0.83: prescribed wake model (_)
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From page 864... ...
Figure 19 displays the maximum thickness, which we recall is only a rough estimate of the cavity true maximum thickness, versus a length Ic taken as the square root of the attached cavitation area Ac; hence, the values of IC are only indicative. The numerical results fall on a straight line, whereas the experimental data follow the same linear trend, with the additional dispersion due to the coarse thickness evaluation.
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From page 865... ...
Gn > 1.5 at J = 0.71, 0.77, and 2%~ 1% 0% _ o · J=0.710+4 E-4 ~ J=0.769 + 6 E-4 · J=0.830 + 2 E-4 · J=0.879 + 3 E-4 J=0.71, free wake model J=0.77, free wake model J=0.83, free wake model J=0.88, free wake model 3 4 Figure 18: Effect of parameters J and 6,' on the cavity maximum thickness ho. Comparison between measurements and numerical results (free wake model)
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From page 866... ...
The methodology includes an accurate evaluation of the trailing wake vorticity path by means of a wake alignment techn~que. Comparison with the experimental measurements shows that the present theoretical methodology is able to accurately predict the sheet cavitation area across a wide range of advance ratios and of cavitation number values.
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From page 867... ...
and Fine, N E., "A nonlinear boundary element method for the analysis of propeller sheet cavitation99' in Proc.
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