Determination of Cavity Detachment for Sheet Cavitation

[+] Author and Article Information
Eduard Amromin

 Mechmath LLC, Prior Lake, MN 55372-1283amromin@aol.com

J. Fluids Eng 129(9), 1105-1111 (Mar 05, 2007) (7 pages) doi:10.1115/1.2754312 History: Received September 22, 2005; Revised March 05, 2007

Sheet cavitation has been traditionally analyzed with ideal fluid theory that employs the cavitation number as the single parameter. However, characteristics of cavitation can significantly depend on location of cavity detachment. According to known experimental data, this location is influenced by the freestream speed and the body/hydrofoil size. As shown in this paper, it takes place because of the combined effect of the Reynolds number and Weber number. Here, sheet cavitation is considered as a special kind of viscous separation caused by the cavity itself. The viscous-inviscid interaction concept is employed to analyze the entire flow. Validation of the suggested approach is provided for hydrofoils and bodies of revolution. The effects of flow speed, the body size, and its surface wettability are illustrated by comparison of computed cavity length/shape to the known experimental data. The difference between cavity detachment in laminar and turbulent boundary layers is discussed.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 3

Comparison of ideal cavitation and the CCVL: The top plot shows cavity shapes; there is the vertical fictitious body in the tail of ideal cavity and separation zone behind the CCVL cavity, whereas the cavity detachment zone is too small to be visible here; arrows show direction of time-average water flux through the cavity in the CCVL. The middle plot presents corresponding pressure distribution over the body in the vicinity of cavity. The bottom plot shows the cavity detachment zone in more detail; here, β is the angle between outer normal to liquid on the liquid-cavity and liquid-body boundaries.

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Figure 4

Correspondence of the variables {X1,X2} and {C,σ} for the EN-hydrofoil at Re=1.5×106

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Figure 5

Comparison of theoretical (lines) and measured positions of cavity detachment points (after (5), shown by symbols) on axisymmetric body of D=0.045m with hemispherical head. The arc coordinate of detachment point is normalized by the head radius D∕2. The number in the legend indicates U∞ (in feet per second)

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Figure 6

Computed and measured (23) abscissas of cavity detachment X0 on ellipsoids (x∕D)2+(2y∕D)2+(2z∕D)2=1 made from different materials: D=0.05m, U∞=18m∕s. Curve B–V means ideal cavitation with Brillouin–Villat condition.

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Figure 1

Cavity length on the EN-hydrofoil at Re=1.5×106, α=4.2deg: Vertical segments show experimental data with their dispersion. Curve A shows our result obtained with the CCVL. Curves R&B-1 and R&B-2 show results for different cavity closure schemes in ideal fluid (1).

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Figure 2

Cp distributions on the body with hemispherical head computed by the author for Re=1.36×105. Stars show experimental data (after (8)). One can see that a distribution without minimum of Cp may be also in a good accordance with the measured Cp.

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Figure 7

Effect of cavity detachment on cavity length: Solid curves give results of the CCVL for D and U∞ employed in Figs.  56; dashed curves give results of ideal cavitation with Brillouin–Villat condition

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Figure 8

Cavitation patterns on the body of revolution at α=3deg. Body head similar to ITTC body head, but a little bit blunter (its block coefficient, 2.5% greater). Solid lines show the body contour (abscissa is normalized by D). Dashed and dotted curves limit the computed cavity patterns. Observed cavity patterns are shown by double arrows.

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Figure 9

Cavity length over the ITTC body. Triangles and rhombs show observed maxima and minima of L; the curve is the computation result.

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Figure 10

Cavitation inception number for bodies with hemispherical head versus Reynolds number for different calibers D: “2” shows measurements with low air contain for D=0.02m, “5-T” show measurements for D=0.05m with a turbulence stimulator, and “5” shows measurements for this body without this stimulator. Indexes of our computational curves correspond to symbol indexes.

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Figure 11

Boundary layer effect on cavity shapes for σ=0.3 on the body with hemispherical head. Curve 1 is the body contour; curve 2 is Cp for cavitation-free flow; curve 3 is the cavity section at Re=5×105, D=0.05m in turbulent boundary layer; curve 3a is the cavity section at Re=5×105, D=0.05m in laminar boundary layer; curve 3b is the cavity section at Re=107, D=1m turbulent boundary layer.



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