Twenty-First Symposium on Naval Hydrodynamics (1997) / Chapter Skim
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Examination of the Flow Near the Leading Edge and Closure of Stable Attached Cavitation
Examination of the Flow Near the Leading Edge and Closure of Stable Attached Cavitation
Pages 783-793
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From page 783... ...
Cavity detachment from a ventilated sphere is examined, and the relationship between the location of cavity detachment and flow separation is related to the geometry of the cavity near detachment. The flow field near the closure of a natural partial cavity is investigated with Particle Imaging Velocimetr~r (PIV)
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From page 784... ...
This pressure difference was related to the test section velocity using LDV measurements of the average flow velocity in the center of the empty test section. The free and dissolved air content of the BDWT can be qualitatively controlled through deaeration and by allowing free gas bubbles to reach the free surfaces in the two tanks.
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From page 785... ...
Franc and Miche} also recognized the relationship between the presence of non-cavitating laminar boundary layer separation and the formation of attached cavitation, and they proposed a method to predict the location of cavity detachment on smooth surfaces. Their method recognizes that the presence of a cavity will alter the pressure distribution around the cavitating object, and this will modify the growth of the boundary layer upstream of the point of cavity detachment.
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From page 786... ...
First, we examined the noncavitating flow around the sphere to determine whether blockage effects were significant and to determine the accuracy with which we can determine boundary layer separation with dye injection. Figure 4 presents the angle of flow separation measured from the front stagnation point as a function of Reynolds number, Re = UoD / if, where D is the diameter of the sphere and v is the liquid kinematic viscosity.
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From page 787... ...
These time exposed images reveal slowly moving particles recirculating in the separation region bounded by the cavity interface and the separation streamline. The cavity has a finite thickness near the point of detachment which forms a forward facing step.
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From page 788... ...
suggested that the momentum thickness of the boundary layer just upstream of cavity detachment strongly influences the region of cavity detachment. We do see that h is dependent on the Reynolds number, but the dependence is approximately linear, while the momentum thickness will vary as Red for laminar boundary layers.
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From page 789... ...
The data represents flows in which re-entrant jets did not disturb the cavity detachment region.
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From page 790... ...
Detailed measurements near attached cavities are made difficult by the large range of flow scales, the presence of two phases, and the unsteadiness of the cavity surface and closure region. We are currently examining the flow field near the closure region of partial cavities using Particle Imaging Velocimetry (PIV)
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From page 791... ...
Icy= qua ~_~ _ _ . _ In- ~ :~ ~~ -:55— ~ ~ i:=—::29'~- -~ .~- so :~ - :~ ~\ :(O Figure 16: Three images of the closure region of a partial cavity- (a)
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From page 792... ...
By employing fluorescent flow tracers, it is possible to detect Lagrangian flow tracers in the bubbly region just downstream of the cavity closure. We currently are employing particle tracking, to analyze the PIV images, and we are striving to increase the density of vectors Silica can be measured.
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From page 793... ...
1993. Partial Cavities: Pressure Pulse Distribution Around the Cavity ]
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