Twenty-First Symposium on Naval Hydrodynamics (1997) / Chapter Skim
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24-inch Water Tunnel Flow Field Measurements During Propeller Crashback
24-inch Water Tunnel Flow Field Measurements During Propeller Crashback
Pages 136-146
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From page 136... ...
and the complete flow cycle of propeller operation was discussed by Durand [23. The highly unsteady motion of the ring vortex was observed and visualized by towing tank t32 and water tunnel experiments at DTMB.
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3 Figure 1. Photos of propeller ring vortex.
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Detailed quantitative measurements are needed for better understanding the phenomena and for advancing numerical modeling. The objective of the present research program was to measure the propeller induced flow field at the blade tip region.
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The laser beam was expanded to a 6-mm thick light sheet by a combination of c~rliu~rical and spherical lenses. This light sheet illuminated a desired section of the propeller flow field through a window on the bottom of the 24-inch WT test section.
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Time sequence photos of Propeller 4381 at J = -0.472.
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Time sequence photos of Propeller 4381 at J = -0.732.
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This non-dimensionalized number, mD/Vo, is about 0.5 at -2 < 1/J < -1 for the Propeller 4381. PDV IMAGE PROCESS The PDV images collected during the test were digitized and analyzed to obtain quantative flow information including velocity vectors and vorticities.
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CONCLUSIONS AND RECOMMENDATIONS The 24-inch water tunnel experiment demonstrated that the shedding ring vortex associated with a braking propeller is related to He propeller reverse flow and that the unsteadiness is a speeddependent phenomena. Typically, a low frequency of about 0.5 Hz is readily observed in the flow field photos and it matches the unsteady frequency of the propeller side forces at corresponding J's.
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Vector map and `~orticity distribution at J = -0.472.
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O.R7 108 1.28 _ Figure 10. Vector map and vorticity distribution at J = -0.732.
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on Laser Anemometry. ASME Fluid Engineering Division Summer Meeting, Lake Tahoe, NV (June 1994~.
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