Experimental Methods for the Prediction of the Effect of Viscosity on Propeller Performance.
MASSACHUSETTS INST OF TECH CAMBRIDGE DEPT OF OCEAN ENGINEERING
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A Laser Doppler Velocimeter LDV was used to perform a propeller wake survey for DTNSRDC propellers 4381 and 4383. Three components of the velocity were measured and from this, the velocity field and the vorticity field were constructed. Through a coordinate transformation, the vorticity field was separated into two parts i.e., trailing vorticity and boundary layer type vorticity in the viscous wake. The data was used for the prediction of propeller blade profile drag viscous sectional drag. The idea of hypothetical flow by Betz was extended to propeller flow and a formula for the profile drag was derived in terms of velocities, which is suitable for LDV application. The radial distribution of profile drag was computed using the velocity data. It was shown that the value of Cd is close to that of 2-dimensional section at mid-radius range, but becomes substantially lower at inner and outer radii and that it goes up again near the tip and the hub. This trend is consistent with the behavior of profile drag of a finite span wing. Author
- Marine Engineering
- Fluid Mechanics