AN EXPERIMENTAL INVESTIGATION OF PROPELLER WAKES USING A LASER DOPPLER VELOCIMETER (AERODYNAMICS, PROPULSION, TESTING)
Abstract
This report presents a detailed investigation of the performance and flowfield of three single rotation propellers. These propellers were designed to demonstrate the efficiency improvements attainable by using proplets and biblades. Direct measurement of thrust by a parallelogram balance and power by measuring the input to the propulsion unit (DC motor) was used to determine the efficiency of the propellers. The force measurements demonstrated that the use of proplets did produce an efficiency improvement under high loading conditions in static operation as well as with forward speed. The improvement in static thrust by using proplets was comparable with that of a shrouded propeller. The flow field in the wake of the propellers was investigated with an LDV system. The measured velocity field is compared with the theoretical velocity field. Biot-Savarts' law was applied to the theoretically assumed vortex geometry in the wake to determine the theoretical velocity field. The vast amount of LDV data acquired is presented in compact cascade, vector and color intensity plots to determine quantitative and qualitative geometry of the vortex system behind a propeller. Tip vortex trajectories behind the three configurations are compared with theoretically assumed geometry of the vortex lattice model. Circumferentially averaged velocities in the wake are used to compute the radial distributions of the thrust and power coefficients in the wake and this is compared with the corresponding distributions obtained by analyzing the velocity field of the vortex lattice model. The integrated thrust and power coefficients from momentum analysis of the measured velocity field, with values from force and power input measurements and with the prediction of the vortex lattice model. Finally detailed scans behind one of the propellers was used to compute the three components of vorticity vector in the flow behind the propeller. The results plotted in vector and color intensity plots show the rolled up tip vortex and the weaker inboard vortex sheet.
Degree
Ph.D.
Subject Area
Aerospace materials
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