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INVESTIGATION OF PROPELLER EFFICIENCY IN A FLOW Aero Engineering Laboratory AOE 4154 Lab Instructor: Dr. Roger Simpson Lab TA: Scott Burger Lab Section: Friday 3:55 – 5:20 Date Performed: October 30, 2009 Student Name: Craig Sossi Student Number: 904512344 Honor Pledge: By submitting this document I pledge that I have neither given nor received unauthorized aid. Craig Sossi Page | 1
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Prop 4767A. An open jet wind tunnel is used to produce the flow conditions for the tests, and a series of data acquisition tools along with a computer are used to record data. Of importance are the propeller advance ratio, the thrust and torque coefficients, and the propeller efficiency. It can be seen through data plots that as the advance ratio increases, the thrust and torque coefficients decrease. As the advance ratio increases, the efficiency increases up to a value then decreases. The “propeller”, “air brake” and “windmill” sections of the plots can also be determined from the signs of the thrust and torque coefficients. INTRODUCTION A propeller is a device that is used to transform rotational motion into directed thrust. Thrust is produced by a pressure differential between the front and back side of the blades of the propeller. Marine propellers typically consist of three to five helicoidal blades that effectively “screw” through the water, propelling the ship forward. There are many different blade configurations that yield different performance characteristics, all of which can be determined through extensive testing or with theoretical calculations. For this lab, one type of propeller will be analyzed theoretically and experimentally, and the results compared. The propeller unit is mounted to a strain gauge and placed in the test section of an open throat wind tunnel. The propeller will be rotated at a constant RPM (revolution per minute) while the speed of the free-stream exiting the tunnel will be varied. The thrust and torque coefficients of the propeller will be measured, along with the propeller efficiency. These values will then be compared to the theoretically calculated values. To compute the theoretical values for the propeller, it is necessary to first determine the speed of the flow exiting the wind tunnel. The dynamic pressure measured in the tunnel is used to find the speed, and the calculation is shown in equation 1. (1) The coefficients and efficiency determined from the theory and experiment will be plotted against the advance coefficient, J , which is the ratio of the free-stream velocity to the propeller blade tip speed. This ratio is calculated using equation 2.
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