Measurement of propulsive power and evaluation of propulsive performance from the wake of a self-propelled vehicle.
Propulsive efficiency is a key indicator of propulsive performance, but it can be difficult to measure when the propulsion system is integrated into the vehicle body because the average rate of useful work done propelling the vehicle (Wu) and/or the average mechanical power expended propelling the vehicle (Pmech) is not known directly. A general approach would be to determine either or both of (Wu) and (Pmech) from the vehicle wake. The present discussion demonstrates that only (Pmech) can be determined from the flow crossing a plane a fixed (average) distance downstream of the vehicle. A method for measuring (Pmech) is presented using the observation that the power required to tow a permeable obstruction behind the vehicle depends on (Pmech). Several methods for evaluating propulsive performance using [Formula: see text] are proposed, including the definition of an equivalent jet velocity and corresponding Froude efficiency if the time-averaged mass flow rate through the propulsion system is known. If only (Pmech) is known, the recommended measure of propulsive performance is a power coefficient defined analogous to a drag coefficient.
Department of Mechanical Engineering, Southern Methodist University, Dallas, TX 75275, USA. pkrueger@engr.smu.edu
P S
PS
Krueger
D032701:Biomimetics / Q000379:methods*; D003198:Computer Simulation; D004735:Energy Transfer; D019544:Equipment Failure Analysis / Q000379:methods*; D008962:Models, Theoretical; D009038:Motion; D018986:Motor Vehicles; D012212:Rheology / Q000379:methods*