Aerodynamic analysis of propeller-type windmills with helical trailing vortices
To improve the strip theory for computing the performance of a propeller-type windmill, a more realistic analysis is formulated to include the wake effect. In this dissertation, the finite-wing theory is applied to a rotor blade to find its circulation distribution with the downwash determined from a direct integration of Biot-Savart's law based on the entire helical trailing vortex system. Since no simple analytical solutions can be found for the circulation and the interference factors along a windmill blade, an iterative procedure has been developed to determine the sectional properties at some selected stations. A computer program is constructed for the computation, in which the empirical lift and drag data of the blade airfoil section are programmed. The torque, thrust and power output of the windmill are then obtained by integrating the sectional aerodynamic properties from hub to tip along the blades. Two windmills, one with twisted and tapered blades and the other with uniform blades, are used as examples in predicting the performances. The power computed for the latter windmill agrees well with the measured data. It has been found, according to the computations for the first windmill, that the helical wake may cause a reduction up to 30% in power output of the windmill. The problems of finding the optimum pitch angle for a uniform blade and the optimum distribution of twist angle for a blade of constant chord are considered as some applications of the method derived in this dissertation.
- Research Organization:
- Colorado Univ., Boulder (USA)
- OSTI ID:
- 6209581
- Resource Relation:
- Other Information: Thesis
- Country of Publication:
- United States
- Language:
- English
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