Analytical investigation of Darrieus-rotor aerodynamics. Final report
This report covers analytical modelling of Darrieus Rotor aerodynamics. The performance limits of vertical axis windturbines are discussed. An actuator disk-type analysis is developed for the Giromill. It is found the Betz limit applies to vertical axis machines. Expressions for the axial and crosswind force are also given. Streamlines and velocity profiles are illustrated for several loading conditions. A fixed wake analysis is developed for the Darrieus Rotor flow field. The bound and shed vorticity system is modeled as circular rings in a complex plane, having an unknown spatial distribution in their strengths. The total flow field is formed from a superposition of the free stream velocity and the inductions from the bound and shed vorticity system. These inductions are computed via series expansions whose coefficients are determined by satisfying boundary conditions of the rings of vorticity. The field is numerically mapped out for various degrees of loading and is displayed in several plots of the streamline. A free vortex analysis of a single-bladed rotor is covered. The results show the effects of the various unsteady terms on the forces and moments. Rational approximations are suggested. The four methods used to analyze Darrieus Rotor aerodynamics are compared. Extensive illustrations compare the forces, moment, velocity, field, circulation and angle of attack history. It is concluded that a hybrid flow model, using a fixed wake determination of the induced flow field along with quasi-steady aerodynamics (including pitching and apparent mass terms) to determine loads, would be a significant advance. In particular, Darrieus Rotor performance envelopes can be increased significantly by taking advantage of the asymmetry of the induced velocity field.
- Research Organization:
- Oregon State Univ., Corvallis (USA). Dept. of Mechanical Engineering
- DOE Contract Number:
- AT06-76EV71023
- OSTI ID:
- 5876734
- Report Number(s):
- DOE/EV/71023-4; ON: DE83014674
- Resource Relation:
- Other Information: Portions are illegible in microfiche products
- Country of Publication:
- United States
- Language:
- English
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