The primary theoretical contribution of this work is an enhanced Blade Element Momentum (BEM) method. Utilizing vortex theory to model induction, computationally efficient corrections are derived that are key in more accurately predicting performance for coned rotors. The theory is extended to include wake expansion, dynamic inflow, and yawed conditions, as well as considering centrifugal and radial-flow induced stall-delay. The theory is favourably validated against Computational Fluid Dynamics (CFD) and experimental results for both real and idealized rotors. BLADED<sup>TM</sup> was to be modified with the enhanced BEM method for dynamic analyses. To support these analyses, a beam sectional model and Finite Element Method (FEM) approach to the generalized centrifugally stiffened beam problem were implemented. Ultimately, the linear structural theory in current codes precluded accurate predictions at large flap angles. In lieu of a fully non-linear flexible-body simulation, a rigid-body dynamic model of the system was developed. The coupled aerodynamic and structural models were then used to analyse steady-state and dynamic operation, including optimal control schedules. Parametric optimization studies were used to examine the interplay between design variables for the coning rotor, relative to a reference conventional machine. Increased blade length, shape and airfoil choice were found to be tightly coupled, yielding energy gains of 10-30% over conventional rotors. Airfoil choice and control mechanism were found critical to limiting torque and thrust. The fundamental non-linear open-loop dynamics were also examined, including flap and edgewise damping behaviour. Low-Frequency Noise (LFN) was computed with a properly implemented physics-based model, to quantify sensitivity to design and operational parameters. The current work is a preliminary, but critical step, in proving the worth of the coning rotor. Controlled design and an accurate flexible-body code will be required for full load-set simulations, to affect detailed component design and costing. Ultimately, prototype testing will be needed to validate the complicated stalling behaviour of the coning rotor.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:598134 |
| Date | January 2007 |
| Creators | Crawford, C. A. |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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