High resolution methods for the aerodynamic design of helicopter rotors

Brocklehurst, Alan High resolution methods for the aerodynamic design of helicopter rotors. Doctor of Philosophy thesis, University of Liverpool.

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Abstract

The research reported here was driven by a desire to obtain a prediction method for helicopter rotor performance that would have sufficient resolution to evaluate changes to the design of the blade tip. This thesis examines the effectiveness of Computational Fluid Dynamics (CFD) methods to solve this problem. An accurate, high-fidelity prediction is essential to quantify the performance of a new rotor tip shape which hitherto could not be properly assessed by a traditional approach. The CFD method lends itself to the resolution of the compressible, viscous flow around the helicopter blade tip. Starting from the surface shape required to generate a grid, together with the flow conditions, the flowfield naturally evolves from the numerical solution of the Navier-Stokes equations, based on the principles of conservation of mass, momentum and energy. Thus both the flow physics and the geometry of the tip are fully modelled by this technique. In order to demonstrate the process, the Helicopter Multi-block solver (HMB) is used to predict the performance of a series of example tail rotor configurations. The various tip shapes are evaluated and compared, initially using an Euler approach to economically cover a wide range of designs, before going on to apply the Navier-Stokes method. The concepts behind each of the tail rotor blade (TRB) tip designs are explained in the thesis. As further computational resources became available, the datum blade, and the down-selected Kuchemann-like and anhedral-Kuchemann tip blades were the subject of Navier-Stokes predictions. Early in this work, the numerical method was validated against published data, and was also compared to existing model tail rotor test data for blades having different twist. In the central part of this thesis, the computational results are further analysed to reveal the influence of blade design changes on the time-averaged induced flow, and to extract more familiar aerodynamic parameters such as the angle of attack from the 3D rotor computations. Steady Navier-Stokes predictions were obtained over a range of pitch angles such that the induced power factor could be reliably determined and the trends on profile power could also be established for the selected tip shapes. The research reported in this thesis has established that this numerical approach provides a good prediction of rotor performance, adequately resolving the flow-field and tip aerodynamics. Since the assessment of helicopter rotors may involve additional interactional effects, or a degree of unsteady flow due to operating at high pitch angles near the onset of stall, an unsteady case was also demonstrated for a tail rotor blade adjacent to a fin. It is concluded that only by using a CFD approach can a sufficiently high-fidelity prediction be obtained for helicopter rotor aerodynamics to allow progressive enhancements of future helicopter blade designs.

Item Type:	Thesis (Doctor of Philosophy)
Additional Information:	Date: 2013-06-06 (completed)
Uncontrolled Keywords:	helicopter rotor blade tip shapes, tip design, tail rotor tip design and performance evaluation, CFD
Subjects:	?? TL ??
Divisions:	Faculty of Science and Engineering > School of Engineering
Depositing User:	Symplectic Admin
Date Deposited:	02 Aug 2013 09:40
Last Modified:	16 Dec 2022 04:39
DOI:	10.17638/00012213
Supervisors:	Barakos, George Badcock, Ken
URI:	https://livrepository.liverpool.ac.uk/id/eprint/12213