Implicit computational fluid dynamics methods for fast analysis of rotor flows

Woodgate, M. A. and Barakos, G. N. (2012) Implicit computational fluid dynamics methods for fast analysis of rotor flows. AIAA Journal, 50(6), pp. 1217-1244. (doi: 10.2514/1.J051155)

Abstract

Computational fluid dynamics (CFD) based on the Navier–Stokes equations is by far the most useful predictive method available today for helicopter analysis and design. The main drawback of CFD, and perhaps the reason for its slow acceptance by design offices of helicopter manufacturers, is apparently due to the substantial requirements of CPU time and the relatively slow turnaround times in comparison to lower-order methods. However, progress with CFD algorithms and parallel computing has allowed CFD analyses to be used more routinely. Typical applications include computations of aerofoil data that feed rotor performance codes and analyses of rotors in hovering flight. The computation of unsteady flow cases is, however, still challenging. This paper presents alternative ways of tackling unsteady flow problems pertinent to rotorcraft using methods that aim to reduce the time-marching unsteady computations to more manageable steady-state solutions. The techniques investigated so far by the CFD laboratory of Liverpool include time-linearized and harmonic-balance methods. The details of the methods are presented along with their implementation in the framework of the helicopter multiblock CFD solver. Results were obtained for several flow cases, ranging from pitching/translating aerofoils to complete rotors. The results highlight some of the limitations of the time-linearized method and the potential of the harmonic-balance technique. It was found that the time-linearized method can provide adequate results for cases where the unsteady flow is a rather small perturbation of a known mean. The harmonic-balance method proved to have a larger range of applicability and provided adequate results for the analysis of unsteady flows. The required CPU time was reduced, and the required core computer memory was increased. Overall, the harmonic-balance method appears to be a possible alternative to timemarching CFD for a wide range of problems.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Barakos, Professor George and Woodgate, Dr Mark
• Authors: Woodgate, M. A., and Barakos, G. N.
• College/School: College of Science and Engineering > School of Engineering > Autonomous Systems and Connectivity
• Journal Name: AIAA Journal
• Publisher: American Institute of Aeronautics and Astronautics, Inc.
• ISSN: 0001-1452
• ISSN (Online): 1533-385X