Optimizing Rotor Blades with Approximate British Experimental Rotor Programme Tips

Abstract

This work presents a framework for the optimization of certain aspects of a British Experimental Rotor Programme-like rotor blade in hover and forward flight so that maximum performance can be obtained from the blade. The proposed method employs a high-fidelity, efficient computational fluid dynamics technique that uses the harmonic balance method in conjunction with artificial neural networks as metamodels, and genetic algorithms for optimization. The approach has been previously demonstrated for the optimization of blade twist in hover and the optimization of rotor sections in forward flight, transonic aerofoils design, wing and rotor tip planforms. In this paper, a parameterization technique was devised for the British Experimental Rotor Programme-like rotor tip and its parameters were optimized for a forward flight case. A specific objective function was created using the initial computational fluid dynamics data and the metamodel was used for evaluating the objective function during the optimization using the genetic algorithms. The objective function was adapted to improve forward flight performance in terms of pitching moment and torque. The obtained results suggest optima in agreement with engineering intuition but provide precise information about the shape of the final lifting surface and its performance. The main computational cost was associated with the population of the genetic algorithms database necessary for the metamodel, especially because a full factorial method was used. The computational time of the optimization process itself, after the database has been obtained, is relatively insignificant. Therefore, the computational time was reduced with the use of the harmonic balance method as opposed to the time marching method. The novelty in this paper is twofold. Optimization methods so far have used simple aerodynamic models employing direct "calls" to the aerodynamic models within the optimization loops. Here, the optimization has been decoupled from the computational fluid dynamics data allowing the use of higher-fidelity computational fluid dynamics methods based on Navier-Stokes computational fluid dynamics. This allows a more realistic approach for more complex geometries such as the British Experimental Rotor Programme tip. In addition, the harmonic balance method has been used in the optimization process.

Rotor-Blade Planform Design Based on an Overset Harmonic-Balance-Adjoint Optimization Framework

“…The majority of these studies are performed using non-gradient based optimisation methods, which are very expensive in their nature, due to the number of evaluations required being of order n 2 − n 3 [21], where n is the number of design parameters. To minimize the computational costs, surrogate modelling based on various techniques such as kriging [22], neural networks [23] or latin hypercube sampling (LHS) and radial basis functions (RBF) [24,25] have been employed. Variable-fidelity surrogate models have also been proven to be successful [26,27], although highlighted the importance of including high-fidelity simulations in the optimisation framework [26].…”

Aeromechanical Stability of a Bearingless Rotor Helicopter with Double-Swept Blades

“…Studies of the double-swept rotor blade have been primarily focused on using either the experimental or computational methods to determine the aerodynamic and aeroacoustic characteristics [16][17][18][19]; however, there are relatively fewer studies examining its dynamics. The offset of the lift acting on the blade relative to the pitch axis due to the fore-aft swept blade design could lead to a strong coupling of flap and torsion motions, which is suspected to lead to aeroelastic problems.…”

Numerical Simulations of Various Rotor Designs in Hover and Forward Flight

“…Since the development of this rotor [11] and with the exception of some works [12], [13], [14] not much validation has been performed for BERP blades. Optimisation of BERP-like tip geometries were performed by Johnson and Barakos [15], but the final shape was not tested in a wind tunnel. To date, the only experimental data concerning BERP-like blades was performed at NASA by Yeager et al [1].…”