Toward Vehicle-Level Optimization of Compound Rotorcraft Aerodynamics

Abstract

This paper presents high-fidelity, as well as, simplified CFD modelling approaches within an optimisation framework for compound rotorcraft configurations with rotor/propeller aerodynamic interactions. Simulations of a axial-flight ducted propeller and a rotor/wing test case are first presented to validate the in-house HMB3 solver and to assess the actuator disk/line models for the simplified main rotor modelling. The actuator disk/line models are then used to represent the main rotor for simulations of a generalised rotor/propeller combination. The propeller performance is analysed in detail, and large variations are observed in the single blade loading due to the main rotor wake. A simplified model for the rotor/propeller interaction simulation is also put forward, and an inflow distortion metric is proposed to quantify the aerodynamic interactions. With the help of a Kriging surrogate model and the inflow distortion metric, aerodynamic interferences through the propeller disk are quantitatively visualised with variations in the propeller position, propeller thrust, and main rotor advance ratio. Optimisation of the propeller position under the main rotor for minimised interference with rolling/pitching moment constraints are also attempted using both gradient-based (adjoint) and gradient-free (efficient global optimisation) approaches. The optimisation results are verified using blade resolved simulations, and fluctuations of the propeller single blade loading were effectively reduced due to the optimisation. The work is a first step towards high-fidelity methods for vehicle and configuration optimisation. Nomenclature Latin a = Speed of Sound, m/s b = Wing Span Length, m C = Main Rotor Chord, m Cp

Multi-fidelity aerodynamic design and analysis of propellers for a heavy-lift eVTOL

“…This property makes the adjoint formulation especially suitable for aerodynamic shape optimisation. Details of the HMB3 adjoint formulations can be found in previous optimisation studies of rotors, wings, and ducted propellers [12,[19][20][21].…”

“…The design variables considered were again the blade pitch and chord distributions along the blade span. Note that the HMB3 adjoint is capable of arbitrary shape changes [20,21], but the current work focused only on the twist and chord for consistency and for reduced computational costs. The HMB3 adjoint treated the twist and chord changes as arbitrary surface deformations regardless, through the IDW mesh deformation [19,33,34] module.…”

“…The selected designs were then converted into CAD (Computer-Aided Design) models and meshed with chimera grids and an automatic meshing framework [16,17]. High-fidelity CFD (Computational Fluid Dynamics) simulations and adjoint-based optimisation were then performed using the in-house HMB3 solver [18][19][20][21]. Compared to the simple initial design, the low-fidelity stage yielded a 3% performance improvement, and the final high-fidelity-optimised design showed a further 2.2% improvement.…”