Toward Vehicle-Level Optimization of Compound Rotorcraft Aerodynamics

Abstract

This paper presents high-fidelity and simplified computational fluid dynamics modeling approaches within an optimization framework for compound rotorcraft configurations with rotor/propeller aerodynamic interactions. Simulations of an axial-flight ducted propeller and a rotor/wing test case are first presented to validate the in-house Helicopter Multi-Block 3 solver and to assess the actuator disk/line models for the simplified main rotor modeling. The actuator disk/line models are then used to represent the main rotor for simulations of a generalized rotor/propeller combination. The propeller performance is analyzed 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 visualized with variations in the propeller position, propeller thrust, and main rotor advance ratio. Optimization of the propeller position under the main rotor for minimized interference with rolling/pitching moment constraints is also attempted using both gradient-based (adjoint) and gradient-free (efficient global optimization) approaches. The optimization results are verified using blade resolved simulations, and fluctuations of the propeller single blade loading were effectively reduced due to the optimization. The work is a first step toward high-fidelity methods for vehicle and configuration optimization.