JAXA-ONERA-DLR Cooperation: Results from Multi-Point Aerodynamic Optimization of a Rotor in Hover and Forward Flight

Abstract

The three research organizations, JAXA, ONERA and DLR have decided to combine their efforts in 2019 to compare and improve their own aerodynamic simulation and optimization strategies. The first two work packages of this collaboration involved single-objective optimizations in hovering flight and then in forward flight. The objective of the study presented in this paper is to perform and compare multi-point aerodynamic optimizations combining these two antagonistic flight cases. The optimization procedures are based on surrogate models, generated by low- and high- fidelity simulation codes. Chord and twist distributions are optimized to improve the performance in hover, and the effective lift-to-drag ratio in cruise. The Pareto fronts are generated and three designs are analyzed in details: Best Cruise, Multi-Purpose, and Best Hover. Similar trends are identified for optimum designs obtained by each partner. In hover, the most influential parameter is a negative twist at the tip, to delay stall occurrence at high thrust values. The estimated power benefit in the Best Hover designs is about 5%. For the selected cruise configuration, with a high advance ratio equal to 0.7 (due to a reduced RPM), the Best Cruise designs present a near-zero twist slope and a chord distribution with a thinning at the root and the tip, balanced by a thickening at mid-span, which reduce the effective drag in the advancing side of the blade. The power benefits are about 15%. The Multi-Purpose designs have a blade planform close to the Best Cruise designs. The twist slope is slightly less than the Baseline. The aero-dynamic behaviors in hover and cruise are fairly close to those of the Baseline, with a range of performance gains between 1 and 3% in hover and cruise.