JAXA-ONERA-DLR cooperation: results from rotor optimization in hover

Abstract

A cooperation between JAXA, ONERA and DLR puts the focus on the aerodynamic optimization of helicopter rotors. This paper represents the conclusions from the first phase: optimization of a hovering rotor. The HART-II blade is first investigated with low-fidelity tools and compared against state-of-the art CFD simulations. Afterwards, the chord distribution and twist of the HART-II blade are optimized using the low-fidelity tools as well as CFD. Since the partners observed differences in the outcome of the CFD simulations for the low-fidelity optimized blades, a deeper investigation of the effects of the turbulence modelling approach, elasticity and grid topology is conducted. The findings show that the chosen flight condition is close to the thrust of the maximum Figure of Merit and that the vortex-triggered separation on the outboard sections of the blade has to be modelled correctly. In this study, the blade grids had the most noticeable effect on the results, followed by the turbulence model and elasticity. With respect to the optimization, low-fidelity methods require special care, whereas CFD optimized blades were found to lead to more robust designs, even though they have only been optimized for a single point. This is explained by the more accurate modelling of the stall phenomenon with respect to geometrical changes.