Hovering helicopter rotor experiments and simulations in a closed-circuit wind tunnel

A closed-circuit wind tunnel currently used to perform high-speed helicopter rotor tests is here used to perform hovering rotor tests. Since ONERA S1 Modane wind tunnel is a closed-circuit wind tunnel and since the rotor is tilted at 90 degrees, a climb flight is experimentally simulated due to recirculating flow created by the rotor downwash. Several wind tunnel configurations are thus considered to block the rotor downwash and decrease the upstream velocity. Thanks to these different configurations, the paper shows how to extrapolate the results in order to determine experimental hovering flight performance. A numerical study is then presented: the elsA Navier-Stokes code is confronted to the detailed experimental data that include blade pressure measurements. The computational results show that the low axial climb velocity should be taken into account and allows then a very good agreement between computations and experiment. A method based on momentum theory is proposed to determine this low axial climb velocity from experimental measurements. Finally, the differences between hover flight and climb flight computation results are discussed.