Experimental evaluation of the aerodynamic rotor/propeller interactions for high-speed helicopter
Helicopters are widely used for civil and military needs. The assets of the rotorcrafts are numerous: vertical take-off and landing, hovering and mobility in all directions … However, amongst other limitations, the conventional configurations have a speed limited of about 300 km/h. In this context, the high-speed helicopters were created. Equipped with additional rotors and/or lifting devices, these configurations allow to unload the rotor and to increase the aerodynamic efficiency of the aircraft. However, the multiplication of rotating
elements generates an increase of the interactions that can lead to a loss of performances, and even to critical flight situations. Thus, this thesis proposes to experimentally study the rotor/propeller interactions depending on the flight conditions for compound helicopters, of which the Eurocopter X3 and the Airbus RACER are examples. To date, numerical studies have been conducted but the complex phenomenon could not be
transcribed entirely. In parallel, only few experimental data is available. Experimental studies are lead to underline the influence of the advance ratio, of the rotational velocity of the propeller and of its position on the performances of the rotors. The tests are conducted on a 1/7.7 scale Dauphin 365N equipped with a propeller whose position is modifiable in all three directions. The entire campaign is conducted in the ONERA large-size L2 wind tunnel. Efforts and velocity fields measurements highlighted the absence of direct rotor/propeller interaction at high speed. In hover, however, the propeller is entirely immersed in the rotor wake, which generates an increase of its performances. At low speed, the propeller is partially immersed in the rotor wake. In this context, a translation of the propeller towards the tail of the helicopter leads to increased interactions and propeller thrust. The absence of benefits consequent to the vertical or lateral translation has also been shown. Finally, the negligibility interactions of the propeller on the rotor has been highlighted for all the flight configurations.