Actuator disc modelling for helicopter rotors

Abstract

The helicopter project CHANCE contains, among other developments, the quasi-steady approximation to modelling rotors with actuator discs. This reduces the cost of an unsteady simulation down to a stationary one. In testing existing approches in the literature, the source term implementation proved to perform best, especially in forward flight: source terms located on the disc bottom side impart impulse and energy to the fluid. These are obtained from a loose coupling between DLR codes: the flow solver FLOWer and the rotor code S4. The latter provides a rotor map, a radial and azimuthal force distribution, to the former converting it to the actuator disc map (source terms). Low velocities are accounted for using preconditioning. A more flexible Chimera approach can be used. The actuator disc feature has been developed in a parallel framework for shorter turn-around times. Capturing the fuselage/disc interaction using the Chimera capability is demontrated on the HELIFUSE C1 configuration. Next the BO-105 fuselage is used to validate the source term approach by means of a uniform pressure jump. The potential disturbance appears clearly on the disc inflow and pressures on the top centreline match with experimental points. Last, the Dauphin 365N configuration has been used to assess the non-uniform actuator disc. It is checked that previous ONERA results are correctly reproduced with a map provided by ONERA. An actuator disc map derived from S4 is used for further investigation. In particular, it is shown that the vorticity field is particularly well captured.