CFD simulation of flapped rotors

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Dehaeze, F.
Baverstock, K.D.
Barakos, G.N.
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The use of active trailing edge flaps on rotors may lead to performance benefits as well as noise and vibration reduction. In this work, the HMB CFD solver is used, and the trailing edge flaps are modelled using a combination of surface and mesh deformation. Starting from a baseline blade design, the flap is first assessed using dMdt computations, that account for the simultaneous variations of pitch and Mach around the azimuth. It was shown that enhanced lift was obtained while inspection of the moment coefficient showed negative damping for the flap for a limited set of conditions. Due to the 2D formulation, dMdt computations are fast to perform and can be used to inform codes predicting the rotor performance. The flap was then assessed in hover, and only allowed for limited improvement in blade performance at high thrust. In forward flight, the flap was actuated in a 1-per-rev fashion and was found to have a strong effect on the loads on the retreating side. The effect on the moments was even stronger. The flight envelope of the blade was explored, and clean and flapped cases were compared. The most noticeable changes occur at high and medium thrust. The CFD method was found to be efficient and robust, without any substantial penalties in CPU time over the tested conditions.