After the mobility company UBER published its white paper [1] on electrical vertical takeoff and landing (eVTOL) concepts there is a 'gold rush' [2] in the VTOL community. While it is possible to lift loads vertically by using a purely electrical propulsion system, it is still questionable as to whether this is feasible for urban transport or not.
Abstract. A methodology is presented for generating 360° airfoil polars and aeroacoustic characteristics by means of CFD and CAA. The aerodynamic procedure is validated against experimental data of the well-known airfoils DU-93-W-210 and DU-97-W-300. While a better prediction of the aerodynamic coefficients in the range of −30° and 30° is achieved by a combination of the k-ω SST turbulence model and a C-topology mesh, for the remaining angles of attack more confidence is gained with the SA negative turbulence model in combination with an O-topology mesh. Therefore the two data sets are subsequently fused to one complete data set using a kriging interpolation approach. The result of ten different airfoils using the proposed method is presented. For providing the aeroacoustic characteristics for a wide operation range four computations and a bilinear interpolation are needed, since the aeroacoustic is dependent on the Mach and Reynolds number. The bilinear interpolation approach is verificated by a comparison between the originally simulated and the emulated result at a fifth computational set for six different airfoils. The corresponding overall sound pressure level (OASPL) for four angles of attack for these airfoils is presented and the difference between a fully turbulent computation and simulations with fixed transition is assessed. The aeroacoustic results further include high-fidelity directivity functions.
The design of new helicopter rotor blades is a challenging task. The individual blade sections undergo very different flow conditions during the various flight regimes of the helicopter. In forward flight, the advancing side operates in a transonic regime where potentially shock waves can occur, while on the retreating side little flow velocities at high angle of attacks are seen up to reverse flow. In hover, the oncoming tip vortex of the previous blade drastically influences the inflow on the rotor. This paper joins the classical blade shape design with numerical optimization techniques. Opposing to the direct solution process of directly modifying the blade shape, the rotor blade is conventionally considered as a set of airfoils, a planform and a twist distribution. First, rotor airfoils are found through numerical optimization and then placed on the reference rotor. The planform and twist of this rotor are then also numerical optimized. The obtained trade-off blade for hover and forward flight drastically improved the performance over the reference HART-II blade (11% in forward flight, 5% in hover flight). In order to arrive at industrial relevant blades, further work including more disciplines becomes necessary.
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