Simulation of Rotor Blade Element Turbulence

https://doi.org/10.21949/14036091995PDFTech ReportRotor bladesTurbulenceSimulationHelicopter rotorsRotorcraftTurbulence modelingMcFarland, R.E.Duisenberg, KenAmes Research CenterUnited States. National Aeronautics and Space AdministrationNTL-AVIATION-AVIATIONUS Transportation CollectionA piloted, motion-based simulation of Sikorsky's Black Hawk helicopter wasused as a platform for the investigation of rotorcraft responses to verticalturbulence. By using an innovative temporal and geometrical distributionalgorithm that preserved the statistical characteristics of the turbulence overthe rotor disc, stochastic velocity components were applied at each of twentyblade-element stations. This model was implemented on NASA Ames' VerticalMotion Simulator (VMS), and ten test pilots were used to establish that themodel created realistic cues.The objectives of this research included the establishment of simulation-technology basis for future investigations into real-time turbulence modeling.This goal was achieved; our extensive additions to the rotor model added lessthan a 10 percent computational overhead. Using a VAX9000 computer the entiresimulation required a cycle time of less than 12 msec.Pilot opinion during this simulation was generally quite favorable. Forlow speed flight the consensus was that SORBET (acronym for title) was betterthan the conventional body-fixed model, which was used for comparison purposes,and was determined to be too violent (like a washboard). For high speed flightthe pilots could not identify differences between these models. These opinionswere something of a surprise because only the vertical turbulence component onthe rotor system was implemented in SORBET. Because of the finite-elementdistribution of the inputs, induced outputs were observed in all translationaland rotational axes. Extensive post-simulation spectral analyses of the SORBETmodel suggest that proper rotorcraft turbulence modeling requires that verticalatmospheric disturbances not be superimposed at the vehicle center of gravitybut, rather, be input into the rotor system, where the rotor-to-body transferfunction severely attenuates high frequency rotorcraft responses.84