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This study examines the effect of aerodynamic interactions on a two-rotor pair in cruise, and a propeller acting in the presence of a wing. The two-rotor system with a forward and an aft rotor in-line is considered at different disk loadings (6, 8, 12 lb/ft² for a fixed cruise speed and different cruise speeds (20, 40, 60 knots) for a fixed disk loading. Loads for these rotors are generated using the CFD solver AcuSolve to capture the aerodynamic interactions on the rear rotor due to the front rotor. These loads are used as inputs to an acoustic solver (PSU-WOPWOP, ANOPP2) to predict noise at observers in the rotor plane, with noise compared to that from isolated rotors in the absence of aerodynamic interactions, to quantify the interaction effects. The rotor wing case, with the rotor in front of the wing operating in axial propeller mode, is simulated at 24 knots cruise and 8 degree wing angle of attack. Loads for the rotor with a wing and a rotor acting in isolation are generated using the CFD solver AcuSolve. These loads are used as inputs to an acoustic solver, with observers placed in the plane of the rotor, in the plane containing the wing chord cut through the rotor hub, and a vertical plane through the hub in the wind direction. The two-rotor system simulation results show that the presence of aerodynamic interactions on the rear rotor results in changes in noise levels of less than 2 dB in the plane of the rotors. The rotor wing results show that the aerodynamic interactions increase the overall noise by up to 8 dB, with the largest increase being above and behind the prop-rotor.

This study models an infinite rotor-wing unit based on the CRC-20 quad-rotor bi-plane at an angle of attack of 8° and rotor modeled using the actuator line method (ALM). Parametric variations to the rotor-wing geometry are considered. These include rotor-wing chordwise separation, rotor-wing vertical offset and rotor-rotor spanwise separation. Large eddy simulation (LES) and delayed detached eddy simulation (DDES) approaches with and without the transition model are used to analyze the baseline configuration. DDES with the transition model is found to compare well with LES and is selected for the parametric study to balance the computational cost. Compared to isolated wing and rotor cases, baseline rotor-wing case shows 5.46% lower power loading, 14.42% higher lift and 4.45% higher L/D ratio. From the parametric study, varying the rotor-wing chordwise spacing did not significantly influence rotor power loading but placing rotor further from the wing improved L/D ratio by 7.64% compared to baseline due to reduction in sectional drag. The rotor-wing vertical offset cases show that placing the rotor below the wing significantly reduces the L/D ratio while placing it above yields similar L/D ratio to baseline but lowers the power loading by 6.69%. Finally, the spanwise rotor-rotor separation cases show that higher separation yields a 5.66% improvement to L/D ratio with no effect on the rotor power loading, again due to reduction in sectional drag.

Atmospheric turbulence is applied to a 1200 lb quadcopter to evaluate the aircraft’s rigid body response together with the rotor speed and motor current responses. Turbulence is generated using TurbSim to produce a full-field flow which is convected downstream over the aircraft. Three levels of turbulence intensity (mild, moderate, and severe) are applied to the aircraft, with the increasing levels of turbulence corresponding to higher velocity fluctuation in the f low-field. An outer loop flight controller, tuned to meet Level 1 handling qualities, is used to reject the disturbances to the aircraft airspeed. Various levels of turbulence produce larger aircraft response, with the severe case producing the largest peak-to-peak values for rigid body, rotor speed, and motor current response (4.74◦, 114 RPM, and 160A, respectively). While the severe turbulence case is the most demanding on the motors, it is less than what has been previously seen for typical maneuvers. Therefore, motor size is limited by aircraft maneuver constraint, given the turbulence cases considered.