Numerical simulation of unsteady flows around a complete helicopter was conducted, and the effect of rotor downwash on the behavior of free-flight rockets air-launched from the helicopter and their plume was investigated. For this purpose, a three-dimensional inviscid flow solver based on unstructured meshes was developed, and an overset mesh technique was adopted to handle the relative motion of the main rotor, tail rotor, fuselage, and traveling rockets. The flow solver was coupled with six-degrees-of-freedom equations of motion to describe the trajectory of the free-flight rockets. To validate the flow solver for simulating the plume flow from the rocket nozzle, calculations were made for a jet flow impinging on flat plates. To demonstrate the accuracy of the flow solver for predicting rotor downwash, a rotor-fuselage aerodynamic interaction flow was calculated, and the results were compared with available experimental data. The trajectory simulation of an external store released from a fixed wing was also performed to validate the present flow solver coupled with the six-degrees-of-freedom equations of motion. Then the present method was applied to the simulation of free-flight rockets air-launched from a complete helicopter configuration. It was found that rotor downwash has nonnegligible effects on the trajectory of the air-launched rockets and their plume development, which may potentially affect the safety and the reliability of other equipments installed on the mother helicopter.Nomenclature A e = area of the rocket nozzle exit A 0 = collective pitch angle A 1 = longitudinal cyclic pitch angle B 1 = lateral cyclic pitch angle= mass flow rate at the rocket nozzle exit p e = pressure at the rocket nozzle exit p 1 = pressure of free stream Q = solution vector of the conservative variables R = rotor radius T = temperature U e = velocity at the rocket nozzle exit u, v, w = Cartesian velocity components x, y, z = Cartesian coordinate directions i = induced inflow normal to tip-path plane = advancing ratio i = induced inflow parallel to tip-path plane = density = solidity of rotor blade = azimuth angle

Numerical simulation of unsteady flows around helicopters was conducted to investigate the aerodynamic interaction of main rotor and other components such as fuselage and tail rotor. For this purpose, a three-dimensional inviscid flow solver has been developed based on unstructured meshes. An overset mesh technique was used to describe the relative motion between the main rotor, and other components. As the application of the present method, calculations were made for the rotorfuselage aerodynamic interaction of the ROBIN (ROtor Body INteraction) configuration and for a complete UH-60 helicopter configuration consisted of main rotor, fuselage, and tail rotor. Comparison of the computational results was made with measured time-averaged and instantaneous fuselage surface pressure distributions for the ROBIN configuration and thrust distribution and available experimental data for the UH-60 configuration. It is demonstrated that the present method is efficient and robust for the simulation of complete rotorcraft configurations.