Numerical Simulation of Free-Flight Rockets Air-Launched From a Helicopter

Abstract

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

Coupled Simulation of CFD and Flight Mechanics with a Two-Species-Gas-Model for the Hot Staging of a Multistage Rocket

“…10, " NP Z " states the nozzle-to-plate distance which is measured from the nozzle exit to the plate along the jet axis, and " DN " is the diameter of the nozzle exit. In the experiments of Lamount and Hunt 33 , the jet is produced by compressed air supporting to the chamber of a convergent-divergent type nozzle, therefore, the jet gas can be assumed to be a "cold air" (" 1.4 The experiments of Lamount and Hunt 33 have already been well numerically reproduced by several authors with CFD codes solving standard Navier-Stokes equations (single-species-gas) [34][35][36][37] . In principle, the jet should be produced by a solid motor for the validation work, but the authors have no available test data for the plume impingement of a solid motor at the moment.…”

Unguided Rocket Trajectory Analysis under Rotor Wake and External Wind

“…Moreover, it was difficult to grasp the detailed effect of the downwash because of using coefficients. Lee et al [2] simulated the initial motion of an unguided rocket launched in the rotor wake region, which was calculated by full CFD with unstructured overset mesh.…”

Dynamic Beam Solutions for Real-Time Simulation and Control Development of Flexible Rockets

“…Traditionally, rockets are considered as rigid bodies in their flight dynamic modeling [1][2][3][4][5]. The 6-dof dynamic equations describing the trajectory of the rigid body are usually established by applying the Newton's Second Law or the Lagrange equation [6].…”