Near-body modeling of payload airdropped from aircraft and helicopter -Fluid / Structure Interaction Approach-

摘要

The trajectory and attitude of a payload during its exit of a cargo hold are critical aspects of an airdrop sequence. As much for aircraft than for helicopter, and as much for a lateral exit than for an axial exit, the first seconds of an airdrop are a risked phase for the airdropped equipment, for the release aircraft and for the operators. This sequence begins when the load starts its tipping and ends at a sufficient distant of the aircraft or when the static line (extraction) is stretched. During this instant the load is in free-fall that means it is only submitted to its own inertial movement. Its attitude and its near-body trajectory on the immediate outskirts of the aircraft will influence the rest of the airdrop as the opening of the parachute and also risks involved during the test or the current operation. Consequently, many studies or flight tests are set up at DGA Aeronautical Systems, a French Ministry of Defense's agency, to analyze this critical phase in order to draw the necessary recommendations in term of sizing, setting or process of airdrop. In the aim to complete and/or to reduce the number of tests necessary to study this airdrop phase, DGA Aeronautical Systems has initiated works of numerical simulations to get confident and robust models. Indeed, thanks to the last LS-Dyna® release which includes an advanced fluid solver, called Incompressible Computational Fluid Dynamic (ICFD), it becomes possible to establish efficient numerical models thanks to an enhanced approach of the Fluid-Structure Interaction (FSI). The aim of this paper is to give an accurate overview of the numerical models made with the ICFD solver to represent the first seconds of flight of an airdropped load by the different exits of an aircraft (door, ramp). Then an overview will be given on the models of the release of a load from the lateral side of an aircraft and a helicopter. Note that in this last case, a double flow inlet has been considered in the setting of the ICFD model to reproduce the movement of the helicopter and the rotor influence. The case of the extraction of a heavy load by the axial exit of an aircraft will be also detailed. The validity of each numerical model will be brought through the paper in relation with the physical theories put in stake during the free-fall movement and in correlation to the real data from flight tests. At the end, this paper will give the main information of development of each model and the demonstration of the level of reliability reached by the numerical simulation for this kind of study.