Computational analyses of gravitational (free fall) store separation in different flight conditions

Abstract

Numerical investigations of several different typical cases of a low-speed light weapon delivery from a representative aircraft wing are performed in ANSYS FLUENT using unstructured overset meshing with dynamic/moving meshes. These simplified three-dimensional, symmetric, 3DOF (degrees-of-freedom) simulations are conducted in order to check the expected missile trajectory after gravity (free fall) separation and assure both aircraft and weapon safety since carrier and missile interference can be rather complex and dangerous in certain (unfavorable) operating conditions. The transient behavior of incompressible flow is computed by Unsteady Reynolds Averaged Navier-Stokes (URANS) equations closed by a two-equation k−ω SST turbulence model, while the rigid body motion is governed by the aerodynamic (pressure and shear) and gravitational forces acting on the weapon. Carrier velocity and flying height, missile mass and inertial properties and CG location as well as its initial position on the aircraft are just some of the factors that can be varied to obtain different flight conditions and resulting flight paths. Here, special attention was given to two input parameters: angle-of-attack and CG longitudinal coordinate. For validation, the obtained numerical results, that include horizontal, vertical and angular displacements of the ejected object, are compared to available experimental data obtained in real flights, wind tunnels etc. as well as values estimated by a simpler numerical model. The satisfactory correspondence between different sets of results proves the applicability of the tested method, i.e. computational approach.