Estimation of Captive Flight Loads Using Grid-Free Euler Solver

Abstract

NTEGRATION of a new weapon to a highly agile aircraft is an exigent task, as the weapon and its supporting systems should structurally endure during stern maneuvers of the aircraft. Fighter aircraft has maneuvering capability of about 9 g and, therefore, the support systems of flight vehicles (launcher, launcher rail, launch shoe, and adapter) on the fighter aircraft should be designed to withstand the loads experienced by the vehicle at critical maneuvering conditions. Guidelines for weapon-aircraft integration are provided through military specification MIL-STD-8591 [1]. The specification provides weapon design load requirements for unusual flightconditionsthatsometimeariseonspecificaircraft.Itisbasedon using actual or predicted aircraft flight performance data to examine the full flight envelope and generate consistent set of inertial and aerodynamic loads [2]. In the present work, aerodynamic characterization of the flight vehicle mounted on a fighter aircraft has been carried out using an in-house developed 3-D grid-free Euler solver [3]. Further, the numerical simulations are carried out to estimate the captive loads acting on the flight vehicle integrated with fighteraircraftatspecified flowconditionsandthemaximumloading conditions are identified. The load distribution is extracted at that condition to verify the structural integrity of the flight vehicle and supporting systems. Grid generation around a complex fighter aircraft is the most time consuming task in the numerical simulation and presence of flight vehicle poses a formidable challenge. A grid-free q-LSKUM [3] (entropyvariables-basedleast-squareskineticupwindmethod)Euler solver has been used for the computational fluid dynamics (CFD) analysis. The grid-free solver requires a cloud of points around the configuration and a set of neighbors around each point. The cloud of points was obtained by overlapping grids around fighter aircraft and flightvehicles.CADmodelsof flightvehicleand fighteraircraftwere imported, repaired, and cleaned up to obtain watertight solid models suitableforgridgeneration.Simpleunstructuredgridsaround fighter aircraft and flight vehicles are generated independently and then the grids are overlapped to get the distribution of points around the full configuration. An efficient preprocessor [4] has been developed and applied to generate the connectivity. A parallel version of the 3-D grid-free Euler solver q-LSKUM has been used to obtain the aerodynamic characteristics of the aerospace vehicle configuration. Inviscidsteady flowsimulationfor fighteraircrafthasbeencarried out using q-LSKUM code. The simulations at various Mach numbers, angles of attack, and sideslip angles have been carried out to obtain aerodynamic forces and moments acting on the integrated fighter aircraft with flight vehicles. The captive loads on all the four flight vehicles are computed at specified critical flow conditions.