Fuel Jet Spread Modeling for Numerical of Aircraft Fuel Dumping Simulation

Abstract

An analytical jet spread model has been developed for determining the boundary of an axisymmetric jet ejecting into a two-fluid, coflowing stream. When the circumferential velocity of the jet is assumed to be small, the model can be coupled with the conventional computational fluid dynamics (CFD) method for simulation of the fuel dumping from an aircraft. Application of the model is demonstrated by considering the fuel dumping from a V-22 aircraft flying at Mach 0.345 and angles of attack from 7 and 16 deg. The model provides a first-order correction to the CFD simulated results with the jet dispersion boundaries to yield an integrated solution that represents a realistic aircraft fuel dumping environment. UMPING excessive fuel from an aircraft before landing may be necessary due to safety concerns. During fuel dumping, massive fuel can be successfully dumped without any contact be- tween the fuel jet and the aircraft surface. Fuel mist, which is caused by the thickening of the fuel jet boundary, may impinge onto the aircraft even though the main fuel stream does not touch the surface. The thickening of the jet boundary is commonly known as the jet dispersion, the jet spread, or the jet entrainment. It consists of par- ticles of the surrounding medium carried along with it and particles of the jet itself that have been slowed down. To avoid any fuel and/or fuel mist impingement onto any part of the aircraft surface during dumping, the geometry of the fuel jettison probe (FJP) must be properly designed and its location carefully de- termined. This is an important aerodynamic issue requiring resolu- tion by combining the results from wind-tunnel tests, computational fluid dynamics (CFD) simulations, and flight tests. The role of the CFD simulation is to provide an initial design study regarding the FJP geometry configuration, jet orientation, and its location on the aircraft, and also to gain insights into the complex flowfield about a complete aircraft with the FJP for fuel jettison. The problem is complicated not only by the complex geometry, but also the fuel jet characteristics due to jet dispersion. The jet dispersion, or the jet spread, is a subproblem that is embedded in the overall flowfield. It must be accounted for if the simulation truly represents a realistic aircraft fuel dumping environment. Unfortunately, the present capability of the conventional CFD method 1−4 lacks the ability to solve the whole problem in one formulation. The problem would have to be solved separately for the aircraft flowfield and for the embedded jet flow and then coupled together to yield an overall solution that depicts the physical problem. In the present paper, an analytical jet spread model for the fuel dispersion is proposed and described. The model can be coupled with the conventional, Navier-Stokes solution-based CFD method for simulation of the aircraft fuel dumping. The coupling is per- formed by a first-order correction in which the jet boundary due to the jet spread is calculated based on the simulated flowfield, but the flowfield is not updated by the presence of the jet volume. Al- though the work is specially aimed at the V-22 aircraft fuel dumping,