Transient CFD analysis of fuel siphoning under a sudden inertial load

This paper presents the results of CFD investigations of siphoning between tanks of an aircraft fuel system under high-g conditions typical of an extreme pull-up maneuver. Negative gauge pressures in the siphon tank can occur, potentially breaking the siphon and decreasing the available fuel flow to the engine. A representative configuration of a system has been modeled, consisting of two fuel tanks plus a vent tank, fuel transfer lines, and gas lines for venting and supply of inert gas to the fuel tank ullage spaces. The fuel pressures and dynamics are simulated using a time-dependent Volume-of-Fluid modeling with normal force increasing rapidly from 1 to 9 g corresponding to an extended period of rapid pull-up during which the main supply tank becomes empty. Realistic values for engine fuel flow rate and fuel properties (JP-8) are used. This work is part of a broad effort to investigate fuel system performance issues that are difficult to test. Four simulations were performed in total, comparing 1 g flight and a 9 g pull-up both with and without a low-capacity pump assisting the siphon transfer. We find that the pump influences the siphon flow rate, the siphon break characteristics as the supply tank empties, and the magnitude of negative gauge pressures that occur in the siphon tank.