Numerical Simulation And Analysis Of Nitrogen-Enriched Air Flow In A Civil Airplane Center Wing Tank

The fire explosion suppression ability of aircraft fuel tank is directly related to the aircraft survivability and passenger’s lives and property security. The ullage washing skill prevents the fuel tank from explosion by inerting with the nitrogen-enriched air(NEA). It can control the oxygen concentration on the ullage of aircraft fuel tank at safe level.In this paper, a civil transport aircraft center wing tank(CWT) was set as the research object. In order to research the inerting flow of the aircraft fuel tank, a numerical simulation model of fuel washing was established by CFD. Based on the numerical model, how the parameters affect the inerting flow in the CWT under different ground and flight conditions were studied. The parameters include the distribution methods、flux rate and oxygen concentration of the NEA, the fuel load and vent pressure of the CWT, and the fuel burn rate of the aircraft.Firstly, the CFD method was used to simulate the inerting flow in the CWT under different ground conditions. The influence of distribution methods、flux rate and oxygen concentration of the NEA,and the fuel load of the CWT on the inerting flow were studied. The results show:The corresponding NEA consumption of fuel washing is related to distribution methods、oxygen concentration and fuel load, and has no relation to the flux rate of the NEA. The VTE is related to the distribution method and oxygen concentration, and has no relation to the flux rate and fuel load.Secondly, the simulation of inerting flow in the unloaded CWT were carried out under shortest flight profile, and the influence of vent pressure on the inerting flow during nosedive stage were studied.The results show:The average oxygen concentration of the bay where the vent is designed significantly increases with the vent pressure increasing,and the rebound of the average oxygen concentration can be reduced or eliminated by changing the distribution method or increasing flux rate of the NEA.Finally, in order to research the rules of the change of oil level on the inerting flow, the simulation of inerting flow in the loaded CWT were carried out under extended flight profile. The results show:The average oxygen concentration in the CWT increases with the fuel burning during cruise and nosedive stage, when inerting the CWT with the maximum diving boosted flow can prevent the oxygen concentration increasing, and the space distribution of oxygen concentration become uniformity with the inerting finish.