Research On Sloshing Properties Of Cryogenic Propellant In Liquid Hydrogen Tank For Aircraft

In order to improve the maneuverability and carrying capacity of aircraft such as high altitude long endurance unmanned aerial vehicle and cryogenic launch vehicles,propellant needs to be stored in one or two large cryogenic tanks,which account for a large proportion of the entire aircraft mass.In this case,the propellant sloshing in the cryogenic tank is seriously threatens the stability and structural safety of the aircraft system.During taxiing,take-off and flight of the aircraft,the propellant in the cryogenic storage tank will slosh violently under the external sloshing excitation,which will generate additional torque to the cryogenic storage tank and disturb the gas-liquid interface in the tank.Large area contact between supercooled liquid hydrogen and superheated hydrogen at the gas-liquid interface causes the gas phase condensation,and the pressure in the tank drops rapidly,which in turn leads to cavitation of the engine pump and a drop in thrust when the engine is running.In severe cases,the pump will be damaged and cut off,making the engine unable to work normally.Based on the above analysis,a CFD numerical model of liquid sloshing considering external heat leakage and interfacial phase was constructed for 160 L high vacuum multilayer insulation liquid hydrogen tank for high altitude long endurance aircraft.VOF method combined with Mesh motion setting was used to track the phase interface.The thermal-dynamic coupled characteristics of cryogenic propellant in liquid hydrogen tanks under different sloshing excitations and the sloshing dynamics characteristics under different initial liquid temperatures and different initial filling rates were numerically studied.The main research work and related conclusions are as follows:(1)The numerical model of liquid hydrogen sloshing in the aircraft tank under external sloshing excitation disturbance was constructed,and the validity and accuracy of the model were verified by liquid nitrogen sloshing experiments.The results show that the numerical simulation does not consider the liquid phase thermal stratification near the gas-liquid interface,and the ullage pressure value obtained is generally less than the experimental value.In the numerical calculation process of 40 s,except for the deviation between the simulated value and the experimental value in the first 9 s and the last 3 s(the maximum deviation is 18%),the errors of both are less than 5% in the rest of the time.(2)The thermal-dynamic coupled characteristics of cryogenic liquid hydrogen tank under different sloshing excitations were simulated.The results show that the greater the sloshing excitation,the greater the pressure drop in the ullage space.When the sloshing excitation is 0.11 m/s,0.22 m/s and 0.44 m/s,the ullage pressure drop is60.15 times,3042.25 times and 4579.15 times that of the non-sloshing excitation.The change trend of liquid pressure and ullage pressure is basically the same,but the liquid pressure fluctuates obviously during sloshing.The greater the sloshing excitation,the greater the heat exchange.The heat exchanges when the sloshing excitation is 0.11 m/s,0.22 m/s and 0.44 m/s are 60.31 times,3049.88 times and4590.62 times that of no sloshing excitation.The fluid temperature in the tank presents a distribution trend of high ullage temperature,low liquid phase temperature,high temperature around the tank,and low center temperature.The greater the sloshing excitation,the greater the sloshing force on the tank.When the sloshing excitation is 0.44 m/s,the sloshing force is 2.33 times and 1.46 times that of 0.11 m/s and 0.22 m/s.The sloshing moment and the sloshing force have a consistent fluctuation trend,and the sloshing force is the main factor that determines the sloshing moment.(3)The sloshing dynamic characteristics under different initial liquid temperature and different initial filling rate were studied.The results show that under the same sloshing excitation,the lower the initial liquid temperature and the greater the initial filling rate,the greater the trend of large non-linear reduction of gas and liquid pressure.The ullage pressure drop when the initial liquid temperature is 20.0 K and 21.0 K is 1.56 times and 1.35 times that when the initial liquid temperature is21.5 K.The ullage pressure drop at the initial filling rate of 70% is 4.38 times,2.22 times,1.37 times and 1.29 times that at the initial filling rates of 30%,40%,50% and60%,respectively.There are obvious fluctuations in the liquid phase pressure drop.The lower the initial liquid temperature and the greater the initial full rate,the more violent the sloshing dynamic fluctuations of the tank body will increase,and the faster the rate of reaching the maximum value.Subsequently,the fluctuation is reduced by the influence of liquid nonlinear sloshing and sloshing damping.The fluid reaction sloshing moment is directly related to the sloshing force,and the two have opposite fluctuating trends.