Study On Flow Characteristics Of Cryogenic Cavitation Considering Thermal Effect Under Different Scales

The cavitation of propellant for liquid rocket engine occurs during transportation and combustion under different sizes,which makes the instability of flow field increase and causes strong mechanical vibration,thus reducing the reliability and stability of liquid rocket operation.Therefore,it has important engineering application value to master the flow characteristics and prediction methods of cryogenic cavitation at different scales.In this paper,based on the thermal effect of cryogenic fluid cavitating,the numerical study of cryogenic cavitation under various scales were investigated,respectively.The specific work carried out is as follows:On the platform of commercial software Fluent,considering the thermal effect on cryogenic cavitation,the source item were added to the energy equation through UDF(user defined function)to correct the cavitation mass transfer rate.The effects of different turbulence model,cavitation model and the related parameters on the calculation results are simulated and analyzed.Finally,the mixture model,RNG k-ε turbulence model and the modified Zwart cavitation model considering thermal effect were coupled to establish a set of numerical method for calculating the cryogenic cavitating considering thermal effect under different scales.Based on the numerical method developed in this paper,The two-dimensional axisymmetric steady numerical simulation of liquid nitrogen cavitating in a biconical throttling device at conventional scale was carried out.The effects of field parameters and geometric parameters on liquid nitrogen cavitating in the biconical throttling device were numerically investigated,It is found that the cavitation of liquid nitrogen in the biconical throttle device can be suppressed when decreasing the inlet velocity and increasing the outlet pressure.Among the four working fluids of liquid oxygen,liquid nitrogen,liquid hydrogen and liquid helium,the biconical throttling device has the strongest cavitation of liquid oxygen and the weakest of liquid hydrogen.When the front cone angle is increased,the cavitation at the front end of the throat is enhanced,while the cavitation at the rear end is weakened.With the increase of rear cone angle,the low pressure area,temperature drop and the cavity shape at the front end of the throat almost unchanged.While the parameters reach the maximum value when the rear cone angle is 60°.The changing of laryngeal length mainly affects the location of the two cavitation zones.The hot water cavitating in a three-dimensional venturi channel at small scale was numerically studied.It can be draw that the hot water cavitating in venturi can be promoted by increasing the inlet velocity,reducing the outlet pressure,increasing the fluid temperature and increasing the inflow angle.Among liquid hydrogen,liquid nitrogen,hot water and liquid oxygen,the liquid oxygen cavitating in venturi channel is the strongest,while liquid hydrogen is the weakest.When the outflow angle is less than 60°,the cavitation is weakened with the increase of the outflow angle.When the outflow angle reaches 90°,the cavity falls off from the wall of venturi channel throat and deviates a distance along the flow direction.The unsteady cavitation characteristics of liquid nitrogen in a three dimensional micro orifice were numerically studied.It can be concluded that with the decreasing of outlet pressure,the flow stability of liquid nitrogen in the micro orifice increases,the boundary of the negative pressure zone in the flow field is more straight,the periodic development of secondary flow appears at the back of the cavity,the length of the cavity increases,and the cryogenic region becomes longer.By comparing with the numerical results of cryogenic cavitation at conventional scale,small scale and micro scale,we can find that unlike the full development of cryogenic cavity vertical to flow direction at conventional scales,the development of cryogenic cavity is limited by the channel width in that direction at small scale,while this limitation is more obvious at micro scale.And there is a distinct negative pressure zone in the channel when the cryogenic cavitation occurs at micro scale.The maximum temperature drop decreases with the increasing of cavitation number at different scales.And at the small cavitation number,the maximum temperature drop at micro scale is the largest,while the maximum temperature drop at small scale is the smallest.