The Study Of Two-phase Flow Characteristics Of Floating Ring Seals In Cryogenic And Highspeed Conditions

Based on developments at home and abroad,it is not hard to figure out that researches on floating ring seals working with water or gas are already mature and comprehensive enough,despite the fact that the applications are basically limited to industry.Besides,researches based on aerospace field are mainly stuck in the stage of single phase and steady state presumptions.Consequently,it is highly necessary to study the two-phase flow in floating ring seals working with cryogenic fluid.Not only does the paper enrich and enlarge the contents of cryogenic floating ring seals in aerospace field,but also offers great reference for design.Thus,the paper holds deep value in engineering application.The simulations in the paper are based on a floating ring seal maturely applied in some liquid rocket engine(LRE)turbopump.The paper has actualized two-phase flow in the clearance of the seal,accomplished the transient calculations based on mesh deformation and ascertained the influencing factors on flow characteristics,sealing properties and dynamic coefficients under single phase and two-phase conditions using software ANSYS CFX.The paper finishes the steady simulations of cryogenic floating ring seal model with transitions under single phase and two-phase conditions and analyzes the features of results from three different angles:typical flow field,influencing factors on flow characteristics and on sealing properties.The study of flow characteristics shows that pressure at larger clearances is lower than that at smaller ones in single phase flow under eccentric state,but greater in the vicinity of seal exit when two-phase presumption is applied.The existence of inlet transitions results in a pressure drop near the seal entrance,followed by a quick rebound and the larger the flow clearance is,the bigger the drop becomes.Plus,the pressure loss near the seal entrance intensifies as rotor speed decreases or inlet pressure and seal radius clearance(flow clearance)increase,leading to a lower extent of cavitation near the seal exit,but a higher level near the seal entrance at large clearance,even a possibility of"cavitation transfixion".Furthermore,inlet temperature has little influence on single phase flow field,while the increase of which could not only attenuates the pressure loss near the seal entrance,but also promotes cavitation near the seal exit.The study of sealing properties also indicates that leakage rate and seal force both increase as rotor speed decreases or inlet pressure and eccentricity increase,whose values are also lower under two-phase presumption.Besides,leakage rate and seal force both increase as inlet temperature drops in two-phase flow,while being almost impervious to temperature change in single phase flow.Furthermore,all parameters have little impact on angle of displacement in single phase flow,suggesting the direction of seal force is always in close proximity to the position of minimum clearance with a great ability of centric recovery,while the fluctuation of which is relatively more acute and intends to intensify when a raise in temperature occurs under two-phase condition.Also,inlet flow loss coefficient slightly increases when there is a drop in eccentricity or a raise in rotor speed and inlet pressure in single-phase simulation,while being much more sensitive to changes in all parameters in two-phase flow suggesting a poor regularity.The paper acquires three coefficients(direct stiffness K_d,cross-coupled stiffness K_c and direct damping C_d)and a stability criterion(whirling rateγ)based on mesh deformation and Fast Fourier Transform(FFT)method and further discusses the influence of transitions,inlet pressure,rotor speed,seal radius clearance and seal length on sealing dynamic characteristics.Numerical results show below.On one hand,after taking transitions into account,K_d andK_c increase,C_d decreases in single phase flow,whileK_c andC_d increase,K_d varies little in cavitation flow.After raising the inlet pressure,all three coefficients increase in both single phase and cavitation flow.After raising the rotor speed,K_d andC_d decrease in both types of simulation with a raise inK_c in single phase flow and little variation in cavitation flow.After enlarging the radius clearance,K_d andC_d decrease,K_c increases in single phase flow,whileK_candC_d decrease,K_d varies little in cavitation flow.After lengthening the seal,K_d decreases and C_d increases in both types of simulation with a raise in K_c in cavitation flow and little variation in single phase flow.On the other hand,from the full prospective of whirling rateγ,the existence of transitions go against the sealing stability.Plus,the increase of inlet pressure and seal length and the decrease of rotor speed and seal radius clearance favour the sealing stability under single phase presumption,but weaken the stability in cavitation flow.