For ventilated cavitating flows in a closed water tunnel, the wall effect may exert an important influence on cavity shape and hydrodynamics, An isotropic mixture multiphase model was established to study the wall eff...For ventilated cavitating flows in a closed water tunnel, the wall effect may exert an important influence on cavity shape and hydrodynamics, An isotropic mixture multiphase model was established to study the wall effect based on the RANS equations, coupled with a natural cavitation model and the RNG k-ε turbulent model. The governing equations were discretized using the finite volume method and solved by the Gauss-Seidel linear equation solver on the basis of a segregation algorithm. The algebraic multigrid approach was carried through to accelerate the convergence of solution. The steady ventilated cavitating flows in water tunnels of different diameter were simulated for a conceptual underwater vehicle model which had a disk cavitator. It is found that the choked cavitation number derived is close to the approximate solution of natural cavitating flow for a 3-D disk. The critical ventilation rate falls with decreasing diameter of the water tunnel. However, the cavity size and drag coeflicient are rising with the decrease in tunnel diameter for the same ventilation rate, and the cavity size will be much different in water tunnels of different diameter even for the same ventilated cavitation number.展开更多
挤压油膜阻尼器(squeeze film damper,SFD)正常工作时避免不了会出现油膜空穴,为了研究SFD长时间运行时转子基频振动变化以及SFD油膜空穴效应对SFD内外环金属表面空化侵蚀情况,基于全尺寸航空发动机高压转子试验台开展了低供油压力(0.02...挤压油膜阻尼器(squeeze film damper,SFD)正常工作时避免不了会出现油膜空穴,为了研究SFD长时间运行时转子基频振动变化以及SFD油膜空穴效应对SFD内外环金属表面空化侵蚀情况,基于全尺寸航空发动机高压转子试验台开展了低供油压力(0.02~0.05 MPa)下SFD空穴效应试验研究,考察SFD在临界转速处长时间运行时转子基频振动变化,以及长时间运行后油膜空穴对SFD内外表面形貌的影响,试验结果表明:长时间运行后SFD油膜空穴会对SFD内环表面产生侵蚀作用,形成水滴形、椭圆形以及形状不规则的凹坑群,证明了在临界转速附近考核SFD空穴效应是SFD低供油压力下安全运行必要的试验内容.展开更多
The cavitation is ubiquitous in the water delivery system of high hydraulic head navigation locks.This paper studies the choked cavitation characteristics of the gap flows in the valve lintel of the navigation locks a...The cavitation is ubiquitous in the water delivery system of high hydraulic head navigation locks.This paper studies the choked cavitation characteristics of the gap flows in the valve lintel of the navigation locks and analyzes the critical self-aeration conditions.The cavitation gap flow in the valve lintel is experimentally and numerically investigated.A visualized 1:1 full-scale slicing model is designed,with a high-speed camera,the details of the cavitation flow is captured without the reduced scale effect.Moreover,the numerical simulations are conducted to reveal the flow structures in the gap.The experimental results show that the flow pattern of the gap flow in the valve lintel could be separated into four models,namely,the incipient(1)the developing,(2),the intensive,(3),and the choked(4)cavitation models.The numerical simulation results are consistent with the experimental data.The choked cavitation conditions are crucial to the gap flow in the valve lintel.When the choked cavitation occurs,the gap is entirely occupied by two cavitation cloud sheets.The gap pressure then decreases sharply to the saturated water vapor pressure at the operating temperature.This water vapor pressure is the ultimate negative pressure in the gap that remains unchanged with the continuous decrease of the downstream pressure.The volumetric flow rate reaches a peak,then remains constant,with the further decrease of the pressure ratio or the cavitation number.At the choking point,the volumetric flow rate is proportional to the root mean square of the difference between the upstream pressure(absolute pressure)and the saturated pressure of the water.Moreover,the pressure ratio is linearly correlated with the downstream cavitation number with a slope of(1+ζc).展开更多
The theory of failure of rolling contact bearings is based on fluctuating high level loading and material fatigue. This theory is unimodal, considering only the solid components of the bearing, and ignoring the liquid...The theory of failure of rolling contact bearings is based on fluctuating high level loading and material fatigue. This theory is unimodal, considering only the solid components of the bearing, and ignoring the liquid phase, which is the lubricant. Bearing life is rather dispersed, reaching a ratio of 20 between the extreme values. Since this theory was established, several exceptional phenomena were detected that could not be explained by it, such as: 1) Pitting damage beyond the contact path;2) Detrimental effect of a minute quantity of water in the lubricant on bearing life. 25 ppm of water in the lubricant brought about shorter bearing life by over than 30%. The bimodal failure theory considers both solid and liquid bearing components. The damaging process of the lubricant evolves from its cavitation. During this process vapor filled cavities are formed in low pressure zones. When these cavities reach high pressure zones they implode exothermally. These implosions cause local high pressure pulses reaching 30,000 at accompanied by a temperature rise of about 2000 degrees K [<a href="#ref1">1</a>]. This paper includes cavitation erosion test results on stainless steel samples by vibratory and water tunnel test rigs. Various methods of lubricant dehydration are presented and evaluated. The main conclusion from this analysis is the use of water-free lubricants, for long life of RC bearings and more uniform service life thereof.展开更多
The orifice plate energy dissipater is an economic and highly efficient dissipater. However, there is a risk of cavitaion around the orifice plate flow： In order to provide references for engineering practice, we exa...The orifice plate energy dissipater is an economic and highly efficient dissipater. However, there is a risk of cavitaion around the orifice plate flow： In order to provide references for engineering practice, we examined the cavitation mechanism around the orifice plate and its influencing factors by utilizing mathematical analysis methods to analyze the flow conditions around the orifice plate in view of gas bubble dynamics. Through the research presented in this paper, the following can be observed： The critical radius and the critical pressure of the gas nucleus in orifice plate flow increase with its initial state parameter r0 ; the development speed of bubbles stabilizes at a certain value after experiencing a peak value and a small valley value; and the orifice plate cavitation is closely related to the distribution of the gas nucleus in flow. For computing the orifice plate cavitation number, we ought to take into account the effects of pressure fluctuation. The development time of the gas nucleus from the initial radius to the critical radius is about 107-10-5 s; therefore, the gas nucleus has sufficient time to develop into bubbles in the negative half-cycle of flow fluctuation. The orifice critical cavitation number is closely related to the orifice plate size, and especially closely related with the ratio of the orifice plate radius to the tunnel radius. The approximate formula for the critical cavitation number of the square orifice plate that only considers the main influencing factor was obtained by model experiments.展开更多
基金the National Natural Science Foundation of China ( Grant No. 10372061).
文摘For ventilated cavitating flows in a closed water tunnel, the wall effect may exert an important influence on cavity shape and hydrodynamics, An isotropic mixture multiphase model was established to study the wall effect based on the RANS equations, coupled with a natural cavitation model and the RNG k-ε turbulent model. The governing equations were discretized using the finite volume method and solved by the Gauss-Seidel linear equation solver on the basis of a segregation algorithm. The algebraic multigrid approach was carried through to accelerate the convergence of solution. The steady ventilated cavitating flows in water tunnels of different diameter were simulated for a conceptual underwater vehicle model which had a disk cavitator. It is found that the choked cavitation number derived is close to the approximate solution of natural cavitating flow for a 3-D disk. The critical ventilation rate falls with decreasing diameter of the water tunnel. However, the cavity size and drag coeflicient are rising with the decrease in tunnel diameter for the same ventilation rate, and the cavity size will be much different in water tunnels of different diameter even for the same ventilated cavitation number.
文摘挤压油膜阻尼器(squeeze film damper,SFD)正常工作时避免不了会出现油膜空穴,为了研究SFD长时间运行时转子基频振动变化以及SFD油膜空穴效应对SFD内外环金属表面空化侵蚀情况,基于全尺寸航空发动机高压转子试验台开展了低供油压力(0.02~0.05 MPa)下SFD空穴效应试验研究,考察SFD在临界转速处长时间运行时转子基频振动变化,以及长时间运行后油膜空穴对SFD内外表面形貌的影响,试验结果表明:长时间运行后SFD油膜空穴会对SFD内环表面产生侵蚀作用,形成水滴形、椭圆形以及形状不规则的凹坑群,证明了在临界转速附近考核SFD空穴效应是SFD低供油压力下安全运行必要的试验内容.
基金supported by the National Key Research and Development Program of China(Grant No.2016YFC0402007)the National Nature Science Foundation of China(Grant No.51779151).
文摘The cavitation is ubiquitous in the water delivery system of high hydraulic head navigation locks.This paper studies the choked cavitation characteristics of the gap flows in the valve lintel of the navigation locks and analyzes the critical self-aeration conditions.The cavitation gap flow in the valve lintel is experimentally and numerically investigated.A visualized 1:1 full-scale slicing model is designed,with a high-speed camera,the details of the cavitation flow is captured without the reduced scale effect.Moreover,the numerical simulations are conducted to reveal the flow structures in the gap.The experimental results show that the flow pattern of the gap flow in the valve lintel could be separated into four models,namely,the incipient(1)the developing,(2),the intensive,(3),and the choked(4)cavitation models.The numerical simulation results are consistent with the experimental data.The choked cavitation conditions are crucial to the gap flow in the valve lintel.When the choked cavitation occurs,the gap is entirely occupied by two cavitation cloud sheets.The gap pressure then decreases sharply to the saturated water vapor pressure at the operating temperature.This water vapor pressure is the ultimate negative pressure in the gap that remains unchanged with the continuous decrease of the downstream pressure.The volumetric flow rate reaches a peak,then remains constant,with the further decrease of the pressure ratio or the cavitation number.At the choking point,the volumetric flow rate is proportional to the root mean square of the difference between the upstream pressure(absolute pressure)and the saturated pressure of the water.Moreover,the pressure ratio is linearly correlated with the downstream cavitation number with a slope of(1+ζc).
文摘The theory of failure of rolling contact bearings is based on fluctuating high level loading and material fatigue. This theory is unimodal, considering only the solid components of the bearing, and ignoring the liquid phase, which is the lubricant. Bearing life is rather dispersed, reaching a ratio of 20 between the extreme values. Since this theory was established, several exceptional phenomena were detected that could not be explained by it, such as: 1) Pitting damage beyond the contact path;2) Detrimental effect of a minute quantity of water in the lubricant on bearing life. 25 ppm of water in the lubricant brought about shorter bearing life by over than 30%. The bimodal failure theory considers both solid and liquid bearing components. The damaging process of the lubricant evolves from its cavitation. During this process vapor filled cavities are formed in low pressure zones. When these cavities reach high pressure zones they implode exothermally. These implosions cause local high pressure pulses reaching 30,000 at accompanied by a temperature rise of about 2000 degrees K [<a href="#ref1">1</a>]. This paper includes cavitation erosion test results on stainless steel samples by vibratory and water tunnel test rigs. Various methods of lubricant dehydration are presented and evaluated. The main conclusion from this analysis is the use of water-free lubricants, for long life of RC bearings and more uniform service life thereof.
基金supported by the National Natural Science Foundation of China (Grant No.50879021)
文摘The orifice plate energy dissipater is an economic and highly efficient dissipater. However, there is a risk of cavitaion around the orifice plate flow： In order to provide references for engineering practice, we examined the cavitation mechanism around the orifice plate and its influencing factors by utilizing mathematical analysis methods to analyze the flow conditions around the orifice plate in view of gas bubble dynamics. Through the research presented in this paper, the following can be observed： The critical radius and the critical pressure of the gas nucleus in orifice plate flow increase with its initial state parameter r0 ; the development speed of bubbles stabilizes at a certain value after experiencing a peak value and a small valley value; and the orifice plate cavitation is closely related to the distribution of the gas nucleus in flow. For computing the orifice plate cavitation number, we ought to take into account the effects of pressure fluctuation. The development time of the gas nucleus from the initial radius to the critical radius is about 107-10-5 s; therefore, the gas nucleus has sufficient time to develop into bubbles in the negative half-cycle of flow fluctuation. The orifice critical cavitation number is closely related to the orifice plate size, and especially closely related with the ratio of the orifice plate radius to the tunnel radius. The approximate formula for the critical cavitation number of the square orifice plate that only considers the main influencing factor was obtained by model experiments.
