Unsteady cavitation causes noise,damage,and performance decline in the marine engineering and fluid machinery systems.Therefore,finding a method to control the cavitation and its destructive effects is important for t...Unsteady cavitation causes noise,damage,and performance decline in the marine engineering and fluid machinery systems.Therefore,finding a method to control the cavitation and its destructive effects is important for the industrial applications.In this work,we proposed a passive method to control the unsteady behavior of transient cavitation at the medium Reynolds number.For this aim,we performed an experimental study using a high-speed camera to analyze the effects of hemispherical vortex generators(VGs)on the cavitation dynamics around a hydrofoil surface.In addition,the pressure pulsations induced by the collapse of the cavity structures in the wake region of the hydrofoil were captured with a pressure transducer mounted on the wall downstream of the hydrofoil.The results showed that the instability behaviors of the cavity structures on the hydrofoil were mitigated using the proposed cavitation passive control method.In addition,the pressure pulsations in the wake region of the hydrofoil were reduced significantly.It can be concluded that the suppression of cavitation instabilities can improve the operating life and reliability of the marine and hydraulic systems.展开更多
A previous multiple-AGCM study suggested that Indian Ocean Warming （IOW） tends to warm and weaken the southern polar vortex.Such an impact is robust because of a qualitative consistency among the five AGCMs used.How...A previous multiple-AGCM study suggested that Indian Ocean Warming （IOW） tends to warm and weaken the southern polar vortex.Such an impact is robust because of a qualitative consistency among the five AGCMs used.However,a significant difference exists in the modeled strengths,particularly in the stratosphere,with those in three of the AGCMs （CCM3,CAM3,and GFS） being four to five times as strong as those in the two other models （GFDL AM2,ECHAM5）.As to which case reflects reality is an important issue not only for quantifying the role of tropical ocean warming in the recent modest recovery of the ozone hole over the Antarctic,but also for projecting its future trend.This issue is addressed in the present study through comparing the models＇ climatological mean states and intrinsic variability,particularly those influencing tropospheric signals to propagate upward and reach the stratosphere.The results suggest that differences in intrinsic variability of model atmospheres provide implications for the difference.Based on a comparison with observations,it is speculated that the impact in the real world may be closer to the modest one simulated by GFDL AM2 and ECHAM5,rather than the strong one simulated by the three other models （CCM3,CAM3 and GFS）.In particular,IOW during the past 50 years may have dynamically induced a 1.0℃ warming in the polar lower stratosphere （～100 hPa）,which canceled a fraction of radiative cooling due to ozone depletion.展开更多
文摘Unsteady cavitation causes noise,damage,and performance decline in the marine engineering and fluid machinery systems.Therefore,finding a method to control the cavitation and its destructive effects is important for the industrial applications.In this work,we proposed a passive method to control the unsteady behavior of transient cavitation at the medium Reynolds number.For this aim,we performed an experimental study using a high-speed camera to analyze the effects of hemispherical vortex generators(VGs)on the cavitation dynamics around a hydrofoil surface.In addition,the pressure pulsations induced by the collapse of the cavity structures in the wake region of the hydrofoil were captured with a pressure transducer mounted on the wall downstream of the hydrofoil.The results showed that the instability behaviors of the cavity structures on the hydrofoil were mitigated using the proposed cavitation passive control method.In addition,the pressure pulsations in the wake region of the hydrofoil were reduced significantly.It can be concluded that the suppression of cavitation instabilities can improve the operating life and reliability of the marine and hydraulic systems.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA05090406)the National Key Basic Research Program of China (Grant Nos. 2012CB417403 and 2010CB428602)
文摘A previous multiple-AGCM study suggested that Indian Ocean Warming （IOW） tends to warm and weaken the southern polar vortex.Such an impact is robust because of a qualitative consistency among the five AGCMs used.However,a significant difference exists in the modeled strengths,particularly in the stratosphere,with those in three of the AGCMs （CCM3,CAM3,and GFS） being four to five times as strong as those in the two other models （GFDL AM2,ECHAM5）.As to which case reflects reality is an important issue not only for quantifying the role of tropical ocean warming in the recent modest recovery of the ozone hole over the Antarctic,but also for projecting its future trend.This issue is addressed in the present study through comparing the models＇ climatological mean states and intrinsic variability,particularly those influencing tropospheric signals to propagate upward and reach the stratosphere.The results suggest that differences in intrinsic variability of model atmospheres provide implications for the difference.Based on a comparison with observations,it is speculated that the impact in the real world may be closer to the modest one simulated by GFDL AM2 and ECHAM5,rather than the strong one simulated by the three other models （CCM3,CAM3 and GFS）.In particular,IOW during the past 50 years may have dynamically induced a 1.0℃ warming in the polar lower stratosphere （～100 hPa）,which canceled a fraction of radiative cooling due to ozone depletion.
