The paper aims at summarizing the author’s recent phenomenological study of the orthe, developmeot and identification of vortical structures in internal aerodynamics.A connection between evolution of these structures...The paper aims at summarizing the author’s recent phenomenological study of the orthe, developmeot and identification of vortical structures in internal aerodynamics.A connection between evolution of these structures and flow separation in closed cUrVed channels is also discussed. It has been shown that in real fluids the individual vortex cores very soon lose their identity and merge into a new dissipative structure, the properties of which still have to be defined.展开更多
Due to their low-attitude and relatively low-speed fight profiles, helicopters are subjected to serious threats from radio, infrared （IR）, visual, and aural detection and tracking. Among these threats, infrared dete...Due to their low-attitude and relatively low-speed fight profiles, helicopters are subjected to serious threats from radio, infrared （IR）, visual, and aural detection and tracking. Among these threats, infrared detection and tracking are regarded as more crucial for the survivability of helicop- ters. In order to meet the requirements of infrared stealth, several different types of infrared sup- pressor （IRS） for helicopters have been developed. This paper reviews contemporary developments in this discipline, with particular emphasis on infrared signature suppression, advances in mixer-ejectors and prediction for helicopters. In addition, several remaining challenges, such as advanced IRS, emissivity optimization technique, helicopter infrared characterization, etc., are proposed, as an initial guide and stimulation for future research. In the future, the comprehen- sive infrared suppression in the 3-5 μm and 8-14 μm bands will doubtfully become the emphasis of helicopter stealth. Multidisciplinary optimization of a complete infrared suppression system deserves further investigation.展开更多
The flow structure in relatively narrow channels has a strong three-dimensional character with complex flow phenomena, including regions of localized separation, various vortical smictures, etc., all of which have to ...The flow structure in relatively narrow channels has a strong three-dimensional character with complex flow phenomena, including regions of localized separation, various vortical smictures, etc., all of which have to be considered when dealing with the problem of supersonic-subsonic transition. In this paper only the following three problems are considered: 1. the effect of channel width on transition from supersonic to subsonic velocities, 2. transition from supersonic to subsonic velocities in a system of shock waves - pseudoshock wave, 3. transition from subsonic to supersonic velocities in a critical cross section at the end of a duct with fully developed turbulent channel flow. Problems connected with vortical structures and flow separation were discussed by the same author elsewhere (see References).展开更多
The concentric bluff-body jet burner is widely used in industrial combustion systems.This kind of burner often generates a considerably complex recirculation zone behind the bluff body.As a result, the fuel often rema...The concentric bluff-body jet burner is widely used in industrial combustion systems.This kind of burner often generates a considerably complex recirculation zone behind the bluff body.As a result, the fuel often remains in the recirculation zone,achieving stability of flame.This study investigates, by means of experiments,the variations of the aerodynamics as the fluid is injected into a combustion chamber through a double concentric burner with a bluff-body.The observation and measurement of the aerodynamics in our experiment are conducted under a cold flow.The controlled parameters in our experiment are:variations in the blockage ratio of the center bluff body,the cone angle of the bluff body,and the velocity ratio(U_s/U_p)of the secondary jet and primary jet;the injection of helium bubbles into the primary and secondary jets to observe the recirculation zone behind the bluff body;using Tufts for observing the characteristics of corner recirculation zone in a combustion chamber,measuring the average velocity of each point within the aerodynamics by the 5-hole pitot tube;measuring the distribution of static pressure of the combustion chamber walls with a static pressure tap.展开更多
文摘The paper aims at summarizing the author’s recent phenomenological study of the orthe, developmeot and identification of vortical structures in internal aerodynamics.A connection between evolution of these structures and flow separation in closed cUrVed channels is also discussed. It has been shown that in real fluids the individual vortex cores very soon lose their identity and merge into a new dissipative structure, the properties of which still have to be defined.
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文摘Due to their low-attitude and relatively low-speed fight profiles, helicopters are subjected to serious threats from radio, infrared （IR）, visual, and aural detection and tracking. Among these threats, infrared detection and tracking are regarded as more crucial for the survivability of helicop- ters. In order to meet the requirements of infrared stealth, several different types of infrared sup- pressor （IRS） for helicopters have been developed. This paper reviews contemporary developments in this discipline, with particular emphasis on infrared signature suppression, advances in mixer-ejectors and prediction for helicopters. In addition, several remaining challenges, such as advanced IRS, emissivity optimization technique, helicopter infrared characterization, etc., are proposed, as an initial guide and stimulation for future research. In the future, the comprehen- sive infrared suppression in the 3-5 μm and 8-14 μm bands will doubtfully become the emphasis of helicopter stealth. Multidisciplinary optimization of a complete infrared suppression system deserves further investigation.
文摘The flow structure in relatively narrow channels has a strong three-dimensional character with complex flow phenomena, including regions of localized separation, various vortical smictures, etc., all of which have to be considered when dealing with the problem of supersonic-subsonic transition. In this paper only the following three problems are considered: 1. the effect of channel width on transition from supersonic to subsonic velocities, 2. transition from supersonic to subsonic velocities in a system of shock waves - pseudoshock wave, 3. transition from subsonic to supersonic velocities in a critical cross section at the end of a duct with fully developed turbulent channel flow. Problems connected with vortical structures and flow separation were discussed by the same author elsewhere (see References).
文摘The concentric bluff-body jet burner is widely used in industrial combustion systems.This kind of burner often generates a considerably complex recirculation zone behind the bluff body.As a result, the fuel often remains in the recirculation zone,achieving stability of flame.This study investigates, by means of experiments,the variations of the aerodynamics as the fluid is injected into a combustion chamber through a double concentric burner with a bluff-body.The observation and measurement of the aerodynamics in our experiment are conducted under a cold flow.The controlled parameters in our experiment are:variations in the blockage ratio of the center bluff body,the cone angle of the bluff body,and the velocity ratio(U_s/U_p)of the secondary jet and primary jet;the injection of helium bubbles into the primary and secondary jets to observe the recirculation zone behind the bluff body;using Tufts for observing the characteristics of corner recirculation zone in a combustion chamber,measuring the average velocity of each point within the aerodynamics by the 5-hole pitot tube;measuring the distribution of static pressure of the combustion chamber walls with a static pressure tap.
