Computations and Experiments were performed to get an understanding of the flow field around a rectangular supersonic air intake with pointed cowl [90°] at different back pressures for Mach 2.2. The effect of Cow...Computations and Experiments were performed to get an understanding of the flow field around a rectangular supersonic air intake with pointed cowl [90°] at different back pressures for Mach 2.2. The effect of Cowl shape on the ramp surface pressure distribution is discussed and compared with existing V-Notch [90°] intake model at free exit condition. It was found that using pointed cowl [90°] intake model, a better pressure recovery was achieved compared to the V-Notch [90°] intake model at Mach 2.2. Both Pointed and V-Notch intake models showed good starting characteristics. For change in back pressure, the occurence of normal shock, flow separation zone and flow reversal were observed. All experiments are performed only for the Pointed cowl [90°] intake model. All the 3-D computations were performed by using software available at B.I.T, Mesra, Ranchi.展开更多
In this study, the cold ocean/warm land （COWL） pattern was identified from the leading empirical orthogonal function （EOF） of the monthly 1000-hPa geopotential height field poleward of 20°N. Traditionally, th...In this study, the cold ocean/warm land （COWL） pattern was identified from the leading empirical orthogonal function （EOF） of the monthly 1000-hPa geopotential height field poleward of 20°N. Traditionally, the leading EOF has been recognized as the Arctic Oscillation （AO）, or Northern Annular Mode （NAM）, which causes annular surface air temperature （SAT） anomalies over high-latitude regions of the Northern Hemisphere. A new finding of the present study is that the total AO events defined by the large AO index actually include a distinct type of events that are characterized by a less-annular spatial structure, i.e., the COWL pattern, which shows an NAO-like distribution in the Atlantic sector and a center of action over the North Pacific with the same sign as that over the Arctic. In addition, unlike canonical AO events, the COWL events also show a less-annular pattern in the stratosphere. Statistically, at least one-third of the AO events can be categorized as the COWL events. The SAT anomalies associated with the COWL pattern have an annular distribution over the high-latitude region of the two continents in the Northern Hemisphere. In contrast, if the COWL events are removed from the total AO events, the remainder shows less annular SAT anomalies. Thus, the typical annular SAT anomalies associated with AO events are in large part due to the contribution of the COWL pattern. Furthermore, the monthly variability and the interannual variability of all the AO events are equally important.展开更多
Under hypersonic flight conditions,the sharp cowl-lip leading edges have to be blunted because of the severe aerodynamic heating.This paper proposes four cowl-lip blunting methods and studies the corresponding flow ch...Under hypersonic flight conditions,the sharp cowl-lip leading edges have to be blunted because of the severe aerodynamic heating.This paper proposes four cowl-lip blunting methods and studies the corresponding flow characteristics and performances of the generic hypersonic inlets by numerical simulation under the design conditions of a flight Mach number of 6 and an altitude of 26 km.The results show that the local shock interference patterns in the vicinity of the blunted cowl-lips have a substantial influence on the flow characteristics of the hypersonic inlets even though the blunting radius is very small,which contribute to a pronounced degradation of the inlet performance.The Equal Length blunting Manner(ELM)is the most optimal in that a nearly even reflection of the ramp shock produces an approximately straight and weak cowl reflection shock.The minimal total pressure loss,the lowest cowl drag,maximum mass-capture and the minimal aeroheating are achieved for the hypersonic inlet.For the other blunting manners,the ramp shock cannot reflect evenly and produces more curved cowl reflection shock.The Type V shock interference pattern occurs for the Cross Section Cutting blunting Manner(CSCM)and the strongest cowl reflection shock gives rise to the largest flow loss and drag.The cowl-lip blunted by the other two blunting manners is subjected to the shock interference pattern that transits with an increase in the blunting radius.Accordingly,the peak heat flux does not fall monotonously with the blunting radius increasing.Moreover,the cowl-lip surface suffers from severe aerothermal load when the shear layer or the supersonic jet impinges on the wall.展开更多
文摘Computations and Experiments were performed to get an understanding of the flow field around a rectangular supersonic air intake with pointed cowl [90°] at different back pressures for Mach 2.2. The effect of Cowl shape on the ramp surface pressure distribution is discussed and compared with existing V-Notch [90°] intake model at free exit condition. It was found that using pointed cowl [90°] intake model, a better pressure recovery was achieved compared to the V-Notch [90°] intake model at Mach 2.2. Both Pointed and V-Notch intake models showed good starting characteristics. For change in back pressure, the occurence of normal shock, flow separation zone and flow reversal were observed. All experiments are performed only for the Pointed cowl [90°] intake model. All the 3-D computations were performed by using software available at B.I.T, Mesra, Ranchi.
基金Supported by the National Basic Research and Development(973)Program of China(2009CB421406)National Science and Technology Support Program of China(2009BAC51B02)National Natural Science Foundation of China(40975033)
文摘In this study, the cold ocean/warm land （COWL） pattern was identified from the leading empirical orthogonal function （EOF） of the monthly 1000-hPa geopotential height field poleward of 20°N. Traditionally, the leading EOF has been recognized as the Arctic Oscillation （AO）, or Northern Annular Mode （NAM）, which causes annular surface air temperature （SAT） anomalies over high-latitude regions of the Northern Hemisphere. A new finding of the present study is that the total AO events defined by the large AO index actually include a distinct type of events that are characterized by a less-annular spatial structure, i.e., the COWL pattern, which shows an NAO-like distribution in the Atlantic sector and a center of action over the North Pacific with the same sign as that over the Arctic. In addition, unlike canonical AO events, the COWL events also show a less-annular pattern in the stratosphere. Statistically, at least one-third of the AO events can be categorized as the COWL events. The SAT anomalies associated with the COWL pattern have an annular distribution over the high-latitude region of the two continents in the Northern Hemisphere. In contrast, if the COWL events are removed from the total AO events, the remainder shows less annular SAT anomalies. Thus, the typical annular SAT anomalies associated with AO events are in large part due to the contribution of the COWL pattern. Furthermore, the monthly variability and the interannual variability of all the AO events are equally important.
基金supported by the National Natural Science Foundation of China(Grant Nos.90716014 and 91216115)
文摘Under hypersonic flight conditions,the sharp cowl-lip leading edges have to be blunted because of the severe aerodynamic heating.This paper proposes four cowl-lip blunting methods and studies the corresponding flow characteristics and performances of the generic hypersonic inlets by numerical simulation under the design conditions of a flight Mach number of 6 and an altitude of 26 km.The results show that the local shock interference patterns in the vicinity of the blunted cowl-lips have a substantial influence on the flow characteristics of the hypersonic inlets even though the blunting radius is very small,which contribute to a pronounced degradation of the inlet performance.The Equal Length blunting Manner(ELM)is the most optimal in that a nearly even reflection of the ramp shock produces an approximately straight and weak cowl reflection shock.The minimal total pressure loss,the lowest cowl drag,maximum mass-capture and the minimal aeroheating are achieved for the hypersonic inlet.For the other blunting manners,the ramp shock cannot reflect evenly and produces more curved cowl reflection shock.The Type V shock interference pattern occurs for the Cross Section Cutting blunting Manner(CSCM)and the strongest cowl reflection shock gives rise to the largest flow loss and drag.The cowl-lip blunted by the other two blunting manners is subjected to the shock interference pattern that transits with an increase in the blunting radius.Accordingly,the peak heat flux does not fall monotonously with the blunting radius increasing.Moreover,the cowl-lip surface suffers from severe aerothermal load when the shear layer or the supersonic jet impinges on the wall.
