A recent formula for the lift force on a low speed wing of circular arc cross-section [<span style="font-family:Verdana;"><span style="font-family:Verdana;"><b><span style=&quo...A recent formula for the lift force on a low speed wing of circular arc cross-section [<span style="font-family:Verdana;"><span style="font-family:Verdana;"><b><span style="font-family:Verdana;"><a href="#ref1">1</a></span></b></span></span><span><span></span></span><span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">] is adapted to the upward pressure force on the crests of a surface gravity wave propagating in the wind. In both cases</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">,</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> the main feature is the utilization of the air’s compressibility. At and near a wave crest</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">,</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> it is predicted that the air density is increased over the ambient value and that the air density decreases inversely as the square of the upward distance from the radius of curvature of the crest. As a consequence</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">,</span></span></span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;"> the air pressure also decreases upward inversely as the square of the same distance. Therefore, an upward pressure force on each crest occurs which presumably will make the crests grow. Growth rates are largest for small </span><span style="font-family:Verdana;">wavelengths and large mean slopes of the wave surface. Contrary winds should produce </span><span style="font-family:Verdana;">wave growth (not damping) as well as no wind at all.</span></span></span></span>展开更多
Spillway tunnels are a key structure in large-scale water conservancies. The high-head water inlet makes the water surface-velocity extremely high, and the air is driven by the free surface of the water to move downst...Spillway tunnels are a key structure in large-scale water conservancies. The high-head water inlet makes the water surface-velocity extremely high, and the air is driven by the free surface of the water to move downstream. This paper studies the air velocity distribution above the water surface through the model tests, under the assumption that the airflow is a turbulent boundary layer with a rough interface, and the influence of the water depth and the water velocity on the air velocity distribution is analyzed. It is shown that the air velocity is in an exponential distribution. As the measured position moves upward, the air velocity gradually decreases, and the gradient decreases. When the water depth increases, the air velocity increases but with the same distribution form. With the increase of the water surface-velocity, the air velocity at the same measuring point increases, the variation range near the water surface is large, the air boundary layer height increases slightly, and the index coefficient of the air velocity distribution function decreases. Through numerical fitting, the calculation formula of the air boundary layer thickness at different water surface velocities is obtained, along with the numerical value of the index coefficient.展开更多
Recently,development of high technology has been required for the formation of uniform thin film in manufacturing processes of semiconductor as the precision instruments become more sophisticated.A method called spin ...Recently,development of high technology has been required for the formation of uniform thin film in manufacturing processes of semiconductor as the precision instruments become more sophisticated.A method called spin coating is often used for spreading photoresist on a wafer surface and drying photoresist film.In spin coating process,photoresist is uniformly spread on the wafer surface by centrifugal force caused by rotating wafer.However,it is a serious concern that streaky lines,which are caused by spiral vortices,appear on the wafer surface and prevent the formation of uniform film in the case of high rotating speed.On the other hand,in the case of low rotating speed,a small hump of the film is formed near the wafer edge.The main purpose of this study is to make clear the drying characteristics of the flowing liquid film on the rotating wafer.Temperature distribution of the flowing liquid film is captured by an infrared thermal video camera and radial gradient of the film temperature is introduced in order to evaluate the drying characteristic of the flowing film under steady state condition.Effects of the flow rate of the liquid film on the film temperature are investigated.The film temperature gradually decreases in the radial direction in all cases.At low rotating speed,the radial gradient of the film temperature is almost constant widely.On the other hand,at high rotating speed,the radial gradient of the film temperature takes a certain maximum value.It is found that the location of the gradient peak corresponds with the transition region of the air boundary layer,in which spiral vortices swirl,and shifts to the inner side of the disk with an increase of the liquid flow rate.展开更多
文摘A recent formula for the lift force on a low speed wing of circular arc cross-section [<span style="font-family:Verdana;"><span style="font-family:Verdana;"><b><span style="font-family:Verdana;"><a href="#ref1">1</a></span></b></span></span><span><span></span></span><span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">] is adapted to the upward pressure force on the crests of a surface gravity wave propagating in the wind. In both cases</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">,</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> the main feature is the utilization of the air’s compressibility. At and near a wave crest</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">,</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> it is predicted that the air density is increased over the ambient value and that the air density decreases inversely as the square of the upward distance from the radius of curvature of the crest. As a consequence</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">,</span></span></span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;"> the air pressure also decreases upward inversely as the square of the same distance. Therefore, an upward pressure force on each crest occurs which presumably will make the crests grow. Growth rates are largest for small </span><span style="font-family:Verdana;">wavelengths and large mean slopes of the wave surface. Contrary winds should produce </span><span style="font-family:Verdana;">wave growth (not damping) as well as no wind at all.</span></span></span></span>
基金supported by the Sichuan Science and Technology Program(Grant No.2020YJ0320).
文摘Spillway tunnels are a key structure in large-scale water conservancies. The high-head water inlet makes the water surface-velocity extremely high, and the air is driven by the free surface of the water to move downstream. This paper studies the air velocity distribution above the water surface through the model tests, under the assumption that the airflow is a turbulent boundary layer with a rough interface, and the influence of the water depth and the water velocity on the air velocity distribution is analyzed. It is shown that the air velocity is in an exponential distribution. As the measured position moves upward, the air velocity gradually decreases, and the gradient decreases. When the water depth increases, the air velocity increases but with the same distribution form. With the increase of the water surface-velocity, the air velocity at the same measuring point increases, the variation range near the water surface is large, the air boundary layer height increases slightly, and the index coefficient of the air velocity distribution function decreases. Through numerical fitting, the calculation formula of the air boundary layer thickness at different water surface velocities is obtained, along with the numerical value of the index coefficient.
文摘Recently,development of high technology has been required for the formation of uniform thin film in manufacturing processes of semiconductor as the precision instruments become more sophisticated.A method called spin coating is often used for spreading photoresist on a wafer surface and drying photoresist film.In spin coating process,photoresist is uniformly spread on the wafer surface by centrifugal force caused by rotating wafer.However,it is a serious concern that streaky lines,which are caused by spiral vortices,appear on the wafer surface and prevent the formation of uniform film in the case of high rotating speed.On the other hand,in the case of low rotating speed,a small hump of the film is formed near the wafer edge.The main purpose of this study is to make clear the drying characteristics of the flowing liquid film on the rotating wafer.Temperature distribution of the flowing liquid film is captured by an infrared thermal video camera and radial gradient of the film temperature is introduced in order to evaluate the drying characteristic of the flowing film under steady state condition.Effects of the flow rate of the liquid film on the film temperature are investigated.The film temperature gradually decreases in the radial direction in all cases.At low rotating speed,the radial gradient of the film temperature is almost constant widely.On the other hand,at high rotating speed,the radial gradient of the film temperature takes a certain maximum value.It is found that the location of the gradient peak corresponds with the transition region of the air boundary layer,in which spiral vortices swirl,and shifts to the inner side of the disk with an increase of the liquid flow rate.
