液滴撞擊平面液膜的流動特性和換熱性能數(shù)值模擬
發(fā)布時間：2019-04-26 12:21
【摘要】：在我們的生活和工業(yè)生產(chǎn)中隨時隨處都可以看到液滴撞擊液膜這種現(xiàn)象,研究這種現(xiàn)象的內(nèi)部機理可以為實際工程應(yīng)用帶來重要的理論依據(jù)。本論文采用一種新的算法CLSVOF,對單液滴撞擊水平液膜后產(chǎn)生水花現(xiàn)象、雙液滴撞擊水平液膜后流體的動力學特性及雙液滴撞擊熱壁面液膜后換熱性能及其影響因素進行了數(shù)值模擬和分析。主要結(jié)論如下： (1)單液滴撞擊水平液膜的數(shù)值模擬結(jié)果表明,撞擊后之所以產(chǎn)生飛濺是因為流體內(nèi)界面的不穩(wěn)定造成的,模擬結(jié)果還發(fā)現(xiàn)了氣泡夾帶現(xiàn)象；當液滴直徑較小時,沒有小氣泡產(chǎn)生,液滴直徑不斷增大產(chǎn)生的小氣泡數(shù)目逐漸增多,并且氣泡消失的時間越長。 (2)不同水平間距的兩液滴同時撞擊液膜的數(shù)值結(jié)果表明,雙液滴以不同速度撞擊液膜后會形成表面波動、皇冠狀水花、飛濺產(chǎn)生二次液滴,而且兩表面波相向運動時碰撞會產(chǎn)生中心射流,其在向上運動時會斷裂產(chǎn)生飛濺液滴；we數(shù)決定了水花邊緣是否產(chǎn)生飛濺,we較小時不產(chǎn)生二次液滴,當we數(shù)逐漸增大,水花的厚度變薄,且產(chǎn)生的二次液滴數(shù)目增多；we數(shù)的增大,水花高度越大,射流高度越大,而水花高度、射流高度開始回落的時間也隨we數(shù)的增大而提前；液滴間距的變化對剛開始水花高度幾乎沒有影響,一段時間后,液滴間距越大水花高度反而越小,在這之后,液滴水平間距越小水花高度越��；而對射流高度,在撞擊剛開始,液滴水平間距越大射流高度越��；一段時間后,液滴間距越大射流高度越大。 (3)雙液滴先后撞擊液膜的計算結(jié)果顯示,液滴間距不同,撞擊后流動形態(tài)出現(xiàn)很大差異,液膜厚度對液膜及水花形態(tài)影響不大,但對氣泡消失影響很大。液膜厚度越大,氣泡消失時間越長；液滴間距較小時,水花底部直徑隨時間逐漸增大,且液膜厚度越大,水花底部直徑越��；當液滴間距較大時,水花底部直徑先增大后減小在增大。 (4)不同垂直間距的兩液滴先后撞擊熱壁面液膜的數(shù)值結(jié)果表明,液滴撞擊速度越大,壁面平均熱流密度也就越大,液滴直徑、雙液滴間垂直間距和液膜厚度對平均熱流密度的影響較��；撞擊區(qū)域的熱流密度隨液膜厚度、垂直間距和液滴直徑的增大而減小,交界區(qū)的熱流密度隨液膜厚度和雙液滴垂直間距的增大而增大;液滴直徑不同,交界區(qū)的熱流密度先隨液滴直徑的增大而減小,后隨液滴直徑的增大而增大,交界區(qū)熱流密度的波動幅度隨液膜厚度、垂直間距和液滴直徑的增大而減小。
[Abstract]:The phenomenon of droplet impinging on liquid film can be seen everywhere in our daily life and industrial production. The study of the internal mechanism of this phenomenon can bring important theoretical basis for practical engineering application. In this paper, a new algorithm, CLSVOF, is used to produce water blossoms after a single droplet impinges on a horizontal liquid film. Numerical simulation and analysis are carried out on the dynamic characteristics of the fluid after the double droplets impact on the horizontal liquid film and the heat transfer performance of the liquid film after the double droplet impinges on the hot wall and the influencing factors are simulated and analyzed. The main conclusions are as follows: (1) the numerical simulation results of the impact of a single droplet on a horizontal liquid film show that the spatter is caused by the instability of the internal interface of the fluid, and the phenomenon of bubble entrainment is also found in the simulation results; When the droplet diameter is small, no small bubbles occur, and the number of small bubbles produced by increasing the droplet diameter increases gradually, and the longer the bubble disappears, the longer the bubble disappears. (2) the numerical results of the simultaneous impact of two droplets with different horizontal spacing on the liquid membrane show that after the two droplets hit the liquid membrane at different speeds, there will be surface fluctuations, crown-shaped water blossoms and spatter to produce secondary droplets. Moreover, when the two surface waves move in opposite direction, the central jet will be generated, and the spatter droplets will break when the two waves move upward. The we number determines whether spatter occurs at the edge of the flower, and the secondary droplets are not produced when we is small. When the number of we increases gradually, the thickness of the blossoms becomes thinner, and the number of secondary droplets increases. With the increase of we number, the higher the water blooming height, the greater the jet height, and the time when the water blooming height and jet height began to fall back also advance with the increase of we number. After a period of time, the larger the droplet spacing is, the smaller the flower height is, and after that, the smaller the horizontal distance between the droplets is, the smaller the flower height is. For the jet height, the larger the droplet spacing is, the smaller the jet height is at the beginning of the impact, and after a period of time, the larger the droplet spacing is, the greater the jet height is. (3) the calculation results of the double droplets impinging on the liquid membrane show that there is a great difference in the flow morphology after the impact with different droplet spacing. The thickness of the liquid film has little effect on the liquid film and water flower morphology, but it has a great effect on the disappearance of bubbles. The larger the film thickness is, the longer the bubble disappearance time is, and the smaller the droplet spacing is, the larger the thickness of liquid film is, the smaller the diameter of the bottom of water flower is, the larger the thickness of liquid film is, the more the diameter of the bottom of water flower increases with time. When the droplet spacing is large, the diameter of the bottom of the water floss increases first and then decreases. (4) the numerical results show that the larger the velocity of liquid drop impact, the greater the mean heat flux and the diameter of the liquid film on the hot wall with two droplets with different vertical spacing. The vertical spacing between two liquid droplets and the thickness of liquid film have little effect on the mean heat flux. The heat flux density in the impact region decreases with the increase of film thickness, vertical spacing and droplet diameter. The heat flux density in the boundary region increases with the increase of liquid film thickness and the vertical distance between two droplets. When the droplet diameter is different, the heat flux density in the boundary region decreases first with the increase of the droplet diameter, and then increases with the increase of the droplet diameter. The fluctuation amplitude of the heat flux density in the boundary region decreases with the increase of the film thickness, the vertical spacing and the droplet diameter.
【學位授予單位】：大連理工大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：TB611
本文編號：2466061
[Abstract]:The phenomenon of droplet impinging on liquid film can be seen everywhere in our daily life and industrial production. The study of the internal mechanism of this phenomenon can bring important theoretical basis for practical engineering application. In this paper, a new algorithm, CLSVOF, is used to produce water blossoms after a single droplet impinges on a horizontal liquid film. Numerical simulation and analysis are carried out on the dynamic characteristics of the fluid after the double droplets impact on the horizontal liquid film and the heat transfer performance of the liquid film after the double droplet impinges on the hot wall and the influencing factors are simulated and analyzed. The main conclusions are as follows: (1) the numerical simulation results of the impact of a single droplet on a horizontal liquid film show that the spatter is caused by the instability of the internal interface of the fluid, and the phenomenon of bubble entrainment is also found in the simulation results; When the droplet diameter is small, no small bubbles occur, and the number of small bubbles produced by increasing the droplet diameter increases gradually, and the longer the bubble disappears, the longer the bubble disappears. (2) the numerical results of the simultaneous impact of two droplets with different horizontal spacing on the liquid membrane show that after the two droplets hit the liquid membrane at different speeds, there will be surface fluctuations, crown-shaped water blossoms and spatter to produce secondary droplets. Moreover, when the two surface waves move in opposite direction, the central jet will be generated, and the spatter droplets will break when the two waves move upward. The we number determines whether spatter occurs at the edge of the flower, and the secondary droplets are not produced when we is small. When the number of we increases gradually, the thickness of the blossoms becomes thinner, and the number of secondary droplets increases. With the increase of we number, the higher the water blooming height, the greater the jet height, and the time when the water blooming height and jet height began to fall back also advance with the increase of we number. After a period of time, the larger the droplet spacing is, the smaller the flower height is, and after that, the smaller the horizontal distance between the droplets is, the smaller the flower height is. For the jet height, the larger the droplet spacing is, the smaller the jet height is at the beginning of the impact, and after a period of time, the larger the droplet spacing is, the greater the jet height is. (3) the calculation results of the double droplets impinging on the liquid membrane show that there is a great difference in the flow morphology after the impact with different droplet spacing. The thickness of the liquid film has little effect on the liquid film and water flower morphology, but it has a great effect on the disappearance of bubbles. The larger the film thickness is, the longer the bubble disappearance time is, and the smaller the droplet spacing is, the larger the thickness of liquid film is, the smaller the diameter of the bottom of water flower is, the larger the thickness of liquid film is, the more the diameter of the bottom of water flower increases with time. When the droplet spacing is large, the diameter of the bottom of the water floss increases first and then decreases. (4) the numerical results show that the larger the velocity of liquid drop impact, the greater the mean heat flux and the diameter of the liquid film on the hot wall with two droplets with different vertical spacing. The vertical spacing between two liquid droplets and the thickness of liquid film have little effect on the mean heat flux. The heat flux density in the impact region decreases with the increase of film thickness, vertical spacing and droplet diameter. The heat flux density in the boundary region increases with the increase of liquid film thickness and the vertical distance between two droplets. When the droplet diameter is different, the heat flux density in the boundary region decreases first with the increase of the droplet diameter, and then increases with the increase of the droplet diameter. The fluctuation amplitude of the heat flux density in the boundary region decreases with the increase of the film thickness, the vertical spacing and the droplet diameter.
【學位授予單位】：大連理工大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：TB611
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