本文選題：移動接觸線　切入點：復雜幾何固體壁面　出處：《中國科學技術大學》2016年博士論文　論文類型：學位論文

【摘要】：帶有移動接觸線的復雜多相界面流動現象廣泛存在于自然、日常生活和工業(yè)應用中。這類流動現象及其機理的研究具有重要的科學意義和廣泛的應用前景。然而,由于涉及移動接觸線、復雜幾何形狀固體壁面和流固耦合等因素,難以進行直接數值模擬,亟待數值模擬方法方面的研究。為此,本文發(fā)展了基于笛卡爾均勻網格的系列數值模擬方法,并針對具有復雜幾何固壁及流固耦合的移動接觸線問題進行了若干研究。主要工作及研究成果如下：(1)發(fā)展了蝕刻多塊多相方法用來處理帶有尖角的固體壁面上的移動接觸線問題。該方法結合了擴散界面模型、幾何形式的移動接觸線模型及多塊劃分思想。擴散界面模型和幾何形式的移動接觸線模型能夠模擬帶有移動接觸線的大密度比的多相流動問題；多塊劃分思想可以實現塊與塊之間信息的自然交換并能有效地施加并行方法。通過方柱繞流和小孔滴水問題驗證了該方法的準確性。我們采用蝕刻多塊多相方法對小孔滴水問題進行了研究,發(fā)現當接觸線釘扎在尖角時,隨著的We數增大會依次出現四種周期性滴落模態(tài)：帶有衛(wèi)星液滴的滴落模態(tài)、單周期滴落模態(tài)、雙周期滴落模態(tài)和射流模態(tài)；當接觸線可以跨過尖角自由移動時,液滴不容易出現周期性滴落現象,只有在We數較小時會出現帶有多個衛(wèi)星液滴的周期滴落模態(tài)。(2)發(fā)展了擴散界面-浸入邊界數值方法用來模擬彎曲固體壁面上的動態(tài)浸潤問題。該方法基于笛卡爾均勻網格,結合了三相擴散界面模型、浸入邊界法和特征線法移動接觸線模型。三相擴散界面模型能夠防止液相和氣相因為擴散而滲透到固相中；浸入邊界法能夠在壁面上準確施加無滑移條件,從而使得氣液兩相無法因為對流而穿透固體壁面。這兩點的結合有效地保證了計算過程中各相的質量守恒性。特征線法移動接觸線模型不僅可以讓接觸線自由移動,還可以讓接觸線在切向隨空間變化的壁面上能保持設定的角度。為了驗證該方法的準確性,我們模擬了一系列算例：圓柱上液滴平衡、平板上液滴動態(tài)潤濕過程、液滴撞擊圓球和液滴穿透多孔介質。我們采用所發(fā)展的擴散界面-浸入邊界數值方法研究了圓球入水問題,發(fā)現隨著圓球壁面上接觸角的增大,入水后會依次出現三種模態(tài)：完全浸沒,氣泡附著以及產生空腔；同時發(fā)現We數也會影響入水后模態(tài),隨著We數的增大,越來越容易出現產生空腔的模態(tài)。(3)提出了適用于移動固體上的混合毛細力模型,基于擴散界面-浸入邊界數值方法,發(fā)展了界面-流固耦合數值方法用來模擬流體界面與固體之間的相互作用。混合毛細力模型可以準確計算流體界面對固體施加的毛細力：當界面處于平衡狀態(tài)時,采用銳利界面毛細力模型；當界面處于非平衡狀態(tài)時,采用擴散界面毛細力模型。我們模擬了一系列算例來驗證該方法的準確性：單相圓柱勻速下沉、重力影響下圓球上的軸對稱液滴的平衡狀態(tài)、界面上圓柱自由下沉、液滴與自由圓球正面碰撞和界面上漂浮圓柱自組裝問題。我們還采用界面-流固耦合數值方法,在與前人實驗定量對比良好的基礎上,研究了密度大于水的疏水圓球撞擊水面后的下沉模態(tài)和反彈模態(tài),尤其是圓球表面浸潤特性和水域寬度的影響,并且給出相應的尺度律。通過理論分析和數值模擬都得到了一致的結果：在足夠寬的水域中,下沉與反彈的臨界轉換條件受到圓球表面浸潤性(即接觸角θ)的影響：而在有限水域寬度下(小于2倍圓球直徑),We～sin(θ/2)4;臨界轉換條件還受到水域寬度L的影響：其中kWe～(C(θ,k)L+D(k)L-1)2,是唯一擬合參數。(4)將雙網格方法推廣至移動接觸線問題的數值模擬,進一步提高界面的網格分辨率,同時發(fā)展了高效求解壓力泊松方程的多重網格方法。結果顯示兩種加速方法都能大幅提升計算效率,均能提速達到80%以上。
[Abstract]:The complex flow phenomena with multi phase interface moving contact line widely exists in nature, daily life and industrial applications. This kind of flow phenomenon and its mechanism are of great scientific significance and wide application prospect. However, because of the moving contact line, the complex geometric shape of solid wall and fluid solid coupling and other factors. It is difficult to direct numerical simulation research to numerical simulation method. Therefore, this paper developed a series of numerical simulation method of Descartes based on uniform grids, and do some research for the moving contact line with complex geometric solid wall and fluid solid coupling problems. The main work and research results are as follows: (1) the development of the mobile contact a plurality of multi phase line etching method used to deal with the sharp corners of the solid wall on the surface of the problem. This method combines the diffusion interface model, moving contact line geometry model and multi Block partition. Diffusion moving contact line interface model and geometry model can simulate the moving contact line with large density ratio of multiphase flow; multi block partition can realize the information exchange between blocks of natural and can be effectively applied in parallel method. The accuracy of this method was verified by flow around a square cylinder and a small problem. We use water multiphase method of etching a plurality of holes in water was studied, and found that when the contact line pinning at a sharp point, with the increase in the number of We conference there are four kinds of periodic dripping mode: with dripping mode of satellite droplets, single cycle dripping mode, double cycle and dripping mode jet mode; when the contact line can move freely across the corner when the droplet is not prone to periodic drop phenomenon, only when the We number is small will appear with the cycle of dropping multiple satellite droplet model State. (2) the development of dynamic diffusion interface - immersed boundary numerical method is used to simulate the bending on solid wall infiltration problem. This method based on Descartes uniform grid, combined with the phase diffusion interface model, the immersed boundary method and characteristic line method of moving contact line model. The three-phase interface diffusion model can prevent liquid phase and gas phase because the diffusion and penetration into the solid phase; the immersed boundary method can accurately applied no slip conditions at the wall, so that the gas-liquid two-phase convection cannot because and penetrate the solid wall. The combination of the two can effectively ensure the quality of conservation of each phase in the process of calculation. The characteristic method can not only make the moving contact line model of contact line freedom of movement, also can make the contact line can maintain the set angle in the tangential changes of the wall. In order to verify the accuracy of the method, we simulate a series of examples: cylinder Droplet balance plate droplet dynamic wetting process, droplet impact ball and droplet penetration of porous media. The diffusion interface - we use the numerical method to study the immersed boundary ball into the water, found that with the increase of the contact angle on the wall surface of the ball, water will be followed by three modes: completely immersion, bubble attachment and cavity; also found that the We number will also affect after entry mode, with We number increasing, more and more prone to produce a cavity mode. (3) presents a hybrid capillary force model for mobile solid, diffuse interface - immersed boundary numerical method based on the development of the interface fluid solid coupling numerical method is used to simulate the interaction between fluid and solid interface. Mixed capillary force model can accurately calculate the capillary force of the solid fluid interface applied: when the interface is in balance, with a sharp circle The surface of capillary force model; when the interface is in a non-equilibrium state, the diffusion interface capillary force model. We simulate a series of examples to verify the accuracy of this method: single cylinder sinking speed, under the influence of gravity on the axisymmetric spherical droplet equilibrium interface cylindrical free sinking, self assembling problem solution drop ball head-on and with free interface. We also adopt the floating cylinder interface - flow solid coupling numerical method, based on comparing with previous experimental quantitative good, the hydrophobic ball density greater than water hit the water after sinking mode and rebound mode, especially on the surface of the sphere and the width of the water infiltration characteristics. The scaling laws, and gives corresponding. Through theoretical analysis and numerical simulation are consistent with results in the wide waters, critical transition condition and rebound of the sinking by the surface of the sphere 嫻告鼎鎬，

本文編號：1585012