本文選題：多相空泡流　切入點(diǎn)：數(shù)值模擬方法　出處：《上海交通大學(xué)》2013年博士論文

【摘要】：近年來，水下航行體超空泡減阻概念的提出，使得空泡流的研究成為水動力學(xué)領(lǐng)域的重要課題。當(dāng)水下航行體被包裹在超空泡中運(yùn)動時，能夠大大減小其受到的阻力，從而極大地提高其在水中運(yùn)動的極限速度。從技術(shù)方面來說，通氣使水中航行體容易在較低的速度下實(shí)現(xiàn)超空泡狀態(tài)；在實(shí)際應(yīng)用中，通氣也可作為自然空泡的一種輔助方式用于控制空泡的形態(tài)特性和水動力特性。此時，航行體周圍充滿水、蒸汽和不可凝結(jié)氣體，介質(zhì)在物體表面發(fā)生相變、摻混，氣泡的發(fā)展和蒸汽空化之間互相影響，形成了非常復(fù)雜的多相空泡湍流流動。 本文的研究目的就是建立能夠準(zhǔn)確描述這一物理現(xiàn)象的數(shù)學(xué)模型與精確、高效的數(shù)值計算方法，開發(fā)具有自主知識產(chǎn)權(quán)的計算軟件，探索氣、汽、液多相空泡流的流動特性及其機(jī)理，為試驗(yàn)研究和工程應(yīng)用提供有益的理論依據(jù)和技術(shù)手段。 本文主要研究內(nèi)容和創(chuàng)新性成果如下： （1）從求解全流場RANS方程入手，構(gòu)建了基于均質(zhì)平衡流假設(shè)的氣、汽、液多相空泡流動的數(shù)學(xué)模型，引入四種輸運(yùn)方程類空化模型和六種渦粘性湍流模式，以量化汽-液相變與湍流影響。建立了基于有限體積法與SIMPLE算法的數(shù)值計算方法，引入了多個高階及高精度離散格式，，解決對流項(xiàng)所引起的穩(wěn)定性與數(shù)值擴(kuò)散等問題，提高了計算精度，能更好地捕捉空泡界面兩側(cè)物理量存在大梯度的特性。 （2）自主研發(fā)了非定常多相空泡湍流流動的三維計算程序，對于復(fù)雜計算域和物理模型具有良好的適用性和計算效率。程序擁有多種邊界設(shè)置，多種空化模型和湍流模式可供選擇；根據(jù)輸入的網(wǎng)格文件及邊界條件，通過組合應(yīng)用不同的程序模塊，可以計算二維及三維通氣或氣、汽、液多相空泡湍流流動。并可通過自編的接口程序，引入GAMBIT生成的網(wǎng)格，實(shí)現(xiàn)了前處理過程的界面化。 （3）研究了水槽中楔形翼上的基通氣空泡流動特性。計算得到的通氣空泡的單波波動流態(tài)與試驗(yàn)現(xiàn)象相符。計算結(jié)果表明：給定來流條件下存在空泡發(fā)生波動的臨界通氣率，通氣空泡波動時其形態(tài)、泄氣模式與泡內(nèi)壓力均呈現(xiàn)周期性變化，劇烈的空泡表面波動會導(dǎo)致空泡后部的斷裂與脫落。相同通氣率下，浸深的增加會導(dǎo)致平均空泡長度的增大與波動頻率變小。 （4）研究了繞水下航行體的氣、汽、液空泡流動特性。給出了通氣率、自然空化數(shù)與通氣空化數(shù)、空泡尺度和阻力系數(shù)的相關(guān)性，分析了蒸汽空化和通氣空化之間的相互影響。計算結(jié)果表明：通氣過程引起蒸汽空化的減弱與潰滅，蒸汽空泡的潰滅導(dǎo)致局部流場內(nèi)的壓力振蕩及壓力波的傳播；通氣率較小時氣體在蒸汽空泡表面的邊界層內(nèi)被主流夾帶向下游遷移，并在沒有蒸汽空泡的區(qū)域匯集，在空泡尾部形成泄氣。
[Abstract]:In recent years, the concept of supercavitation drag reduction of underwater vehicle has been put forward, which makes the study of cavitation flow become an important subject in hydrodynamics.When the underwater vehicle is wrapped in a supercavitation, it can greatly reduce the resistance of the underwater vehicle, thus greatly increasing the limit speed of the underwater vehicle movement in the water.From the technical point of view, aeration can easily realize supercavitation at low velocity, and it can also be used as an auxiliary way to control the morphology and hydrodynamic characteristics of cavitation in practical applications.At this time, the navigation body is filled with water, steam and non-condensable gas, the medium phase transition on the surface of the object, mixing, the development of bubbles and steam cavitation interact with each other, forming a very complex multi-phase cavitation turbulent flow.The purpose of this paper is to establish a mathematical model that can accurately describe this physical phenomenon and an accurate and efficient numerical calculation method, to develop a calculation software with independent intellectual property rights, and to explore gas and steam.The flow characteristics and mechanism of liquid multiphase cavitation flow provide useful theoretical basis and technical means for experimental research and engineering application.The main contents and innovative results of this paper are as follows:1) based on the assumption of homogeneous equilibrium flow, a mathematical model of gas, vapor and liquid multiphase cavitation flow is constructed by solving the RANS equation of the whole flow field. Four kinds of cavitation models of transport equations and six kinds of vortex-viscous turbulence models are introduced.The effects of vapor-liquid phase variation and turbulence are quantified.The numerical calculation method based on finite volume method and SIMPLE algorithm is established. Several high order and high precision discrete schemes are introduced to solve the problems of stability and numerical diffusion caused by the convection term, and the calculation accuracy is improved.It can better capture the large gradient of the physical quantities on both sides of the cavitation interface.2) A 3D program for unsteady multiphase cavitation turbulent flow has been developed, which has good applicability and efficiency for complex computational domain and physical model.The program has a variety of boundary settings, a variety of cavitation models and turbulence models to choose from. According to the input grid files and boundary conditions, different program modules can be combined to calculate two-dimensional and three-dimensional ventilation or gas, steam, etc.Liquid multiphase cavitation turbulent flow.The interface of preprocessing process can be realized by introducing the mesh generated by GAMBIT through the interface program made by ourselves.The flow characteristics of base aerated cavitation on wedge-shaped airfoil in the flume are studied.The calculated single wave wave flow pattern of the aerated cavitation is in agreement with the experimental phenomena.The calculated results show that the critical ventilation rate of cavitation fluctuates under the given flow conditions, and its morphology, discharge mode and pressure in the bubble vary periodically when the cavitation fluctuates.Violent fluctuations in the surface of the cavitation can lead to the fracture and shedding of the posterior part of the cavitation.Under the same ventilation rate, the increase of immersion depth will result in the increase of average cavitation length and the decrease of fluctuation frequency.The flow characteristics of gas, steam and liquid bubble around underwater vehicle are studied.The correlation between aeration rate, natural cavitation number and aeration cavitation number, cavitation size and drag coefficient is given, and the interaction between steam cavitation and aeration cavitation is analyzed.The results show that steam cavitation decreases and collapses during aeration, and the collapse of steam bubbles leads to pressure oscillation and pressure wave propagation in local flow field.When the aeration rate is small, the gas is entrapped downstream in the boundary layer on the surface of the steam bubble, and then accumulates in the region where there is no steam cavitation, and the gas is deflated at the tail of the cavitation.
【學(xué)位授予單位】：上海交通大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2013
【分類號】：O35

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