【摘要】：水翼繞流的水動(dòng)力特性及其空化流動(dòng)機(jī)理的研究對(duì)提高水力機(jī)械的空化性能及其運(yùn)行穩(wěn)定性具有重要的工程意義及應(yīng)用價(jià)值。本文分別通過(guò)實(shí)驗(yàn)研究與數(shù)值計(jì)算的手段對(duì)三維水翼繞流流場(chǎng)及空化流動(dòng)進(jìn)行了深入研究。首先,通過(guò)水翼空化水洞實(shí)驗(yàn)成功捕捉了初生空化、片空化、云空化、超空化階段空化形態(tài)及各階段空穴結(jié)構(gòu)的周期性變化。實(shí)驗(yàn)捕捉了初生空化時(shí)翼型頭部微小空穴及其產(chǎn)生-增長(zhǎng)-脫落-壓縮-潰滅的發(fā)展過(guò)程;附于翼型表面的片空化只在小攻角條件產(chǎn)生,隨時(shí)間逐漸增大,演變?yōu)閺奈膊块_(kāi)始與水翼表面部分脫離形成云空化。隨空化數(shù)的進(jìn)一步降低,水翼空化流動(dòng)進(jìn)入云空化階段,小攻角條件下云空化產(chǎn)生于翼型頭部,隨空化數(shù)降低,空穴逐漸增大;大攻角條件下,在翼型頭部和尾部同時(shí)存在云空化的周期性脫落,且翼型尾部流場(chǎng)出現(xiàn)空化渦街,繼續(xù)降低空化數(shù),空化區(qū)完全覆蓋翼型上表面并延伸至流動(dòng)下游,與主流區(qū)域間形成明顯分界面,即為超空化現(xiàn)象。針對(duì)三維高雷諾數(shù)湍流計(jì)算,基于格子Boltzmann方法(LBM)Chapman-Enskog多尺度分析和大渦模擬(LES)思想,引入考慮湍流特性的等效松弛時(shí)間概念,聯(lián)合LBM單松弛模型與LES亞格子尺度應(yīng)力模型,構(gòu)建了 LBM-LES耦合模型,對(duì)雷諾數(shù)Re = 2.5×104的三維水翼繞流進(jìn)行數(shù)值計(jì)算,不同攻角流場(chǎng)流動(dòng)特性及旋渦數(shù)量、位置和尺度的計(jì)算結(jié)果與水翼繞流實(shí)驗(yàn)結(jié)果吻合性較好,且數(shù)值方法能捕捉實(shí)驗(yàn)中難以捕捉的小尺度渦。并對(duì)壓力系數(shù)和升阻力系數(shù)進(jìn)行了定量定性分析,所有結(jié)果均驗(yàn)證了 LBM-LES模型對(duì)水翼湍流計(jì)算的可行性與準(zhǔn)確性。針對(duì)氣液兩相大密度比的特點(diǎn),基于Carnahan-Starling(C-S)氣體狀態(tài)方程對(duì)立方型氣體狀態(tài)方程斥力項(xiàng)修正而具有高計(jì)算精度的優(yōu)勢(shì)及其采用適當(dāng)?shù)牧Ｗ娱g相互作用勢(shì)計(jì)算方式,將C-S氣體狀態(tài)方程與Shan-Chen模型耦合,構(gòu)建了三維空化流SC-CS(Shan-Chen-Carnahan-Starling)模型,并成功預(yù)測(cè)了不同溫度下三維相分離過(guò)程,獲得超過(guò)2×104的氣液相密度比,通過(guò)Maxwell等面積曲線分布驗(yàn)證了該模型對(duì)空化數(shù)值研究的適用性,并將空化流SC-CS模型成功應(yīng)用于三維氣核空化的發(fā)生發(fā)展和收縮潰滅及復(fù)現(xiàn)過(guò)程,計(jì)算結(jié)果符合能障理論。溫度、氣核內(nèi)外壓差和氣核初始半徑等影響因素研究表明,氣核空化過(guò)程中溫度越高,內(nèi)外壓差越大,空化越容易發(fā)生,且氣核膨脹速度越快;氣核收縮潰滅過(guò)程中半徑變化規(guī)律相似,氣核越小,潰滅速度越快。將空化流SC-CS模型進(jìn)一步應(yīng)用于水翼空化三維繞流,開(kāi)展了液體內(nèi)存在的氣核從液體中析出形成空泡的非均質(zhì)空化和翼型上表面低壓區(qū)相變引起的均質(zhì)空化研究。非均質(zhì)空化模擬了水翼流場(chǎng)中存在的氣泡當(dāng)與液相壓差足夠克服表面張力作用而發(fā)生空化再收縮潰滅的過(guò)程。均質(zhì)空化模擬了翼型前緣附近低壓區(qū)相變產(chǎn)生的初生空化發(fā)生發(fā)展脫落潰滅過(guò)程。通過(guò)相關(guān)工況均質(zhì)空化計(jì)算與空化實(shí)驗(yàn)結(jié)果對(duì)比,得到了基本一致的空化發(fā)生位置、發(fā)展?jié)邕^(guò)程及潰滅位置,驗(yàn)證了三維空化流SC-CS模型對(duì)模擬復(fù)雜邊界條件下復(fù)雜流場(chǎng)空化的有效性,拓展了 LBM應(yīng)用領(lǐng)域。為提高三維水翼繞流及三維空化流動(dòng)計(jì)算效率,采用MPI消息傳遞接口,通過(guò)C++語(yǔ)言程序編寫(xiě),建立基于三維空化流SC-CS模型的并行算法,通過(guò)并行效能分析得到針對(duì)本研究的數(shù)值模擬采用5個(gè)進(jìn)程進(jìn)行的并行計(jì)算執(zhí)行時(shí)間最短,加速比最大,且具有較高的通信效率。
[Abstract]:The hydrodynamic characteristics of turbulent flow and its cavitation flow mechanism have important engineering significance and application value to improve the cavitation performance and operational stability of hydraulic machinery. In this paper, the three-dimensional turbulent flow field and cavitation flow are studied by means of experimental research and numerical calculation respectively. Firstly, primary cavitation, cavitation, cloud cavitation, cavitation morphology and periodic variation of hole structure at various stages were successfully captured through the experiment of cavitation tunnel. The experimental results show that the microcavitation and the generation-growth-shedding-compression-collapse development of the airfoil at primary cavitation are captured. The cavitation of the blade attached to the airfoil surface is only generated at small angle of attack, and gradually increases with time. Evolving into cloud cavitation from the tail and from the bottom surface portion. With the further reduction of cavitation number, the cavitation flow enters the cavitation stage of the cloud, the cloud cavitation is generated at the head of the airfoil under the condition of small attack angle, the cavity gradually increases along with the cavitation number, and under the condition of large attack angle, the periodic shedding of the cloud cavitation exists at the head part and the tail part of the airfoil at the same time, and the cavitation area completely covers the upper surface of the airfoil and extends to the downstream of the flow. Based on the Lattice Boltzmann method (LBM) Hellman-Enskog multiscale analysis and large eddy simulation (LES), the equivalent relaxation time concept considering the turbulent characteristics is introduced, and the LBM-LES coupling model is constructed by combining the LBM single relaxation model and LES subgrid scale stress model. The numerical calculation of the three-dimensional turbulent flow of Reynolds number Re = 2.5 Mt. 104, the flow characteristics of different attack angle flow field and the number, position and scale of vortex flow are good, and the numerical method can capture the small-scale vortex which is difficult to capture in the experiment. Based on the quantitative analysis of the pressure coefficient and the lift resistance coefficient, all the results verify the feasibility and accuracy of the LBM-LES model on the turbulent flow calculation. According to the characteristics of the two-phase bulk density ratio of gas liquids, based on Carnahan-Starling (C-S) gas state equation, the advantages of high calculation accuracy and the suitable inter-particle interaction potential calculation method are adopted to couple the C-S gas state equation to the Shan- Chen model. A three-dimensional cavitating flow SC-CS (Shaan-Chen-Carnahan-Starling) model is constructed, and the three-dimensional phase separation process at different temperatures is successfully predicted, and the gas-liquid density ratio of more than 2 ppmw 104 is obtained, and the applicability of the model to the cavitation numerical research is verified through an area curve distribution such as a neutron source and the like. and the cavitation flow SC-CS model is successfully applied to the development and contraction collapse and reproduction process of the three-dimensional gas core cavitation, and the calculation result is consistent with the barrier theory. It is shown that the higher the temperature, the greater the internal and external pressure difference, the easier the cavitation and the faster the gas-core expansion velocity, the smaller the radius of the gas core during the collapse of the gas core, the smaller the gas core, the higher the temperature, the internal and external pressure difference of the gas core and the initial radius of the gas core. the faster the collapse speed is. In this paper, the cavitation flow SC-CS model is further applied to the cavitation three-dimensional swirling flow, and the non-homogeneous cavitation of the gas core in the liquid and the homogeneous cavitation caused by the phase change of the low pressure zone on the upper surface of the airfoil are developed. The non-homogeneous cavitation simulates the process of cavitation and collapse when the pressure difference between the bubbles and the liquid phase is sufficient to overcome the surface tension. Homogeneous cavitation simulates the development of primary cavitation in the low-pressure zone near the leading edge of the airfoil. Compared with the experimental results of cavitation, the equivalent cavitation location, the development collapse process and the collapse position are obtained, and the effectiveness of the three-dimensional cavitation flow SC-CS model on complex flow field cavitation under complex boundary conditions is verified, and the application of LBM is extended. in ord to improve that computational efficiency of three-dimensional cavitation flow and three-dimensional cavitation flow, a parallel algorithm based on the three-dimensional cavitation flow SC-CS model is established by the MPI message passing interface and written by C ++ language program. The parallel performance analysis results in the shortest execution time, maximum acceleration ratio and higher communication efficiency for the numerical simulation of this study.
【學(xué)位授予單位】：中國(guó)農(nóng)業(yè)大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2017
【分類(lèi)號(hào)】：O35

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本文編號(hào)：2301785