【作者】 霍岩；

【导师】 周允基；

【作者基本信息】 哈尔滨工程大学 ， 一般力学与力学基础， 2010， 博士

【摘要】 有限开口空间内的热驱动流动广泛存在于火灾、通风、水力、机械、化工和环境保护等领域中,并在工程上有大量的应用。由于浮力的作用,引起密度不均匀形成分层流,从而使湍流呈现出非常复杂的行为,增强了热分层流研究的难度。鉴于有限开口空间内的浮力驱动分层流动在工程中的广泛性及其应用的重要性,本文采用实验与数值模拟相结合的方法,从基本的数学物理模型建立和求解入手,针对典型情况的有限开口空间内的热驱动浮力分层流问题进行了研究。在本文中,首先阐述了适用于有限开口空间内的多组分热驱动流的控制方程及附加方程的推导、简化和变形过程,并基于大涡模拟(LES)技术的主要思想对方程组进行了滤波,简要讨论了亚格子模型,随后给出了方程的数值求解过程和收敛标准。以NIST开发的FDS5.0程序为基础,将Vreman亚格子模型应用于有限开口空间热浮力驱动流计算中,并针对在有门开口的房间内由火源产生热流场情况,进行了模型验证工作。利用函数分析法将模拟结果与实验测量值进行了对比分析,进而确定了滤波宽度△=0.05 m时,适用于计算室内火灾分层流的Vreman亚格子模型的常数Cv为0.1。通过在有门开口的单室环境中进行的火灾实验和数值模拟,比较了Smagorinsky和Vreman亚格子模型对于热流场计算的适用性。结合双室火灾环境、室内置换通风环境、无尘室垂直层流场火灾环境的模拟值和实验测量值对比结果,得到了在没有外界送风动量的扰动情况下,对于室内这种有限开口空间内的火灾热流场来说,对FDS5.0软件改’进后的计算结果与实验测量值的接近程度在整体上要优于其原有模型。以两端开口的狭长型空间热流场为研究对象,进行了小尺寸火灾实验和数值模拟研究,验证了Vreman亚格子模型对狭长通道热流场模拟的有效性。根据实验和数值模拟结果,在通道上壁面无开缝和两种侧开缝宽度时的四种倾斜角度状态下,对通道内的高温区域偏移情况和两端开口处的流速及中性面的变化进行了比较分析,对存在一定倾角的通道排烟设计提出了参考意见。以顶部开口的竖直通道空间为研究对象,在9m高的大尺寸单侧开缝竖直通道内进行了火灾实验和数值模拟,对由不同宽度的侧开缝引射空气所引起的火焰和流场的旋转情况、浮力与科氏力的作用关系、旋转中心的偏移进行了分析；在此基础上,利用数值模拟方法研究了4m高以上的侧开缝宽度限制为0.15m后给通道内流场所带来的影响。在2m高的小尺寸竖直通道内进行了不同宽度双侧同方向对开缝火灾实验,结果表明：在一定的热释放率和开缝宽度条件下,双侧同方向对开缝条件也可形成火旋风,并且,在开缝的宽度较小、火源热释放率较大时更容易形成强烈的火旋风。本文的研究结果可为加深物理问题的理解提供依据,典型场景的热浮力驱动流研究可为工程应用提供参考和帮助。同时,为今后进一步的深入研究工作奠定了基础。更多还原

【Abstract】 Thermal stratification is a complicated fluid flow phenomenon due to density difference driven by buoyancy. This kind of fluid flow is commonly encountered in building fire, room ventilation, hydraulic system, machinery, chemicals and environmental protection systems. And it is used widely in the project applications. The stratified fluid is a kind of fluid due to different densities driven by buoyancy, which makes the thermal fluid appear complex behaviors. Therefore, it adds difficulties to research on the thermal stratified fluid. The objective of this thesis is to study thermal stratified fluid in an enclosure with openings.In consideration of the widespread popularity and importance of the thermal stratified fluid in an enclosure with openings, researches on typical cases of the thermal stratified fluid in an enclosure with openings were conducted. A mathematical model was set up by combining the associated physical phenomena. Derivation and simplification of the key equations concerned were presented. Discretization in numerical analysis was then outlined. Flow in an enclosure with openings with low Mach number and multi-species were introduced. Turbulence was simulated by large eddy simulation with the model equations filtered. Subgrid-scale models were applied with the numerical solution and convergence criteria described.The advanced Computational Fluid Dynamics software Fire Dynamics Simulator (FDS) released by the National Institute of Standards and Technology in the U.S.A. was modified with such analysis. Vreman subgrid-scale model was applied in simulating the thermal stratified flow in an enclosure with openings. This subgrid-scale model was justified by several fire scenarios of compartment with a vertical vent. The numerical values and experimental data were compared using functional analysis. In the numerical simulation of thermal stratified fluid in an enclosure with openings, the corresponding Vreman subgrid-scale constant Cv for the filter width of 0.05 m was fitted to be 0.1.Based on the fire experiment on compartment with a vent and the associated numerical simulations, Smagorinsky and Vreman subgrid-scale models for simulating the thermally-induced flow field were compared. In addition to comparing with fire experiments, predicted results in a double compartment, a ventilation displacement in an office and laminar flow in clean room environment, predicted results were closer to experiment in using this improved model developed from FDS without disturbed by additive momentum of the supplying ventilations.Scale model experiments and numerical simulations for thermally-induced flow in a long tunnel with two open-ends were carried out. The adaptability of Vreman subgrid-scale model for the thermal flow field in this long tunnel was analyzed. Based on the experimental data and numerical simulation results for different gap widths and inclined angles, the shift characteristics of the higher temperature zone in the tunnel, the variation of flow speed and the height of central plane at openings were analyzed. The results can provide sufficient data for designing smoke management system for an inclined tunnel.Large-scaled fire experiment and numerical simulation were carried out for vertical shaft with a single corner gap and top open. The effects of the different gap widths on the rotation of fire and flow field, the correlations of buoyancy and the Coriolis force, the shift characteristics of the fire whirl was analyzed. The flow field in the vertical shaft was studied using the numerical simulation when the corner gap width of above 4 m was set at 0.15 m. Small-scaled fire experiments were also conducted in 2 m tall vertical shaft with dual corner gaps. The results showed that fire whirls can be generated under a certain heat release rate and corner gap width. A fire whirl would be generated with appropriate corner gaps.Results of this thesis provided the basics for better understanding the thermal flow driven by buoyancy. The study of the thermal flow field driven by buoyancy may offer some reference and help for the research on application in engineering. At the same time, this dissertation paved a way for the further study.更多还原