【作者】 柴雅彬；

【导师】 姜楠；

【作者基本信息】 天津大学 ， 流体力学， 2004， 硕士

【摘要】 本文为了配合西气东输工程中采用管道壁面涂料减阻技术,应用热线测速技术,对风洞中壁面覆盖减阻涂料的平板湍流边界层进行减阻机理的实验研究。在风洞中用IFA300智能化热线风速仪和单丝边界层微型热线探针精细测量了不同壁面涂料的壁湍流平均速度剖面,利用壁湍流对数律平均速度剖面与壁面摩擦速度、流体粘性系数等内尺度物理量的关系以及壁面摩擦速度与壁面摩擦切应力的关系,通过非线性迭代拟合其中的壁面摩擦速度,用平均速度剖面法测量壁湍流的壁面摩擦阻力和壁面摩擦系数,对三种涂料的壁面减阻性能进行了比较实验研究,为进一步认识壁面减阻机理提供实验依据。这三种涂料分别是聚氨脂、环氧树脂、沥青,每种涂料三种厚度涂层,加上对比壁面,一共十块实验模型。每一块实验模型在风洞中用三个雷诺数(来流速度)吹风。u?用子波分析对平板湍流边界层不同法向位置的流向速度的时间序列信号进行多尺度分解,用自相关法确定了不同尺度湍流结构的时间尺度,用子波系数的瞬时强度因子、平坦因子检测壁湍流中的多尺度相干结构。提取了湍流边界层不同法向位置多尺度相干结构的条件相位平均波形,研究了多尺度相干结构猝发的动力学过程。用子波系数的概率密度函数分析多尺度相干结构对间歇性的影响。实验发现,具有减阻效果的涂料使近壁区流向平均速度增加,缓冲层增厚,对数律区上移,产生减阻效果。通过改变平板湍流边界层中不同尺度相干结构的能量分布、条件相位平均波形、平坦因子、相对强度、发生概率,使湍流结构相干性增强,流动有序化程度提高,从而对平板湍流边界层中原有的多尺度相干结构进行控制,以达到壁面减阻的目的。在对数律区以外涂料对流动结构的性质基本不产生影响。更多还原

【Abstract】 In this paper, coat is applied to the project of gas pipe flow from west to east. Thetechnique of constant temperature anemometry is used to study the mechanism ofdrag reduction for turbulent boundary layer coated on the surface of wall.Mean velocity profile of wall turbulence with different coat boundary has beenfinely measured by IFA300 constant-temperature anemometer and single wire probe.There has some relation between skin friction velocity and the logarithmic law ofmean velocity profile. The skin friction velocity and the shear stress are calculatedthrough fitting the logarithmic law of mean velocity profile. The ability of dragreduction with three kind of coat are studied, which provide experiment bases to theresearch of drag reduction mechanism. In this experiment, each coat has threethickness. Ten flat-plates, including a no-coat flat-plates, are studied with threedifferent Reynold number.The velocity time sequence signal at different vertical locations in a turbulentboundary layer are analyzed by wavelet transform with multi-scale. The scales ofmulti-scale eddy structures are determined by self-correlation function. The coherentstructures are identified by flatness factor based on locally averaged velocity structurefunctions. Phased-average evolution shapes for multi-scale coherent eddy structures inturbulent boundary layer are extracted by this conditional sampling technique. Thedynamic course of multi-scale coherent eddy structures’bursting is researched. Theintermittency features, studied through the probability density function of the waveletcoefficients, are found influenced by multi-scale coherent eddy structures.It is found that coat with drag reduction make the stream-wise mean velocityincreased near the wall region. At the same time the buffer layer is incrassated, andthe log-law region moves upwards. The coat change the distributing of energy, thephased-average evolution shapes and the flatness factor, enhance the coherentstructures, make the flow regular, and work on and control the multi-scale coherenteddy structure in a turbulent boundary layer, in order to reduce the resistance of thewall.In the log-law region, the spraying has no effect on the flow structures.更多还原