【作者】 常跃峰；

【导师】 姜楠；

【作者基本信息】 天津大学 ， 流体力学， 2009， 博士

【摘要】 本文对V型沟槽壁面湍流边界层的减阻机理进行了实验研究。用IFA300热线风速仪和TSI-1211-T1.5、TSI-1240-T1.5、TSI-1243-T1.5、TSI-1244-T1.5四种型号热线探针精细测量了沟槽壁面及光滑壁面湍流边界层在不同雷诺数下、不同法向位置的瞬时流向、法向、展向速度分量的时间序列信号。利用壁湍流对数律平均速度剖面与壁面摩擦速度、流体黏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,测量沟槽壁面及光滑壁面湍流边界层壁面摩擦速度、壁面摩擦切应力和壁面摩擦系数,结果证明沟槽壁面使得边界层近壁区黏性底层增厚,缓冲层和对数律层上移,沟槽壁面消弱了缓冲层内与多尺度相干结构相联系的脉动速度和雷诺应力分量。将湍流多尺度相干结构的概念引入沟槽壁面湍流边界层减阻机理的研究。以湍流边界层瞬时流向脉动速度子波系数作为特征量,检测、提取了沟槽壁面及光滑壁面湍流边界层中的多尺度相干结构流向、法向、展向速度分量和瞬时雷诺应力分量的条件相位平均波形。与光滑平板相比,不论喷射过程还是扫掠过程,沟槽壁面相干结构在喷射和扫掠过程中的流向、法向、展向脉动速度分量和雷诺应力分量< u ’ v’>、< u ’ w’>幅值均明显降低,过程趋缓,时间尺度缩短。其中沟槽壁面使相干结构展向脉动强度降低最明显,使相干结构的展向动量交换减小,削弱了相干结构对湍流产生的贡献。搭建了一套包括流动显示水槽、氢气泡发生装置、数字图像采集及分析软件相结合的氢气泡流动显示实验系统。应用“帧间比较”定量分析方法,通过处理和分析水槽中近壁面区湍流相干结构的氢气泡流动显示图像,获得了平面流场中流向脉动速度、展向脉动速度和法向涡量的平面分布。研究表明,沟槽壁面使壁湍流大尺度高低速条带结构间的动量交换减小,有效削弱了壁湍流流向、展向脉动,降低了脉动动量和脉动涡量的强度。更多还原

【Abstract】 In this paper, the mechanism of drag reduction in turbulent boundary layer with a V-groove riblets surface was studied experimentally. Time sequence of longitudinal, vertical and spanwise velocity component along different normal positions in turbulent boundary layer which is controlled by a V-grooved plate and a flat-plate with different Reynolds numbers has been finely measured by IFA300 constant temperature anemometer with TSI-1211-T1.5、TSI-1240-T1.5、TSI-1243-T1.5、TSI-1244-T1.5 four types probes.According to the relationship of the logarithmic law of mean velocity profile and skin friction velocity, fluid viscosity coefficient etc.,inner scale physics quantities the relationship of skin friction velocity and skin friction shear stress,nonlinear iterating was carried out to calculate the parameter of the logarithmic law and skin friction velocities for turbulent boundary layers over a V-grooved plate and a flat-plate respectively. The result verified the thickening of the viscous sublayer and the up-shift of logarithmic and buffer sublayer in the near wall region over V-grooved surface. It is confirmed that the V-grooved surface weakens the fluctuations of velocities and Reynolds stresses related to multi-scale coherent structures in buffer sublayer.It is employed the concept of multi-scale coherent structures to study the mechanism of riblet surface drag reduction in turbulent boundary layer. Wavelet coefficients of longitudinal velocity component are used as the index of detecting multi-scale coherent structures and extracting the phased-average waveforms of streamwise, vertical and spanwise fluctuating velocities, as well as Reynolds stress of in turbulent boundary layer over riblets and plate surface. Compared with smooth plate surface, both for eject and sweep process, the amplitudes of streamwise, vertical and spanwise fluctuating velocity components, as well as Reynolds stress , < u ’ v’>,< u ’ w’> are reduced clearly, progress tend to be laggardly, temporal scales of multi-scale coherent structures are becoming shorten. Among them, the reduction of spanwise fluctuation intensity of coherent structure over V-grooved surface is apparent, and spanwise momentum exchanges of coherent structures are reduced, so the contribution of coherent structures to turbulence production is decreased.A set of flow visualization experimental apparatus including of water channel, hydrogen bubble producing equipment and flow digital image acquisition and procession software is established. Using a‘comparing-two-frame’quantitative analysis technique, the two-dimensional plane distributions of streamwise, spanwise velocity and vertical vorticity are obtained through processing and analyzing hydrogen bubble flow visualization images. The results indicate that the V-groove riblets surface weakens the streamwise, spanwise velocity and vorticity fluctuation through manipulating momentum exchanges of large-scale high and low-speed streaks in turbulent boundary layer.更多还原