槽道流壁面展向周期振动减阻的一维谱分析

One-Dimensional Spectral Analysis of Drag Reduction with Spanwise-Wall Osillation in Channel Flow

通过直接数值模拟(DNS)对壁面做展向周期运动的槽道湍流进行研究,建立了槽道湍流数据库。发现通过改变振幅大小和振动周期,可以使壁面摩擦阻力明显减少。对减阻前后一维湍流脉动能谱进行了定量分析,结果表明,控制后湍流脉动能普遍下降,流向和展向速度脉动都受到了很大的抑制,并且总动能在减少的同时,能量从时间尺度大的脉动向时间尺度小的脉动传输。分析了阻力变化周期中三个特征时段拟涡能谱的变化规律,发现总涡能在得到不同程度抑制的同时,具有不同的变化特征。结合近壁湍流拟序结构的变化规律,进一步揭示了壁面展向周期振动减阻的内在机理。

A turbulent channel flow subjected to spanwise wall oscillation was investigated by direct numerical simulation （DNS）. The DNS results show that the friction drag can be reduced significantly by changing the amplitude and the period of the oscillation. The one-dimensional energy spectra analyses of velocity fluctuations were carried out quantitatively. It is found that turbulence kinetic energies are reduced remarkably, and that the streamwise and spanwise velocity fluctuations are suppressed dramatically. Simultaneously, there is a transfer of energy from the large-timescale to small-timescale turbulence eddies by the periodic spanwise-wall oscillation. The differences of the vorticity energy spectra of three typical drag reduction phases in a drag reduction periodicity were analysed. It is found that the suppressions of total vorticity energy for these three phases are different. Three kinds of changes in the structures of near-wall turbulence were analyzed. The mechanisms of turbulence suppression and drag reduction via spanwise wall oscillation were further clarified.