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基于不同雷诺数平板湍流边界层平均速度剖面,分别采用黏性底层拟合、对数律区拟合以及Spalding公式拟合算法计算了壁面摩擦速度,并对平均速度剖面进行无量纲化。通过比较无量纲化的平均速度剖面与理论规律曲线,验证了三种拟合计算方法的有效性。通过比较三种拟合算法所得的壁面摩擦速度与油膜干涉法直接测得的壁面摩擦速度之间的误差,并分析不同拟合算法误差形成的内在机制,验证了三种拟合算法计算结果的准确性与可靠性。结果表明Spalding拟合算法计算结果的准确性和可靠性都要优于其他两种拟合算法。 相似文献
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Influence of uniform momentum zones on frictional drag within the turbulent boundary layer 下载免费PDF全文
Based on a set of experimental databases of turbulent boundary layers obtained from particle image velocimetry in the streamwise-wall-normal plane at friction-velocity-based Reynolds number Reτ=612,the influence of uniform momentum zones(UMZs)on the skin-friction drag is investigated.The skin-friction drag is measured by the single-pixel ensemble correlation method.The results show that the velocity fields with the number of UMZs larger than the mean value have a relatively low skin-friction drag,while the velocity fields with the number of UMZs less than the mean value have a relatively high skin-friction drag.By analyzing the statistical characteristics of UMZs,the dynamic correlation between the UMZs and skin-friction drag is explored.The velocity fields with a low number of UMZs present a sweep event.These sweep motions intensify the small-scale Reynolds shear stress in the near-wall region by modulation effects.The enhancement of small-scale Reynolds shear stress is the direct reason for the high skin-friction drag.Increasing the proportion of velocity fields with high UMZs amount may be a direction to reduce the skin-friction drag within the TBL. 相似文献
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Experimental investigation on drag reduction in a turbulent boundary layer with a submerged synthetic jet 下载免费PDF全文
This work investigates the active control of a fully developed turbulent boundary layer by a submerged synthetic jet actuator.The impacts of the control are explored by measuring the streamwise velocities using particle image velocimetry,and reduction of the skin-friction drag is observed in a certain range downstream of the orifice.The coherent structure is defined and extracted using a spatial two-point correlation function,and it is found that the synthetic jet can efficiently reduce the streamwise scale of the coherent structure.Proper orthogonal decomposition analysis reveals that large-scale turbulent kinetic energy is significantly attenuated with the introduction of a synthetic jet.The conditional averaging results show that the induction effect of the prograde vortex on the low-speed fluid in a large-scale fluctuation velocity field is deadened,thereby suppressing the bursting process near the wall. 相似文献
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Active control of wall-bounded turbulence for drag reduction with piezoelectric oscillators 总被引:1,自引:0,他引:1 下载免费PDF全文
An experimental investigation was performed for active control of coherent structure bursting in the near-wall region of the turbulent boundary layer. By means of synchronous and asynchronous vibrations with double piezoelectric vibrators,the influence of periodic vibration of the double piezoelectric vibrators on the mean velocity profile, drag reduction rate, and coherent structure bursting is analyzed at Re_θ= 2766. The case with 100 V/160 Hz-ASYN is superior to other conditions in the experiment and a relative drag reduction rate of 18.54% is exciting. Asynchronous vibration is more effective than synchronous vibration in drag reduction at the same voltage and frequency. In all controlled cases, coherent structures at large scales are regulated while the small-scale structures are stimulated. The fluctuating velocity increases significantly. A periodic regulating effect on the coherent structure can be seen in the ASYN control conditions at the frequency of 160 Hz. 相似文献
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