Drag reduction on a rectangular bluff body with base flaps and fluidic oscillators
Drag reduction on a rectangular bluff body with base flaps and fluidic oscillators
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DOI：
10.1007/s00348-015-2018-3
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发表时间：
2015-07
影响因子：
2.4
通讯作者：
H. Schmidt;R. Woszidlo;C. Nayeri;C. Paschereit
中科院分区：
文献类型：
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作者：
H. Schmidt;R. Woszidlo;C. Nayeri;C. Paschereit
本文研究了通过使用底部襟翼并用流体振荡器控制流动分离来减少矩形钝体上的阻力。进行风洞实验以评估各种参数的影响。襟翼长度必须足够长，以便将尾流结构向下游移动远离基板足够远。襟翼长度的任何额外增加不会产生任何进一步的好处。襟翼角度必须足够大，以提供足够的外流向内偏转。如果角度太大，则由于底部周边的另一侧施加的压力梯度，致动变得低效。此外，处于高偏转角的襟翼为低压沿流向作用提供了额外的区域，因此抵消了致动的积极效果。对于不同的振荡器间距，所需的驱动强度最好由射流速度与自由流速度之间的比率控制。对于 20° 的襟翼角，在速度比为 4.5 时获得最小的净阻力。此外，最有效减阻的最佳速度比随襟翼角度线性变化。较小的襟翼偏转需要较小的速度比，以便在不同的振荡器间距下实现最佳控制。当通过动量输入校正阻力时，在 20° 襟翼角度下测得的净阻力减少约 13%。即使通过能量系数对测得的阻力进行保守修正，也能实现 7% 的净改进。对于当前的设置，最有效的减阻仍然是在较小的襟翼角度和较低的动量输入下获得的。然而，所提出的结果支持这种减阻方法的总体可行性，并留有很大的优化空间。
The present paper investigates drag reduction on a rectangular bluff body by employing base flaps and controlling flow separation with fluidic oscillators. Wind tunnel experiments are conducted to assess the influence of various parameters. The flap length has to be sufficiently long to shift the wake structures far enough downstream away from the base plate. Any additional increase in flap length does not yield any further benefits. The flap angle has to be large enough to provide a sufficient inward deflection of the outer flow. If the angle is too large, actuation becomes inefficient due to the pressure gradient imposed by the opposite side of the base perimeter. Furthermore, the flaps at high deflection angles provide additional area for low pressure to act in the streamwise direction and therefore negate the positive effects of actuation. The required actuation intensity is best governed by the ratio between jet and freestream velocity for varying oscillator spacing. For a flap angle of 20°, the smallest net drag is obtained at a velocity ratio of 4.5. Furthermore, the optimal velocity ratio for the most efficient drag reduction changes linearly with flap angle. Smaller flap deflections require a smaller velocity ratio for optimal control at different oscillator spacing. A net drag reduction of about 13 % is measured at a flap angle of 20° when the drag is corrected by the momentum input. Even if the measured drag is conservatively corrected by the energy coefficient, a net improvement of 7 % is achieved. For the current setup, the most efficient drag reduction is still obtained at smaller flap angles with a lower momentum input. However, the presented results support the general feasibility of this drag reduction approach with significant room left for optimization.