Transient process of separation and attachment over a NACA 0015 airfoil controlled by fluidic vortex generators
Transient process of separation and attachment over a NACA 0015 airfoil controlled by fluidic vortex generators
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发表时间：
2008
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通讯作者：
W. L. Siauw
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作者：
W. L. Siauw
本文对NACA 0015翼型的流动分离和附着的瞬变过程进行了实验研究。试验是在雷诺数为100万的情况下进行的，翼型的俯仰角度为11度。非受控状态的特征是，在模型振动最小的情况下，分离尺寸在后缘上游30%。一个由44个有角度的射流涡流发生器(FVG)组成的跨距阵列被放置在从前缘起弦的30%处，以控制流动分离。FVG的作用特点是在受控稳定状态下CL提高了16%，CD减少了30%。当FVG在1赫兹的频率下以“开-关”的方式操作时，这些条件允许尾迹和剪切层的确定性变化。从条件平均后的PIV数据的本征正交分解估计，分离(ΔT+~20)所需的时间是附着(ΔT+~10)的两倍。基于占POD能量98%的前四个时间模，实现了一个降阶模型。在第二个实验中，翼型分离区的压力信号被用作条件信号，利用线性随机估计(LSE)技术来估计脉动速度的演变。速度是由xA/c=2时尾迹中的交叉导线和xA/c=0时的剪切层得到的。91.在基线失控情况下，尾迹层和剪切层分别出现了双涡街和单涡街。对于FVG展开过程中的尾迹瞬变过程，涡街尺寸先增大后减小。在相反的过程中，剪切层逐渐重新建立，尾迹逐渐扩大。压力信号描述相干结构演化的能力促使其移动均方根的使用，经过滤波以保留包含流动尺度的能量，以预测流动分离的开始。
This is an experimental study dedicated to the transient processes of flow separation and attachment over a NACA 0015 airfoil. Tests are performed at a Reynolds number of 1 million with the airfoil pitched at an incidence of 11o. The uncontrolled state is characterised by a separation size of 30% upstream from the trailing edge with minimal model vibration. A spanwise array of 44 angled fluidic vortex generators (FVG) is positioned at 30 percent of chord from the leading edge to control flow separation. Effects of the FVG are characterized by 16% improvement in CL and 30% reduction in Cd during the controlled steady state. These conditions allow deterministic changes in the wake and shear layer when operating the FVG in an “on-off” manner at a frequency of 1 Hz. It is estimated from the Proper Orthogonal Decomposition (POD) of the conditional averaged PIV data in the wake that the time taken for the separation (ΔT+~20) is twice that of attachment (ΔT+~10). A reduced order model has been realized based on the first four temporal modes, which represent 98% of the energy, of the POD. In a second experiment, pressure signals in the separated zone of the airfoil, are used as conditional signals to estimate the evolution of the fluctuating velocities using technique of Linear Stochastic Estimation (LSE). The velocities are acquired from a crosswire traversing in the wake at xA/c=2 and the shear layer at xA/c=0. 91. A double and single vortex streets has been estimated in the wake and shear layer, respectively for the baseline uncontrolled case. In the case of the transient process in the wake during FVG deployment, there is an increase in the size of the vortex streets followed by a decrease in size. In the reverse process, there is a gradual re-establishment of the shear layer and gradual enlargement of the wake. The ability of the pressure signals in describing evolution of coherent structures motivates the use of its moving rms, after being filtered to retain the energy containing scales of the flow, to anticipate the onset of flow separation.