Purpose

The purpose of this paper is to analyze experimentally subsonic wake of a supercritical airfoil undergoing a pitch–hold–return motion. The focus of the investigation has been narrowed to concentrate on the steadiness of the flow field in the wake of the airfoil and the role of reduced frequency, amplitude and the hold phase duration.

Design/methodology/approach

All experiments were conducted in a low sub-sonic closed-circuit wind tunnel, at a Reynolds number of approximately 600,000. The model was a supercritical airfoil having 10% thickness and wall-to-wall in ground test facilities. To calculate the velocity distribution in the wake of the airfoil, total and static pressures were recorded at a distance of one chord far from the trailing edge, using pressure devices. The reduced frequency was set at 0.012, 0.03 and the motion pivot was selected at c/4.

Findings

Analysis of the steadiness of the wake flow field ascertains that an increase in reduced frequency leads to further flow time lag in the hold phase whereas decreases the time that the wake remains steady after the start of the return portion. Also, the roles of amplitude and stall condition are examined.

Practical implications

Examination of a pitch–hold–return motion is substantial in assessment of aerodynamics of maneuvers with a rapid increase in angle of attack. Moreover, study of aerodynamic behavior of downstream flow field and its steadiness in the wake of the airfoil is vital in drag reduction and control of flapping wings, dynamic stability and control of aircrafts.

Originality/value

In the present study, to discuss the steadiness of the flow field behind the airfoil some statistical methods and concept of histogram using an automatic algorithm were used and a specific criterion to characterize the steadiness of flow field was achieved.

中文翻译：

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俯仰-保持-返回运动中翼型尾流稳定性的实验研究

目的

本文的目的是分析超音速机翼经历俯仰-保持-返回运动的亚音速尾流。研究的重点已缩小到集中在翼型尾流后流场的稳定性以及降低频率，幅度和保持阶段持续时间的作用上。

设计/方法/方法

所有实验均在低亚音速闭路风洞中进行，雷诺数约为600,000。该模型是超临界机翼，其厚度为10％，并且在地面测试设施中壁对壁。为了计算翼型尾流的速度分布，使用压力装置在距后缘一弦距离处记录了总压力和静压力。降低的频率设置为0.012、0.03，运动枢轴选择为c / 4。

发现

对尾流场的稳定性的分析确定，减小的频率的增加导致在保持阶段中进一步的流动时间滞后，而减少了在返回部分开始之后尾流保持稳定的时间。此外，还检查了振幅和失速条件的作用。

实际影响

俯仰-保持-返回运动的检查对于评估气动性能和快速增加迎角是很重要的。此外，研究下游流场的空气动力学行为及其在翼型尾流中的稳定性对于减小阻力和控制襟翼，动态稳定性和控制飞机至关重要。

创意/价值

在本研究中，为了讨论机翼后面流场的稳定性，使用了一些统计方法和直方图的概念，使用了一种自动算法，并提出了一个表征流场稳定性的特定准则。