Application of BOS velocimetry to full-scale helicopter flight tests

IF 2.3 3区 工程技术 Q2 ENGINEERING, MECHANICAL
Johannes N. Braukmann, C. Christian Wolf, Anthony D. Gardner
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引用次数: 0

Abstract

Time-resolved background-oriented schlieren (BOS) data are used to calculate the two-dimensional velocity field in the wake of free-flying full-scale helicopters in ground effect. The calculation is performed based on the density gradient pattern of the helicopter engine exhaust gas passing the BOS field of view. A classical BOS evaluation allows the visualization of density gradients such as vortices and the exhaust plume. The result is the BOS displacement field. Applying the two-dimensional divergence to these data results in a pattern that is constant in shape across multiple BOS images, but convects downstream with the outwash velocity of the helicopter. Quantitative two-dimensional velocity fields are calculated using the divergence of the BOS shift as input to a second, time-resolved evaluation. Choosing an appropriate strategy for preparing and evaluating the data is critical to a reliable velocity estimation. Another important aspect is to distinguish between reliable velocity data and erroneous results in areas of reduced signal intensity due to a lack of thermal structures. The velocity data obtained are compared with an analytical outwash model and constant temperature anemometry data acquired simultaneously with the BOS images. The data show good quantitative agreement in areas of sufficient thermal structures within the field of view. This demonstrates the feasibility of BOS velocimetry to investigate large flow fields in full-scale helicopter flight tests.

BOS测速在直升机全尺寸飞行试验中的应用
利用时间分辨背景定向纹影(BOS)数据,计算了全尺寸自由飞行直升机在地面效应下的二维速度场。根据直升机发动机废气通过BOS视场的密度梯度模式进行计算。经典的BOS评估可以可视化密度梯度,如涡流和排气羽流。结果就是BOS位移场。将二维散度应用到这些数据中,结果是在多个BOS图像中形状不变的模式,但随着直升机的外流速度下游对流。定量二维速度场计算使用发散的BOS位移作为输入到第二个,时间分辨评估。选择适当的策略来准备和评估数据对于可靠的速度估计至关重要。另一个重要方面是区分可靠的速度数据和由于缺乏热结构而导致信号强度降低的区域的错误结果。将得到的速度数据与解析外溢模型和与BOS图像同时获得的恒温风速数据进行了比较。在视场内热结构充足的区域,数据显示了良好的定量一致性。这证明了BOS测速技术在直升机全尺寸飞行试验中研究大流场的可行性。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Experiments in Fluids
Experiments in Fluids 工程技术-工程:机械
CiteScore
5.10
自引率
12.50%
发文量
157
审稿时长
3.8 months
期刊介绍: Experiments in Fluids examines the advancement, extension, and improvement of new techniques of flow measurement. The journal also publishes contributions that employ existing experimental techniques to gain an understanding of the underlying flow physics in the areas of turbulence, aerodynamics, hydrodynamics, convective heat transfer, combustion, turbomachinery, multi-phase flows, and chemical, biological and geological flows. In addition, readers will find papers that report on investigations combining experimental and analytical/numerical approaches.
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