Date

2022-6-16

Author

Andırın, Mert Ali

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Wind tunnels are designed to operate at low turbulence intensities, which makes it unfeasible to study the turbulent and gusty flows that are observed in nature and in engineering applications. To conduct such studies number of unconventional methods are adopted in wind tunnels, one of which is the use of active grids. Active grids consist of motor-driven rods which accommodate flaps and they are generally placed at the inlet of wind tunnel test sections. By regulating the motion of the agitator wings, flows with high turbulence intensities and tunable properties can be achieved or atmospheric boundary layers or gusts can be generated. Active grids are usually used to generate three-dimensional flow structures. There are also more primitive devices compared to active grids to generate gust flows which are called gust generators or 2-D active grids. In this context, the main objective of this thesis is to design an active grid on an open-loop suction-type wind tunnel and investigate the gust flow characteristics of the flow field of the near wake of the active grid using experiments. For this purpose, a more primitive design, a 2D two-wing active grid, a gust generator, is used to examine the gust produced by the flapping wing in the wake region of the gust generator. Firstly, the reduced frequency values of the vanes are changed at fixed pitching amplitude and secondly, the pitching amplitude is changed at fixed reduced frequency to investigate the gust characteristics of the flow. Unlike most of the literature, in this study, instead of using hot-wire anemometry measurements in the test section, particle image velocimetry measurements are taken in the wake of the agitator wings, which allows for exploring the physical relation between the wake structures and downstream flow profile. By the helpf of observing the whole flow field behind the gust vanes it is observed that even well-defined sinusoidal profiles of the transverse and stream-wise gust ratio in a period can be obtained using in-phase and out-of phase motion of the gust vanes, the one should be careful of the drawback of flow separation and number of coherent vortices shed into the wake.

Subject Keywords

Active Grid, Gust, Wind tunnel, Particle Image Velocimetry

URI

https://hdl.handle.net/11511/98159

Collections

Graduate School of Natural and Applied Sciences, Thesis