Andırın, Mert Ali
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.


Design and Experimental Investigation of a Wind Tunnel Gust Generator
Yığılı, İmge; Perçin, Mustafa; Department of Aerospace Engineering (2022-9-01)
In the design, certification and operation cycles of air vehicles, wind turbines, etc., it is critically important to quantitatively demonstrate the capability of the vehicle to withstand any environmental and meteorological condition. Of several atmospheric conditions, one very common and significant one is the atmospheric gust. Therefore, capacity to generate gust in a fully controlled manner is of utmost importance. In wind tunnels, gust generation is done by means of gust generators, which are devices p...
Experimental Investigation of the Effects of Winglets on the Tip Vortex Behavior of a Model Horizontal Axis Wind Turbine Using Particle Image Velocimetry
Ostovan, Yasar; Akpolat, M. Tugrul; Uzol, Oğuz (2019-02-01)
This study presents an experimental investigation on the effects of winglets on the near wake flow around the tip region and on the tip vortex characteristics downstream of a 0.94 m diameter three-bladed horizontal axis wind turbine (HAWT) rotor. Phase-locked 2D particle image velocimetry (PIV) measurements are performed with and without winglets covering 120 deg of azimuthal progression of the rotor. The impact of using winglets on the flow field near the wake boundary as well as on the tip vortex characte...
Experimental investigation of the effects of different helicopter rotor tip geometries on aerodynamic performance and tip vortex characteristics
Uluocak, Sinem; Hazaveh, Hooman Amiri; Perçin, Mustafa; Akpolat, M Tuğrul; Uzol, Oğuz (Netherlands Association of Aeronautical Engineers; 2018-09-05)
In this study, the effects of different tip geometries (rectangular, anhedral, swept-tapered and swept-tapered-anhedral) on the rotor hover performance and tip vortex characteristics are investigated experimentally. A scaled rotor model set-up, instrumented with thrust and torque sensors, is used for aerodynamic performance measurements in hover and a two-dimensional (2D) particle image velocimetry (PIV) is used to obtain the tip vortex characteristics such as vortex trajectory, maximum tangential velocity,...
Investigation of inertial support limits in wind turbines and the effects on the power system stability
Duymaz, Erencan; Keysan, Ozan; Department of Electrical and Electronics Engineering (2019)
In this study, the inertial support implementation is studied for variable speed wind turbines with a full-scale power electronics. To increase the active power as desired, Machine Side Converter is modified with an additional control loop. In the first part of the thesis, active power of the wind turbine is increased to the limits and the maximum achievable active power is found out to be restricted by the wind speed. It is found that the wind turbine can increase its output power by 40% of rated power in ...
Flow characteristics of translating flexible wings at low reynolds numbers
Yazdanpanah, Mahdi; Perçin, Mustafa; Department of Aerospace Engineering (2019)
This study experimentally investigates the flow field around surging-translating wings that are started from rest and compares the flow field characteristics with that of surging-revolving wings. Three wings with different level of chordwise flexural stiffness (i.e., highly flexible, moderately flexible and rigid) were studied. The experiments were performed in an octagonal water tank at the Reynold number of 7360 based on the terminal velocity of 0.08 m/s, and the wing chord length of 92 mm. Two-dimensiona...
Citation Formats
M. A. Andırın, “GENERATION AND EXPERIMENTAL INVESTIGATIONS OF GUSTY FLOWS IN WIND TUNNELS,” M.S. - Master of Science, Middle East Technical University, 2022.