Browsing by Author "Skeledzic, T."

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Characterization of turbulence generated by an active grid with individually controllable paddles
(Springer, 2018) Skeledzic, T.; Krauss, J.; Lienhart, H.; Ertunç, Özgür; Jovanovic, J.; Mechanical Engineering; ERTUNÇ, Özgür
An active grid with individually controllable paddles was constructed to generate strong turbulence (Reλ>200). Measurements of turbulence quantities using the hot-wire technique were conducted in a wind tunnel along the flow on the centre line and on an off-centred line in the wake of this grid. The effect of two different motion sequences of the active grid paddles as well as the influence of the clock rate of the paddles were tested. Finally, measurements with a fixed paddle angle were carried out. The results confirmed that the active grid is suitable to generate the intended strong turbulence. Maximum Reλ was obtained when the uniform probability density distribution was used. Turbulence generated with fixed paddle angle still delivered turbulence with Reλ~100.
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Effect of the motion pattern on the turbulence generated by an active grid
(Springer, 2021) Herbert, M.; Skeledzic, T.; Lienhart, H.; Ertunç, Özgür; Mechanical Engineering; ERTUNÇ, Özgür
In the field of turbulence research, many experiments are performed using turbulence generated under reproducible conditions. In the past mostly static grids having a fixed blockage were adopted, but in order to generate turbulence with high intensity and high turbulence Reynolds numbers, so called active grids can be used. Therefore, an experimental study has been carried out to investigate the effect of the motion pattern on the turbulence generated by an active grid with individually controllable paddles in the wind tunnel. Measurements were performed using the hot-wire technique. In comparison to former experiments, modifications of the active grid had been made concerning the arrangement of the paddles. The results show that the homogeneity of the turbulence could be improved using the modified grid. Turbulence Reynolds numbers could reach values up to 540. In order to produce even higher integral time scales or higher turbulence Reynolds numbers, synchronous movement of adjacent paddles was tested but did not show the intended improvements. In this paper, the results of the experimental study are presented in more detail.