Browsing by Author "Dogan, S."

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Citation - WoS: 9
Citation - Scopus: 8
Experimental Study on Cylinder Wake Control Using Forced Rotation
(Elsevier B.V., 2024) Aksoy, M.H.; Yagmur, S.; Dogan, S.; Goktepeli, I.; Ispir, M.
The study focused on the flow over a rotating circular cylinder in the context of flow control. Particle Image Velocimetry was employed to examine flow characteristics at 2.5 × 103 ≤ Re ≤ 10 × 103. The rotation rates (α) were considered up to 1.57. The mean drag coefficients (CD‾) and Strouhal numbers (St) were examined. The vortex formation length was obtained as approximately 2.1 times the cylinder diameter for α = 1.57. For the stationary cylinder, the length was 1.2 times the diameter from Re = 2.5 × 103 to Re = 10 × 103. Forced rotation enhanced the momentum for the boundary layer and postponed the flow separation on the upper side of the body, leading to flow attachment at α = 1.57. The values decreased from CD‾ = 1.029 to CD‾ = 0.907 as α increased from 0 to 0.39 due to the shrinkage of the wake at Re = 10 × 103. Drag reduction was 3.5 % for α = 0.13, 5.7 % for α = 0.26, and 11.8 % for α = 0.39 thanks to active flow control. The St was attained as 0.17 ≤ St ≤ 0.21 for Re varied, while it remained relatively stable for different α values at the same Re. © 2024 Elsevier Ltd
Citation - WoS: 4
Citation - Scopus: 3
The Groove Effect on Wake Characteristics of Rotating Cylinders
(American Institute of Physics, 2024) Yagmur, S.; Aksoy, M.H.; Dogan, S.; Goktepeli, I.; Ispir, M.
In the present study, active and passive flow control methods have been implemented to investigate their effects on the wake flow structures of a circular cylinder. Grooves having circular, rectangular, and triangular cross sections have been applied to the cylinders exposed to the rotation rates, α, from 0 to 0.79. The experiments have been conducted by particle image velocimetry at a Reynolds number of Re = 5 × 103. The contour graphics of time-averaged results have been presented. Moreover, the variations in velocity profiles have also been depicted. The experimental results revealed significant variations for flow patterns, wake structures, and turbulence parameters due to the effects of both groove geometries and rotational motion. In the stationary cases, for turbulence intensity, the circular grooved cylinder exhibited a 15% increase, while the triangular grooved cylinder showed a slightly higher increase of around 20% compared to that of the bare cylinder (BC). Conversely, in non-stationary cases, the rectangular grooved cylinder displayed the most prominent reduction in turbulence intensity, decreasing by approximately 10% compared to that of the BC. The groove type has considerably affected the flow structures of the wake regions, especially for the lower rotation rates. © 2024 Author(s).
Citation - WoS: 12
Citation - Scopus: 13
Improvement of Turbulent Flow in a Bend Using Rotational Guide Vane: a Shape Optimization
(American Institute of Physics Inc., 2023) Yagmur, S.; Gumus, M.S.; Dogan, S.; Kalyoncu, M.
The present study aims to minimize velocity disruption using rotational guide vane (RGV) before the 90° pipe bend where the curvature ratio is r/D = 1.0 at Re = 3 × 104. The combination of computational fluid dynamics and genetic algorithm is used as a tool for the geometric optimization of RGV. The SST k-ω turbulence model was preferred in flow analysis. The number of blade, the blade angle, and the location of RGV are the geometric parameters to be optimized. A new evaluation method of the velocity distribution after the bend is proposed. The objective function is defined as velocity distribution mean squared error that is based on the comparison of the velocity distribution on the cross section after the bend with the fully developed flow in a straight pipe under the same conditions. As a result of a series of optimization processes, velocity distribution at the 90° bend exit is compared between optimized RGV and without guide vane. The results show that the optimized RGV improves velocity distribution at the bend exit. Compared to the without guide vane case, the optimized RGV has delayed flow separation from α = 37° to 56°, and the flow reattachment point moves from x/D = 0.5 to 0 at the bend exit. Thanks to optimized RGV, the counter-rotating Dean vortices merged to form a single vortex at the center of the pipe. In addition, significant reduction in turbulent kinetic energy was observed, approximately 50% when using the optimized RGV compared to the without guide vane case. © 2023 Author(s).