Durhasan, Tahir; Ekinci, Fırat; Firat, Erhan; Akilli, Huseyin

The vortex street suppression in the near wake region of the cylinder with parallel plates was investigated using particle image velocimetry (PIV) at Reynolds number of Re = 7500. The rigid plates are designed as flat, parallel with the free-stream direction, and located on both sides of the cylinder. Two different plate lengths (0.5D and 1D based on the cylinder diameter, D) were examined at gap ratios of g/D = 0.1, 0.3, 0.5, 0.7, and 0.9, respectively. Proper Orthogonal Decomposition (POD) analyses were also employed to reveal vortex mechanism in the near wake region. The gap ratio significantly influences the interaction of the vortices. At low gap ratios, the plates directly affect the development of shear layers on both side of the cylinder. The shear layers elongate downstream with a reduction of the vortex shedding frequency. Moreover, Reynolds shear stress, vortex shedding instabilities and vortex street are suppressed in the near wake region with the help of using parallel plates. On the other hand, vortex shedding reinforces instabilities at higher gap ratios. Besides, the most effective gap ratio is different for each the plate lengths to suppress instabilities.

AtıfScopus9·WoS8·OpenAlex9

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Tunay, Tural; Firat, Erhan; Sahin, Besir

Crosswinds which stem from on-road flow conditions can deteriorate a ground vehicle's driving performance. In spite of the numerous studies investigating aerodynamics of the ground vehicles in the previous literature, there is still a need for thorough understanding of the underlying flow phenomena related to crosswind sensitivity of the ground vehicles. Therefore, the present study is aimed to investigate characteristics of the flow features around the ground vehicles under steady crosswind conditions within a range of yaw angles 0° ≤ β ≤ 15° using the Ahmed vehicle model with rear slant angles of α = 25° and 35°. Throughout the investigations, flow visualizations using dye injection technique and velocity measurements using particle image velocimetry PIV technique are conducted. The Reynolds number of the flow which is based on the free stream flow velocity U = 200 mm/s and height of the model H = 72 mm is ReH= 1.4 × 104. Results are presented in terms of time-averaged vorticity <ω> contours and streamline <ψ> patterns together with velocity magnitude ((<u>2+<w>2)1/2/U) of the flow fields. Additionally, turbulence quantities such as Reynolds stresses <u'w'>/U2 and turbulent kinetic energy TKE are presented and discussed in details. Results of the present study show that characteristics of the flow features in the near wake region downstream of the Ahmed model are very sensitive to the effects of the crosswind.

AtıfScopus36·WoS35·OpenAlex39

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