Yazar "Firat, Erhan" seçeneğine göre listele

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    Öğe
    An experimental investigation of the flow control of a circular cylinder in near wake with parallel plates at Re=7500
    (Elsevier Science Inc, 2024) Durhasan, Tahir; Ekinci, Firat; 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 shed-ding 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.
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    Öğe
    An investigation of the near-wake flow structure of a cylinder with guiding plates
    (E D P Sciences, 2018) Ekinci, Firat; Firat, Erhan; Ozkan, Gokturk M.; Akilli, Huseyin
    this study, the flow behind a circular cylinder with a pair of outer identical guiding plates was investigated using particle image velocimetry (PIV) for various angular positions of the plates (i.e. alpha=+/- 70 degrees, +/- 100 degrees, and +/- 130 degrees). The gaps between these plates and cylinder are equal and are 0.3D. Experiments were carried out at a subcritical Reynolds (Re=rho.U infinity.D/mu) number of 7500, based on the cylinder diameter (D) and the flow velocity (U infinity). The features of the near-wake with and without the guiding plates were interpreted in terms of patterns of time-averaged vorticity and streamlines, time-averaged and fluctuating velocity components. The spectral analysis was also carried out to determine the time-dependent variation of the transverse velocity at given locations in the near-wake. Two-dimensional computations of flow around circular cylinders with and without guiding plates have also been performed to predict the time-averaged and root-mean-square of force coefficients of the various models. It was seen that the guiding plates at an appropriate angular position can lead to substantial attenuation, or retardation, of the process of large-scale vortex formation in the near-wake, thus can lead to vortex-induced vibration (VIV) suppression without any increase in drag.
  • [ X ]
    Öğe
    Experimental investigation of the flow around a simplified ground vehicle under effects of the steady crosswind
    (Elsevier Science Inc, 2018) 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 degrees <= beta <= 15 degrees using the Ahmed vehicle model with rear slant angles of alpha = 25 degrees and 35 degrees. 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 Re-H = 1.4 x 10(4). Results are presented in terms of time averaged vorticity contours and streamline 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' >/U-2 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.