Yazar "Akilli, Huseyin" seçeneğine göre listele
Listeleniyor 1 - 12 / 12
Sayfa Başına Sonuç
Sıralama seçenekleri
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, HuseyinThe 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.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, Huseyinthis 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.Öğe Effect of Yaw Angles on Aerodynamics of a Slender Delta Wing(Asce-Amer Soc Civil Engineers, 2019) Karasu, Ilyas; Sahin, Besir; Tasci, M. Oguz; Akilli, HuseyinIn the present investigation, flow structures over a slender delta wing with a 70 degrees sweep angle, ? at an angle of attack, alpha of 30 degrees, and under the variation of yaw angles within the range of 0 degrees <=beta <= 20 degrees were investigated experimentally. To analyze the flow structure qualitatively and quantitatively, dye visualizations, surface oil visualizations, surface pressure measurements, and velocity measurements using the stereo particle image velocimetry (PIV) were conducted at Reynolds numbers of Re=2x10(4) and Re=1x10(5). Instantaneous and time-averaged flow data were analyzed to demonstrate the effect of yaw angle (beta) on the alterations of leading-edge vortex formation, vortex breakdown, and also vortical flow structures over the wing surface. Time-averaged distributions of streamwise velocity component, u over bar /U, transverse velocity component v over bar /U, patterns of streamline, psi, and distributions of turbulent kinetic energy TKE/U2 were presented to reveal the physics of flow structures under yaw angle (beta) variations. Distribution of pressure coefficients, (-Cp) at various x/c and y/c locations were also presented. The experimental results demonstrated that the variation of yaw angles (beta) has a strong effect on the alterations of the flow structure, the leading-edge vortex formation, and its breakdown. An increase of yaw angle (beta) causes asymmetrical flow structures and hence expands this asymmetrical flow domain further. (c) 2019 American Society of Civil Engineers.Öğe Experimental study on passive flow control of circular cylinder via perforated splitter plate(Techno-Press, 2021) Sahin, Serdar; Durhasan, Tahir; Pinar, Engin; Akilli, HuseyinPresent experimental investigation aims to reduce the shedding of vortex in the near wake region of a circular cylinder using a perforated splitter plate. Perforated plates were placed in the wake region of the cylinder and aligned with the streamwise direction. The length of the plates was equal to the diameter of the cylinder. Different plate porosities and locations were examined and obtained results were compared to the baseline cylinder. Flow measurements downstream of the cylinder were performed in a water channel by employing a particle image velocimetry technique (PIV) at a Reynolds number of Re=5×103. It is observed that the effect of the porosity on the flow characteristics of the cylinder depends on the location of the plate. The strength of shear layers and flow fluctuations in the near wake region of the cylinder are considerably diminished by the perforated splitter plate. It is found that the porosity of ?=0.3 is the most effective control element for gap ratio of G/D=0.5. On the other hand, proper gap ratio is determined as G/D=2 for porosity of ?=0.7. It is concluded in the present study that the perforated splitter plate could be used as alternative passive flow control technique in order to reduce vortex shedding of the cylinder. Copyright © 2021 Techno-Press, Ltd.Öğe Flow comparison around horizontal single and tandem cylinders at different immersion elevations(Pergamon-Elsevier Science Ltd, 2019) Ozdil, N. Filiz Tumen; Akilli, HuseyinFlow characteristic around a horizontal cylinder and tandem horizontal cylinders were compared in shallow water of which height was kept constant as h(w) = 60 nun in this study. The other parameters, taken constant, were free stream velocity and diameter of circular cylinders of which values were U =167 mm/s and D = 30 mm, respectively. To evaluate the time-averaged and instantaneous velocity vector area in the wake zone at Reynolds number; Re-D = 5000 basis on the diameter of cylinder, Particle Image Velocimetry (PIV) was operated. The gap (L) between the tandem cylinders was enhanced from 0 until 90 mm through 15 mm enhancements and it was enhanced from 90 up to 150 mm through 30 nun enhancements in order to observe effect of the gap on flow characteristics. Moreover, another important parameter was the submersion level that ranged from 7.5 until 60 mm through 7.5 mm increments (h(D)/D = 0.25-2) during the experiments. Five hundred instantaneous images were used in order to obtain Reynolds stress correlation, corresponding streamline topology and the mean velocity vector field. The investigation represented that the alternative cylinder attenuates the dimension of the wake zone in accordance with L/D = 0 location. The wake zone obviously happens between tandem cylinders at the starting of L/D =1 location. When the space between tandem cylinders deepens the dimension of the wake zone rises.Öğe FLOW CONTROL OF A CIRCULAR CYLINDER BY PERMEABLE SPLITTER PLATE WITH DIFFERENT POROSITIES AND ANGLE VALUES(Turkish Soc Thermal Sciences Technology, 2024) Sahin, Serdar; Durhasan, Tahir; Pinar, Engin; Akilli, HuseyinFlow control of bluff bodies has been studied extensively to eliminate adverse effects of wake flow such as vibration and acoustic noise or resonance. The circular cylinder has been studied as the bluff body since it is basic geometry and has been used in engineering applications such as heat exchanger tubes, power transmission lines, chimney stacks, bridges, radio telescopes, power lines, offshore drilling rigs etc. In this study, a permeable splitter plate was located at various downstream locations to control the wake flow of the cylinder. All experiments were carried out in a large-scale closed-loop water channel in the Fluid Mechanics Laboratory at Cukurova University. PIV was used to measure the instantaneous velocity vector field in the wake region of the cylinder at Reynolds number Re=5000, which is based on the cylinder diameter, D. Four different splitter plate angle values (0 =0 degrees; 15 degrees; 30 degrees; 45 degrees), three different porosity values (epsilon=0.30; 0.50; 0.70) were investigated. The porosity (epsilon) of the separator plates is defined as the ratio of the total hole area to the plate surface area. All lengths are nondimensionalized by dividing by the cylinder diameter and shown with the * index. The splitter plate length kept to constant during the experiment as ls*=1. The distance between the leading edge of the splitter plate and the cylinder (lg*) is variable due to the rotation of the separator plate at certain angles in the flow direction. To overcome this, the distance between the splitter plate rotation axis and the cylinder was taken as a parameter and shown with the **. The gap between splitter plate midpoint and cylinder (lg**) kept to constant during the experiments as lg**=1.5. When the plates are rotated, the cross-section parallel to the flow decreases, which increases the interaction between the boundary layers. Since the permeable separator plates prevent the interaction of the boundary layers formed in the flow around the cylinder, the effect of the permeable separator plates increases in the downstream regions where the interaction of the boundary layers increases. Thus, the fluctuations are reduced, and a more stabilized trail flow occurs downstream of the cylinder. It was observed that the vortex formation was delayed with the increase of the separator plate angle. In this study, the effect of the separator plate angle and the effect of the plate permeability were clearly observed.Öğe Flow investigation of circular cylinder having different cavities in shallow water(Elsevier Science Inc, 2021) Tantekin, Atakan; Ozdil, N. Filiz Tumen; Akilli, Huseyin; Caliskan, MeltemThe control of the unsteady flow structure formed behind a cylinder placed horizontally in shallow water was analyzed experimentally using bare cylinder and cylinders with cavities having square and rectangular geometries, respectively. Reynolds number, Froude number and water height had been chosen as 5000, 0.27 and 90 mm, respectively and also these parameters were kept constant for all experiments. To consider the influence of height (h), the cylinder level was located at various heights from h: 0 mm to 60 mm. Furthermore, cavity angle (a) had been selected from 0 degrees, 80 degrees, 85 degrees, 90 degrees and 95 degrees to consider influence of cavity angle on flow. With the help of Particle Image Velocimetry (PIV), average velocity vectors were measured in two dimensions at many points simultaneously in a planar flow area. The results uncovered that large negative counter was observed at h: 37.5 mm in bare cylinder as well as cylinders having square and rectangular cavities at h: 45 mm. Also, no negative counter was observed for cylinders having rectangular cavity at h: 0 mm and a: 90 degrees and 95 degrees due to the bottom effect. Due to surface effects, a foci point was formed in all cylinders where close to the surface and close to the base. Two foci points and a saddle point were seen as they moved away from the surface for all cylinders. Also, the smallest vortex region was observed for cylinders having rectangular cavity at h: 37.5 mm and a: 90 degrees and 95 degrees in whole cylinders. Also, the highest drag coefficient (Cd) value was obtained for cylinder having square cavity at h: 52.5 mm and a: 80 degrees while the highest drag coefficient value was obtained for cylinder having rectangular cavity at h: 37.5 mm and a: 95 degrees.Öğe Investigation of crossflow features of a slender delta wing(Techno-Press, 2020) Tasci, Mehmet O.; Karasu, Ilyas; Sahin, Besir; Akilli, HuseyinIn the present work, the main features of primary vortices and the vorticity concentrations downstream of vortex bursting in crossflow plane of a delta wing with a sweep angle of Lambda=70 degrees were investigated under the variation of the sideslip angles, beta. For the pre-review of flow structures, dye visualization was conducted. In connection with a qualitative observation, a quantitative flow analysis was performed by employing Particle Image Velocimetry (PIV). The sideslip angles, beta were varied with four different angles, such as 0 degrees, 4 degrees, 12 degrees, and 20 degrees while angles of attack, alpha were altered between 25 degrees and 35 degrees. This study mainly focused on the instantaneous flow features sequentially located at different crossflow planes such as x/C=0.6, 0.8 and 1.0. As a summary, time-averaged and instantaneous non-uniformity of turbulent flow structures are altered considerably resulting in non-homogeneous delta wing surface loading as a function of the sideslip angle. The vortex bursting location on the windward side of the delta wing advances towards the leading-edge point of the delta wing. The trajectory of the primary vortex on the leeward side slides towards sideways along the span of the delta wing. Besides, the uniformity of the lift coefficient, C-L over the delta wing plane was severely affected due to unbalanced distribution of buffet loading over the same plane caused by the variation of the sideslip angle, beta. Consequently, dissimilarities of the leading-edge vortices result in deterioration of the mean value of the lift coefficient, C-L.Öğe Investigation of flow characteristics for triangular grooved shape cylinder at different heights in shallow water(Pergamon-Elsevier Science Ltd, 2021) Caliskan, Meltem; Tantekin, Atakan; Ozdil, N. Filiz Tumen; Akilli, HuseyinThis study is an investigation and comparison of the flow characteristic around triangular grooved and bare cylinders, positioned horizontally in shallow water using Particle Image Velocimetry (PIV). Throughout the experiment, Reynolds number, Froude number and water height have been selected as 5000, 0.27 and 90 mm, respectively. To observe the effect of height (h) on the flow structure, cylinder is positioned at h: 0 mm, 15 mm, 22.5 mm, 30 mm, 37.5 mm, 45 mm, 52.5 mm and 60 mm. Moreover, grooved angle (a) has been changed from 0 degrees, 80 degrees, 85 degrees, 90 degrees and 95 degrees in shallow water to investigate the effect of grooved angle. The results show that the vortex forms vary according to the groove angle. It is seen that the vortex, the cylinders especially positioned at h: 0 mm and h: 60 mm, are affected owing to the surface and bottom effect. Furthermore, the largest Reynolds stress is observed at the h: 37.5 mm while the largest wake region is observed at the h: 52.5 mm. Also, the maximum Drag Coefficient (C-d) and Turbulence Kinetic Energy (TKE) are observed at h: 0 mm, a: 90 degrees for grooved cylinder and at h: 37.5 mm for bare cylinder, respectively.Öğe Investigation of flow structure around a horizontal cylinder at different elevations in shallow water(Pergamon-Elsevier Science Ltd, 2015) Ozdil, N. Filiz Tumen; Akilli, HuseyinFlow characteristics around a horizontal circular cylinder were investigated in shallow water. The diameter of circular cylinder, the height of shallow water and free stream velocity were kept constant during the experiments as D=30 mm, h(w)=60 mm and U=167 mm/s, respectively. Particle Image Velocimetry (PIV) was used to measure instantaneous and time-averaged velocity vector fields in the near wake region. In order to investigate the effect of immersion, the cylinder was placed at eight different elevations (h(p)) between bottom and free surface (from 7.5 to 60 mm with 7.5 mm increments). Instantaneous and time-averaged velocity vector field, corresponding streamline patterns and Reynolds stress correlation were used to analyze the behavior of the flow downstream of horizontal cylinder. The mean velocity vector field, corresponding streamline topology and Reynolds stress correlation were obtained using 500 instantaneous images. As the immersion level ratio (h(D)/D) increases, the magnitude of jet-like flow velocity goes up ranged from h(D)/D=0.25-1. Time averaged flow characteristics show that there is a difference between primary and developing circulation bubble depending on direction of rotation. This occurrence causes the entrainment and this stimulates the momentum transfer between the core and wake flow region for h(D)/D=1 and 2 cases. (C) 2014 Elsevier Ltd. All rights reserved.Öğe Near-surface particle image velocimetry measurements over a yawed slender delta wing(Sage Publications Ltd, 2021) Karasu, Ilyas; Tumse, Sergen; Tasci, Mehmat O.; Sahin, Besir; Akilli, HuseyinIn this study, extensive instantaneous velocity measurements were conducted within a flow area by stereo particle image velocimetry (SPIV) to investigate the influence of the yaw angle, beta, on the vortical flow structure formed on a slender delta wing. This sideslip angle, beta, in the yaw plane was varied from 4 degrees up to 20 degrees with an interval of 4 degrees at two critical angles of attack, alpha = 25 degrees and 35 degrees, respectively. In order to reveal the influence of the yaw angle, beta over the flow structure of the delta wing, time-averaged flow statistics, and instantaneous flow data obtained by the SPIV technique in the plan-view plane close to the suction surface of the delta wing were presented. It was observed that even a low yaw angle, for instance beta = 8 degrees, becomes to be effective on the flow characteristics of the delta wing, and this effect was augmented with increasing beta. The influence of beta is quite high on the vortical flow structure at alpha= 35 degrees compared to the angle of attack of alpha = 25 degrees. The flow structure that is symmetrical with respect to the centerline of the wing in the case of no yaw has disrupted with the existence beta. Furthermore, the extent of the asymmetry enlarges with increasing beta. The leading-edge vortex (LEV) on the windward side broken earlier and dominated the flow on the wing surface. It is concluded that this asymmetric flow structure can deteriorate the aerodynamic performance and cause other adverse effects such as unsteady loading.Öğe The impact of the pitching motion on the structure of the vortical flow over a slender delta wing under sideslip angle(Springer, 2021) Tasci, Mehmet Oguz; Pektas, Mehmet Can; Tumse, Sergen; Karasu, Ilyas; Sahin, Besir; Akilli, HuseyinThe primary purpose of this investigation is to observe the effect of the pitching motion on the vortical flow structure and bursting of leading-edge vortices over a delta wing under the sideslip angle, beta using a dye visualization technique. In the current work, a delta wing with a sweep angle of ? = 70 degrees was oscillated in upstroke and downstroke direction to be able to discover the influence of pitching motion on the flow characteristics of the delta wing. The values of mean angles of attack were selected as alpha(m) = 25 degrees and alpha(m) = 35 degrees, and the sideslip angle was altered from beta = 0 to 16 degrees. The delta wing oscillated with the various periods of T-e = 5 s, 20 s, and 60 s, respectively. Amplitude of motion was adjusted as alpha(o) = +/- 5 degrees. It is found that the pitching motion of the delta wing under the sideslip angle beta varies the location of the vortex bursting and vortical flow structure substantially.
