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Öğe Dye visualization over double delta wing with various kink angles(Springer, 2019) Durhasan, Tahir; Karasu, IlyasIn this study, the aim is to exhibit vortical behaviors of flow on double delta wings having 70 degrees strake sweep angle and kink angles of 150 degrees, 160 degrees and 165 degrees using dye visualization technique in a water channel. Experiments were performed at Reynolds numbers based on the chord length Re=10,000 and 25,000 for angle of attack in the range 5 degrees to 35 degrees. The visualizations were performed for both end-view and cross-flow planes. The results revealed that the kink angle has a significant role on the interaction of vortices and the strake vortex breakdown locations. The interaction between the strake vortex and the wing vortex is dominant on the flow behaviors at alpha <= 10 degrees. The flow behavior is affected by the kink angle. Two interaction mechanisms which are spiral and enveloping are observed. The spiral interaction alternates to enveloping interaction with increasing Reynolds number. Moreover, the trajectory of the strake vortex core moves outboard with increasing Reynolds number at alpha=10 degrees. For alpha >= 15 degrees, Reynolds number is less effective on the strake vortex breakdown location and also the vortex breakdown locations move the apex gradually with increasing angle of attack. Wake-alike flow structure takes place after occurrence of the vortex breakdown since vortex core splits into disorganized small-scale vortices. On the other hand, development of the wing vortex is more complex than the strake vortex since it collapses near the vicinity of the junction.Öğe Effect of ground on flow characteristics and aerodynamic performance of a non-slender delta wing(Elsevier France-Editions Scientifiques Medicales Elsevier, 2021) Tumse, Sergen; Tasci, Mehmet Oguz; Karasu, Ilyas; Sahin, BesirThe aerodynamic performance and the structure of vortical flow on a delta wing are affected by the influence of the ground in take-off and landing stages. In this context, the effect of the ground on a delta wing having a sweep angle of 40 degrees was investigated by employing Particle Image Velocimetry (PIV), aerodynamic force measuring system and the dye flow visualization technique. Flow characteristics of delta wing were examined under two different angles of attack, alpha = 8 degrees and 11 degrees and variation of the distance between trailing edge of the wing and ground, h normalized with the root chord length, c of the wing. It was observed that the existence of the ground attenuates the magnitude of peak values of primary and secondary vortices due to incomplete development of vortices. The ground effect caused the outboard movement of the leading-edge vortex in a spanwise direction as well as an increase in the size of vortices. Furthermore, the presence of the ground induced a decrease in Strouhal number, St due to the slowing down of vortex formation. Lift and drag coefficient, C-L, and C-D of the delta wing were observed to increase with descending from unbounded flight region into ground effect region. Finally, it was found that C-L/C-D increases by reducing the distance between ground and wing, h/c, and a rise of C-L/C-D is much more effective under the lower angles of attack, alpha. (C) 2020 Elsevier Masson SAS. All rights reserved.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 Investigation of Ground Effect on the Vortical Flow Structure of a 40° Swept Delta Wing(Asce-Amer Soc Civil Engineers, 2022) Tumse, Sergen; Karasu, Ilyas; Sahin, BesirThe ground effect influences the flow structure on a delta wing during landing and take-off processes. In this regard, comprehensive instantaneous velocity measurements and flow visualizations were carried out by particle image velocimetry and dye flow visualization techniques to reveal the ground effect on leading-edge vortex characteristics of a 40 degrees swept delta wing. The flow behaviors on the delta wing under the impact of the ground were analyzed at two angles of attack, 8 degrees and 11 degrees, and the space between the ground and lower surface of the wing was nondimensionalized with the wing's chord length. It was found that the presence of the ground caused premature leading-edge vortex breakdown due to the increasing adverse pressure gradient on the wing's suction side along the chord direction. The ground effect caused an increase in peak value and distributions of turbulent kinetic energy on the wing surface that depended on the earlier leading-edge vortex bursting and complex and disorganized flow structures. The value of time-averaged vertical velocity was lower when the delta wing descended from the free-stream flow zone into the ground effect zone because of the blocking of fluid flow in the gap between the ground and pressure surface of the wing. Thus, it can be concluded that the ground effect is very influential on the change of vortical flow characteristics of nonslender delta wings.Öğe Experimental investigation of the ground effect on a wing without/with trailing edge flap(Iop Publishing Ltd, 2020) Sekhoune Ozden, Khalida; Karasu, Ilyas; Serdar Genc, MustafaIn this study, the ground effect over a wing without/with a flap at low Reynolds numbers was investigated experimentally. Three-dimensional flow fields over and behind a flapped wing and single (without flap) wing in/out of ground effect at several clearances and Re numbers (0.75 x 10(5), 1 x 10(5)and 1.5 x 10(5)) were investigated using three different experimental methods. From flow visualization with smoke technique, a succession of recorded photographs allowed to reveal the interactions of flow and ground. The changes caused by the employment of trailing-edge flap and ground effect were visualized and compared with data obtained from Constant Temperature Anemometer (CTA). According to force measurement results, the flapped wing near the ground conduced to the increase of lift and drag forces for all clearances. From smoke wire results, the separation zone above the flap appears and contributes to a higher turbulence level in the wake region. The leading-edge vortices, tip vortices behind the wing interact with the ground boundary layer and the flow coming out from the section between the trailing edge of the wing and the ground. For this, dominant vortex frequencies were detected using the spectral analysis from velocity measurements at the wake region of the wing. Further, the ground effect enabled the control of the laminar separation bubble (LSB) on the wing at low angles of attack in low Reynolds flows, the bubble gets smaller as clearance increased; however, the ground effect is not effective in controlling the LSB at high angles of attack. As the Reynolds number raised, improvement of ground effect on the wing increased. When all these results were considered, the flap should not be brought too close to the ground to benefit from the ground effect. The flapped configuration with/without ground effect presented the best performance at low angles of attack.Öğe Flow Characteristics over Double Delta Wings at Low Reynolds Numbers(Asce-Amer Soc Civil Engineers, 2020) Karasu, Ilyas; Durhasan, TahirWithin the scope of this study, a quantitative investigation was carried out employing the particle image velocimetry (PIV) technique to determine vortical flow characteristics of 70 degrees/40 degrees, 70 degrees/50 degrees, and 70 degrees/55 degrees double delta wings (DDWs). Experiments were performed in four chordwise sections (x/c=0.5, 0.6, 0.8, and 1) at two Reynolds numbers (R=1x104 and 2.5x104) and different angles of attack (alpha=5 degrees, 10 degrees, 15 degrees, and 25 degrees). It was observed that the secondary vortex is dominant on flow characteristics of double delta wings at low Reynolds numbers. The strengths of vortices increase with increases of both the wing sweep angle and Reynolds number. Furthermore, the location of wing vortex breakdown moves farther downstream as the wing sweep angle increased. Depending on the angle of attack, Reynolds number, and the wing sweep angle, either dual (strake and wing) or triple (strake, wing, and secondary) leading-edge vortices were observed. At a Reynolds number value R=1x104 and angles of attack in the range of alpha <= 15 degrees, the interactions of the vortices influence the flow structure significantly. Dominant frequencies of the vortices are detected near the shear layer formed between the strake vortex and secondary vortex, generally. Moreover, the spectral analyses indicated that bursting of the vortices causes complicated flow patterns over double delta wings, including small-scale vortices. It was found that the transverse Reynolds normal stress concentrates at chordwise sections where secondary vortices are dominant, whereas the locations of peak magnitude of vertical Reynolds normal stress coincide with the strake vortex cores.Öğe Flow control over a diamond-shaped cylinder using slits(Elsevier Science Inc, 2020) Karasu, IlyasIn this experimental study, flow control over a diamond-shaped cylinder using slits was investigated using Particle Image Velocimetry (PIV). The slits used to form self-generating jet flows were placed in the middle of the four sides of the diamond-shaped cylinder at a Reynolds number of 8.6 x 10(3). To investigate the effect of the slit width/diameter ratio (theta) on the flow over the diamond-shaped cylinder, different theta s, such as 0.035, 0.07, 0.105, 0.14 and 0.175 were studied. Various physical parameters such as the time-averaged streamline topology, the streamwise velocity profile, the rms (root mean square) velocity components, the turbulent kinetic energy and the estimated drag coefficient have been presented. In addition to these parameters, Fast Fourier Transform (FFT) and Proper Orthogonal Decomposition (POD) analyses were performed to expand on the flow behaviors. Results showed that while values of theta up to 0.07 for slits did not significantly affect the flow, beyond theta = 0.105, significant changes were observed for the flow structure in the wake region. With increasing theta, the shear layers were smaller, thicker and the strength of the vortex shedding of the diamond-shaped cylinder was attenuated by the jet flows emanating from the slits. The slits caused a considerable decrease in the root mean square (rms) values of velocity and turbulence kinetic energy (TKE/U-infinity(2)) in the wake region, which resulted in a decrease of the estimated drag by 37%. FFT results demonstrated that as theta increased, the Strouhal number (St) of the first dominant peak increased, while the amplitudes of the first dominant peaks reduced because of vortex shrinkage in the wake. In the POD analysis, it was observed that theta was influential on the vortex shedding behavior, and higher rolling-ups formed when the control was applied. According to the results, using slits could be an effective passive control technique for diamond-shaped cylinders.Öğe Green touch for hydrogen production via alkaline electrolysis: The semi-flexible PV panels mounted wind turbine design, production and performance analysis(Pergamon-Elsevier Science Ltd, 2020) Demirdelen, Tugce; Ekinci, Firat; Mert, Basak Dogru; Karasu, Ilyas; Tumay, MehmetThe novel solar-wind integrated system has been firstly used for hydrogen production in literature with validating theoretical, simulated and experimental studies. This integrated system consists of two main parts; solar-assisted wind turbine and alkaline electrolysis cell. In the first part of this system, the semi-flexible PV panels are smoothly integrated on the vertical axis wind turbine blade. This is a unique design in literature, unlike the hybrid systems that include wind turbines and solar PV panels in published literature. The production and testing of the hybrid integrated system in a single structure were performed both in laboratory conditions and also the system was set up the roof of ATU (Adana Alparslan Turkes Science and Technology University) in Adana. The second part includes hydrogen production via alkaline electrolysis system. The cathodes consist of nickel-coated copper (Cu/Ni) and nickel-vanadium binary coated copper (Cu/NiV), that was produced via electrodeposition technique by self-supporting. The performance of electrodes was compared in 1 M KOH solution via I-V behavior, electrochemical impedance spectroscopy, and long term cathodic polarization analysis. Results showed that polarization resistance was decreased almost 4 times by NiV when comparing the Ni. The surface inhomogeneity values were 0.91 and 0.81 for Cu/Ni and Cu/NiV respectively. The hydrogen gas evolved at the cathodes was also measured and higher volumes were detected for NiV binary coating. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.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 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 Performance Assessment of Transition Models for Three-Dimensional Flow Over NACA4412 Wings at Low Reynolds Numbers(Asme, 2018) Karasu, Ilyas; Ozden, Mustafa; Genc, Mustafa SerdarThe performance of the transition models on three-dimensional (3D) flow of wings with aspect ratios (AR) of 1 and 3 at low Reynolds number was assessed in this study. For experimental work; force measurements, surface oil and smoke-wire flow visualizations were performed over the wings with NACA4412 section at Reynolds numbers of 2.5 x 10(4), 5 x 10(4), and 7.5 x 10(4) and the angles of attack of 8 deg, 12 deg, and 20 deg. Results showed that the AR had significant effects on the 3D flow structure over the wing. According to the experimental and numerical results, the flow over the wing having lower ARs can be defined with wingtip vortices, axial flow, and secondary flow including spiral vortex inside the separated flow. When the angle of attack and Reynolds number was increased, wing-tip vortices were enlarged and interacted with the axial flow. At higher AR, flow separation was dominant, whereas wing-tip vortices suppressed the flow separation over the wing with lower AR. In the numerical results, while there were some inconsistencies in the prediction of lift coefficients, the predictions of drag coefficients for two transition models were noticeably better. The performance of the transition models judged from surface patterns was good, but the k-k(L)-omega was preferable. Secondary flow including spiral vortices near the surface was predicted accurately by the k-k(L)-omega. Consequently, in comparison with experiments, the predictions of the k-k(L)-omega were better than those of the shear stress transport (SST) transition.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.
