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    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, Besir
    The 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.
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    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, Besir
    The 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.
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    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, Huseyin
    In 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.
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    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, Huseyin
    The 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.