Wall proximity effects on flow over cylinders with different cross sections

Bayraktar, Seyfettin; Yayla, Sedat; Öztekin, Alparslan; Ma, Haolin

doi:10.1139/cjp-2013-0692

Cited by 10 publications

(5 citation statements)

References 27 publications

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“…The performance of these turbulence models is presented in Table 2 by comparing the change in drag coefficient with the data of Talay, 1975. It is seen that both SKO and SKE are unfavorable while the C D obtained with their derivatives such as SSTKO and RKE are closer to the data of Talay, 1975. In comparison with the results obtained by S-A these two-equation turbulence models may also be eliminated since there is only 4.2% difference between the reported C D of Talay, 1975 and the one found by S-A. These results are not surprising since such problems are commonly analyzed by S-A turbulence model due to its less simulation time and robustness in problems related to the aerodynamics, (Bayraktar et al, 2014).…”

Section: Validationmentioning

confidence: 70%

Numerical investigation of flow over tandem and side-by-side cylinders

Bayraktar¹

2021

Seatific

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In the present paper, two-dimensional unsteady flows over circular cross-section cylinders are analyzed numerically. The effects of placement of the cylinders are investigated for two different arrangements: tandem and side-by-side. Several turbulence models are tested, and it is found that Spalart-Allmaras turbulence model is the best among one-and two-equation turbulence models. The most appropriate time step, which is one of the important parameters in unsteady simulations, is found as 0.002 seconds. After successful validations, the cylinders are positioned as side-by-side and tandem. The effects of the arrangement on flow regime, drag coefficient, lift coefficient and Strouhal number are presented for various distances between the cylinders. It is found that the flow is almost steady without any vortex in the gap when cylinders are in tandem and the gap between them is low. In contrast, the interactions are strong in case of side-by-side arrangement at the lowest gap. When the gap increases, the flow is affected that results in change on the global parameters.

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Section: Validationmentioning

confidence: 70%

Numerical investigation of flow over tandem and side-by-side cylinders

Bayraktar¹

2021

Seatific

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“…It is seen that the Case 4 is the best configuration among the models because it contains few areas of blue-shaded colors which mean minimum flow separation. In the present study, the gap between the ground and the bottom surface of the pickup truck is kept constant and flow structure due to this gap is not investigated, however, the reader may get knowledge in detail about the flow over and beneath a solid body from this one [20]. Flow fields obtained at y/h=0.5 is shown in Figure 10.…”

Section: Resultsmentioning

confidence: 99%

Numerical investigation of aerodynamic characteristics of generic pickup trucks

Atatug¹,

Bayraktar²

2020

Pamukkale J Eng Sci

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ÖzIn the present study, aerodynamic properties of modified generic pickup trucks were investigated by means of finite volume method. Steady, three-dimensional and turbulent flows over the pickup trucks were solved by standard k-epsilon turbulence model. An experimentally investigated two-dimensional pickup truck found in the open literature was used as a benchmark case and some modifications were done on it by closing the sides of the bed first. Then a tonneau was used to close the top of the box and finally, a canopy was used to cover the box completely from the tailgate to the cab roof. Simulations reveal that such modifications that were done on the reference case improve the aerodynamic characteristics of the vehicles in terms of drag coefficient. With respect to the original case, the drag coefficient reduces approximately 50%, 30% and 20% by using a canopy, a tonneau and closing all sides except top of the bed. Such decreases in drag coefficient was achieved because every modification prevents the flow separation more effectively around the bed and behind the cab. Regardless of the shape of the bed, the drag coefficient decreases with increasing Reynolds (Re) number up to Re=12010 3 . It seems that this is the critical Reynolds number since drag coefficient does not change considerably with Re any more. Bu çalışmada, modifiye edilerek oluşurulmuş kamyonetlerin aerodinamik özellikleri sonlu hacimler metodu ile incelenmiştir. Kamyonetler etrafındaki daimi, üç-boyutlu ve türbülanslı akışlar standart k-epsilon türbülans modeli ile çözülmüştür. Açık literatürde bulunan ve deneysel olarak iki-boyutlu-olarak incelenmiş bir kamyonet referans alınarak, kasası üzerinde bir takım modifikasyonlar yapılmıştır. Bunun için, kasanın yanlarının dışında, üst kısmı da düzlemsel bir yüzeyle örtülmüştür. Son olarak, kasanın üstü, yanlarıyla beraber kamyonet kasasından kabin üst yüzeyine kadar her tarafından tamamen kapatılmıştır. Yapılan simülasyonlar, referans araç üzerinde yapılan değişikliklerin, direnç katsayısı dikkate alındığında, araçların aerodinamik karakteristiklerini iyileştirdiğini ortaya koymuştur. Orijinal duruma nazaran aracın kabinden kasanın üstüne kadar kaplanmasıyla %50, kasanın arka, üst ve yanlarının kapatılmasıyla %30 ve sadece kasanın arka ve yanlarının kapatılıp üst tarafının açık bırakılmasıyla direnç değerinde, %20 düşüş sağlanmıştır. Dirençteki bu azalmaların sebebi, kasa etrafında ve kasa ile kabin arasındaki bölgede akış ayrılmasının önlenmesidir. Kasanın şekli ne olursa olsun, direnç katsayısı Reynolds (Re) sayısının Re=12010 3 'e kadar arttırılmasıyla azalmıştır. Bu değerden sonra direnç değerleri Re sayısıyla artık çok fazla değişmediği için bu değerin kritik Reynolds sayısı olduğu görülmüştür.

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“…Increasing the diffuser angle reduces the drag coefficient until =15 and after that drag coefficient increases gradually and reaches its maximum. It is demonstrated by several researchers that a symmetrical body in a free stream has zero lift coefficient when the side walls of the computational domain are far away from the cylinder [23], however, as the cylinder is moved toward one of the side walls the flow along the underside of the cylinder is constrained and causing flow acceleration and resulting decrease in static pressure. Therefore, it is not surprise to see a suction on the underbody.…”

Section: Resultsmentioning

confidence: 99%

Effects of under body diffuser on the aerodynamics of a generic car

Bayraktar

Bilgili²

2018

International Journal of Automotive Engineering and Technologies

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Flow structure and other aerodynamic properties such as drag and lift coefficients of one of the extensively investigated generic cars so-called Ahmed body are reported in the present numerical study for the fixed ground and upswept rear. For this purpose, Ahmed body with the slant angle of 25 is considered and its rear bottom edge is upswept with various angles from 5 to 30 by 5 increments without any side plates. It is observed that the sizes of the upper and lower recirculation bubbles seen in the profile section are decreased compared with the classical Ahmed body, however, the existence of some additional recirculation bubbles are observed when the upswept angle increases. At the highest upswept angle, the upper and bottom vortices called counter-rotating vortices (CVP) become nearly symmetric in the nearfar region however they merge and only one CVP forms behind the body in the far-field. Effects of the upswept angles on the drag and lift coefficients reveal that drag coefficient reduces the upswept angle to 15and then rises at 20 while lift coefficient increases after 25.

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Wall proximity effects on flow over cylinders with different cross sections

Cited by 10 publications

References 27 publications

Numerical investigation of flow over tandem and side-by-side cylinders

Numerical investigation of flow over tandem and side-by-side cylinders

Numerical investigation of aerodynamic characteristics of generic pickup trucks

Effects of under body diffuser on the aerodynamics of a generic car

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