40 results on '"Bayraktar, Seyfettin"'
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2. Three-dimensional computational analysis of flow over twisted hydrofoils
- Author
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Oksuz, Sinem, Celik, Fahri, and Bayraktar, Seyfettin
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- 2023
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3. Comparison study of vertical and horizontal elastic wall on vented square enclosure filled by nanofluid and hexagonal shape with MHD effect
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Al-Amir, Qusay Rasheed, Hamzah, Hameed K., Ali, Farooq H., Bayraktar, Seyfettin, Arıcı, Müslüm, and Hatami, Mohammad
- Published
- 2022
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4. Mixed convection heat transfer and entropy generation of water inside a square vented enclosure with and without four vibrating cylinders in horizontal and vertical directions.
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Almensoury, Mushtaq F., Al-Srayyih, Basil Mahdi, Al-Amir, Qusay Rasheed, Hamzah, Hameed K., Abed, Azher M., Ali, Farooq H., Bayraktar, Seyfettin, Arıcı, Müslüm, and Hatami, Mohammad
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HEAT convection ,HEAT transfer ,NATURAL heat convection ,NUSSELT number ,ENTROPY ,CURTAIN walls - Abstract
The control and improvement of heat transfer in enclosures is very important in several engineering applications. In the current two-dimensional numerical study, the mixed convection and entropy generation of water flowing inside a square vented enclosure that contains four vibrating cylinders with relatively low frequencies fr = 1, 2, 3, 5 Hz in the vertical and horizontal directions are reported. The effects of Reynolds and Richardson numbers, vibration frequency, vibration amplitude, and the direction of the cylinders' vibration on heat transfer and entropy generation are presented for various cases. The horizontal walls of the enclosure are kept adiabatic while the vertical left and right walls are hot and cold, respectively. The linear regression analysis was used to reveal the rate of increase in the Nusselt number with the Reynolds and Richardson numbers number for each cases. Series of analyses show that the existence and the vibration of the cylinders increases heat transfer but the vibration in the horizontal direction is more effective since the top and bottom walls of the enclosure are adiabatic. It is found that the entropy generation due to heat transfer is low at the center of the enclosure. The direct relationship between the heat transfer and both Reynolds and Richardson numbers is reported. In terms of heat transfer, it is found that the critical vibration frequency and amplitude are fr = 4 and A = 0.05L and 0.075L. [ABSTRACT FROM AUTHOR]
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- 2024
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5. Innovative computational modal analysis of a marine propeller
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Uslu, Seckin, Bayraktar, Meral, Demir, Cihan, and Bayraktar, Seyfettin
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- 2021
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6. Mixed convection heat transfer and entropy generation of water inside a square vented enclosure with and without four vibrating cylinders in horizontal and vertical directions
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Almensoury, Mushtaq F., primary, Al-Srayyih, Basil Mahdi, additional, Al-Amir, Qusay Rasheed, additional, Hamzah, Hameed K., additional, Abed, Azher M., additional, Ali, Farooq H., additional, Bayraktar, Seyfettin, additional, Arıcı, Müslüm, additional, and Hatami, Mohammad, additional
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- 2023
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7. Flow and heat transfer investigation of a circular jet issuing on different types of surfaces
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Bolek, Abdullah and Bayraktar, Seyfettin
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- 2019
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8. Heat and Fluid Flow Analyses of an Impinging Jet on a Cubic Body
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Bolek, Abdullah, primary and Bayraktar, Seyfettin, additional
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- 2018
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- View/download PDF
9. List of Contributors
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Acar, Canan, primary, Acarkan, Bora, additional, Ahmed, Mahmoud, additional, Akkurt, Gülden G., additional, Alaefour, Ibrahim E., additional, Alimoradiyan, Hamed, additional, Alpaydın, Güvenç U., additional, Alptekin, Ersin, additional, Altinkaynak, Mehmet, additional, Altun, Ayşe F., additional, Arsan, Zeynep D., additional, Asadian, Elnaz, additional, Avci, Ali, additional, Avcı, Atakan, additional, Aydin, Ebubekir S., additional, Aydin, Mustafa, additional, Azari, Katayoun T., additional, Baissi, Mohaled T., additional, Bayat, Mutlucan, additional, Bayraktar, Seyfettin, additional, Ben cheikh el hocine, Hanane, additional, Bilgin, Atilla, additional, Bolek, Abdullah, additional, Borhani, Tohid N.G., additional, Boyaghchi, Fateme A., additional, Bozbağ, Selmi E., additional, Brahim, Ammar B., additional, Brendlé, Jocelyne, additional, Calli, Ozum, additional, Corumlu, Vahit, additional, Coşkun, Turgay, additional, Demir, Onur, additional, Deniz, Emrah, additional, Dincer, Ibrahim, additional, Dincer, Selim, additional, Dönmez, Aydın H., additional, Durgun, Orhan, additional, Eker, Aysegul A., additional, Eker, Bulent, additional, El-Naas, Muftah H., additional, Emam, Mohamed, additional, Emir, Turgay, additional, Erdogan, Anil, additional, Erkey, Can, additional, Ermis, Kemal, additional, Ezan, Mehmet A., additional, Fellah, Ali, additional, Gönül, Ersan, additional, Gönülol, Okay, additional, Güler, Mehmet Güray, additional, Gülhan, Özcan, additional, Gülüm, Mert, additional, Gunerhan, Huseyin, additional, Hacioglu, Aynur, additional, Haloui, Hafsia, additional, Hamdi, Boualem, additional, Hamdullahpur, Feridun, additional, Hamed, Mouna, additional, Hamoudi, Souhila A., additional, Heidarnejad, Parisa, additional, Hilmioglu, Nilufer D., additional, Hisar, Gökhan, additional, Hosseini, Mehdi, additional, Kabul, Ahmet, additional, Kalkan, Cem, additional, Karabuğa, Arif, additional, Karadağ, Hazal G., additional, Karakoyun, Yakup, additional, Kayansayan, Nuri, additional, Khelifa, A., additional, Kılıç, Muhsin, additional, Köktürk, Gülden, additional, Küçüka, Serhan, additional, Kurtgoz, Yusuf, additional, Li, Xianguo, additional, Mahmoodnezhad, Motahare, additional, Malek, Ali, additional, Motalebzade, Rogaye, additional, Nergiz, Güven, additional, Nigiz, Filiz U., additional, Noorpoor, Alireza, additional, Norouzi, Rouhollah, additional, Ouellette, David, additional, Ozalp, Mehmet, additional, Özbay, Nurgül, additional, Ozbilen, Ahmet, additional, Özdemir, Esra, additional, Ozden, Adnan, additional, Ozener, Barkın, additional, Özer, Muhammet, additional, Colpan, C. Ozgur, additional, Ozsoy, Ahmet, additional, Öztop, Hakan F., additional, Ozturk, Murat, additional, Pehlivan, Eylem, additional, Polat, M. Furkan, additional, Radwan, Ali, additional, Ratlamwala, Tahir A.H., additional, Rosen, Marc A., additional, Sadikoglu, Hasan, additional, Şahin, Zehra, additional, Şahin, Cem D., additional, Şanli, Deniz, additional, Sari, Elif K., additional, Selbaş, Reşat, additional, Selimefendigil, Fatih, additional, Senpinar, Ahmet, additional, Sevinchan, Eren, additional, Shahgaldi, Samaneh, additional, Siddiqui, Osamah, additional, Singh, Vishavdeep, additional, Söğüt, Mehmet Z., additional, Tabet, Ismail, additional, Tokuç, Ayça, additional, Top, Murat, additional, Touafek, Khaled, additional, Tuti, Mustafa, additional, Ulusoy, Isılay, additional, Ünal, Anıl, additional, Unlu, Derya, additional, Vakili Ardebili, Ali, additional, Vatandas, Sedat, additional, Yakut, Melik Z., additional, Yakut, Ali K., additional, Yaman, Elif, additional, Yarbay Şahin, Rahmiye Z., additional, Yargıç, Adife Ş., additional, Yavuz, Fazıl Erinç, additional, Yiğit, Kenan, additional, Yilmaz, Fatih, additional, Yucel, Ozgun, additional, Yuksel, Yunus E., additional, Yuksel, Ceren, additional, Yumurtacı, Zehra, additional, and Zhang, Zhien, additional
- Published
- 2018
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10. Wall proximity effects on flow over cylinders with different cross sections
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Bayraktar, Seyfettin, Yayla, Sedat, Oztekin, Alparslan, and Ma, Haolin
- Subjects
Navier-Stokes equations -- Research ,Cylinder (Mathematics) -- Research ,Mathematical research ,Physics - Abstract
This paper presents the results of a numerical study on flow characteristics over circular, square, and diamond cross-sectional cylinders. Investigations are performed in a two-dimensional domain using the finite volume discretization method solver for Reynolds number, Re = 20 000. Unsteady Reynolds averaged Navier-Stokes equations with Spalart-Allmaras turbulence model have been used as a turbulence closure. After the validation of the simulations with the available experimental data from the open literature, global characteristics of the flow field around different shaped cylinders near the wall have been presented. Effects of wall proximity on cylinders are investigated for four different gap width (G) to cylinder width (D) ratios. PACS Nos.: 47.11.-j, 47.27.-i, 47.32.-y, 47.32.C. Nous presentons ici les resultats d'une etude numerique sur les caracteristiques d'ecoulement d'un fluide sur la surface de cylindres de section efficace, circulaire, carree et en diamant. Ces etudes se font sur un domaine 2D par voie d'une discretisation en volumes finis, pour une valeur du nombre de Reynolds, Re = 20 000. Nous utilisons les equations de NavierStokes avec decomposition de Reynolds instable, additionnees du modele de turbulence de Spalart-Allmaras utilise pour fermer les equations de turbulence. Apres validation des resultats a l'aide des resultats experimentaux provenant de la litterature disponible, nous presentons les caracteristiques globales du champ d'ecoulement autour des cylindres de differentes formes pres de la couche limite (mur). Nous etudions l'effet de la proximite du mur sur les cylindres, pour quatre differents rapports de largeur d'espacement (G) sur la largeur du cylindre (D). [Traduit par la Redaction], 1. Introduction Flow past a cylinder is a fundamental fluid mechanics phenomenon. Over the years significant attention has been given to the flow over cylinders because of its wide range [...]
- Published
- 2014
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11. Three-Dimensional Computational Analysis of Flow Over Twisted Hydrofoils
- Author
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Öksüz, Sinem, primary, Celik, Fahri, additional, and Bayraktar, Seyfettin, additional
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- 2022
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12. Three-dimensional analysis of temperature field for various parameters affect the film cooling effectiveness
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Bayraktar, Seyfettin and Yılmaz, Tamer
- Published
- 2011
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13. Numerical investigation of flow over tandem and side-by-side cylinders
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MENTESE, Arif and BAYRAKTAR, Seyfettin
- Subjects
Denizcilik ,Tandem cylinders,Side-by-side cylinders,Turbulence,Drag,Lift ,Marine Science - Abstract
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.
- Published
- 2021
14. Experimental analysis of transverse jet using various decomposition techniques
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Bayraktar, Seyfettin and Yilmaz, Tamer
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- 2011
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15. Bir ters-basamak üzerindeki engellerin etrafındaki akışın sayısal olarak incelenmesi
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BAYRAKTAR, Seyfettin, primary
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- 2021
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16. Two-dimensional simulations of vortex-induced vibration of a circular cylinder
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Mutlu, Asim Ozan, primary, Bayraktar, Meral, additional, and Bayraktar, Seyfettin, additional
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- 2021
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17. Numerical investigation of flow over tandem and side-by-side cylinders
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BAYRAKTAR, Seyfettin, primary
- Published
- 2021
- Full Text
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18. LAMINAR FLOW OVER SLOPED DOWNSTREAM HEATED BOTTOM WALL BEHIND A BACKWARD-FACING STEP
- Author
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BAYRAKTAR, Seyfettin
- Subjects
Physics::Fluid Dynamics ,Engineering ,Mühendislik ,Backward-facing step,laminar flow,computational fluid dynamics,flow separation,reattachment length,heat transfer - Abstract
In the present three-dimensional study, laminar flow over a backward-facing step was investigated in the framework of the finite volume method for various Reynolds numbers ranging from 100 to 1000. Attempts were made to clarify the effects of the slope of the downstream heated bottom wall behind the step on the reattachment length and heat transfer. It was found that the length of the recirculation region changes slightly with the slope angles at lower Reynolds numbers while it changes dramatically as Reynolds number increases. The longest length of the recirculation region was obtained at the highest slope angle in the negative vertical-direction while the shortest one was determined at the maximum slope angle in the positive vertical direction. Increasing slope angles in both directions also provide a higher local Nusselt number in some distance behind the step.
- Published
- 2019
19. Numerical investigation of flow over tandem and side-by-side cylinders.
- Author
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MENTEŞE, Arif and BAYRAKTAR, Seyfettin
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UNSTEADY flow ,TURBULENCE ,DRAG coefficient ,REYNOLDS number ,COMPUTER simulation - Abstract
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. [ABSTRACT FROM AUTHOR]
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- 2022
- Full Text
- View/download PDF
20. Numerical investigation of aerodynamic characteristics of generic pickup trucks
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Atatug, Volkan, primary and Bayraktar, Seyfettin, additional
- Published
- 2020
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21. Chapter 2.27 - Heat and Fluid Flow Analyses of an Impinging Jet on a Cubic Body
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Bolek, Abdullah and Bayraktar, Seyfettin
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- 2018
- Full Text
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22. Computational Analysis of Effects of Location of the Diverter Plate and Inlet Velocity on the Efficiency of Two-Phase Flow Separator
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Yayla, Sedat, primary, Kamal, Karwan, additional, and Bayraktar, Seyfettin, additional
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- 2019
- Full Text
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23. LAMINAR FLOW OVER SLOPED DOWNSTREAM HEATED BOTTOM WALL BEHIND A BACKWARD-FACING STEP.
- Author
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BAYRAKTAR, Seyfettin
- Subjects
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NUSSELT number , *FINITE volume method , *REYNOLDS number , *COMPUTATIONAL fluid dynamics , *LAMINAR flow , *FLOW separation - Abstract
In the present three-dimensional study, laminar flow over a backward-facing step was investigated in the framework of the finite volume method for various Reynolds numbers ranging from 100 to 1000. Attempts were made to clarify the effects of the slope of the downstream heated bottom wall behind the step on the reattachment length and heat transfer. It was found that the length of the recirculation region changes slightly with the slope angles at lower Reynolds numbers while it changes dramatically as Reynolds number increases. The longest length of the recirculation region was obtained at the highest slope angle in the negative vertical-direction while the shortest one was determined at the maximum slope angle in the positive vertical direction. Increasing slope angles in both directions also provide a higher local Nusselt number in some distance behind the step. [ABSTRACT FROM AUTHOR]
- Published
- 2020
24. Effects of under body diffuser on the aerodynamics of a generic car
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Bayraktar, Seyfettin, primary and Bilgili, Yilmaz Ogun, additional
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- 2018
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25. Computational fluid dynamics analyses on the hydrodynamic entry length in internal flows
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Kahramanoglu, Emre, primary, Sezen, Savas, additional, and Bayraktar, Seyfettin, additional
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- 2017
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26. Ayrıştırma Plakasının Konumunun ve Giriş Hızının İki-Fazlı Ayrıştırıcı Verimine Olan Etkilerinin Sayısal Analizi.
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YAYLA, Sedat, KAMAL, Karwan, and BAYRAKTAR, Seyfettin
- Abstract
Copyright of Journal of Polytechnic is the property of Journal of Polytechnic and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
- Published
- 2019
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27. Investigation of the Effects of Gurney Flap on the Lift OF NACA 0012 Airfoil in Varying Lengths
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Doğrul, Ali, Cakici, Ferdi, Kinaci, Ömer Kemal, and Bayraktar, Seyfettin
- Published
- 2012
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28. Flow Visualization of Sloshing in an Accelerated Two-Dimensional Rectangular Tank
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Sahin, Gurhan, primary and Bayraktar, Seyfettin, additional
- Published
- 2015
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29. Computational Fluid Dynamics and Heat Transfer Analysis for a Novel Heat Exchanger
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Ma, Haolin, primary, Oztekin, Dennis E., additional, Bayraktar, Seyfettin, additional, Yayla, Sedat, additional, and Oztekin, Alparslan, additional
- Published
- 2015
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30. Çapraz akıştaki türbülanslı jet akışlarının deneysel ve hesaplamalı akışkanlar dinamiği analizi
- Author
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Bayraktar, Seyfettin, Yılmaz, Tamer, and Gemi İnşaat Mühendisliği Anabilim Dalı
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Flow velocity ,Flow ,Flow performance ,Flow equations ,Flow problems ,Flow modellings ,Engineering Sciences ,Flow analysis ,Mühendislik Bilimleri - Abstract
Bilindiği üzere doğadaki hemen hemen tüm akışlar türbülanslıdır. Türbülansın görüldüğü akışlardan biri de çapraz akıştaki jet akışları ya da diğer adıyla çapraz jetlerdir. Çapraz akıştaki jet akışları jet akış yönünün içerisine püskürtüldüğü serbest akış yönünden tamamen farklı olduğu bir akış türünü ifade eder. Serbest akış, sahip olduğu momentumun etkisiyle lüleden püskürtülerek sağlanan jet akışını kendi doğrultusunda akmaya zorlayarak yönünü değiştirir. Çapraz akıştaki jetler, düşük hızlı baca dumanlarından, yüksek hızlara sahip jet motorlarının yanma odalarındaki akışa ve hipersonik roket ve füze kontrol sistemlerine, düşük kütle akışlı sınır tabaka kontrol sistemlerinden, dikey olarak inip havalanabilen V/STOL uçaklara kadar pek çok mühendislik olayında kendini göstermektedir.Bu çalışmada çapraz akıştaki jet akışları problemi deneysel ve hesaplamalı akışkanlar dinamiği (HAD) kullanılarak ele alınmıştır. HAD ile çapraz akıştaki jet akışlarının incelenmesi amacıyla, gerek endüstriyel uygulamalarda mühendislerce, gerekse de üniversite ve araştırma enstitülerinde bilim adamları ve araştırmacılar tarafından yaygın olarak kullanılan FLUENT 6.3.26 programından yararlanılmıştır. Sayısal kısımda lüle kesit geometrisi, lüle sayısı, hız oranlarının etkisinin yanında ayrıca lüle ile çapraz akış arasındaki eğim açısı da dikkate alınarak, bu gibi değişkenlerin akış yapısı üzerindeki etkileri kapsamlı olarak ele alınmıştır. Bunun için dairesel ve kare kesitli olmak üzere iki farklı lüle kesit geometrisi, bir lüle ve üç tane lüle yan yana olmak üzere iki farklı lüle sayısı, R=0.2, 0.5, 1.0 ve 2.0 olmak üzere dört farklı hız oranı ve a=30°, 45°, 60°, 75° ve 90° olmak üzere beş farklı eğim açısı incelenmiştir. Çapraz akıştaki baskın girdap yapılarından en önemli olan zıt-dönüşlü girdap çiftinin hız oranı, eğim açısı ve lüle kesit geometrisi ile nasıl değiştiği araştırılmıştır. Eğim açısı ve hız oranının artmasıyla zıt-dönüşlü girdap çiftinin ölçek olarak büyüdüğü ve yan yana üç tane lüle kullanılması durumunda oluşan zıt-dönüşlü girdap çiftinin, tek bir lüle kullanılmasına göre daha farklı bir yapıda olduğu görülmüştür. Bunun yanında özellikle gaz türbinlerinin film soğutulmasında büyük öneme sahip film soğutma verimi de en uygun lüle kesit geometrisi, eğim açısı ve hız oranı için araştırılarak sonuçlar irdelenmiştir. Film soğutma veriminin en yüksek değeri, eğim açısı 30° için elde edilmiş ve dairesel kesitli lüle kullanılmasının daha iyi olacağı sonucuna varılmıştır.Deneysel ölçümler 304 mm´304 mm´914 mm test kesidine sahip bir rüzgâr tünelinde değişik hız oranları için farklı yatay ve düşey mesafelerde gerçekleştirilmiştir. Lüleden sağlanan jet akışı ve rüzgâr tünelinde gerçekleştirilen serbest akış hızı sabit sıcaklık hızölçeri (sıcak tel hızölçeri) kullanılarak ölçülmüştür. Jet akışının sağlandığı lüle dairesel kesitli olup, ölçümler 90° eğim açısında R=0.5, 1.0 ve 1.5 için gerçekleştirilmiştir. Elde edilen deneysel veriler Fourier, dalgacık (wavelet) ve uygun ortogonal ayrıklaştırma (POD) metotları kullanılarak incelenmiş, akışa ait güç tayfları (power sprectrum), dalgacık haritaları ve frekans-zaman alanındaki değişimleri sunulmuştur. Fourier analizine göre, bir serbest jette lüle çıkışındaki güç tayfı ilerleyen diğer mesafelere göre laminar karakter göstermiş ve lüle çıkış hızı artırıldığında frekans enerjisi düşmüştür. Üç farklı hız oranı (R=0.5, 1.0 ve 1.5) için yapılan mukayesede daha yüksek hız oranında daha düşük frekans enerjisi saptanmıştır. Bu durum lülenin merkezinde jetin çapraz akış önünde bir engel gibi davranarak çapraz akış etkisini sönümlemesi ve ilerleyen mesafelerde etkisini kaybetmesine bağlanmıştır. Verilerin dalgacık (wavelet) analizinde en düşük hız oranı olan R=0.5'te baskın frekansın 45 Hz'te kendini gösterdiği, ancak R=1.0 olduğunda bu değerin 85 Hz ile 105 Hz arasında olduğu gözlenmiştir. Enerjinin modlara göre dağılımlarının gösterildiği uygun ortogonal ayrıklaştırma (POD) metodunda ise düşük hız oranındaki modların yüksek hız oranındaki modlara nazaran daha fazla enerji taşıdıkları görülmüştür. Lüle çıkışından uzaklaşıldıkça toplam enerjinin daha fazla sayıda moda dağıldığı gösterilmiştir.Akım görüntüleme tekniği kullanılarak çapraz akıştaki jet akışlarında görülen büyük ölçekli yapılar ve akış yapısı gösterilmiştir. Bunun için bir duman üreteci ve dijital video kayıt cihazı kullanılarak rüzgâr tüneli ve jet hızları değiştirilerek akış alanı incelenmiştir. Yüksek jet hızlarında lüleden püskürtülen jet, çapraz akış içerisine daha dik bir şekilde nüfuz ederek akmaya devam etmiştir. Lüle hızı kademeli olarak azaltıldığında ise rüzgâr tünelinden sağlanan çapraz akış daha baskın hale gelmiş ve jet akışını yenerek, kendi doğrultusunda akmaya zorlamıştır. Rüzgâr tüneli yüksek hızda çalıştırıldığında bu baskın özellik daha çok görülmüş ve jet akışı gittikçe düzleşerek test kesidinden akmaya başlamıştır. Rüzgâr tüneli ve lülenin düşük hızlarda aktığında saptanan kayma tabakası girdapları, özellikle çapraz akışın yüksek hızlarında tespit edilememiştir.Anahtar Kelimeler: Hesaplamalı akışkanlar dinamiği (HAD), türbülans modelleri, çapraz jet, sabit sıcaklık hızölçeri, dalgacık ayrıklaştırması, uygun ortogonal ayrıklaştırma, Fourier ayrıklaştırması, güç tayfı. As it is well known that, most of the flows in the nature are turbulent. One of the turbulent flows seen in the nature is jet in cross flow or transverse jet. Jet in cross flow expresses the flow at which its direction is completely different from the cross flow. Free stream forces the jet flow to change its direction due to its momentum. Jet in crossflow is encountered from the stack smoke to flow in combustion room and hypersonic misille and rocket control systems, low mass flux boundary layer control systems to V/STOL aircrafts.In this study, jet in cross flow is taken into account by using experimental and computational fluid dynamics (CFD). In computational fluid dynamics calculations a CFD code of FLUENT 6.3.26 which has been used commonly in industry by engineers and in institutions and universities by academicians and researchers are considered. In the numerical section, nozzle geometry, number of nozzles, velocity ratio and inclination angle between the crossflow and nozzle are investigated to explore the effect of these parameters on the flow structure. For this reason two different nozzle section geometries; two different nozzle arrangements; circular and square nozzles, one and three-side by side nozzles, four different velocity ratios; R=0.2, 0.5, 1.0 and 2.0, five different inclination angle; a=0°, 45°, 60°, 75° ve 90° are considered. It was realized that, the high velocity ratio and inclination angle between the channel and nozzle, the more penetration of jet and the enlarge the counter-rotating vortex pair (CRVP) in size. It was also reported that using three nozzles side by side lead to high CRVP in size than the use of one nozzle. Film cooling which is very important for cooling technique was also investigated for different jet inclination angle and blowing ratios. It can be concluded that, the high thermal film cooling efficiency was obtained for the lowest inclination angle of 30°.Experimental measurements are done in a wind tunnel which has 305 mm´305 mm´914 mm test section for different jet-to-crossflow velocity ratios at different stations. Jet in crossflow are measured by using constant temperature anemometer (CTA) which is traditional but most commonly used in the experiments. Nozzles used in the experiments are considered as circular and the inclination angle between the nozzle and crossflow are designed as 90°. All measurements are conducted for R=0.5, 1.0 and 1.5. The results are then decomposed by using Fourier, wavelet and proper orthogonal decomposition (POD) techniques. Besides power spectrums and histograms dealing with the flow, velocity distributions are showed. According to Fourier analysis, the power spectrum at the center of the nozzle are more similar to the laminar character that the streamwise stations. When jet exit velocity was increased, it was seen that the energy of the flow decreased ironically. Comparisons were made for three velocity ratios, (R=0.5, 1.0 and 1.5) and it was seen that, the highest velociy ratio has the lowest energy. At the center of the nozzle, jet acts as an obstacle to the coming crossflow and damps the effect of the crossflow. The most dominant frequency of the flow was detected as 45 Hz at the ratio of R=0.5 by using wavelet technique. At R=1.0, dominant frequencies were seen at 85 Hz to 105 Hz. Energy contribution of the flow was calculated by using proper orthogonal decomposition (POD) technique and it was seen that the lower velocity ratio leads to carry more energy of the flow than the higher velocity ratio.Flow visualization technique was also performed to reveal the flow structure. A fog generator and digital video camera were used for this purpose. The flow field was investigated for different jet to crossflow velocity ratio by changing the velocity of the jet and wind tunnel, respectively. At the highest velocity ratio, jet penetrate directly into the crossflow due to its high momentum and acts as obstacle on the coming crossflow. It was also showed that, when the jet velocity was increased, crossflow become more dominant and sweep the jet flow, bending it to the crossflow direction. Shear layer vortices were detected especially at lower velocity ratio while it could not be seen at high crossflow.Keywords: Computational fluid dynamics (CFD), turbulence models, transverse jet, constant temperature aneometer (CTA), wavelet transform, proper ortogonal decomposition (POD), Fourier decomposition, power sprectrum. 210
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- 2008
31. Boru ve silindirik kanallardaki engellerin akım üzerindeki etkilerinin simülasyonu
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Bayraktar, Seyfettin, Vardar, Nurten, and Diğer
- Subjects
Gemi Mühendisliği ,Navier-Stokes ,Cylindrical coordinates ,Laminar flow ,Simulation ,Marine Engineering - Abstract
ÖZET Bu çalışmada, içerisinde düşey bir engel bulunan borudaki laminar, sürekli ve sıkıştırılamaz akım ve ısı transferi problemleri silindirik koordinatlarda iki boyutlu ve nümerik olarak incelenmiştir. Boru içerisindeki akışı modellemek için süreklilik, enerji, momentum denklemlerinin yatay ve düşey yöndeki bileşenleri ve girdap-akım fonksiyonu metodu kullanılmıştır. Sözü edilen denklemler sonlu faiklar metodu kullanılarak ayrıklaştırılıp eş zamanlı çözüme hazır hale getirildikten sonra, Fortran dilinde yazılmış bir bilgisayar programı ile çözdürülmüşlerdir. Çalışmada, engelin değişik geometrik oranlan ve boru girişine uzaklığının akım alanı ve ısı transferi üzerindeki etkileri gösterilmiştir. Borudan Prandtl sayıları sırasıyla 0.7, 7.0 ve 546 olan hava, su ve kullanılmamış motor yağı geçtiği kabulüyle, Reynolds sayısının 50 ve 500 değerleri için akım hatları ve ısı transferi durumu incelenmiştir. Sonuçlar, literatürden elde edilen çalışmalarla karşılaştırılmış ve benzer sonuçların elde edildiği görülmüştür. Anahtar Kelimeler: Laminar akış, silindirik koordinatlar, engelli boru, Navier-Stokes vııı ABSTRACT In this study, considering the flow is laminar, steady and incompressible, the flow and heat transfer through a pipe employing a vertical obstacle are investigated in cylindrical - coordinates with 2 dimensional numerical analysis. To form a model vertical and horizontal components of the continuity, energy, momentum equations and vorticity-stream function method are included. These equations to be solved simultaneously are discretized employing the finite difference method and they are solved using a computer that has been writtenin Fortran. Through this study, the effects of different ratios relating to the obstacle and the position of the obstacle from pipe entrance on the streamlines and heat transfer are investigated. Air, water and clean engine oil with Prantl numbers of 0.7, 7.0, 546 are let flow through the pipe and the streamlines and heat transfer for the Reynolds numbers of 50 and 500 are investigated. Finally, it is shown that the results obtained are consistent with the reported results in the literature. Keywords : Laminar flow, cylindrical coordinates, pipe with obstacle, Navier-Stokes. IX 46
- Published
- 2001
32. MIXING OF AIR AND CO2 STUDY ON A TURBINE BLADE
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Ozdemir, Yavuz Hakan, primary, Bayraktar, Seyfettin, additional, and Yilmaz, Tamer, additional
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- 2009
- Full Text
- View/download PDF
33. Numerical investigation of a water flow in a rib-roughened channel by using Reynolds stress model
- Author
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Bayraktar, Seyfettin, primary, Bayraktar, Meral, additional, and Vardar, Nurten, additional
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- 2008
- Full Text
- View/download PDF
34. Cfd and Analytical Analysis of Exhaust System of a Gas Turbine Used in a Ship
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Bayraktar, Seyfettin, primary, Safa, Aykut, additional, Yilmaz, Tamer, additional, Simos, Theodore E., additional, Psihoyios, George, additional, and Tsitouras, Ch., additional
- Published
- 2007
- Full Text
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35. Computational Fluid Dynamics and Heat Transfer Analysis for a Novel Heat Exchanger.
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Haolin Ma, Oztekin, Dennis E., Bayraktar, Seyfettin, Yayla, Sedat, and Oztekin, Alparslan
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- 2015
- Full Text
- View/download PDF
36. ÇAPRAZ JETLERDEKİ GİRDAP YAPILARININ İKİNCİ DERECE TÜRBÜLANS MODELİ İLE İNCELENMESİ.
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Bayraktar, Seyfettin and Yilmaz, Tamer
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- *
RESEARCH , *TURBULENCE , *ANALYTICAL chemistry , *DYNAMICS , *DATA structures , *ALISMATACEAE , *ELECTRONIC data processing , *COMPUTER networks , *ENGINEERING - Abstract
In this study, the vortex structures seen in a jet in a crossflow phenomena which has numerous applications are obtained by using Reynolds Stress Turbulence Model. The flow is three-dimensional and fully turbulent in nature so a three-dimensional channel and a pipe are considered. The numerical results are compared with an experimental data found in open literature and it is seen that the velocity components and turbulent kinetic energy variations are in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]
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- 2007
37. Numerical and experimental study of turbulent free surface flow for a fast ship model
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Ozdemir, Yavuz Hakan, BARIS BARLAS, Yilmaz, Tamer, and Bayraktar, Seyfettin
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Physics::Fluid Dynamics ,CFD ,Turbulent free surface flows ,Star CCM+ ,fast hull ,k-ε turbulence model - Abstract
In this study the experimental and computational results for a fast ship model is presented. The Reynolds Averaged Navier Stokes (RANS) equations and the nonlinear free surface boundary conditions are discretized by means of an overset grid finite volume scheme. The experiments are performed at Istanbul Technical University Towing Tank basin. In the numerical turbulent flow calculations, the relationship between the Boussinesq's hypothesis of turbulence viscosity and the velocities are obtained through the standard k-ε turbulence model. Simulations of turbulent free surface flows around the model are performed by using Star CCM+ solver and Volume of Fluid (VOF) model to capture the free surface between air and water. The total resistance of the ship model is compared with the experimental results. Bow and aft wave form developments are also investigated qualitatively. For Froude (Fn) numbers less than 0.25, the computations are found to be well satisfactory, giving efficient and accurate tool to predict curves of resistance. For relatively higher speeds (Fn>0.25) a low Reynolds number turbulence model may be more suitable to predict the resistance.
38. Farklı geometrik yüzeylere sahip tandem silindirler etrafındaki iki boyutlu akışın sayısal olarak modellenmesi
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Öztürk, Enes, Bayraktar, Seyfettin, and Gemi İnşaatı ve Gemi Makineleri Mühendisliği Anabilim Dalı
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Gemi Mühendisliği ,Marine Engineering - Abstract
Bu çalışmada dikdörtgen kesitli bir düzlemde düzenli akım kullanılarak oluşturulmuş bir model içerisine, akıma dik olacak şekilde yerleştirilmiş iki farklı yüzey geometrisine sahip (yivli ve pürüzsüz) silindirler etrafındaki akışın sayısal olarak incelenmesi yapılmıştır. Bunun için sonlu hacimler metodunu kullanan ANSYS-FLUENT 19 paket programı kullanılmıştır. Çalışmada ilk olarak D=0.049m ölçülerinde pürüzsüz yüzeyli 2 silindir modellenerek düzenli akış içerisine tandem düzende yerleştirilmiştir. Re=65×103'de elde edilen değerlerin (Cd ve St) deneysel verilerle karşılaştırması yapılmıştır. Daha sonra model geliştirilerek yine aynı hesap alanında olacak şekilde yivli yüzeyli silindirler yan yana yerleştirilmiştir. Silindirler arasındaki uzaklık (L) değiştirilerek yeni analizler yapılmıştır. Yapılan yüzey geometrisi değişikliğinin ilk modelde elde edilen değerler üzerindeki etkileri incelenmiştir. Elde edilen yeni değerlerin deneysel verilere olan yakınlığı gösterilmiştir. In this study, the flow around the cylinders having two different surface (grooved and smooth) placed perpendicular to the flow into a model formed by using regular flow in a rectangular cross-sectional plane was investigated numerically. For this purpose, ANSYS-FLUENT 19 package program was used which uses finite volume method. In the study, firstly, two cylinders with smooth surface D = 0.049m were modeled and the values obtained in Re=65×103 in regular flow (Cd and St) were compared with experimental values. Then the model was developed and the rollers with rough surfaces were placed side by side in the same calculation area. New analyzes were performed by changing the distance (L) between the cylinders. The effects of surface geometry change on the values obtained in the first model were investigated. The proximity and usability of the obtained new values to the experimental values were determined. 66
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- 2019
39. Two dimensional computational analysis of flow induced vibrations
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Mutlu, Asim Ozan, Bayraktar, Meral, Bayraktar, Seyfettin, and Makine Mühendisliği Anabilim Dalı
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Mechanical Engineering ,Makine Mühendisliği - Abstract
Günümüzde mühendislerin karşılaştığı en zorlu problemlerden biri girdap kaynaklı titreşim problemidir. Girdap kaynaklı titreşimler, bir yapının maruz kaldığı akış sonucunda oluşan girdaplardan dolayı meydana gelir. Bu girdaplar periyodik hale gelerek yapının salınım yapmasına sebep olur. Bu olguya, girdap kaynaklı titreşim denmektedir. Bu salınım, yapıların bozulmasına neden ve ciddi hasarlar almasına sebep olabilir. Günümüzde bilgisayar teknolojilerindeki son gelişmeler sayesinde, girdap kaynaklı titreşimler, birçok araştırmacı tarafından incelenmeye başlanmıştır. Şimdiye kadar kapsamlı araştırmalar yapılmış olmasına rağmen, hala bu konuda geniş çapta araştırılacak yönler bulunmaktadır.Bu çalışmada, girdap kaynaklı titreşimlerin en önemli parametresinden birisi olan sönümleme parametresi incelenmiş ve sonuçlar önceki daha önceden yapılmış deneysel bir çalışma ile karşılaştırılmıştır. Simülasyonlar, tek serbestlik derecesinden akış yönüne dik hareket edebilen, silindirik bir yapıda gerçekleştirilmiştir. Yapılan simülasyonlarda; genel olarak, deneysel sonuçlarla aynı davranış yakalansada, simülasyonlar iki boyutlu alanda gerçekleştirildiğinden dolayı bazı sonuçlarda tutarsızlık gözlemlenmiştir. Birimsiz deplasman, frekans oranı, girdap modları ve faz açısı sonuçları gösterilmiş, genel olarak şu sonuca ulaşılmıştır; sönümleme artırıldığında genliğin azaldığı ve senkronize bölgeye geçişte bir ertelenme olduğu gözlemlenmiştir. Aynı sonuçlar karşılaştırılan deneysel çalışmada da gözlemlenmiştir. One of the difficult challenges that engineers encounter nowadays is the Vortex Induced Vibration (VIV). VIV occurs when a bluff body is subjected to external fluid flow. Vortices shed from the structures cause bluff bodies to oscillate. This oscillation can lead to failures of the structures. With the recent development of computer technologies, VIV have been caught attention by many researchers. Although, extensive research has been done until now, there are still research areas to be investigated on VIV. In this study, one of the most important parameters of VIV, which is damping of the structure, is investigated and the results are compared with the experimental study of the previous research. The simulations are done with 2D cylindrical cross-section structure that is free to move in transverse direction. Overall, the general trend is well captured, however due to 2D limitations some results are not consistent with experimental data. The results are shown and overall, it is concluded that the response of the amplitude decreases with the increased damping of the structure and a shift occurs in the beginning of the lock-in region with increasing damping. 88
- Published
- 2019
40. Farklı düzlemler üzerine çarpan jetlerin akış ve ısı transfer analizleri
- Author
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Bölek, Abdullah, Bayraktar, Seyfettin, and Gemi İnşaatı ve Gemi Makineleri Mühendisliği Anabilim Dalı
- Subjects
Engineering Sciences ,Mühendislik Bilimleri - Abstract
Günümüzde sayısal yöntemler mühendislik problemlerinin çözümünde yaygın olarak kullanılırlar. Bunun nedeni, sayısal çalışmaların deneysel çalışmalara göre hem ekonomik hem de zaman açısından daha avantajlı olmasıdir. Çarpan jet akışları, son yıllarda üzerinde önemli ölçüde çalışmalar yapılan bir konudur. Yüksek ısı transfer oranına sahip olduklarından dolayı endüstride yaygın olarak kullanılırlar. Çarpan jetlerin ısı transfrer karakteristiklerine olan bu ilgi, çarpan jetlerin gaz türbinlerinde ve elektronik parçalarda ısınan parçaların soğutulmasında, tekstil ve kağıt ürünlerinin kurutulması gibi bir çok mühendislik uygulamalarında ki kullanımından kaynaklanır. Ayrıca, kütle transferinde de etkili olduklarından maden havalandırılmasında, tünel operasyonlarında, boya spreylerinde de tercih edilirler.Bu çalışmada, jetlerin farkli düzlemler üzerine çarptırılmasıyla oluşan akış yapıları ve bunların ısı transferi üzerindeki etkileri farklı Reynolds sayıları ve jet-çarpma düzlemi mesafeleri için incelenmiştir. Akışkan yoğunluğundaki değişimleri gözlemleyebilmek için üç farklı metod uyarlanmıştır. Hesaplama ortamı ICEM programında modellenmiş ve daha sonra Ansys Fluent programında analizler gerçekleştirilmiştir. Oluşturulan ağ örgüleri ve türbülans modelleri arasından en uygun olanı belirlenmiştir. Veriler yapılmış olan bir çalışmadan elde edilen sonuçlarla kıyaslanmıştır.Sonuç olarak çarpan jet akışlarında Re sayısıyla Nu sayısı arasında doğru bir orantı olduğu görülmüştür. Maksimum ısı transfer oranı H/D parametresinin 6 olduğu ve Re sayısının 20000 olduğu durumda elde edilmiştir. Sürtünme katsayısı ile Re sayısı arasında ters bir korelasyon olduğu gözlemlenmiştir. Nowadays numerical methods have been generally used to solve engineering problems. This is because numerical methods more economical than the experimental study and more beneficial in terms of time. In the last decades significant studies have been carried on the impinging jets. This impinging jets widely used in industry because of they have high heat transfer rate. To interest of studying this heat transfer mechanism through impinging jets is owing to its many engineering applications such as the drying of textile and paper products, cooling of electronic parts, cooling of gas turbine blades etc.In addition impinging jets are also effective on the mass transfer, they are use in main ventilation, tunnel operation and also in paint spray.In this study impinging jets have been investigated numerically on the different types of planes to observe heat transfer mechanism and flow structure around them for different Re numbers and several jet-target surface distances. In order to detect the alteration on fluid density, three different approaches have been adjusted. The experimental setup drawing and meshing in ICEM CFD programme and then analyzis made by FLUENT. In generated meshs and turbulence models the best have been selected. Parameters according to the plane made by comparing the results obtained from the study will be proposed.Consequently, in impinging jets, the correlation between the Re number and Nu number has been detected. Maximum heat transfer rate has been obtained when Re number equals to 20000 and H/D commensurates to 6. The correlation has been observed between friction coefficient and Re number. 117
- Published
- 2017
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