Browsing by Author "Tastan, Kerem"

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Citation - WoS: 24
Citation - Scopus: 28
Effects of Intake Geometry on the Occurrence of a Free-Surface Vortex
(Asce-amer Soc Civil Engineers, 2018) Yildirim, Nevzat; Tastan, Kerem; 43229; 12654; 06.05. İnşaat Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
Both the profile and orientation of an intake entrance basically determine the characteristics of the flow (especially the velocity distribution and therefore the hydraulically developed subsurface depressions) toward the intake. The profile and orientation of the intake affect (1)the process of accumulation and growth of vorticity (circulation) along the pathway axis of the swirling vortex from the free surface to the intake; (2)position of the pathway of the swirling-vortex filament; and (3)location of the point of entry of the free-surface or subsurface vortex at the entrance of the intake. Test results indicate that the intake-entrance profile has limited effects on the occurrence of the air-core vortex and critical submergence. Regardless of the profile of the intake entrance, one common physical mechanism exists for development of free vortices occurring at intake entrances of different profiles. It is proven that spherical sink surface sectors (SSSSs) are essential for the vortex to exist.
Citation - WoS: 3
Citation - Scopus: 3
Flow Rate Along the Length of the Swirling Vortex Axis at an Intake
(Turkish Chamber Civil Engineers, 2021) Yildirim, Nevzat; Tastan, Kerem; 12654; 06.05. İnşaat Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
In this study, the characteristics of the flow in the region of swirling vortex are examined. The potential flow model based on the summing infinite number of spherical sinks along the vortex core is introduced to predict the flow field and the flow rate along the vortex axis. The flow towards the swirling vortex core has considerable effects on the radial velocity distribution within the ambient fluid flow region near the intake. The agreement between available test data relating to the radial velocity and the method introduced in this study is found to be satisfactory.
Citation - WoS: 3
Citation - Scopus: 2
Improved Equations for the Profile of a Vertical Air-Core Vortex
(Korean Society of Civil Engineers-ksce, 2023) Yildirim, Nevzat; Tastan, Kerem; 12654; 06.05. İnşaat Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
The available formulas for the profile of a vertical non-air-entraining vortex are not practical because they involve unknown parameters and need measurements of the local viscous-core radii across the height of the air-core vortex. Also, these formulas can not be used for the air-entraining vortices. In the present study, the available formulas involving unknown parameters were further improved. Findings are as follows. 1) the magnitudes of the unknown parameters vary across the height of the profile of the air-core vortex and they are the function of the ratio of the height of the air-core vortex to the submergence of the intake; 2) simple charts and formulas were obtained for the variations of the unknown parameters for the air-core vortices with and without an intake; 3) in lieu of the local viscous-core radius, the radius at the half-depth of the profile of the air-core vortex was used; 4) no laborious work of measurements are needed to determine the local viscous-core radii along the profile of the vortex; and 5) the improved formulas are in good agreement with available test data for the profiles of both the non-air-entraining and the air-entraining vortices with or without a vertically flowing downward intake.
Citation - WoS: 1
Citation - Scopus: 1
Occurrence of a Swirling Vortex Without an Intake
(Gazi Univ, 2021) Yildirim, Nevzat; Tastan, Kerem; 12654; 06.05. İnşaat Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
In this study, mechanisms that cause the occurrence of a swirling vortex without an intake are explained. There are more than one different reasons which may cause the occurrence of an air-core vortex or a swirling-vortex flow filament within an ambient fluid. An air-core vortex or a swirling vortex flow filament can also occur in an ambient fluid media without an intake provided that the coaxial subsurface depressions and thereby the imaginary subsurface spherical sink surface sectors are hydraulically developed by any means (such as rotation of the fluid mass of spherical sector-form, impinging or penetrating jet flow, continuously entering solid body or string etc.). Although studies related to occurrence of a swirling vortex in case of an intake can be found in available literature, there are currently no studies which explains the occurrence mechanisms of a swirling vortex without an intake in detail. In this study, it is showed that the causes for the occurrence of the air-core vortex or the swirling vortex filament can be different but the main mechanism of development of the air-core vortex or the swirling vortex filament is identical for all cases.
Prediction of the Profile of a Vertical Air-Entraining Vortex
(Springer, 2025) Al-Hakeem, Yasameen Mansoor A.; Tastan, Kerem; Yildirim, Nevzat; 06.05. İnşaat Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
Air-core vortices occurring at intakes cause efficiency losses, vibrations, operational difficulties, and erosion at affiliated water-conveying structures. Air-core vortices are in the forms of non-air entraining vortex (air-core vortex in suspension) and air-entraining vortex. The profile of an air-core vortex is considered to be one of the main characteristics of the vortex. There are available semi-empirical formulas for the profile of a vertical non-air entraining vortex (air-core vortex in suspension) occurring at a vertically-flowing downward intake. However, there is no available developed formula relating to the profile of a vertical air-entraining vortex occurring at a vertically-flowing downward intake because the height, radii, and other physical quantities of the imaginary section of the air-entraining vortex downstream of the intake entrance are not measurable. Therefore, the profile of a vertical air-entraining vortex needs to be predicted. In the present study, by modifying the available formula relating to the profile of a non-air-entraining vortex and incorporating available test data, a practical methodology is developed for predicting the profile of a vertical air-entraining vortex. This study provides a practical formula and a chart to determine the necessary parameters to predict the profile of a vertical air-entraining vortex. The validation of the proposed methodology is examined and checked with available test data relating to the profile of a vertical air-entraining vortex occurring at a vertically-flowing downward intake. The results of the present study are in good agreement with available test data relating to the profile of vertical air-entraining vortices (the coefficient of determination is between 0.976 and 0.995).
Velocity Distribution Upstream of Circular and Square Intakes
(Korean Society of Civil Engineers-ksce, 2024) Yildirim, Nevzat; Tastan, Kerem; 06.05. İnşaat Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
In the present study, a practical method is developed to predict the radial velocity of the flow towards circular and square intakes. It is shown that one single spherical sink surface passing from the desired points that have radial velocity vectors of identical magnitude within the ambient fluid can be used for the prediction of the radial velocity. The specific imaginary center of the corresponding spherical sink surface should be located on the center-line axis downstream of the entrance of the intake. As opposed to the previous studies, the proposed method does not require the solution of equations in closed-integral form, and it can also be used for the orifice-intake not opening into the atmosphere (submerged outlet), and an intake with a pipe, or intake-pipe projecting into the ambient fluid. It is shown that velocity field can be predicted with the introduced method even in the case of circulation imposed or induced ambient fluid flow. The agreement between the theoretical results and the available experimental/numerical results was found to be good.