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GÜL, MEHMET ZAFER

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Author: YANGAZ, MURAT UMUT × Has files: true ×

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    PublicationOpen Access
    Effect of air pressure on nanofiber production in solution blowing method
    (GAZI UNIV, FAC ENGINEERING ARCHITECTURE, 2020-07-21) EKİCİ, BÜLENT; Polat, Yusuf; Yangaz, Murat Umut; Calisir, Mehmet Durmus; Gul, Mehmet Zafer; Demir, Ali; Ekici, Bulent; Kilic, Ali
    In this study, effect of air pressure on nanofiber diameter and morphology was studied for solution blowing technique. A computational fluid dynamics (CFD) analysis was realized via ANSYS (R) Fluent software, and the results were compared with experimental solutions. The results showed that an increase in air inlet pressure from 100 kPa to 300 kPa has significant effect on nanofiber diameter and morphology. In contrast, as the air inlet pressure increases above 300 kPa to 600 kPa, both nanofiber diameter increases, and the fiber agglomerations are observed due to high turbulence intensity. The droplets were observed at 100 kPa air inlet pressure due to low driving force applied to the polymer solution. The effects of air pressure on nanofiber diameter and morphology have been investigated by using finite volume method, and the results are compared with the experimental results.
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    PublicationOpen Access
    A Two-Time-Scale Turbulence Model and Its Application in Free Shear Flows
    (2024-02-01) GÜL, MEHMET ZAFER; YANGAZ, MURAT UMUT; GÜL M. Z., YANGAZ M. U., Sen S.
    A novel three-equation turbulence model has been proposed as a potential solution to overcome some of the issues related to the k–ε models of turbulence. A number of turbulence models found in the literature designed for compressed turbulence within internal combustion engine cylinders tend to exhibit limitations when applied to turbulent shear flows, such as those occurring through intake or exhaust valves of the engine. In the event that the flow is out of equilibrium where Pk deviates from ε, the turbulence models require a separate turbulence time-scale determiner along with the dissipation, ε. In the current research, this is accomplished by resolving an additional equation that accounts for turbulence time scale, τ. After presenting the rationale behind the model, its application to three types of free shear flows were given. It has been shown that the three-equation k–ε–τ model outperforms the standard k–ε model as well as a number of two-equation models in these flows. Initially, the k–ε–τ model handles the issue of the plane jet/round jet anomaly in an effective manner. Secondly, it outperforms the two-equation models in predicting the flow behavior in the case of plane wake, one that is distinguished by its weak shear form.