Browsing by Author "Okbaz, A."

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Citation - WoS: 3
Citation - Scopus: 4
A Comparison of Rans-Based Turbulence Modeling and Piv Experiments for Flow Over a Simplified Road Vehicle
(Gazi Universitesi, 2023) Aksoy, M.H.; Okbaz, A.; Yaǧmur, S.; Doǧan, S.
The aerodynamic forces on road vehicles and flow structures around them result from complex interactions between fluid and structure. Ahmed body is a simplified car model created to demonstrate and simplify the flow around real-size ground vehicles. In this study, the flow structure on the wake region of Ahmed body with different slant angles (Θ=15°, 25°, and 35°) was investigated. Experimental studies were conducted in a water channel by Particle Image Velocimetry (PIV). The freestream velocity was set to 0.2 m/s, and the Reynolds number defined by the characteristic length of the Ahmed body was 4.16×104 for Computational Fluid Dynamics (CFD) and PIV experiments. CFD simulations were performed using three different turbulence models: realizable k-ϵ, RNG k-ϵ, and SST k-ω, and the results were compared to experiments. The results are presented with different flow features such as time-averaged velocity vectors and velocity contours, streamline topology, vorticity, and Turbulence Kinetic Energy. The closest results to the experiments were obtained by the SST k-ω turbulence model for all slant angles of the Ahmed body. In addition, the drag coefficient is found to be 0.37 for all slant angles analyzed by SST k-ω turbulence models, which are also close to the results in the literature. © 2023 Gazi Universitesi Muhendislik-Mimarlik. All rights reserved.
Citation - Scopus: 19
Flow Control Over a Circular Cylinder Using Vortex Generators: Particle Image Velocimetry Analysis and Machine-Learning Prediction of Flow Characteristics
(Elsevier Ltd, 2023) Okbaz, A.; Aksoy, M.H.; Kurtulmuş, N.; Çolak, A.B.
Controlling the flow around circular cylinders is crucial to mitigate vortex-induced vibrations and prevent structural damage in a range of applications, such as marine and offshore engineering, tall buildings, long-span bridges, transport ships, and heat exchangers. In this study, we aimed to control the turbulent flow structure around a circular cylinder by placing vortex generators (VGs). We examined the flow structure using particle image velocimetry (PIV). This enabled quantitative data acquisition, intuitive flow visualization, and drag coefficient determination from PIV data. We developed artificial neural network (ANN) models that successfully predict both mean and instantaneous flow characteristics for different scenarios. Our findings show that using VGs elongated the wake and increased vortex formation lengths while reducing velocity fluctuations and the drag coefficient. A minimum drag coefficient of 0.718 was achieved with VGs oriented at α = 60° & β = 60°, reducing the drag by 35.3% compared to the bare cylinder. The drag coefficient exhibited a substantial inverse correlation with both wake and vortex formation lengths. This study is significant for controlling flow structures, providing detailed insights into the near-wake region, and highlighting the potential applications of machine learning in fluid dynamics. © 2023 Elsevier Ltd
Citation - Scopus: 1
An Investigation on Fluid-Structure Interaction of Two Tandem Rectangular Cylinders
(Serbian Academic Center, 2023) Tabatabaei, Malazi, M.; Aksoy, M.H.; Okbaz, A.
This paper presents a numerical investigation of the three-dimensional flow field with deformations of two tandem rectangular cylinders. The one-way Fluid-Structure Interaction (FSI) method simulated the deformation domain. The Realizable k-ε turbulence model was utilized to model turbulent flow simulation in the three-dimensional flow domain. The hydrodynamic forces, deformations, and stresses were calculated for different spacing configurations between the rectangular cylinders. Structural steel was chosen for the rectangular cylinders, while water was chosen for the fluid domain. The flow inlet velocity was maintained at 5 m/s for all simulations, resulting in a corresponding Reynolds number of 5×105 based on free stream velocity and cylinder width. The numerical results demonstrated that the cylinder spacing significantly affected the cylinders' deformation. The distance ratio between the two tandem rectangular cylinders to the cylinder height (x/H) was increased from 1 to 5. The front rectangular cylinder endured a higher pressure load than the rear rectangular cylinder, with the maximum deformation of the front cylinder found to be 7.15 mm. Due to the lower pressure on the rear rectangular cylinders, deformation varied between 0.98 mm and 6.02 mm as x/H changed from 1 to 5. This research provides valuable insights into the deformation behavior of tandem rectangular cylinders in three-dimensional flow fields. © 2023 by the authors.