M. E. Vakhshouri; B. Çuhadaroğlu
Abstract
The effects of uniform injection and suction through the surfaces of a perforated square cylinder on the vortex shedding, heat transfer and some aerodynamic parameters have been investigated numerically. The finitevolume method has been used for solving the Navier-Stokes equations for incompressible ...
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The effects of uniform injection and suction through the surfaces of a perforated square cylinder on the vortex shedding, heat transfer and some aerodynamic parameters have been investigated numerically. The finitevolume method has been used for solving the Navier-Stokes equations for incompressible and turbulent near-wake flow (𝑅𝑒21400) with the k-ɛ turbulence model equations. To find the optimum conditions, the effects of injection and suction through the front surface (case Ⅰ), the rear surface (case Ⅱ), top-bottom surfaces (case Ⅲ) and all surfaces (case Ⅳ) with various injection/suction coefficient are studied. The results reveal that parameters such as pressure and drag coefficients and Nusselt number are influenced drastically in some cases as well as flow field parameters. For instance, the maximum reduction of the drag coefficient occurs at case Ⅳ while the maximum increase and reduction of Nu number occur at (|𝛤|) = 0.025 forall cases about 46% and 32%, 61% and 63%, 92% and 60% and 180% and 115% for cases Ⅰ, Ⅱ, Ⅲ and Ⅳ respectively.
Heat and Mass Transfer
Hasan Najafi Khaboshan; Hamid Reza Nazif
Abstract
In this research, the convective heat transfers of turbulent water fluid flow in alternating oval tubes is studied using computational fluid dynamics. The purpose of the study is to analyze the heat transfer enhancement and secondary internal flows under different alternate angles. Also, comparing the ...
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In this research, the convective heat transfers of turbulent water fluid flow in alternating oval tubes is studied using computational fluid dynamics. The purpose of the study is to analyze the heat transfer enhancement and secondary internal flows under different alternate angles. Also, comparing the effect of two schemesfor the domain discretization to be used in the solution variables’ gradients on simulation results is investigated. The secondary flow causes an increase in the numbers of multi-longitudinal vortices (MLV) by changing the angle of pitches. These phenomena permit the cold fluid flow to stream in more paths from center to tube wall and better condition for mixing of fluids. Consequently, the heat transfer enhances by using the alternating oval tubes. However, forming the multi-longitudinal vortices causes an increase in pressure drop. Also, by raising the angle of pitches, the friction factor and the average of Nusselt number are amplified. It is also observed that the average heat transfer coefficient in the transition range is more than other areas. The mean Nussult numbers of this kind of tubes in the angles of 40, 60, 80, and 90 improved 7.77%, 14.6%, 16.93%, and 24.42%, respectively in comparison with the round tube. The performance evaluation criteria (PEC) for all alternating oval tubes under the constant inlet velocity boundary condition indicated that the highest value (PEC=1.09) had been obtained at the lowest Reynolds number (Re=10,000) in the alternating oval tube 90°.
Computational Fluid Dynamics (CFD)
Brahim Rostane; Aliane Khaled; Said Abboudi
Abstract
The aim of our study is to analyze the impact of insertion holes in the middle of obstacles on the flow around a surface-mounted cube, In order to do this; we studied four configurations of obstacles in a channel with a Reynods number based on obstacle height ReH = 40000. The hexahedral structured meshes ...
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The aim of our study is to analyze the impact of insertion holes in the middle of obstacles on the flow around a surface-mounted cube, In order to do this; we studied four configurations of obstacles in a channel with a Reynods number based on obstacle height ReH = 40000. The hexahedral structured meshes were used to solve the fluid dynamics equations .The finite volume method are employed to solve the governing equations using the ANSYS CFX code and the turbulence model k-ω SST. The streamwise velocity profiles, the Time-averaged streamlines, the turbulence kinetic energy and the drag coefficient are presented. The results showed the appearance of a second vortex behind obstacles with hole from diameter D/H=0.2. The turbulence kinetic energy was greater on top of the obstacle, it was more intense for the obstacle without hole, this intensity decreased as the hole diameter increased. The drag coefficient was improved only for the case D/H=0.32
Turbulance
S. F. Ahmed; M. S. A. Sarker Sarker
Abstract
The energy equation for turbulent flow of fiber suspensions was derived in terms of second order correlation tensors. Fiber motion of turbulent energy including the correlation between pressure fluctuations and velocity fluctuations was discussed at two points of flow field, at which the correlation ...
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The energy equation for turbulent flow of fiber suspensions was derived in terms of second order correlation tensors. Fiber motion of turbulent energy including the correlation between pressure fluctuations and velocity fluctuations was discussed at two points of flow field, at which the correlation tensors were the functions of space coordinates, distance between two points, and time.
Fluid Mechanics
S. F. Ahmed
Abstract
Energy equation for turbulent flow in a rotating system was derived in terms of second order correlation tensors, where the correlation tensors were functions of space coordinates, distance between two points and time. To reveal the relationship of turbulent energy between two points, one point was taken ...
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Energy equation for turbulent flow in a rotating system was derived in terms of second order correlation tensors, where the correlation tensors were functions of space coordinates, distance between two points and time. To reveal the relationship of turbulent energy between two points, one point was taken as origin of the coordinate system. Due to rotation, the Coriolis force played an important role in the rotating system of turbulent flow. The correlation between pressure fluctuations and velocity fluctuations at the two points of flow field was applied to the turbulent energy equation, in which the Coriolis force and centrifugal force acted on the fluid.
