Yazar "Turan, Osman" seçeneğine göre listele

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    An acoustic structure design supported by shear thickening fluid for sound absorption
    (Elsevier Ltd, 2021) Aslan, Ramazan; Turan, Osman
    In this study, an acoustic structure consisting of cellular and perforated panel absorbers has been designed to noise control. Then, the sound absorption behaviour of designed acoustic structure has been investigated experimentally by reinforcing with STFs having different rheological properties. In addition, the sound absorption performance of the designed acoustic structure has been compared with the Gyroid which is a type of cellular sound absorber. The findings have indicated that the perforated panel activates significantly the sound absorption performance of the designed acoustic structure especially in the low (f[removed]3500Hz) frequency ranges. In addition, it has been also observed that this effect becomes stronger with STF reinforcement and significantly improves the sound absorption behaviour of the designed acoustic structure. Besides, it has been noticed that the sound absorption performance of the designed acoustic structure increases with increasing molecular weight of PEG for low frequencies (i.e. f[removed]3500Hz). Finally, it has been detected that the effectiveness of STF on the sound absorption performance of designed acoustics structure improves remarkably with increasing silica-nanoparticle ratio in the case of low and high frequencies (i.e. f[removed]3500Hz).
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    The effects of bottom wall heating on mixed convection of yield stress fluids in cylindrical enclosures with a rotating end wall
    (Pergamon-Elsevier Science Ltd, 2018) Turan, Osman; Chakraborty, Nilanjan
    Steady-state laminar mixed convection of Bingham fluids in cylindrical enclosures with a rotating top cover has been numerically analysed for the configuration where the bottom cover is kept at a higher temperature than the rotating top cover. The numerical investigations have been carried out based on steady-state axisymmetric incompressible flow simulations for a range of different values Reynolds, Richardson, and Prandtl number given by 500 <= Re 3000, 0 <= Ri <= 1 and 10 <= Pr <= 500 respectively. The aspect ratio (i.e. height: radius = AR = H/R) of the cylindrical container is considered to be unity (i.e. AR = H/R = 1). The mean Nusselt number (Nu) over bar has been found to decrease sharply with increasing Bn owing to flow resistance arising from yield stress, but subsequently (Nu) over bar asymptotically approaches a value of unity, which is indicative of a conduction-driven transport. In addition, the mean Nusselt number (Nu) over bar has been found to increase with increasing Reynolds number due to the strengthening of advective transport. However, the mean Nusselt number (Nu) over bar exhibits a non-monotonic trend (i.e. increases with increasing Ri for small values of Richardson number before showing a weak decreasing trend) with increasing Ri for Newtonian fluid (i.e. Bn = 0), whereas (Nu) over bar increases with increasing Ri for small values of Richardson number before becoming a weak function of Ri for Bingham fluids. A step change in the mean Nusselt number has also been observed with an increase in Richardson number for some Bingham number values due to a change in flow pattern. The influences of Prandtl, Reynolds, Richardson, and Bingham numbers on the mean Nusselt number have been explained in detail based on both physical and scaling arguments. The simulation data and scaling relations have been utilised to propose a correlation for the mean Nusselt number, which has been shown to capture the numerical findings satisfactorily for the parameter range considered here. 2018 Elsevier Ltd. All rights reserved.
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    The effects of uniform injection and suction on heat transfer with viscous dissipation through a permeable surface in zero pressure gradient
    (Pergamon-Elsevier Science Ltd, 2020) Turan, Osman; Cuhadaroglu, Burhan
    In the present study; the effects of injection/suction velocity and viscous dissipation on the temperature dis-tribution through a permeable surface with constant temperature was investigated theoretically. The hydro-dynamic and thermal wall functions which include the influence of viscous dissipation and injection/suction velocity were obtained for the boundary layer flow with zero pressure gradient in streamwise. The effect of viscous dissipation was considered with a dimensionless parameter of Br-m = u(tau)(3)rho/q(w) which is a modified Brinkman number. It was noted that the temperature distribution in both the laminar and turbulent boundary layers was substantially influenced by the viscous dissipation. Moreover, viscous dissipation induced internal heat generation causes to a jump in the fluid temperature at the wall T-w,T-f for high Br-m values. In addition, it was seen that viscous dissipation effect on temperature distribution can be noticeably controlled by using injection and suction through permeable surface. Viscous dissipation effect weakens with injection (suction) for low (high) Br-m case. Finally, the critical modified Brinkman number Br-m,Br- (crit) where the heat transfer direction begins to change with strengthening viscous dissipation induced internal heat generation in the flow field has been obtained. It has been found that Br-m,Br- (crit) increases with increasing suction velocity while it decreases with in-creasing injection velocity. It has further observed that Br-m,Br- (crit )decreases (increases) with increasing Pr for suction (injection) although it takes the same values for different Pr values in case of no-injection and suction.
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    Effects of wall heating on laminar mixed convection in a cylindrical enclosure with a rotating end wall
    (Elsevier France-Editions Scientifiques Medicales Elsevier, 2018) Turan, Osman; Yigit, Sahin; Chakraborty, Nilanjan
    Steady-state laminar mixed convection in a cylindrical enclosure has been numerically analysed for different values of Reynolds, Richardson and Prandtl numbers given by 500 <= Re <= 3000, 0 <= Ri <= 1 and 10 <= Pr <= 500 respectively. The aspect ratio (i.e. height: radius = AR = H/R) of the cylindrical container is considered to be unity (ie. AR = H/R = 1). The bottom and top covers of the cylindrical enclosure are kept at different temperatures (T-C < T-H), while the cylindrical surface is taken to be adiabatic. The simulations for rotating top and bottom cover configurations yield the same numerical values of the mean Nusselt number (Nu) over bar when the thermal boundary conditions are kept unaltered. For this reason, only rotating top hot wall (ie. C1 configuration) and rotating top cold wall (ie. C2 configuration) have been considered for this analysis. The mean Nusselt number (Nu) over bar has been found to assume higher values in the C2 configuration than in the Cl configuration. Moreover, it has been found that the variation of the mean Nusselt number with Richardson number in the C2 configuration is qualitatively different from that in the C1 configuration. The simulation data has been used to propose a correlation for (Nu) over bar for the range of Re, Ri and Pr considered here for both Cl and C2 configurations. In addition to this, a regime diagram has been proposed for the C2 configuration in order to demarcate different flow regimes.
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    Free convection of power-law fluids in enclosures with partially heating from bottom and symmetrical cooling from sides
    (Pergamon-Elsevier Science Ltd, 2019) Yigit, Sahin; Battu, Madhusudhan; Turan, Osman; Chakraborty, Nilanjan
    Steady-state laminar free convection of power-law fluids in a square enclosure with partial heating from below and symmetrical cooling from sides has been investigated based on numerical simulations. The partially heating is conducted by a centrally heated heat source on the bottom wall for different values of normalised heat source length IA (ranging from 0.2 to 0.8); power-law index n (from 0.6 to 1.8); nominal Rayleigh number (Ra) (from 10(3) to 10(6)) and nominal Prandtl number Pr (from 10 to 10(3)). An increase in the power-law index n leads to weakening of thermal advection owing to the augmentation of viscous resistance. This is reflected as an increment in the mean Nusselt number (Nu) over bar with decreasing value of n. Additionally, (Nu) over bar increases with an increase in Ra and IA for shear thinning (i.e. n < 1), Newtonian (i.e. n = 1) and shear thickening (i.e. n > 1) fluids. The observed influences of Ra, Pr, n and 1/L on (Nu) over bar have been explained by physical and scaling arguments and parameterized by a correlation for the mean Nusselt number. (C) 2019 Elsevier Ltd. All rights reserved.
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    Gypsum-based sound absorber produced by 3D printing technology
    (Elsevier Sci Ltd, 2020) Aslan, Ramazan; Turan, Osman
    The paper presents an alternative gypsum-based porous cellular sound absorber manufactured using 3D printing technology. The effects of cell structure and porosity on sound absorption coefficient have been experimentally investigated for the designed gypsum-based porous metamaterials. In addition to this, the numerical acoustic analyses were also performed to predict sound absorption behaviour of the produced gypsum-based porous metamaterials. Furthermore, the numerical flow analyses were also carried out to gain insight into the basic parameters such as flow resistance and tortuosity that affect the sound absorption behaviour of the designed gypsum-based porous metamaterials. As a result of the experimental and numerical studies, it has been observed that the gypsum specimens produced in porous structure provide a significant sound absorption in comparison to non-porous reference specimen. It has been also noticed that the open-cell gypsum specimens, in which the cells are interaction with each other, are much more efficient in terms of sound absorption than the open-cell structure in which there is no direct interaction between the cells. In addition to this, it was found that the gypsum specimens having Octet unit-cell structure have the highest sound absorption performance in the open cell structures. In other respects, it was also found that the sound absorption behaviour of each unit cell structure is getting worse with the increasing porosity. The numerical flow analyses have indicated that increase in porosity reduces the flow resistance and tortuosity levels of the open unit-cell structures and consequently worsens the sound absorption behaviour. (C) 2019 Elsevier Ltd. All rights reserved.
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    Laminar mixed convection of power-law fluids in cylindrical enclosures with heated rotating top wall
    (Pergamon-Elsevier Science Ltd, 2018) Turan, Osman; Yigit, Sahin; Liang, Ruibin; Chakraborty, Nilanjan
    Laminar mixed convection of inelastic non-Newtonian fluids obeying a power law model in a cylindrical enclosure with a heated rotating top cover has been investigated numerically in this study. The steadystate axisymmetric simulations have been carried out for a range of different nominal Reynolds, Prandtl, Richardson numbers (i.e. 500 <= Re <= 2000; 10 <= Pr <= 500 and 0 <= Ri <= 1) and power-law index (i.e. 0.6 <= n <= 1.8) for an aspect ratio (height/radius) of unity (i.e. AR = 1.0). It has been found that mean Nusselt number (Nu) over bar increases as Re and Pr increase, whereas (Nu) over bar decreases with increasing values of Ri for shear-thinning (i.e. n < 1), Newtonian (i.e. n = 1) and shear-thickening (i.e. n > 1) fluids. It has also been observed that the variation of Ni with n differs depending on the values of Re and Ri. For instance, for small values of Reynolds number, (Nu) over bar exhibits a non-monotonic trend (i.e. increases before reaching a maximum followed by a decreasing trend) with increasing n for small values of Richardson number, whereas (Nu) over bar monotonically increases with increasing values of n for high Richardson number cases. However, in the case of high Reynolds number, (Nu) over bar increases with n before reaching a maximum value which is followed by a decreasing trend for all values of Ri considered here. Detailed physical explanations are provided for the influences of Re, Pr, Ri, and n on (Nu) over bar based on an elaborate scaling analysis. Finally, the numerical findings have been used to propose a correlation for (Nu) over bar for the ranges of Re, Pr, Ri, n considered here. (C) 2018 Elsevier Ltd. All rights reserved.
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    Mixed convection of power-law fluids in cylindrical enclosures with a cold rotating top cover and a stationary heated bottom wall
    (Elsevier, 2020) Turan, Osman; Yigit, Sahin; Chakraborty, Nilanjan
    Steady-state laminar mixed convection in cylinders with a rotating top cold cover and a heated bottom has been numerically analysed for inelastic shear-thinning/shear-thickening fluids by applying power-law model of viscosity. In this analysis, axisymmetric incompressible flow simulations have been conducted for a range of different values of Reynolds, Richardson, Prandtl numbers (i.e. 500 <= Re <= 2000; 0 <= Ri <= 1.0; 10 <= Pr <= 1000) and power-law index (i.e. 0.6 n 1.8) for an aspect ratio (height/radius) of unity (i.e. AR = 1.0). The thermal convective transport has been found to strengthen with increasing Re and Pr, which in turn gives rise to an increase in the mean Nusselt number Nu. By contrast, an increase in Ri leads to a mild increase in Nu for small Richardson number values but Nu becomes insensitive to the changes in Ri for large Richardson numbers within the range of 0 <= Ri <= 1.0 for all values of n considered here. The mean Nusselt number Nu exhibits a nonmonotonic trend (i.e. increases before reaching a maximum followed by a decreasing trend) with the variation of n. The influences of Ra, Pr and Ri on the mean Nusselt number Nu have been explained in terms of scaling arguments. The scaling relations along with the numerical findings have been utilised to propose a correlation for the mean Nusselt number for the configuration and the parameter range considered here.
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    Numerical investigation of laminar mixed convection in a square cross-sectioned cylindrical annular enclosure
    (2020) Turan, Osman
    Abstract:Steady-state laminar mixed convection of Newtonian fluids in a square cross-sectioned cylindrical annular enclosure with rotating inner wall and heated top cover has been numerically analysed based on axisymmetric incompressible flow simulations. ...