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Ehsan Fattahi - One of the best experts on this subject based on the ideXlab platform.

  • lattice boltzmann simulation of deformation and breakup of a droplet under gravity force using interparticle potential model
    International Journal of Engineering, 2013
    Co-Authors: S Mousavi E Tilehboni, Kurosh Sedighi, Mousa Farhadi, Ehsan Fattahi
    Abstract:

    Abstract In this paper interparticle potential model of the lattice Boltzmann method (LBM) is used to simulate deformation and breakup of a falling droplet under gravity force. First this model is applied to ensure that the Surface Tension Effect is properly implemented in this model. Two tests have been considered. First, it has been checked an initial square drop in a 2D domain can freely deform to a circular drop and secondly the coalescence of two static drops that merge to become a single circular drop is simulated. In order to further verify the model, Laplace law for static drops is performed. In the next step, wall Effects on the droplet shape and its average velocity have been studied. it is seen that average velocity of droplet at different times is independent of wall Effects when the ratio of the width of channel to droplet diameter (W/D) is more than 6. In the final section of the paper deformation and breakup of a falling droplet for some range of Eotvos and Ohnesorge numbers are investigated. It is seen that at very low Eotvos numbers, where the Surface Tension force is dominant, the droplet deforms slowly and reaches a steady state without breakup. At higher Eotvos numbers gravitational force overcome the Surface Tension force and the droplet deforms more. For breakup modes at small Ohnesorge number, if Eotvos number be increased to the middle value, the droplet deforms more than from state of low Eotvos number value and eventually forms a backward-facing bag. Finally for high Eotvos numbers, fragments of droplet are sheared from the edges and the shear breakup mechanism is seen. On the other hand the stabilizing Effect of the Ohnesorge number, (the ratio of viscous stresses and Surface Tension) , is shown. At higher Ohnesorge number, the simulations show that the main Effect of increasing Ohnesorge number is to move the boundary between the different breakup modes to higher Eotvos number.

  • lattice boltzmann simulation of deformation and breakup of a droplet under gravity force using interparticle potential model
    International journal of engineering. Transactions A: basics, 2013
    Co-Authors: S Mousavi E Tilehboni, Kurosh Sedighi, Mousa Farhadi, Ehsan Fattahi
    Abstract:

    In this paper interparticle potential model of the lattice Boltzmann method (LBM) is used to simulate the deformation and breakup of a falling droplet under the gravity force. First, this model is applied to ensure that the Surface Tension Effect is properly implemented in this model. Two tests have been considered. First, it has been checked an initial square drop in a 2D domain can freely deform to a circular drop and secondly the coalescence of two static drops that merge to become a single circular drop is simulated. In order to further verify the model, Laplace law for static drops is performed. In the next step, wall Effects on the droplet shape and its average velocity have been studied. It is seen that the average velocity of droplet at different times is ind ependent of wall Effects when the ratio of the width of the channel to droplet diameter (W/D) is more than 6. In the final section of the paper, deformation and breakup of a falling droplet for some range of Eotvos and Ohnesorge numbers are investigated. It is seen that at very low Eotvos numbers, where the Surface Tension force is dominant, the droplet deforms slowly and reaches a steady state without breakup. At higher Eotvos numbers gravitational force overcome the Surface Tension force and the droplet deforms more. For breakup modes at the small Ohnesorge number, if Eotvos number be increased to an intermediate value, the droplet deforms more than from a state of low Eotvos number value and eventually forms a backward-facing bag. Finally, for high Eotvos numbers, fragments of droplet are sheared from the edges and the shear breakup mechanism is seen. On the other hand, the stabilizing Effect of the Ohnesorge number, (the ratio of viscous stresses and Surface Tension) is shown. At higher Ohnesorge number, the simulations show that the main Effect of increasing Ohnesorge number is to move the boundary between the different breakup modes to higher Eotvos number.

Haecheon Choi - One of the best experts on this subject based on the ideXlab platform.

  • Predictions of the Effective slip length and drag reduction with a lubricated micro-groove Surface in a turbulent channel flow
    Journal of Fluid Mechanics, 2019
    Co-Authors: Jaehee Chang, Taeyong Jung, Haecheon Choi
    Abstract:

    We perform direct numerical simulations of a turbulent channel flow with a lubricated micro-grooved Surface to investigate the Effects of this Surface on the slip characteristics at the interface and the friction drag. The interface between water and lubricant is assumed to be flat, i.e. the Surface-Tension Effect is neglected. The solid substrate, where a lubricant is infused, is composed of straight longitudinal grooves. The flow rate of water inside the channel is maintained constant, and a lubricant layer under the interface is shear driven by the turbulent water flow above. A turbulent channel flow with a superhydrophobic (i.e. air-lubricated) Surface having the same solid substrate configuration is also simulated for comparison. The results show that the drag reduction with the liquid-infused Surface highly depends on the lubricant viscosity as well as the groove width and aspect ratio. The amounts of drag reduction with the liquid-infused Surfaces are not as good as those with superhydrophobic Surfaces, but are still meaningfully large. For instance, the maximum drag reduction by the heptane-infused Surface is approximately 13 % for a rectangular groove whose spanwise width and depth in wall units are 12 and 14.4, respectively, whereas a superhydrophobic Surface with the same geometry results in a drag reduction of 21 %. The mean slip length normalized by the viscosity ratio and groove depth depends on the groove aspect ratio. The ratio of fluctuating spanwise slip length to the streamwise one is between 0.25 (ideal Surface without groove structures) and 1 (i.e. isotropic slip), indicating that the slip is anisotropic. Using the Stokes flow assumption, the Effective streamwise and spanwise slip lengths are expressed as a function of groove geometric parameters and lubricant viscosity. We also suggest a predictive model for drag reduction with the heptane-lubricated Surface by combining the predicted Effective slip lengths with the drag reduction formula used for riblets (Luchini et al., J. Fluid Mech., vol. 228, 1991, pp. 87–109). The predicted drag reductions are in good agreements with those from the present and previous direct numerical simulations.

  • Effects of the air layer of an idealized superhydrophobic Surface on the slip length and skin friction drag
    Journal of Fluid Mechanics, 2016
    Co-Authors: Taeyong Jung, Haecheon Choi
    Abstract:

    The anisotropy of the slip length and its Effect on the skin-friction drag are numerically investigated for a turbulent channel flow with an idealized superhydrophobic Surface having an air layer, where the idealized air–water interface is flat and does not contain the Surface-Tension Effect. Inside the air layer, both the shear-driven flow and recirculating flow with zero net mass flow rate are considered. With increasing air-layer thickness, the slip length, slip velocity and percentage of drag reduction increase. It is shown that the slip length is independent of the water flow and depends only on the air-layer geometry. The amount of drag reduction obtained is in between those by the empirical formulae from the streamwise slip only and isotropic slip, indicating that the present air–water interface generates an anisotropic slip, and the streamwise slip length ( $b_{x}$ ) is larger than the spanwise one ( $b_{z}$ ). From the joint probability density function of the slip velocities and velocity gradients at the interface, we confirm the anisotropy of the slip lengths and obtain their relative magnitude ( $b_{x}/b_{z}=4$ ) for the present idealized superhydrophobic Surface. It is also shown that the Navier slip model is valid only in the mean sense, and it is generally not applicable to fluctuating quantities.

R Arunkumar - One of the best experts on this subject based on the ideXlab platform.

  • benard marangoni ferroconvection with magnetic field dependent viscosity
    Journal of Magnetism and Magnetic Materials, 2010
    Co-Authors: C E Nanjundappa, I S Shivakumara, R Arunkumar
    Abstract:

    Abstract The Effect of magnetic field dependent viscosity on the onset of Benard–Marangoni ferroconvection in a horizontal layer of ferrofluid is investigated theoretically. The lower boundary is taken to be rigid with fixed temperature, while the upper free boundary at which temperature-dependent Surface Tension Effect is considered is non-deformable and subject to a general thermal condition. The Rayleigh–Ritz method with Chebyshev polynomials of the second kind as trial functions is employed to extract the critical stability parameters numerically. The results show that the onset of ferroconvection is delayed with an increase in the magnetic field dependent viscosity parameter (Λ) and Biot number (Bi) but opposite is the case with an increase in the value of magnetic Rayleigh number (Rm) and nonlinearity of magnetization (M3). Further, increase in Rm, M3, and decrease in Λ and Bi is to decrease the size of the convection cells.

S Mousavi E Tilehboni - One of the best experts on this subject based on the ideXlab platform.

  • lattice boltzmann simulation of deformation and breakup of a droplet under gravity force using interparticle potential model
    International Journal of Engineering, 2013
    Co-Authors: S Mousavi E Tilehboni, Kurosh Sedighi, Mousa Farhadi, Ehsan Fattahi
    Abstract:

    Abstract In this paper interparticle potential model of the lattice Boltzmann method (LBM) is used to simulate deformation and breakup of a falling droplet under gravity force. First this model is applied to ensure that the Surface Tension Effect is properly implemented in this model. Two tests have been considered. First, it has been checked an initial square drop in a 2D domain can freely deform to a circular drop and secondly the coalescence of two static drops that merge to become a single circular drop is simulated. In order to further verify the model, Laplace law for static drops is performed. In the next step, wall Effects on the droplet shape and its average velocity have been studied. it is seen that average velocity of droplet at different times is independent of wall Effects when the ratio of the width of channel to droplet diameter (W/D) is more than 6. In the final section of the paper deformation and breakup of a falling droplet for some range of Eotvos and Ohnesorge numbers are investigated. It is seen that at very low Eotvos numbers, where the Surface Tension force is dominant, the droplet deforms slowly and reaches a steady state without breakup. At higher Eotvos numbers gravitational force overcome the Surface Tension force and the droplet deforms more. For breakup modes at small Ohnesorge number, if Eotvos number be increased to the middle value, the droplet deforms more than from state of low Eotvos number value and eventually forms a backward-facing bag. Finally for high Eotvos numbers, fragments of droplet are sheared from the edges and the shear breakup mechanism is seen. On the other hand the stabilizing Effect of the Ohnesorge number, (the ratio of viscous stresses and Surface Tension) , is shown. At higher Ohnesorge number, the simulations show that the main Effect of increasing Ohnesorge number is to move the boundary between the different breakup modes to higher Eotvos number.

  • lattice boltzmann simulation of deformation and breakup of a droplet under gravity force using interparticle potential model
    International journal of engineering. Transactions A: basics, 2013
    Co-Authors: S Mousavi E Tilehboni, Kurosh Sedighi, Mousa Farhadi, Ehsan Fattahi
    Abstract:

    In this paper interparticle potential model of the lattice Boltzmann method (LBM) is used to simulate the deformation and breakup of a falling droplet under the gravity force. First, this model is applied to ensure that the Surface Tension Effect is properly implemented in this model. Two tests have been considered. First, it has been checked an initial square drop in a 2D domain can freely deform to a circular drop and secondly the coalescence of two static drops that merge to become a single circular drop is simulated. In order to further verify the model, Laplace law for static drops is performed. In the next step, wall Effects on the droplet shape and its average velocity have been studied. It is seen that the average velocity of droplet at different times is ind ependent of wall Effects when the ratio of the width of the channel to droplet diameter (W/D) is more than 6. In the final section of the paper, deformation and breakup of a falling droplet for some range of Eotvos and Ohnesorge numbers are investigated. It is seen that at very low Eotvos numbers, where the Surface Tension force is dominant, the droplet deforms slowly and reaches a steady state without breakup. At higher Eotvos numbers gravitational force overcome the Surface Tension force and the droplet deforms more. For breakup modes at the small Ohnesorge number, if Eotvos number be increased to an intermediate value, the droplet deforms more than from a state of low Eotvos number value and eventually forms a backward-facing bag. Finally, for high Eotvos numbers, fragments of droplet are sheared from the edges and the shear breakup mechanism is seen. On the other hand, the stabilizing Effect of the Ohnesorge number, (the ratio of viscous stresses and Surface Tension) is shown. At higher Ohnesorge number, the simulations show that the main Effect of increasing Ohnesorge number is to move the boundary between the different breakup modes to higher Eotvos number.

C E Nanjundappa - One of the best experts on this subject based on the ideXlab platform.

  • Effect of coriolis force on benard marangoni convection in a rotating ferrofluid layer with mfd viscosity
    Microgravity Science and Technology, 2015
    Co-Authors: C E Nanjundappa, I S Shivakumara
    Abstract:

    The simultaneous Effect of Coriolis force due to rotation and magnetic field dependent (MFD) viscosity on the onset of Benard-Marangoni convection in a horizontal ferrofluid layer in the presence of a uniform vertical magnetic field is studied. The lower boundary is rigid while the upper free boundary is open to the atmosphere and at which the temperature-dependent Surface Tension Effect is allowed for. The Galerkin technique is employed to extract the critical stability parameters numerically. The results show that the onset of Benard-Marangoni ferroconvection is delayed with an increase in the MFD viscosity parameter Λ, Taylor number T a, magnetic susceptibility χ and Biot number B i but opposite is the case with an increase in the value of magnetic number M 1 and nonlinearity of fluid magnetization M 3. Further, increase in M 1,M 3 and decrease in Λ,T a, χ and B i is to decrease the size of the convection cells. Comparisons of results between the present and the existing ones are made under the limiting conditions and good agreement is found.

  • benard marangoni ferroconvection with magnetic field dependent viscosity
    Journal of Magnetism and Magnetic Materials, 2010
    Co-Authors: C E Nanjundappa, I S Shivakumara, R Arunkumar
    Abstract:

    Abstract The Effect of magnetic field dependent viscosity on the onset of Benard–Marangoni ferroconvection in a horizontal layer of ferrofluid is investigated theoretically. The lower boundary is taken to be rigid with fixed temperature, while the upper free boundary at which temperature-dependent Surface Tension Effect is considered is non-deformable and subject to a general thermal condition. The Rayleigh–Ritz method with Chebyshev polynomials of the second kind as trial functions is employed to extract the critical stability parameters numerically. The results show that the onset of ferroconvection is delayed with an increase in the magnetic field dependent viscosity parameter (Λ) and Biot number (Bi) but opposite is the case with an increase in the value of magnetic Rayleigh number (Rm) and nonlinearity of magnetization (M3). Further, increase in Rm, M3, and decrease in Λ and Bi is to decrease the size of the convection cells.