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Boundary Layer Theory

The Experts below are selected from a list of 237 Experts worldwide ranked by ideXlab platform

Hiroshi Kanayama – 1st expert on this subject based on the ideXlab platform

  • Boundary Layer Theory approach to the concentration Layer adjacent to the ceiling wall of a hydrogen leakage axisymmetric impinging and far regions
    International Journal of Hydrogen Energy, 2009
    Co-Authors: M F Elamin, Hiroshi Kanayama

    Abstract:

    Abstract As hydrogen leaks into a partially open space with a ceiling wall, a Boundary Layer of hydrogen can be constructed under that wall due to the impingement on the wall and the buoyancy force. The resulting Boundary Layer can be divided into two regions, namely the stagnation-point region and the far region. When the geometry of the source of the hydrogen leak is circular, such as a pinhole or an o-ring, the behavior of leakage flow will be axisymmetric due to the resulting radial jet. In contrast, when the geometry of the source of the hydrogen leak is planar, such as a crack, the behavior of leakage flow will be planar due to the resulting planar jet. Previously, we studied the planar case in the context of both the stagnation-point flow region [El-Amin MF, Kanayama H. Boundary Layer Theory approach to the concentration Layer adjacent to a ceiling wall at impinging region of a hydrogen leakage. Int J Hydrogen Energy 2008; 33(21): 6393–00] and the far region [El-Amin MF, Inoue M, Kanayama H. Boundary Layer Theory approach to the concentration Layer adjacent to a ceiling wall of a hydrogen leakage: far region. Int J Hydrogen Energy 2008; 33(24):7642–7]. This paper is concerned with both the stagnation-point flow region and the far region of the axisymmetric concentration Boundary Layer adjacent to a ceiling wall. Flow in the stagnation-point region is treated as Hiemenz flow, while it is treated as Blasius flow in the far region. The current results are compared with the planar cases [El-Amin MF, Kanayama H. Boundary Layer Theory approach to the concentration Layer adjacent to a ceiling wall at impinging region of a hydrogen leakage. Int J Hydrogen Energy 2008; 33(21): 6393–00; El-Amin MF, Inoue M, Kanayama H. Boundary Layer Theory approach to the concentration Layer adjacent to a ceiling wall of a hydrogen leakage: far region. Int J Hydrogen Energy 2008; 33(24):7642–7] for both stagnation-point flow and far regions. Both momentum and concentration Boundary Layer thicknesses are estimated, as well as the local friction factor.

  • Boundary Layer Theory approach to the concentration Layer adjacent to a ceiling wall of a hydrogen leakage far region
    International Journal of Hydrogen Energy, 2008
    Co-Authors: M F Elamin, Masahiro Inoue, Hiroshi Kanayama

    Abstract:

    The field of the hydrogen leakage in partially open space can be divided into two main regions according to the importance of the hydrogen concentration distribution and the flow behavior. These two regions are the jet region and the Boundary Layer region which are adjacent to the ceiling wall of the space, resulting from impinging the hydrogen jet to the wall. The Boundary Layer region in turn can be divided into two regions, according to the modeling of the flow. These regions are the stagnation-point Boundary Layer region and the far Boundary Layer region. Previously, we studied the region of stagnation-point flow (Hiemenz flow) [El-Amin MF, Kanayama H. Boundary Layer Theory approach to the concentration Layer adjacent to a ceiling wall at impinging region of a hydrogen leakage. Int J Hydrogen Energy, in press.]. The current paper is devoted to analyze the far region of the Boundary Layer adjacent to the ceiling wall using the Boundary Layer Theory. Also, an experiment has been conducted on the hydrogen leakage in partially open space to estimate the concentration distribution vertically at the center of the domain under the ceiling wall. In order to verify the Boundary Layer Theory approach, a comparison between the measurements and the Boundary Layer Theory approximations is investigated and the results showed a good agreement. The wall shear stress, the local friction factor, the friction drag and the non-dimensional drag coefficient of the ceiling wall are calculated. Also, both momentum and concentration Boundary Layer thicknesses are estimated.

  • Boundary Layer Theory approach to the concentration Layer adjacent to a ceiling wall at impinging region of a hydrogen leakage
    International Journal of Hydrogen Energy, 2008
    Co-Authors: M F Elamin, Hiroshi Kanayama

    Abstract:

    In this article, the steady-state concentration Boundary Layer adjacent to a ceiling wall of a stagnation-point flow region resulting from hydrogen impinging leakage is investigated. Flow in neighborhood of the stagnation point is treated as Hiemenz flow, while the concentration equation governs the concentration distribution in the Boundary Layer. The assumptions of the Boundary Layer Theory are invoked to simplify both the momentum and the concentration equations. Comparison between the CFD simulation and the current Boundary Layer approximation shows a good agreement. Both momentum and concentration Boundary Layer thicknesses are estimated as well as local friction factor and local mass transfer. Also, the study is extended to include some cases of unsteady leakage. The effects of the unsteadiness parameter on the local friction factor and mass transfer rate as well as momentum and concentration Boundary Layer thicknesses are analyzed.

M F Elamin – 2nd expert on this subject based on the ideXlab platform

  • Boundary Layer Theory approach to the concentration Layer adjacent to the ceiling wall of a hydrogen leakage axisymmetric impinging and far regions
    International Journal of Hydrogen Energy, 2009
    Co-Authors: M F Elamin, Hiroshi Kanayama

    Abstract:

    Abstract As hydrogen leaks into a partially open space with a ceiling wall, a Boundary Layer of hydrogen can be constructed under that wall due to the impingement on the wall and the buoyancy force. The resulting Boundary Layer can be divided into two regions, namely the stagnation-point region and the far region. When the geometry of the source of the hydrogen leak is circular, such as a pinhole or an o-ring, the behavior of leakage flow will be axisymmetric due to the resulting radial jet. In contrast, when the geometry of the source of the hydrogen leak is planar, such as a crack, the behavior of leakage flow will be planar due to the resulting planar jet. Previously, we studied the planar case in the context of both the stagnation-point flow region [El-Amin MF, Kanayama H. Boundary Layer Theory approach to the concentration Layer adjacent to a ceiling wall at impinging region of a hydrogen leakage. Int J Hydrogen Energy 2008; 33(21): 6393–00] and the far region [El-Amin MF, Inoue M, Kanayama H. Boundary Layer Theory approach to the concentration Layer adjacent to a ceiling wall of a hydrogen leakage: far region. Int J Hydrogen Energy 2008; 33(24):7642–7]. This paper is concerned with both the stagnation-point flow region and the far region of the axisymmetric concentration Boundary Layer adjacent to a ceiling wall. Flow in the stagnation-point region is treated as Hiemenz flow, while it is treated as Blasius flow in the far region. The current results are compared with the planar cases [El-Amin MF, Kanayama H. Boundary Layer Theory approach to the concentration Layer adjacent to a ceiling wall at impinging region of a hydrogen leakage. Int J Hydrogen Energy 2008; 33(21): 6393–00; El-Amin MF, Inoue M, Kanayama H. Boundary Layer Theory approach to the concentration Layer adjacent to a ceiling wall of a hydrogen leakage: far region. Int J Hydrogen Energy 2008; 33(24):7642–7] for both stagnation-point flow and far regions. Both momentum and concentration Boundary Layer thicknesses are estimated, as well as the local friction factor.

  • Boundary Layer Theory approach to the concentration Layer adjacent to a ceiling wall of a hydrogen leakage far region
    International Journal of Hydrogen Energy, 2008
    Co-Authors: M F Elamin, Masahiro Inoue, Hiroshi Kanayama

    Abstract:

    The field of the hydrogen leakage in partially open space can be divided into two main regions according to the importance of the hydrogen concentration distribution and the flow behavior. These two regions are the jet region and the Boundary Layer region which are adjacent to the ceiling wall of the space, resulting from impinging the hydrogen jet to the wall. The Boundary Layer region in turn can be divided into two regions, according to the modeling of the flow. These regions are the stagnation-point Boundary Layer region and the far Boundary Layer region. Previously, we studied the region of stagnation-point flow (Hiemenz flow) [El-Amin MF, Kanayama H. Boundary Layer Theory approach to the concentration Layer adjacent to a ceiling wall at impinging region of a hydrogen leakage. Int J Hydrogen Energy, in press.]. The current paper is devoted to analyze the far region of the Boundary Layer adjacent to the ceiling wall using the Boundary Layer Theory. Also, an experiment has been conducted on the hydrogen leakage in partially open space to estimate the concentration distribution vertically at the center of the domain under the ceiling wall. In order to verify the Boundary Layer Theory approach, a comparison between the measurements and the Boundary Layer Theory approximations is investigated and the results showed a good agreement. The wall shear stress, the local friction factor, the friction drag and the non-dimensional drag coefficient of the ceiling wall are calculated. Also, both momentum and concentration Boundary Layer thicknesses are estimated.

  • Boundary Layer Theory approach to the concentration Layer adjacent to a ceiling wall at impinging region of a hydrogen leakage
    International Journal of Hydrogen Energy, 2008
    Co-Authors: M F Elamin, Hiroshi Kanayama

    Abstract:

    In this article, the steady-state concentration Boundary Layer adjacent to a ceiling wall of a stagnation-point flow region resulting from hydrogen impinging leakage is investigated. Flow in neighborhood of the stagnation point is treated as Hiemenz flow, while the concentration equation governs the concentration distribution in the Boundary Layer. The assumptions of the Boundary Layer Theory are invoked to simplify both the momentum and the concentration equations. Comparison between the CFD simulation and the current Boundary Layer approximation shows a good agreement. Both momentum and concentration Boundary Layer thicknesses are estimated as well as local friction factor and local mass transfer. Also, the study is extended to include some cases of unsteady leakage. The effects of the unsteadiness parameter on the local friction factor and mass transfer rate as well as momentum and concentration Boundary Layer thicknesses are analyzed.

Huishen Shen – 3rd expert on this subject based on the ideXlab platform

  • Boundary Layer Theory for the nonlinear vibration of anisotropic laminated cylindrical shells
    Composite Structures, 2013
    Co-Authors: Huishen Shen

    Abstract:

    Abstract A Boundary Layer Theory for the nonlinear flexural vibration of anisotropic shear deformable laminated cylindrical shells is developed. The shell may be embedded in an elastic medium that is modeled as a Pasternak elastic foundation. The material of each Layer of the shell is assumed to be linearly elastic, anisotropic and fiber-reinforced. Two kinds of fiber reinforced composite (FRC) laminated cylindrical shells, namely, uniformly distributed (UD) and functionally graded (FG) reinforcements, are considered. The motion equations are based on a higher-order shear deformation Theory with a von Karman-type of kinematic nonlinearity and including the extension-twist, extension-flexural and flexural-twist couplings. The thermal effects are also included, and the material properties of FRCs are estimated through a micromechanical model and are assumed to be temperature dependent. The equations of motion are solved by a singular perturbation technique to determine the linear and nonlinear frequencies of the FRC laminated cylindrical shells. The effects of material property gradient, the temperature change, shell geometric parameter, stacking sequence, foundation stiffness as well as the end conditions on the vibration characteristics of FRC shells are discussed in detail through a parametric study. The results show that a functionally graded reinforcement has a moderately effect on the linear and nonlinear vibration characteristics of FRC shells.

  • Boundary Layer Theory for the buckling and postbuckling of an anisotropic laminated cylindrical shell part ii prediction under external pressure
    Composite Structures, 2008
    Co-Authors: Huishen Shen

    Abstract:

    Abstract A Boundary Layer Theory for the buckling and postbuckling of anisotropic laminated thin shells is developed. The material of each Layer of the shell is assumed to be linearly elastic, anisotropic and fiber-reinforced. It is also assumed that the well-known von Karman nonlinear strain–displacement relationships are valid. The governing equations with transverse displacement and stress function as independent variables are deduced to a Boundary Layer type, which includes the effects of nonlinear prebuckling deformations, large deflections in the postbuckling range, and initial geometric imperfections of the shell. A postbuckling analysis is presented for axially loaded, perfect and imperfect, anisotropic laminated cylindrical shells with different values of shell parameters and stacking sequence. A singular perturbation technique is employed to determine the buckling loads and postbuckling equilibrium paths. The joint effects played by anisotropy, nonlinear prebuckling deformations, as well as initial geometric imperfections are studied. The new finding is that there exists a compressive stress along with an associate shear stress and twisting when the anisotropic laminated cylindrical shell is subjected to axial compression, and all the results published previously need to be re-examined.