• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.27 no.3
• /
• pp.319-325
• /
• 2003

We investigate the spectra and the pseudospectra in plane Poiseuille flow, plane Couette flow and Blasius flow. At subcritical Reynolds number, the spectra are lied strictly inside the stable complex half-plane, but the pseudospectra are lied in the unstable half-plane, reflecting the large linear transient growth that certain perturbations may excite. It means that the smooth flows may become to turbulent even though all the eigenmodes decay monotonically. We found that pseudospectra is one reason that causes subcritical transition in plane Poiseuille flow and plane Couette flow and bypass transition in Blasius flow.

• Journal of the Korean Society of Visualization
• /
• v.17 no.3
• /
• pp.12-18
• /
• 2019

Direct numerical simulation of a fully developed turbulent plane Couette-Poiseuille flow with a two-dimensional (2-D) rod-roughened wall is performed to investigate the impacts of the surface roughness. It is shown that the logarithmic region in the mean velocity profile over the rough wall Couette-Poiseuille flow is significantly shortened by the surface roughness compared to that over a turbulent Couette-Poiseuille flow with smooth wall. The Reynolds shear stress over the rough wall Couette-Poiseuille flow is decreased compared to that for a smooth case in the outer layer. These results are attributed to weakened turbulence activity or roll-cell mode over the rough wall Couette-Poiseuille flow near the channel centerline due to suppressed development of u'-structure on the top wall, as documented through spanwise energy spectra of the streamwise velocity fluctuations. Inspection of congregation motion near the bottom wall and time evolution of u'-structure reveal weakened co-supporting cycle for the rough wall case.

• Journal of Mechanical Science and Technology
• /
• v.18 no.3
• /
• pp.491-498
• /
• 2004

An analysis of the plane Couette flow between two parallel plates of a viscous, incompressible, micropolar fluid is presented. Especially, the effects of non-zero values of the micro-gyration boundary condition coefficient and pressure gradient on the flow fields are studied. Numerical results show that the micro polar parameter was found to have much more of an impact on the flow behaviors. It is also observed that the micro-gyration boundary condition coefficient influenced on the coefficients of skin friction and couple stress due to its different effect on the surface stress.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
• /
• v.17 no.4
• /
• pp.489-498
• /
• 1988

An analysis has been given for the effect of viscous dissipation on the thermal instability of plane Couette flow between two parallel plates maintained at different constant temperatures. Under the assumption that the principle of the exchange of stabilities holds, stationary disturbance quantities in the form of longitudinal vortices are considered. The magnitudes of disturbance quantities are then represented as fast convergent power series so that the eigenvalue problem for determining the onset conditions of the thermal instability may be reduced to a simplified problem of finding the roots of a $4{\times}4$ determinant. It is shown that as the magnitude of the visucous dissipation increases the flow becomes more susceptible to instabilities, which is in very good agreement with previous results obtained in some related researches.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.27 no.6
• /
• pp.766-772
• /
• 2003

The pseudospectral method for stability analysis was used to find the most influential disturbance mode for transition of plane channel flows and Blasius flow at their critical Reynolds numbers. A number of various oblique disturbance waves were investigated for their pseudospectra and resolvent norm contours in each flow, and an exhaustive search method was employed to find the disturbing waves to which the flows become most unstable. In plane Poiseuille flow an oblique disturbance with a wavelength of 3.59h (where h is the half channel width) at an angle $28.7^{\circ}$ was found to be the most influential for the flow transition to turbulence, and in plane Couette flow it is an oblique wave with a wavelength of 3.49h at an angle of $19.4^{\circ}$. But in Blasius flow it was found that the most influential mode is a normal wave with a wavelength of $3.44{\delta}_{999}$. These results imply that the most influential disturbance mode is closely related to the fundamental acoustic wave with a certain shear sheltering in the respective flow geometry.

• Journal of the Korean Society for Industrial and Applied Mathematics
• /
• v.13 no.2
• /
• pp.73-86
• /
• 2009

The problem of thermal stability of an exothermic reactive viscous fluid between two parallel walls in the plane Poiseuille and Couette flow configurations is investigated for different thermal boundary conditions. Neglecting reactant consumption, the closed-form solutions obtained from the momentum equation was inserted into the energy equation due to dissipative effect of viscosity. The resulting energy equation was analyzed for criticality using the variational method technique. The problem is characterized by two parameters: the Nusselt number(N) and the dynamic parameter($\Lambda$). We observed that the thermal and dynamical boundary conditions of the wall have led to a significant departure from known results. The influence of the variable pre-exponential factor, due to the numerical exponent m, also give further insight into the behavior of the system and the results expressed graphically and in tabular forms.

• Journal of computational fluids engineering
• /
• v.20 no.4
• /
• pp.58-62
• /
• 2015

Recent studies on wall-bounded shear flow have emphasized the significance of the stable manifold of simple nonlinear invariant solutions to the Navier-Stokes equation in the formation of the boundary between the laminar and turbulent regions in state space. In this paper we present newly discovered homoclinic orbits of the Kawahara and Kida(2001) periodic solution in plane Couette flow. We show that as the Reynolds number decreases a pair of homoclinic orbits move closer to each other until they disappear to exhibit homoclinic tangency.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.25 no.5
• /
• pp.705-712
• /
• 2001

The flow between two concentric cylinders, with the inner one rotating and with an imposed pressure-driven axial flow, is studied using numerical simulation. The case without the axial flow was investigated in the preceding paper. This study considers the identical flow geometry as in the experiments of Wereley and Lueptow[Phys. Fluid, 11(12), 1999]. They carried out experiments using PIV to measure the velocity fields in a meridional plane of the annulus in detail. When an axial flow is imposed, the critical Taylor number is increased. The axial flow stabilizes the flow field and decreases the torque required to rotate the inner cylinder. The velocity vector fields obtained also show the same flow features found in the experiments of Wereley and Lueptow.

• Proceedings of the KSME Conference
• /
• 2001.06e
• /
• pp.444-449
• /
• 2001

The flow between two concentric cylinders, with the inner one rotating and with an imposed pressure-driven axial flow, is studied using numerical simulation. This study considers the identical flow geometry as in the experiments of Wereley and Lueptow[Phys. Fluid, 11 (12), 1999]. They carried out experiments using PIV to measure the velocity fields in a meridional plane of the annulus in detail. When an axial flow is imposed, the critical Taylor number is increased. The axial flow stabilizes the flow field and decreases the torque required to rotate the inner cylinder. The velocity vector fields obtained also show the same flow features found in the experiments of Wereley and Lueptow.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.25 no.5
• /
• pp.697-704
• /
• 2001

The flow between two concentric cylinders, with the inner one rotating, is studied using numerical simulation. This study considers the identical flow geometry as in the experiments of Wereley and Lueptow[J. Fluid Mech., 364, 1998]. They carried out experiment using PIV to measure the velocity fields in a meridional plane of the annulus in detail. When Taylor number increases over the critical one, the flow instability caused by curved streamlines of the tangential flow induces Taylor vortices in the flow direction. As Taylor number further increases over another critical one, the steady Taylor vortices become unsteady and non-axisymmetrically wavy. The velocity vector fields obtained also show the same flow features found in the experiments of Wereley and Lueptow.