POF Nameplate
  • Volume/Page
  • Keyword
  • DOI
  • Citation
  • Advanced
   
 
 
 

Flickr Twitter iResearch App Facebook

Search Issue | RSS Feeds RSS
Previous Issue Next Issue

Feb 2013

Volume 25, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Phys. Fluids 25, 025102 (2013); http://dx.doi.org/10.1063/1.4790640 (31 pages)

T. A. Casey, J. Sakakibara, and S. T. Thoroddsen
Enlarge Image | Read More
Return to All Sections
back to top
RSS Feeds
back to top Laminar Flows

Unsteady separated stagnation-point flow of an incompressible viscous fluid on the surface of a moving porous plate

S. Dholey and A. S. Gupta

Phys. Fluids 25, 023601 (2013); http://dx.doi.org/10.1063/1.4788713 (18 pages)

Online Publication Date: 6 February 2013

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Using group-theoretic method, an analysis is presented for a similarity solution of boundary layer equations which represents an unsteady two-dimensional separated stagnation-point (USSP) flow of an incompressible fluid over a porous plate moving in its own plane with speed u0(t). It is observed that the solution to the governing nonlinear ordinary differential equation for the USSP flow admits of two solutions (in contrast with the corresponding steady flow where the solution is unique): one is the attached flow solution (AFS) and the other is the reverse flow solution (RFS). A novel result of the analysis is that in the case of stationary plate (u0(t) = 0), after a certain value of the magnitude of the blowing d (<0) at the plate, only the AFS exists and the solution becomes unique. For a stationary plate (u0(t) = 0), the USSP flow is found to be separated for all values of d in both the cases of AFS and RFS. It is also observed that when u0(t) = 0, in the RFS flow with wall suction d (>0), there are two stagnation-points in the flow but in the presence of blowing d (<0), there is only one stagnation-point in the flow which moves further and further up with increase in |d|. Suction is shown to increase the wall shear stress while blowing has an opposite effect. Streamlines for an USSP flow when u0(t) ≠ 0 are also plotted. It is found that in this case, the USSP flow is not in general separated.
Show PACS
47.20.Ib Instability of boundary layers; separation
47.32.Ff Separated flows
47.56.+r Flows through porous media
02.20.-a Group theory
02.30.Hq Ordinary differential equations
47.15.Cb Laminar boundary layers

Deformation of vortex patches by boundaries

A. Crosby, E. R. Johnson, and P. J. Morrison

Phys. Fluids 25, 023602 (2013); http://dx.doi.org/10.1063/1.4790809 (19 pages)

Online Publication Date: 13 February 2013

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The deformation of two-dimensional vortex patches in the vicinity of fluid boundaries is investigated. The presence of a boundary causes an initially circular patch of uniform vorticity to deform. Sufficiently far away from the boundary, the deformed shape is well approximated by an ellipse. This leading order elliptical deformation is investigated via the elliptic moment model of Melander, Zabusky, and Styczek [J. Fluid Mech. 167, 95 (1986)10.1017/S0022112086002744]. When the boundary is straight, the centre of the elliptic patch remains at a constant distance from the boundary, and the motion is integrable. Furthermore, since the straining flow acting on the patch is constant in time, the problem is that of an elliptic vortex patch in constant strain, which was analysed by Kida [J. Phys. Soc. Jpn. 50, 3517 (1981)10.1143/JPSJ.50.3517]. For more complicated boundary shapes, such as a square corner, the motion is no longer integrable. Instead, there is an adiabatic invariant for the motion. This adiabatic invariant arises due to the separation in times scales between the relatively rapid time scale associated with the rotation of the patch and the slower time scale associated with the self-advection of the patch along the boundary. The interaction of a vortex patch with a circular island is also considered. Without a background flow, the conservation of angular impulse implies that the motion is again integrable. The addition of an irrotational flow past the island can drive the patch towards the boundary, leading to the possibility of large deformations and breakup.
Show PACS
47.32.Ef Rotating and swirling flows
47.32.Ff Separated flows
47.54.Bd Theoretical aspects
47.55.Hd Stratified flows
47.10.-g General theory in fluid dynamics
47.32.C- Vortex dynamics

Numerical simulation of vortex-induced vibration of a square cylinder at a low Reynolds number

Ming Zhao, Liang Cheng, and Tongming Zhou

Phys. Fluids 25, 023603 (2013); http://dx.doi.org/10.1063/1.4792351 (25 pages)

Online Publication Date: 27 February 2013

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Vortex-induced vibrations (VIV) of a square cylinder at a Reynolds number of 100 and a low mass ratio of 3 are studied numerically by solving the Navier-Stokes equations using the finite element method. The equation of motion of the square cylinder is solved to simulate the vibration and the Arbitrary Lagrangian Eulerian scheme is employed to model the interaction between the vibrating cylinder and the fluid flow. The numerical model is validated against the published results of flow past a stationary square cylinder and the results of VIV of a circular cylinder at low Reynolds numbers. The effect of flow approaching angle (α) on the response of the square cylinder is investigated. It is found that α affects not only the vibration amplitude but also the lock-in regime. Among the three values of α (α = 0°, 45°, and 22.5°) that are studied, the smallest vibration amplitude and the narrowest lock-in regime occur at α = 0°. It is discovered that the vibration locks in with the natural frequency in two regimes of reduced velocity for α = 22.5°. Single loop vibration trajectories are observed in the lock-in regime at α = 22.5° and 45°, which is distinctively different from VIV of a circular cylinder. As a result, the vibration frequency in the in-line direction is the same as that in the cross-flow direction.
Show PACS
47.32.-y Vortex dynamics; rotating fluids
47.15.ki Inviscid flows with vorticity
47.11.Fg Finite element methods
02.70.Dh Finite-element and Galerkin methods
47.10.ad Navier-Stokes equations
Return to All Sections
Close

Google Calendar

ADVERTISEMENT

Go to AIP Home   © AIP Publishing LLC
close