Influence Of Velocity Shear Research Articles

Shear Effects on Flow past a Square Cylinder at Moderate Reynolds Numbers

Direct numerical simulation (DNS) and large eddy simulation (LES) with a dynamic Smagorinsky subgrid model are performed to investigate the flow past a square cylinder under the influence of velocity shear at the inlet at moderate Reynolds numbers ( R=150–1,000 ). The shear rate is expressed by a dimensionless shear parameter β , which is based on the velocity gradient, side length of the cylinder, and upstream velocity at the center plane of the cylinder. Shear parameter varies from 0 to 0.2 in this study. Several Reynolds numbers are considered to study the Reynolds number dependence and the Strouhal number were found to have no significant variation with the shear parameter. The peak frequency of drag coefficient fluctuation becomes identical with that of the lift force coefficient when β>0.1 . The vortices on the low-velocity side disappear in the far wake under the strong shear condition. The stagnation point moves to the high-velocity side and the movement increases with an increase in shear paramet...

The Influence of Velocity Shear on Magnetic Buoyancy Instability in the Solar Tachocline

The Sun’s large-scale magnetic field is believed to be generated deep within the Sun, at the base of the convection zone, in a predominantly stably stratified region of strong radial shear, known as the tachocline. Observations indicate that, owing to magnetic buoyancy, this field rises to the surface to form active regions with systematic properties. Whereas previous investigations of magnetic buoyancy instability have generally assumed a static basic state, here we investigate the role of an aligned shear in modifying this instability. We adopt two complementary approaches. Using the energy principle, we derive sufficient conditions for the stability of a magnetic field in a stratified, compressible shear flow. To investigate the nature of the unstable modes, we have performed a series of numerical calculations; these suggest that the shear has an ‘‘axisymmetrizing’’ and stabilizing effect on the magnetic buoyancy instability. We discuss the implications for the instability of the solar magnetic field.

Velocity and diffusion imaging in dynamic NMR microscopy

The imposition of resolution gradients in a pulsed-gradient spin-echo (PGSE) NMR sequence induces motionally dependent phase and amplitude modulation in the image, a technique which we have termed dynamic NMR microscopy. Fourier analysis of this modulation gives a dynamic displacement profile for each pixel which can then be analyzed to obtain velocity and diffusion maps. The application of this method at high spatial resolution is motivated by a desire to measure vascular flow in living plants and variations in molecular self-diffusion under the influence of velocity shear in narrow capillaries. The theory of dynamic NMR microscopy is presented and potential artifacts discussed, including the effect of slice selection gradients, PGSE gradient nonuniformity, and specific problems associated with the measurement of self-diffusion in the presence of velocity gradients. It is demonstrated that a double-echo PGSE pulse sequence can be used to restore coherent phase shifts associated with steady-state flow, and examples of self-diffusion maps and signed velocity maps from sequences of phase-encoded images obtained by projection reconstruction are given. This method has been applied at 20,um transverse resolution in laminar capillary flow.

Correction [to “Influence of Velocity Shear on the Rayleigh‐Taylor Instability”

Geophysical Research LettersVolume 10, Issue 6 p. 492-492 CorrectionsFree Access Correction [to “Influence of Velocity Shear on the Rayleigh-Taylor Instability”] P. N. Guzdar, P. N. GuzdarSearch for more papers by this author P. N. Guzdar, P. N. GuzdarSearch for more papers by this author First published: June 1983 https://doi.org/10.1029/GL010i006p00492Citations: 9AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume10, Issue6June 1983Pages 492-492 RelatedInformation

Correction [to “Influence of velocity Shear on the Rayleigh‐Taylor Instability”

Correction [to “Influence of velocity Shear on the Rayleigh‐Taylor Instability”

Influence of velocity shear on the Rayleigh‐Taylor instability

The influence of a transverse velocity shear on the Rayleigh‐Taylor instability is investigated. It is found that a sheared velocity flow can substantially reduce the growth rate of the Rayleigh‐Taylor instability in the short wavelength regime (i.e., kL > 1 where L is the scale length of the density inhomogeneity), and causes the growth rate to maximize at kL < 1.0. Applications of this result to ionospheric phenomena [equatorial spread F (ESF) and ionospheric plasma clouds] are discussed. In particular, the effect of shear could account for, at times, the 100’s of km modulation observed on the bottomside of the ESF ionosphere and the km scale size wavelengths observed in barium cloud prompt striation phenomena.