Velocity gradient

About: Velocity gradient is a research topic. Over the lifetime, 3013 publications have been published within this topic receiving 77120 citations.

Constraints on the structure of the East Pacific Rise from seismic refraction data

Abstract: University of Washington seismic data taken during ROSE phase 1 have been used to study the structure of the East Pacific Rise in the vicinity of 12°N. Off axis but within 50 km of the axis we find that the oceanic crust can be modeled with a rapid change in velocity in the top 2.5 km, a zone of low but uniform velocity gradient from 2.5 to about 5.5 km and a transitional zone about 1 km thick to mantle material. There is also evidence for substantial anisotropy in mantle velocity gradients, with a positive velocity gradient in the spreading direction and a negative velocity gradient parallel to the rise. Under the rise axis the data allow at most a very narrow zone of low velocity (less than about 2 km wide) in the crust.

Tracing interstellar magnetic field using velocity gradient technique: Application to Atomic Hydrogen data

Abstract: The advancement of our understanding of MHD turbulence opens ways to develop new techniques to probe magnetic fields. In MHD turbulence, the velocity gradients are expected to be perpendicular to magnetic fields and this fact was used by Gonsalvez-Casanova & Lazarian to introduce a new technique to trace magnetic fields using velocity centroid gradients. The latter can be obtained from spectroscopic observations. We apply the technique to GALFA HI survey data and compare the directions of magnetic fields obtained with our technique with the direction of magnetic fields obtained using PLANCK polarization. We find excellent correspondence between the two ways of magnetic field tracing, which is obvious via visual comparison and through measuring of the statistics of magnetic field fluctuations obtained with the polarization data and our technique. This suggests that the velocity centroid gradients can provide a reliable way of measuring of the foreground magnetic field fluctuations and thus provide a new way of separating foreground and CMB polarization signals.

Slip flow of Casson–Maxwell nanofluid confined through stretchable disks

Abstract: This study reports an incompressible electrically conducting Casson–Maxwell fluid flow confined across two uniformly stretchable disks. Buongiorno nanofluid model is implemented in the fluid flow. Cattaneo–Christov theory of double-diffusion is characterized through the heat and mass equations. Velocity, thermal and concentration slip conditions are executed at the lower stretchable disk. The flow model is dimensionalized through the similarity functions and then numerical solution is attained by RKF-45 scheme combined with shooting technique. The results of physical parameters are discussed by plotting the effects of such parameters on velocity, thermal and concentration fields. The results revealed that the Maxwell liquid is highly effected by Lorentz force than the Casson liquid. Thermal gradient of Maxwell liquid is highly influenced by stretching ratio parameter when compared to Casson fluid. Increase in Casson parameter and Deborah number declines the velocity gradient. Rise in the values of Brownian motion parameter declines the concentration gradient. Finally, the upsurge in thermal relaxation time parameter enhances the thermal gradient quickly in absence of thermal slip parameter.

Flame flashback and propagation of premixed flames near a wall

Abstract: The flashback or propagation of premixed flames along the near-wall low-velocity region at the bases of a laminar boundary layer of a reactive mixture has been studied numerically. The analysis, carried out using the constant density approximation for an Arrhenius overall reaction, accounts for the effects of the Lewis number of the fuel. The flow field, as seen by an observer moving with the front, includes the unknown flame front velocity U relative to the wall and the linear velocietygradient A at the base of the boundary layer. Due to this gradient, the flame front is curved with a radius of curvature lF=SLA, proportional to the planar flame velocity SL. The front velocity is changed from SL by a factor which depends on the Karlovitz number, or non-dimensional wall velocity gradient,defined as the ration between the thickness of the planar flame and the front curvature lF. The front velocity has been calculated in the limiting cases of adiabatic and isothermal walls. The front velocity changes from negative to positive when the Karlovitz number decreases below a critical value, determining the onset of flashback. This critical value, which decreases when the Lewis, number of the fuel increases, is smaller for isothermal than for adiabatic walls. In this second case, when the flame is not quenched close to the wall, flashback is prevented by flame stretch associated with flame curvature.

Mixed convection flow of second grade fluid along a vertical stretching flat surface with variable surface temperature

Abstract: In the present study we have explored the effects of thermal buoyancy on flow of a viscoelastic second grade fluid past a vertical, continuous stretching sheet of which the velocity and temperature distributions are assumed to vary according to a power-law form. The governing differential equations are transformed into dimensionless form using appropriate transformations and then solved numerically. The methods here employed are (1) the perturbation method together with the Shanks transformation, (2) the local non-similarity method with second level of truncation and (3) the implicit finite difference method for values of ξ ( = Gr x /Re 2 , defined as local mixed convection parameter) ranging in [0, 10]. The comparison between the solutions obtained by the aforementioned methods found in excellent agreement. Effects of the elasticity parameter λ on the skin-friction and heat transfer coefficients have been shown graphically for the fluids having the values of the Prandtl number equal to 0.72, 7.03 and 15.0. Effects of the viscoelastic parameter and the mixed convection parameter, ξ, on the temperature and velocity fields have also been studied. We notice that with the increase in visco-elastic parameter λ, velocity decreases whereas temperature increases and that velocity gradient is higher than that of temperature.