Experiments were performed to investigate some aspects of turbulence in rotating and non-rotating fluid systems where the turbulence was induced by a horizontal grid oscillating vertically. An earlier theory by the second author made use of a planar source of energy, which appeared to be similar to the energy source of the grid, in determining the characteristics of the turbulence at points some distance away. The simplicity of the theory was in the parameterization of the grid ‘action’ by a single quantity K, with dimensions and characteristics of eddy viscosity.The experimental results provide additional confirmation of the theory in the non-rotating case, and indicate the usefulness of the idealized energy source in the rotating case. In the latter, we measured the propagation of the front separating disturbed and undisturbed fluid, moving along the axis of rotation. The thickness d(t) of the disturbed region increases at first as (Kt)½, as in a non-rotating fluid, until the Rossby number K/Ωd2k becomes of order unity.Beyond this the disturbances are wavelike and rotationally dominated, and the thickness now increases linearly with time, yielding a speed of propagation for the front proportional to the wave speed (KΩ)½. Finally, the disturbances reach the bottom and the vessel is in statistical steady state. Then a region of thickness dk independent of time is found, and it contains motion that resembles ordinary, three-dimensional turbulence. dk ∼ (K/Ω)½ is analogous to the depth of the turbulent Ekman layer H ∼ (K/Ω)½, where K is taken as an eddy viscosity.McEwan constructed a similar rotating experiment, although with a different energy source, and observed vortices parallel to the axis of rotation, provided that the Rossby number was less than a critical value. Our observations and theory indicate that the disappearance of the vortices corresponds to h < dk, where h is the total depth of the fluid. At that point, the whole tank is filled with three-dimensi
Oscillating-grid turbulence including effects of rotation | Journal of Fluid Mechanics | Cambridge Core Search Institution Login Search Hostname: page-component-5d84bcc8dc-mbr72 Total loading time: 0 Render date: 2026-08-11T17:48:54.454Z Has data issue: false hasContentIssue false Home > Journals > Journal of Fluid Mechanics > Volume 126 > Oscillating-grid turbulence including effects of rotation English Français Journal of Fluid Mechanics Article contents Abstract References Oscillating-grid turbulence including effects of rotation Published online by Cambridge University Press: 20 April 2006 Stuart C. Dickinson and Robert R. Long Show author details Stuart C.
An earlier theory by the second author made use of a planar source of energy, which appeared to be similar to the energy source of the grid, in determining the characteristics of the turbulence at points some distance away. The simplicity of the theory was in the parameterization of the grid ‘action’ by a single quantity K , with dimensions and characteristics of eddy viscosity. The experimental results provide additional confirmation of the theory in the non-rotating case, and indicate the usefulness of the idealized energy source in the rotating case. In the latter, we measured the propagation of the front separating disturbed and undisturbed fluid, moving along the axis of rotation.
d k ∼ ( K /Ω) ½ is analogous to the depth of the turbulent Ekman layer H ∼ ( K /Ω) ½ , where K is taken as an eddy viscosity. McEwan constructed a similar rotating experiment, although with a different energy source, and observed vortices parallel to the axis of rotation, provided that the Rossby number was less than a critical value. Our observations and theory indicate that the disappearance of the vortices corresponds to h < d k , where h is the total depth of the fluid. At that point, the whole tank is filled with three-dimensional turbulence. Information Type Research Article Information Journal of Fluid Mechanics , Volume 126 , January 1983 , pp.
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CrossRef Google Scholar Fernando, Harindra J. S. Chen, Rui-Rong and Boyer, Don L. 1991. Effects of rotation on convective turbulence . Journal of Fluid Mechanics, Vol. 228, Issue. , p. 513. CrossRef Google Scholar Dalziel, Stuart B. 1992. Decay of rotating turbulence: some particle tracking experiments . Applied Scientific Research, Vol. 49, Issue. 3, p. 217. CrossRef Google Scholar Fernando, H. J. S. and De Silva, I. P. D. 1993. Note on secondary flows in oscillating-grid, mixing-box experiments . Physics of Fluids A: Fluid Dynamics, Vol. 5, Issue. 7, p. 1849. CrossRef Google Scholar Dalziel, Stuart B. 1993. Flow Visualization and Image Analysis .
Effective airflow management in underground mining is vital for controlling the dispersion of dust and gases, which poses significant safety and operational challenges. Turbulent airflow is crucial for the transport of these substances, directly affecting worker safety and equipment performance. In longwall mining, optimizing ventilation systems requires a thorough understanding of how various factors influence airflow turbulence, which can help mitigate risks associated with dust and gas buildup. This study uses steady-state computational fluid dynamics (CFD) to analyze the impact of rotating cutting drums on airflow patterns in longwall mining, focusing on a rotational speed of 50 RPM. With a ventilation air velocity of 3 m/s, the research examines how drum rotation affects local turbulence and airflow distribution around the shearer. The study also includes a comparative analysis with a scenario where the drums are not rotating. The study finds that the airflow velocity at the tailgate and the intensity of the generated turbulence can reach up to approximately 7 m/s and 360 %, which significantly influences the dispersion of dust and gases. Understanding these effects is essential for enhancing ventilation efficiency. The comparison highlights how drum rotation increases localized turbulence and alters airflow dynamics around the cutting face.
Understanding planetary core convection dynamics requires the study of convective flows in which the Coriolis and Lorentz forces attain a leading-order, so-called magnetostrophic balance. Experimental investigations of rotating magnetoconvection (RMC) in the magnetostrophic regime are therefore essential to broadly characterize the properties of local-scale planetary core flow. Toward this end, we present here the first thermovelocimetric measurements of magnetostrophic, liquid metal convection, which are made using liquid gallium as the working fluid, at moderate rotation rates (Ekman numbers 10 -4 ≤ Ek ≤ 10 -5 ) and in the presence of dynamically strong magnetic fields (Elsasser number Λ = 1). Complementary rotating convection (RC) experiments are performed at the same rotation rates to serve as reference cases. Our RMC velocity measurements adequately follow a geostrophic turbulent scaling for cases in which local-scale convective inertial forces exceed the Lorentz forces in the fluid bulk. In cases where Lorentz forces exceed local-scale inertia (local or convective interaction parameter N ℓ or N C ≳ 3), the root-mean-square RMC velocities are magnetically damped, yielding values below the geostrophic turbulent RC scaling prediction. An enhancement in heat transfer is observed, which we attribute to the increased coherence of vertically aligned magnetostrophic convective flow. Finally, our results and comparisons to dynamo simulations suggest that the system is in the str
A linear stability analysis has been made of the hydrodynamic stability of viscous flow in a thermally stratified rotating channel. To understand the competition mechanism of the flow stabilization and destabilization, an inviscid stability criterion including effects of the rotation and stratification was first formulated for indicating the stable and unstable regimes of the flow. Then, an eigenvalue problem was derived for the viscous flow and solved using a shooting method. The combined effect of the Coriolis force and centrifugal-type buoyancy force on the longitudinal roll-cell instabilit
Meteorologists and astrophysicists interested in large scale planetary and solar circulations have come to recognize the importance of rotation and stratification in determining the character of these flows. In particular, the effect of latitude-dependent Coriolis force on nonlinear convection is thought to play a crucial role in such phenomena as differential rotation on the Sun, cloud band orientation on Jupiter, and the generation of magnetic fields in thermally driven dynamos. The continuous low-gravity environment of the orbiting space shuttle offers a unique opportunity to make laboratory studies of such large-scale thermally driven flows under the constraint imposed by rotation and sphericity. This is possible because polarization forces in a dielectric liquid, which are linearly dependent on fluid temperature, give rise to an effectively radial buoyancy force when a radial electrostatic field is imposed. The Geophysical Fluid Flow Cell (GFFC) is an implementation of this ideal in which fluid is contained between two rotating hemispheres that are differentially heated and stressed with a large a-c voltage. The experiment, to be flown on Spacelab III (currently set for launch April 29, 1985), will explore non-linear mode selection and high Rayleigh number turbulence in a rotating convecting spherical shell of liquid. Experiments will be carried out in a low driving parameter range where some limited numerical experimentation is currently feasible, as well as in a parame
The pressure recovery coefficient of a two-dimensional diffuser (Cp) was found to be significantly affected by the intensity and structure of the inlet free-stream turbulence. Significantly larger values of Cp occurred for the case of highly anisotropic inlet free-stream turbulence with the plane of rotation of the eddies parallel to the free-stream flow and perpendicular to the diverging walls of the diffuser, as compared to the values of Cp for the case of grid-generated near-isotropic inlet conditions. The relatively high values of Cp for the case of the highly anisotropic inlet free-stream turbulence conditions can be attributed to highly effective mixing, where the plane of rotation of the eddies facilitates a direct transport of momentum from the free-stream to the boundary layers along the diverging walls of the diffuser, as compared to the mixing that occurs with grid-generated highly unorganized eddies.
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