Phenomenon Of Turbulent Diffusion Research Articles

NUMERICAL SOLUTION OF A MODEL FOR TURBULENT DIFFUSION

A model is considered for turbulent diffusion which consists of a Riesz space fractional derivative to describe the turbulent phenomenon and also includes advection and classical diffusion. We present a first order explicit numerical method and a second order implicit numerical method to solve our problem and prove convergence results for both methods, including the derivation of stability constraints needed for the explicit numerical method to converge. In the end, to give some insights into the phenomenon of turbulent diffusion described by the Riesz fractional derivative, we show the behavior of the solution when we consider a Gaussian initial condition.

S053032 吸光度法による軸対称乱流噴流中での二成分瞬時濃度測定

Turbulent diffusion phenomena are of practical importance with many engineering and environmental field (e.g., in the reactor design and the prediction of pollutant diffusion). In order to clarify turbulent diffusion field experimentally, it is useful to measure instantaneous concentrations of multiple species simultaneously in a turbulent flow. In the present study, measurement system for concentrations of two species using absorption method has been developed, and instantaneous concentrations of two species in a turbulent jet were measured. Two laser diodes (LDs) with different wavelength are used as light sources; red LD (635 nm) and green LD (532 nm). It is confirmed that the instantaneous concentrations of two species in a turbulent jet can be measured by the present measurement system.

Mixing models for gas stirred metallurgical reactors

The mixing of liquids in ladles, (0.5 ≦L/D ≦ 2.0), agitated by a centrally rising bubble plume, has been analyzed both theoretically and experimentally. An exhaustive review of previous metallurgical literature on mixing in ladles and furnaces demonstrates that the majority of previous investigators in the field consider mixing to be brought about primarily by turbulent diffusion phenomena. The present study clearly shows that mixing is a combination of both convection and eddy diffusion processes, neither of which can be disregarded for gas stirred systems. For predicting mixing times during such gas injection procedures, a simple empirical equation is proposed for axisymmetric systems:τ mαem −1/3L−1R5/3. Hereτ m is the 95 pct mixing time,e m is the specific energy input rate,R is the vessel radius, andL is the depth of liquid. On the basis of physical and mathematical modeling, the rate of liquid mixing in conventional gas injection ladle metallurgy operations is compared with those observed in C.A.S. (composition adjustment by sealed argon bubbling) systems. It was found that mixing in C.A.S. operations is relatively slow and highly insensitive to gas flowrates(i.e., specific energy input rates).

A vortex model to relate eulerian and lagrangian “ turbulent” velocity fields

AbstractThe phenomenon of turbulent diffusion was studied by using computed models. Free pseudo‐turbulent fluid flow was simulated on a digital computer by ensembles of randomly positioned moving and interacting vortices to represent the eddy structure of the turbulence. A vortex model, which had statistical values corresponding to a measured real flow in an Eulerian frame of reference, was then obtained. By considering the motion of a particular vortex or a fluid particle in the computed pseudo‐turbulent flow it was possible to determine measurements in a Lagrangian frame of reference. Estimates of the mean square lateral excursions of a marked particle were obtained and finally the Lagrangian auto correlation was compared with the auto correlation in a moving frame of reference.