Abstract
Diffusion of a solute in turbulent flows through a circular pipe or tunnel is an important aspect of environmental safety. In this study, the diffusion coefficient of turbulent flow in circular pipe has been simulated by the Discrete Tracer Point Method (DTPM). The DTPM is a Lagrangian numerical method by a number of imaginary point displacement which satisfy turbulent mixing by velocity fluctuations, Reynolds stress, average velocity profile and a turbulent stochastic model. Numerical simulation results of points’ distribution by DTPM have been compared with the analytical solution for turbulent plug-flow. For the case of turbulent circular pipe flow, the appropriate DTPM calculation time step has been investigated using a constantβ, which represents the ratio between average mixing lengths over diameter of circular pipe. The evaluated values of diffusion coefficient by DTPM have been found to be in good agreement with Taylor’s analytical equation for turbulent circular pipe flow by givingβ=0.04 to 0.045. Further, history matching of experimental tracer gas measurement through turbulent smooth-straight pipe flow has been presented and the results showed good agreement.
Highlights
The diffusion of gas and other particulate matter in pipe or channel flows is important aspect to meet the safety requirements
The diffusion coefficient of turbulent flow in circular pipe has been simulated by the Discrete Tracer Point Method (DTPM)
When a pulsed substance or solute is injected into a straight pipe flow, it is advected and diffused to a relative reference moving with certain average velocity
Summary
The diffusion of gas and other particulate matter in pipe or channel flows is important aspect to meet the safety requirements. He neglected the contribution of molecular diffusion in both radial and axial directions which are negligibly small compared with turbulent eddy mixing diffusion in high Reynolds number He evaluated velocity at a certain distance from center of pipe and radial diffusivity as a function of universal velocity profile modified from Goldstein [4]. Threadgill and Schnelle [10], while Taylor [2] conducted both in smooth and artificially roughened glass pipes They applied least square fitting method for their measurements, and showed higher prediction values compared to Taylor’s Equation (1). Sasaki, Gautama and Risono [14] conducted tracer gas measurement in an underground mine ventilation airways They found higher diffusion coefficient for the airways flow than those evaluated using Equation (1) for smooth pipe. It is free of grid requirement and the visualization of points’ distribution is simple
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