Publication Date:
1992-03-01
Description:
The concentration distribution resulting from a continuous point source in a fluid with a steady linear variation in velocity is distorted by the flow at distances greater than (k/Eb)½ed where k is the molecular diffusion coefficient and Eb is a characteristic shear rate. The distribution has two distinct shapes depending on the number of principal axes of fluid strain that are expansive and the relative magnitude of irrotational and rotational shears. For irrotational flows a single expansive principal axis of strain results in a tube-like distribution, while two expansive axes results in a disk-like distribution. Approximate analytical solutions, derived by neglecting diffusion along the expansive axes, agree well with concentrations calculated by numerically convolving the exact instantaneous source solution. The effect of fluid vorticity is generally to reorient the distribution away from the principal axes of strain and to reduce the asymmetry of the concentration distribution. Aside from reorientation, the concentration distribution varies little until the vorticity approaches a critical value defined by a kinematic condition for equilibrium orientation in the presence of rotation. For vorticity greater than the critical value, the concentration distribution becomes axisymmetrie around the axis of rotation. Application of these results to numerical simulations of isotropic turbulence suggests that tubes are more common than disks and that vorticity exceeds the critical value in at least 25% of the fluid. © 1992, Cambridge University Press. All rights reserved.
Print ISSN:
0022-1120
Electronic ISSN:
1469-7645
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
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