Use of natural instabilities for enhancement of flow mixing in annuli

Abstract eng:
A technique has been proposed to increase flow mixing in annuli through efficient vortex generation. Corrugations in the form of axisymmetric ribs have been placed at the walls to modulate the axial flow in a manner which leads to centrifugal instabilities which result in the formation of streamwise vortices. This technique results in only a small increase in the pressure drop, unlike other vortex generation methods. A spectral algorithm based on Fourier and Chebyshev expansions has been used to study the stationary state and its stability. Due to the irregularities of the boundaries, the immersed boundary conditions (IBC) method has been used to enforce the flow boundary conditions. The effects of geometric and flow parameters on the pressure losses and on the stability characteristics have been thoroughly investigated. Characteristics of both the vortex mode and the travelling mode of instability, as well as the region of dominance of each mode, have been determined.

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