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Abstract

This numerical study investigates a circular cylinder placed in a uniform stream and moving along a slender figure-8-path, using a 2D computational method based on the finite difference method. The effects of in-line amplitude of oscillation and of frequency ratio are investigated. Computations for varying amplitude values were carried out at Re = 150, 200 and 250 for a clockwise orbit (in the upper loop). Time-mean and rms values of force coefficients yielded smooth curves and tended to increase with amplitude.

The effect of frequency ratio was investigated at Re = 200, 250 and 300 in the lock-in domain for both clockwise (CW) and anticlockwise (ACW) orientation. Results differ substantially depending on the direction of orientation. Mechanical energy transfer was always positive in ACW direction, which may lead to vortex-induced vibration, and always negative for CW orientation. The time-mean of drag was much lower for CW over the whole frequency ratio domain investigated. For the CW orbit vortex switches were found at specific frequency ratios at Re = 250 and 300. Limit cycle curves for the CW orbit before and after a jump were symmetric, mirror images, and quite complex, while vorticity contours were close to symmetry. These results indicate the possibility of symmetry-breaking bifurcation.

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Abstract  

Mathematical modeling of toluene oxidation under unsteady state catalyst created by forced oscillations of concentration of toluene in the reactor inlet was carried out. It is shown that, under periodic reactor operation, the benzaldehyde yield was up to several times higher than the steady state value. This was explained by the participation of different oxygen species in the partial and total oxidation on the catalyst surface.

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] Badia J. R. , Farré R. , Montserrat J. M. , Ballester E. , Hernandez L. , Rotger M. , Rodriguez-Roisin R. , Navajas D. Forced oscillation technique for the evaluation of severe sleep apnoea

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