Electromagnetic control of an oscillating turbulent jet in a confined cavity

Abstract

Control of self-sustained jet oscillations in confined cavities is of importance for many industrial applications. It has been shown that the mechanism underlying these oscillations consists of three stages: (i) growth of the oscillation, (ii) amplitude limitation and (iii) delayed destruction of the recirculation zone bounding the jet. It has also been shown that oscillations may be enhanced or suppressed by applying (e.g. electromagnetic) body forces.In the current paper we study the influence of electromagnetic forces oriented aligned with or opposite to the direction of the jet on the oscillation mechanism. The influence of the forcing is found to depend on the Stuart number N in relation to a critical Stuart number Ncrit. We demonstrate that for |N| < Ncrit, the oscillation mechanism is essentially unaltered, with moderate modifications in the jet oscillation amplitude and frequency compared to N=0. For N > Ncrit, electromagnetic forcing leads to total suppression of the self-sustained oscillations. For N < Ncrit, electromagnetic forces dominate over inertia and lead to strongly enhanced oscillations, which for N≪−Ncrit become irregular.As was earlier demonstrated for N=0, the present paper shows that for −6Ncrit<N<Ncrit the oscillatory behaviour, i.e. frequencies, oscillation amplitudes and wave shapes, can be described quantitatively with a zero-dimensional model of the delay differential equation (DDE) type, with model constants that can be a priori determined from the Reynolds and Stuart number and geometric ratios.