Experimental and numerical investigations on the effect of rotating cylindrical disc on an unconfined isothermal annular swirling jet

Abstract

Swirl flows have many practical engineering applications such as in gas turbine engines, industrial furnaces, diesel engines, boilers etc. An important feature of many swirling flows encountered in practice is the existence of strongly curved streamlines that introduce sufficient radial and axial pressure gradients to cause the formation of a toroidal recirculation zone which intensifies turbulent fluctuations, enhances fuel air mixing and stabilizes the flame in turbulent combustion. Therefore, the study of the combined effects of bluff body and swirling jet at high and moderate Reynolds numbers may provide insight into the physical phenomena and offer some ways to extend the applicability of swirling jets. In the present work, experimental and numerical investigations have been carried out to study the combined effect of a rotating circular disc, placed at the end of a bluff body, on the mean flow and turbulent characteristics of a turbulent annular swirling free jet of air issuing into still air surroundings. The objective of the work is to provide an improved understanding of swirling flows passing over a rotating cylindrical disc which could rotate at a speed of 12000 rpm. Numerical investigations were carried out by using a CFD software, FLUENT. Modeling was done using GAMBIT. From the numerical results it is seen that the counter rotation case is having four typical flow patterns based on the speed of rotation of the cylindrical disc and critical swirl number: Of the three cases, counter rotation is showing a beneficial effect of forming a closed toroidal structure with a stagnation point on the axis even for smaller swirl and Reynolds numbers. The stagnation point is one of the critical factors in flame stabilization. More over the formation of vortex breakdown even in lower swirl numbers, induced by rotation of the cylindrical disc, gives a beneficial effect in the mixing point of view. Therefore this becomes a scope for further research with still lower Reynolds number and other parameters newline