Effect of side dilution jets on the velocity field and mixing in swirl and bluff-body stabilised annular confined flows

Abstract

Stationary and mobile power generation systems, as well as those for aero propulsion, continue to rely heavily on gas turbines. Operational envelopes which critically depends on (flame) jet stabilisation mechanisms, such as swirl, are also affected by considerations for emissions control. In this context, the evolving swirling flow domains feature injection of side (peripheral) dilution air. Despite this, the role of side dilution jets on modifying the flow, turbulence, and mixing fields of turbulent bluff-body (BB) stabilised (swirling) annular flows has not been investigated. This study uses three-dimensional simulations, supported with experimental data to establish boundary conditions, to investigate the interaction of side dilution jets (Red = 18,000) with both non-swirling (S = 0) and swirling (S = 0.3) turbulent BB stabilised annular flows (Res = 35,500). Constant Temperature Anemometry (CTA) measurements are conducted to resolve inlet boundary conditions. The Reynolds Stress Model (RSM) and species transport model (isothermal) are used with validations against benchmark datasets. Results show that the introduction of side dilution jets into a confined domain, whether swirling or not, induces (asymmetrical) Peripheral Recirculation Zones (PRZ). However, the strength, length, and location of PRZ varies with swirl and the downstream positioning of side dilution jets (H = 2.6D, 6.6D). Additionally, side dilution jets increase centreline velocity decay for both, non-swirling and swirling BB flows. In terms of turbulence characteristics, addition of side dilution jets leads to significant gains in shear layer turbulence with an increase of 72% and 35% in turbulent kinetic energy for non-swirling and swirling BB flows, respectively. Analysis of the mixing characteristics shows negligible impact of side dilution jets in the upstream region, however, from x/D > 3 considerable improvement in central jet (fuel) mixing is observed.