Experimental study of combustion and scalar mixing in swirling jet flows

Abstract

Turbulent mixing of passive scalar field and combustion of gaseous fuel were studied in the context of a non-premixed isothermal and reacting swirling jets discharged from a swirl-stabilised burner, as a function of swirl number. The rate of molecular mixing, which was quantified by the scalar dissipation rate was computed from measured scalar fields that were recorded by using Planar Laser Induced Fluorescence (PLIF) of acetone. The influence of the swirl number on the scalar mixing, unconditional and conditional scalar dissipation rate statistics was investigated. Scalar fields were measured with an average error of 3%. Scalar dissipation rate was measured with an average error of 12% after de-nosing.

The influence of swirl number on combustion characteristics was examined by using Rayleigh scattering with accuracy of 90%. The flow fields in non-reacting and reacting swirling jets were investigated by using Particle Image Velocimetry (PIV). The effect of swirl number on a recirculation zone was shown and discussed. The flow structures were evaluated by using Proper Orthogonal Decomposition.

Experimental assessment of presumed filtered density function and subgrid scale (SGS) scalar variance models that are being developed in the context of Large Eddy Simulation (LES) was performed by using the data obtained from measured scalar fields.

Measurements were performed in a flow formed by discharging a central jet in the annular stream of swirling air. This is a typical geometry used in swirl-stabilised burners where the central jet is the flow. The measurements were performed at a constant Reynolds number of 28662, based on the area-averaged velocity of 8.46 (m/s) at the exit of the swirl-stabilised burner and the diameter of the annular swirling stream of 50.8(mm). Three swirl numbers S = {0.3, 0.58, 1.07} of the annular swirling stream were considered.