Development of a turbulence scale controllable burner and turbulent flame structure analysis

Abstract

A turbulence controllable premixed turbulent Bunsen burner was developed to study the separate effects of turbulence intensity and integral scale on the premixed turbulent flame. Circular and slot perforated plates with adjustable plate positions were designed to produce quasi-isotropic and uniform turbulence field containing scale-expanded vortices with normalized turbulence intensity ranging from 5% to 40%. The method to attain the controlled turbulence with multi-layer perforated plates were discussed. Especially, the order of the plate and the distance between the plates were proposed to be vital. Eight burner configurations of the plates and twelve conditions of the CH4/air flames at two constant bulk velocities (corresponding to two Reynolds numbers 4000 and 6777) were adopted. The flame front structure of the flames was captured with OH-PLIF technique. Results show that under the same turbulence intensity, the increase of integral scale at the higher Reynolds number reduces the turbulent burning velocity and increases the flame volume, while at the lower Reynolds number it shows marginal effect. Turbulent burning velocity and flame volume both increase almost monotonously, but the flame brush thickness decreases with the increase of turbulence intensity. With both two Reynolds numbers, small integral scale leads to decreased brush thickness. Both strong turbulence intensity and small integral scale decrease the curvature radius to induce finer flame front, which should be the main reason of the increased turbulent burning velocity. However, the flame surface density seems to be ambiguously correlated with the turbulence intensity and integral scale. The turbulence intensity shows more direct and intensive effects on the flames compared to the integral scale according to the PDF distributions of the curvature radius. The present study is useful for the interpretation of the basic mechanism of turbulence intensity and integral scale as well as the evaluation of numerical results.