Session: 04-42 Combustion dynamics - flow instabilities

Paper Number: 129127

129127 - Effect of Flare Angle in a Counter-Rotating Dual Radial Swirler on the Stability of a Swirl-Stabilized Flame 

In this study, an experimental investigation is carried out to understand the influence of flare angle on the flame and
the reacting flow field generated by a high-shear counter-rotating dual swirl injector in a laboratory scale model gas
turbine combustor. Most of the modern aircraft engine combustors feature high-shear injectors, that facilitate optimal
fuel distribution and promotes rapid mixing of fuel and air. These injectors feature various geometric parameters
that is found to impact the static and dynamic stability of the flame. Time resolved OH* chemiluminescence,
stereoscopic-PIV and dynamic pressure measurements are carried out to understand the impact of flare angle on the
swirl-stabilized flame.
The high-shear injectors employed in this study consists of a dual counter-rotating radial swirlers with a fuel
nozzle positioned at its center. The flare, located at the end of the swirler, serves as a diverging exit for the upstream
swirl flow. Three different flare angles (0◦ , 30◦ , and 50◦ ) are investigated in this study. The flare angle is measured
with respect to the swirler axis. OH* chemiluminescence experiments are conducted at four different inlet Reynolds
numbers (10000 - 17000) and eight different global equivalence ratios (ranging from 0.4 to 1.1) for all three flare
angles. Stereoscopic-PIV experiments are performed at selected conditions to understand the nature of the reacting
flow with three flare angles.
The results reveal discernible changes in flame shape associated with variations in flare angle. The variation in
flame shapes are relatively insignificant in response to changes in inlet Reynolds number and equivalence ratio, but
they are notably pronounced as the flare angle increases from 0◦ to 50◦ . For a 0◦ flare angle, the swirl stabilized
flame is found to be a long and narrow flame for all the flow Re and flame power. Conversely, as the flare angle is
increased to 50◦ , a wider and shorter V-shaped flame is formed. Similarly, the time averaged velocity field show
a significant change in the size and location of the central recirculation zone (CTRZ) with a change in flare angle.
Furthermore, the flame stability limits are highly dependent on flare angle and inlet Reynolds number. For a 0◦ flare
angle, the flame is stable for global equivalence ratio up to 0.7, across all the Re. For the flare angle of 30◦ , this
limit extends to a global equivalence ratio of 1. For a 50◦ flare angle, the flame is observed to be stable up to a global
equivalence ratio of 1.4. It is also observed that for most of the test conditions the swirl stabilized flames have a self-
excited longitudinal instability. The instability is seen to transition from a limit cycle oscillation to an intermittent
instability with increase in the fuel flow rate. In case of 50◦ flare angle there is a suppression in the instability
which is marked by a transition from an attached V-shaped flame to a lifted V-shaped flame. Correspondingly, the
time average flow structure shows a transition from a bubble type vortex breakdown (BVB) to a conical type vortex
breakdown (CVB). Spectral proper orthogonal decomposition (SPOD) is carried out on the flow and flame images to
identify the dynamically dominant flow structures present in the swirling jet. This study shows that for a high shear
injector with a counter-rotating pair of radial swirlers, a larger flare angle can lead to swirling flames with better
stability limits.

Presenting Author: Darshan Rathod Indian Institute of Science

Presenting Author Biography: PhD student at ICER department of IISc. He works on combustion and flow diagnostics on gas turbine combustor.

Authors:

Darshan Rathod Indian Institute of Science
Thirumalaikumaran S K Indian Institute of Science
Sonu Kumar King Abdullah University of Science and Technology
Pratikash Panda Indian Institute of Science
Saptarshi Basu Indian Institute of Science