Short Helical Combustor: Dynamic Flow Analysis in a Combustion System With Angular Air Supply

Abstract

A novel gas turbine combustor which features a helical arrangement of the burners around the turbine shaft has been subject of a detailed flow analysis. A fundamental investigation of the combustor concept has been conducted in the authors previous work [1]. The main design parameters for such a combustor were identified based on kinematic assessments of the flow fields predicted by CFD. In particular, it has been shown in the previous work that the swirl rotational direction of adjacent burners determines the overall flow pattern in such a staggered design of the combustor dome. However, for the optimal configuration the exit mean flow angle was lower than the half of its initial value at the combustor inlet. The reason for this unwanted decay of the initial high angular momentum flux was not clear. In the present work a comprehensive global flow analysis of such a short helical combustor is performed. The underlying physics of large changes of the flow pattern and exit flow angle are elucidated by the analysis of the different terms (momentum, pressure and friction) in the integral balance equation of angular momentum. The term “dynamic flow analysis” is used in contrast to the “kinematic flow analysis” in our previous work and does not refer to transient flow phenomena. It is shown that the flow in the vicinity of the burners is governed by inertial forces associated to an asymmetric pressure distribution on the sidewall and the combustor dome. Downstream the sidewalls, the swirl rotational direction of circumferentially adjacent burners determines the structure of vortex-breakdown and the flow pattern in the primary combustion zone. It is shown that the turbulent mixing phenomena have minor effects on the flow structure at the combustor exit. To compare mean flow quantities of different combustor designs, a consistent averaging method is introduced which is based on the work of the Pinako and Wazelt [2]. This analysis can also be applied to conventional combustors to assess different swirl configurations regarding the resulting flow pattern, mixing performance and total pressure loss.