Investigation of Unsteady Flow Phenomena in First Vane Caused by Combustor Flow With Swirl

Abstract

The flow at the combustor turbine interface of power generation gas turbines with can combustors is characterized by high and non-uniform turbulence levels, lengthscales and residual swirl. These complexities have a significant impact on the first vanes aerothermal performance and lead to challenges for an effective turbine design. To date, this design philosophy mostly assumed steady flow and thus largely disregards the intrinsic unsteadiness. This paper investigates the steady and unsteady effects of the combustor flow with swirl on the turbines first vanes. Experimental measurements are conducted on a high-speed linear cascade that comprises two can combustors and four nozzle guide vanes. The experimental results are supported by a Large Eddy Simulation performed with the inhouse CFD flow solver TBLOCK. The study reveals the highly unsteady nature of the flow in the first vane and its effect on the heat transfer. A persistent flow structure of concentrated vorticity is observed. It wraps around the unshielded vane’s leading edge at midspan and periodically oscillates in spanwise direction due to the interaction of the residual low-pressure swirl core and the vane’s potential field. Moreover, the transient behavior of the horseshoe-vortex system due to large fluctuations in incidence is demonstrated.

The Influence of Combustor Swirl on Pressure Losses and the Propagation of Coolant Flows at the Large Scale Turbine Rig (LSTR): Experimental and Numerical Investigation

“…At the LE, this gradient triggers a secondary flow feature: the swirler causes positive incidence near the casing and negative incidence near the hub and thereby the stagnation line moves. A span-wise pressure gradient results and causes the vortex to travel towards the casing, as illustrated by Jacobi et al [7]. Contrary to Jacobi's experiment, a radial P t gradient with a central annulus minimum at the turbine inlet is also observed for SWP clocking at the LE.…”

“…Recent experimental work in the field of combustor-turbine interaction is also described by Jacobi et al [7]. They investigate the outflow from a can combustor into a vane row.…”

The Influence of Combustor Swirl on Pressure Losses and the Propagation of Coolant Flows at the Large Scale Turbine Rig (LSTR)

“…At the LE, this gradient triggers a secondary flow feature: The swirler causes positive incidence near the casing and negative incidence near the hub and thereby the stagnation line moves. A span wise pressure gradient results and causes the vortex to travel towards the casing, as illustrated by Jacobi et al [2016]. On the contrary to Jacobi's experiment, a radial P t gradient with a central annulus minimum at turbine inlet is also observed for SWP clocking at the LE.…”

“…Recent experimental work in the field of combustor turbine interaction is also described by Jacobi et al [2016]. They investigate the outflow from a can combustor into a vane row.…”

Unsteady Phenomena at the Combustor-Turbine Interface

“…Harrison [9] suggests that behind the passage vortex near to the vane there is a new, laminar boundary layer formed. The passage vortex is often considered as a steady state phenomena, but some studies indicate that highly turbulent inflow conditions can result in a mobile, time varying passage vortex [10].…”