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 nonuniform 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 (NGVs). The experimental results are supported by a large eddy simulation (LES) performed with the inhouse computational fluid dynamics (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 (LE) 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.

Coupled Effect of Expansion Ratio and Blade Loading on the Aerodynamics of a High-Pressure Gas Turbine

“…Finally, the aero-thermal behavior of the HPT is further complicated by the film cooling and the interaction with the combustor, which introduces time-dependent gradients in total pressure and total temperature as well as whirling flow at the stage inlet. These features were found to considerably affect the aerodynamics and the heat transfer [22][23][24] as well as the aero-acoustic behavior [25] of the HPT.…”

Parameterised Model of 2D Combustor Exit Flow Conditions for High-Pressure Turbine Simulations

“…These vortices drive fluid away from the vane surface, thus thickening the boundary layer and decreasing heat transfer locally. They are induced by the low pressure zone at the inlet swirl core that causes the vortices to roll-up at the leading edge as described by Jacobi et al [19]. …”

“…Different authors have studied the isolated effects of inlet swirl (Giller et al [14], Qureshi et al [15], Schmid et al [16], Beard et al [17], Insinna et al [18], and Jacobi et al [19]), hot streaks (He et al [20], Basol et al [21], and Beard et al [22]) and elevated turbulence (van Fossen et al [23]). However, there are few data, and no unifying theory exists with respect to their combined effects.…”

Hot Streak Evolution in an Axial HP Turbine Stage

“…These features might significantly alter the blade surface temperature, with noteworthy implications on the rotor cooling effectiveness [2]. In addition to detailed investigations on the aerothermal features of the flow released by combustors ( [8], among others), recent studies have considered more realistic configurations, combining the hot streak with a local streamwise vorticity [9] and studying the potential for clocking between the burners and the stator blades [10]. The residual hot streak entering the rotor induces even more complex features within the rotor blade row, including the generation of further vorticity cores which are pushed towards the endwalls [11], altering the wall temperature in these regions and triggering the development of novel cooling techniques [12].…”

“…The device was allowed to reach 390 K in the core of the hot streak, as measured on a traverse placed one vane axial chord upstream of the vane leading edge. This temperature peak corresponds to an increase of 20% of the main stream temperature, which is a realistic representation of hot-streak-induced temperature perturbation; just to set a general context, [9,12] documented a temperature ratio of ~1.09 while [8,10] imposed a ratio greater than 1.5. The hot streaks were injected at 70% of the span in the stream-wise direction, with the aim of minimizing the injector blockage and of limiting the jet interaction with the vane secondary flows.…”