A combustor-representative swirl simulator for a transonic turbine research facility

Tighter aircraft emissions regulations have let to considerable improvement in gas turbine combustion in the past few decades. Modern combustors employ aggressive swirlers to increase mixing and to improve flame stability during the combustion process. The flow at combustor exit can therefore have high residual swirl. The impact of this swirl on the aerodynamic and heat transfer characteristics of the HP turbine stage has not yet received much attention. In order to investigate the effects of swirl on the HP turbine stage, an inlet swirl simulator has been designed and commissioned in an engine scale, short duration, rotating transonic turbine facility. The test facility simulates engine representative Mach number, Reynolds number, nondimensional speed and gas-to-wall temperature ratio at the turbine inlet. The target swirl profile at turbine stage inlet was based upon extreme exit swirl conditions for a modern low-NO_x combustor with peak yaw and pitch angles over ±40°. A number of candidate swirler designs were considered during a pilot study that was conducted in a subsonic wind tunnel to achieve suitable swirler design. The swirl simulator was developed based upon the pilot study results, which achieved a good match to the target profile after commissioning in the facility. This article mainly deals with the design and development of the swirl generator. It presents the experimental and computational results of the pilot study, followed by the description of the installation and commissioning of the swirl simulator on the test facility. Novel instrumentation was required to survey the swirl profile, which is also described. A comparison of the measured and computational aerodynamic results with and without swirl, at 10 per cent and 90 per cent span of HP nozzle guide vane is also presented. The comparison highlights significant impact of swirl on the vane incidence angle, and therefore a considerable affect on the loading distribution of the vane.