In aero engines the combustors are subjected to critical thermal conditions in terms of high temperatures and corrosive environment, which could affect the service life of the entire system. As well known, Thermal Barrier Coatings (TBC) and above all cooling systems represents the state-of-the-art in the nowadays protecting methods: the maximization of this beneficial effect is achieved by defining an optimal cooling arrangement and developing suitable manufacturing technologies for these systems. In modern aero-engine combustors, one of the most effective cooling scheme for liners is composed by an effusion perforation coupled with a slot system to start the film cooling. The cooling performances are deeply influenced by the mutual interactions between swirling and cooling flows. In addition, for typical Rich-Quench-Lean (RQL) combustor architectures, the injection of air provided to promoting the local break-down of the flame mixture fraction, deeply interacts with the swirled flow, generating recirculating structures capable of affecting the development of film cooling and making the design of cooling systems very challenging.
A new test facility for testing effusion test plates for RQL combustors applications has been developed with the final aim of comparing different cooling strategies and at the same time to collect data for numerical model validation. The experimental set-up consists of a non-reactive planar sector rigs with 5 engine-scale swirlers fed with air up to 250 °C and 3 bar. The rig was equipped with outer/inner dilution ports, and a simple inner liner cooling scheme composed of effusion and a slot system: all these features, fed with air at ambient temperature, can be independently controlled in terms of mass flow.
Using dedicated optical accesses, InfraRed (IR) camera tests were performed to retrieve overall effectiveness data imposing a temperature difference between swirling and cooling flows. To better understand those results, Pressure Sensitive Paint (PSP) technique was used to obtain reliable film effectiveness data decoupling the contribution of slot and effusion flows. The thermal characterization was supported by Particle Image Velocimetry (PIV) investigations on the median plane. Tests were performed at different pressure drops across swirler and varying the mass flows of slot and inner/outer liners. The analysis of the data highlighted the influences of the swirling flow on the overall thermal performance and the behaviour of the film cooling system.