Development of a Steady-State Experimental Facility for the Analysis of Double-Wall Effusion Cooling Geometries

The continuous drive for ever higher turbine entry temperatures is leading to considerable interest in high performance cooling systems which offer high cooling effectiveness with low coolant utilization. The double-wall system is an optimized amalgamation of more conventional cooling methods including impingement cooling, pedestals, and film cooling holes in closely packed arrays characteristic of effusion cooling. The system comprises two walls, one with impingement holes, and the other with film holes. These are mechanically connected via pedestals allowing conduction between the walls while increasing coolant-wetted area and turbulent flow. However, in the open literature, experimental data on such systems are sparse. This study presents a new experimental heat transfer facility designed for investigating double-wall systems. Key features of the facility are discussed, including the use of infrared thermography to obtain overall cooling effectiveness measurements. The facility is designed to achieve Reynolds and Biot (to within 10%) number similarity to those seen at engine conditions. The facility is used to obtain overall cooling effectiveness measurements for a circular pedestal, double-wall test piece at three coolant mass-flows. A conjugate computational fluid dynamics (CFD) model of the facility was developed providing insight into the internal flow features. Additionally, a computationally efficient, decoupled conjugate method developed by the authors for analyzing double-wall systems is run at the experimental conditions. The results of the simulations are encouraging, particularly given how computationally efficient the method is, with area-weighted, averaged overall effectiveness within a small margin of those obtained from the experimental facility.