The Metal Effectiveness Rotor Cooling (MERC) facility at the University of Oxford is a new blow-down linear cascade tunnel developed for aerothermal research of turbine rotor blade and rotor platform cooling systems. A high level of engine similarity is achieved with matched Mach numbers, Reynolds numbers, coolant-to-mainstream pressure ratios, and Biot number (using DMLS components of appropriate conductivity). The modular working section includes five blade passages, including platform and fir tree root geometries, and engine representative hub seals. The facility is designed to allow high accuracy IR camera measurement of the blade and platform surfaces (for metal effectiveness measurements) and downstream area traverse measurements. Detailed traverse measurements are possible in a single run, because of the long run time of the facility (up to 5 minutes).
The facility is being used for development and optimisation research of novel blade and platform cooling systems, with an emphasis on overall thermal performance of parts (metal effectiveness). Modular cassettes allow the blade components to be rapidly interchanged, and for variations to the designs of the front and rear hub seals. The engine representative seals and coolant feed paths allow for all engine leakage flows to be replicated in the experiment. This is important, because they are influential in determining the platform cooling flow structure (character and extent of secondary flow) and overall metal effectiveness result. Coolant supplied to each of the hub seals, and blade shank pocket can be independently varied to achieve required mass flows and pressure ratios. Rotor blades are typically manufactured using DMLS, allowing fast development and optimisation of fully-featured cooling systems at significantly reduced cost compared to traditional casting techniques.
To demonstrate the capability of the new facility, we present full-surface metal-effectiveness measurements of the rotor blade platforms (post-processed using high-accuracy infrared thermography techniques separately developed at the University of Oxford.)
The purpose of this paper is to outline the capabilities of the facility, describe the prior work and research context which led to its development, and to demonstrate the accuracy of the measurement techniques employed by presenting typical measured data. An argument is made for the importance of including realistic hub seal leakage paths in experiments investigating platform cooling flows by illustrating their significant impact on overall cooling performance. The MERC facility is a response to the need to develop more advanced rotor platform cooling schemes for future engines.