An Experimental Investigation Into Particle Deposition in Double-Wall Effusion Cooling Systems

As Turbine Entry Temperatures of modern aeroengines continue to rise in pursuit of greater turbine thermal efficiencies, increasingly innovative and complex cooling systems are required to maintain turbine component temperatures at acceptable levels. Double-Wall Effusion Cooling Systems are one possible answer to this challenge — by combining dense arrays of impingement holes and pedestals for internal cooling with tightly packed effusion holes for external cooling, high metal cooling effectiveness can be achieved at relatively low rates of coolant consumption. However, the intricate nature of these cooling schemes leaves them vulnerable to the deposition of ingested particulate matter, which can eventually lead to cooling passage blockage and the failure of the cooling system. This paper details an experimental investigation into four factors affecting deposition: the metal temperature, the cooling system geometry, the particulate matter’s composition, and the metal the cooling system is produced from. These tests were carried out using the Oxford Thermofluids Institute’s High Temperature Rig, capable of operating at metal temperatures exceeding 1200 K. Deposition was evaluated both in terms of the proportion of inputted particulate matter that adhered to the metal surface, and where said deposition took place — the latter of which was done using a 3D Profilometer. Results are used to identify situations where measures would need to be put in place to limit the ingestion of particles into the turbine’s secondary air system. In particular, deposition rates are seen to increase as the metal temperature increases, and as the impingement spacing to diameter ratio decreases.