Experimental Investigation on the Effects of a Large Recirculating Area on the Performance of an Effusion Cooled Combustor Liner

An experimental analysis of a realistic engine cooling scheme was performed on a test article replicating a slot injection and an effusion array with a central large dilution hole. A test section consists of a rectangular cross-section duct with a flat plate comprised of 270 effusion holes arranged in 29 staggered rows (D = 1.65 mm, Sx/D = 7.6, Sy/D = 6, L/D = 5.5, α = 30 deg) and a dilution hole (D = 18.75 mm) located at the 14th row. Both effusion and dilution holes are fed by a channel replicating a combustor annulus, which allows to control of cold gas side cross-flow parameters, especially in terms of Reynolds number of both annulus and effusion holes. Upstream the first row, a 6 mm high slot ensures the protection of the very first region of the liner. In order to simulate the combustor flowpath, a backward facing step was installed upstream the slot to generate a large recirculating area. Adiabatic effectiveness, heat transfer coefficient and net heat flux reduction were evaluated and compared with non- recirculating experiments. Measurements were performed by means of a steady-state Thermochromic liquid crystals (TLC) technique with a thin Inconel heating foil for the heat transfer measurements. A data reduction procedure based on a finite element approach has been developed to take into account the non uniform heat generation and conduction due to the large amount of holes. Experiments were carried out considering the combined effects of slot, effusion and dilution holes. Three different effusion blowing ratios (BR = 3-5-7) are investigated, keeping constant the slot flow parameters (BR = 1.3). Results highlight that the presence of the step leads to a general reduction of effectiveness while does not have effects on the heat transfer coefficient.