Experimental and Theoretical Investigation of Thermal Effectiveness in Multiperforated Plates for Combustor Liner Effusion Cooling

Abstract

State-of-the-art liner cooling technology for modern combustors is represented by effusion cooling (or full-coverage film cooling). Effusion is a very efficient cooling strategy based on the use of multiperforated liners, where the metal temperature is lowered by the combined protective effect of the coolant film and heat removal through forced convection inside each hole. The aim of this experimental campaign is the evaluation of the thermal performance of multiperforated liners with geometrical and fluid-dynamic parameters ranging among typical combustor engine values. Results were obtained as the adiabatic film effectiveness following the mass transfer analogy by the use of pressure sensitive paint, while the local values of the overall effectiveness were obtained by eight thermocouples housed in as many dead holes about 2 mm below the investigated surface. Concerning the tested geometries, different porosity levels were considered: such values were obtained by both increasing the hole diameter and pattern spacing. Then the effect of the hole inclination and aspect ratio pattern shape were tested to assess the impact of typical cooling system features. Seven multiperforated planar plates, reproducing the effusion arrays of real combustor liners, were tested, imposing six blowing ratios in the range 0.5–5. Additional experiments were performed in order to explore the effect of the density ratio (DR=1;1.5) on the film effectiveness. Test samples were made of stainless steel (AISI304) in order to achieve the Biot number similitude for the overall effectiveness tests. To extend the validity of the survey a correlative analysis was performed to point out, in an indirect way, the augmentation of the hot side heat transfer coefficient due to effusion jets. Finallyv,in order to address the thermal behavior of the different geometries in the presence of gas side radiation, additional simulations were performed considering different levels of radiative heat flux.