Effect of Blowing Configurations on Heat Transfer Augmentation With Multihole Sweeping Jet Film Cooling

Abstract Film cooling is one of the most efficient external cooling method used to ensure the proper functionality of modern gas turbine engines. The use of sweeping jets as a coolant stream is a recent addition to the field of film cooling, gaining popularity due to its improvement in performance over steady jets. With an increasing abundance of investigations on the topic surprisingly, sweeping jets are rarely explored for the leading edge film cooling. In this study, numerical investigations were performed to study the effects of various blowing configurations on the multihole sweeping jet film cooling at the leading edge of an HP turbine NGV. Three sweeping jets were studied with transitional periodicity and the blowing ratio was varied as BR = 0.5, 0.75, and 1.0 in two configurations. When the BR of the middle hole was increased keeping others the same it was termed as ‘jet focusing’ and when the BR of all the holes was increased it was termed as ‘straight blowing’. A detailed discussion of the heat transfer augmentation results is presented along with the unsteady aerodynamics and thermal fields produced by a row of sweeping jets. It was observed that sweeping jets placed in a row interact in a non-synchronized and highly unpredictable manner. This results in an asymmetrical distribution of coolant over the target surface. A new feature of reversed hole configuration was found where the coolant stream comes out of the cooling hole in the form of lumps of cold fluid. This phenomenon was termed as ‘blobbing’. The results also showed that jet focusing may result in a 9% reduction in heat transfer augmentation without affecting the film cooling effectiveness in the leading edge region. Increasing the coolant flow rate with straight blowing proves to be detrimental to leading-edge film cooling.