Heat transfer and aerodynamic losses of additively manufactured turbine alloy blades with different surface enhancement post-processing

With increasing temperatures and pressure ratios, the requirements for rocket engine turbine blades become more demanding. Additive manufacturing (AM) enables production of complex geometries for such an application environment, while using novel alloys, such as GRX-810, an alloy with superior strength and durability at elevated temperatures compared to currently employed alloys. An inherent characteristic of such additively manufactured components is a rough surface texture, which varies depending upon the surface enhancement post processing procedure. With the present investigation, procedures which are considered include as built (AM0 blade), abrasive flow machining (AM5 blade), and chemical polishing in combination with chemical mechanical polishing (AM4 blade). The effects of the resulting surface textures are considered as they affect turbine blade aerodynamic losses, and turbine blade tip surface heat transfer coefficient distributions. To acquire these data, a transonic linear cascade within a transonic/supersonic wind tunnel is utilized, with centrally installed, and additively manufactured GRX-810 turbine blades, which are instrumented for aerodynamic loss and surface heat transfer measurements. Measured wake profile variations for the AM0, AM4, and AM5 blades are a consequence of multiple physical effects and phenomena, with different relative consequences, which depend upon the blade wake location, local blade shape alterations, as well as the character and magnitude of surface roughness. Dimensional heat transfer coefficient values along the tips of the turbine alloy blades are generally larger with the rougher surface textures, which are associated with increased tip gap flow friction, and locally lower tip gap flow Mach numbers.