Session: 12-12-01: Gas Turbine Heat Transfer and heat exchanger

Paper Number: 165448

Additive Manufacturing Effects on Turbine Film Cooling Effectiveness 

Modern gas turbines operate at extremely high temperatures to maximize power output and efficiency, subjecting turbine blades to intense thermal loads that can degrade their structural integrity. Film cooling, wherein a thin layer of coolant is ejected over the turbine blade surface, plays a pivotal role in managing these thermal stresses. Additive manufacturing (AM) has opened new possibilities for designing and fabricating complex film cooling geometries, but it also introduces unique challenges—most notably surface roughness . These roughness features, inherent to layer-by-layer deposition, can alter the aerodynamic and thermal behavior of cooling holes. Despite the high potential for AM to optimize turbine cooling layouts and reduce manufacturing time, small-scale surface defects may disrupt coolant flow, reducing film effectiveness and risking higher blade temperatures. The objective of this work is to experimentally quantify the impact of in-hole surface roughness on adiabatic cooling performance.

Experiments will be conducted on a baseline 777 diffuser hole and a roughened variant derived from computed tomography scans of an additively manufactured metal 777 hole. Both holes are manufactured in test coupons at 5x engine scale to facilitate detailed diagnostics and modularity. The coupons were printed using stereolithography and integrated into a optically transparent test section. Water is used as the working fluid and planar laser-induced fluorescence is used to measure the time-resolved coolant concentration external to the holes. Dynamic similarity is used to achieve engine relevance. The holes are operated at blowing ratios between 1 and 2, which corresponds to Reynolds numbers of 2.900 and 5,800, respectively, based on the metering hole diameter. A turbulent boundary is generated upstream of the holes, and the boundary layer momentum thickness was measured to be about 1/10^th of the metering hole diameter.

Two distinct PLIF measurement planes are employed to capture the spatial and temporal evolution of the coolant flow. The first plane, oriented perpendicular to the main flow and passing through the film cooling jet, allows direct visualization of the windward shear layer where the coolant interacts and mixes with the free stream. Instantaneous images from this plane reveal transient features such as vortical structures, while time‐averaged results provide an overall mixing profile that can be compared against predicted flow fields. The second plane, positioned parallel to the turbine blade surface, captures the coolant distribution over the surface itself, directly relating to local adiabatic effectiveness. This view is critical for mapping how well the coolant film shields the underlying surface from the hotter mainstream flow. Time‐averaged measurements in this plane illustrate the overall film coverage pattern, whereas instantaneous data demonstrates unsteady phenomena that can locally impact cooling performance. Together, these two planes offer a more complete understanding of the difference in film cooling behavior between the smooth and rough 777 hole.

Presenting Author: Sebastian English United States Military Academy

Presenting Author Biography: Sebastian English is a Cadet at the United States Military Academy, majoring in Mechanical Engineering. His research focuses on thermal-fluids, particularly in energy conversion systems and turbine engines.

Authors:

Sebastian English United States Military Academy
Connor Danelson United States Military Academy
Andrew Banko United States Military Academy