Impact of AM-Induced Upscaled Surface Roughness on Flow Dynamics, Heat Transfer and Friction Properties: A Particle Image Velocimetry Study

The increase in global energy demand has driven technological advancements aimed at improving the performance of machines used for energy production, particularly Land-Based Gas Turbines (LBGT). In the last decade, enhancements in compression ratio and Turbine Inlet Temperature (TIT) have led to a 40% improvement in efficiency, made possible by the adoption of Additive Manufacturing (AM), as opposed to traditional casting techniques. This study examined the flow dynamics under irregular texture typical of AM-produced products. Cooling channels were sectioned and up-scaled for testing on a rig, where PIV (Particle Image Velocimetry) technique was employed for the analysis. The validation of the setup and measurements enabled the examination of three multi-scale rough surfaces with irregular patterns. Mean and turbulence statistics were assessed using drag information, highlighting the variability in the turbulent nature of the flow across the three investigated rough surfaces as a function of roughness scale. Aerodynamic data were correlated with thermal data to determine flow characteristics in areas of high and low heat transmission. The analysis also explored how roughness parameters affect the friction coefficients of surfaces. It was found that, despite difference of up to 800% in certain roughness parameters, the friction coefficient was altered by only 5%. In stark contrast, the Rz roughness parameter demonstrated a significantly greater impact on the friction coefficients. These findings suggest that Rz may be the predominant influencing factor on the friction coefficient behavior of the examined surfaces.