This body of work provides an initial study of modeling both surface roughness and heat transfer concurrently in a numerical simulation of micro-channels representative of those that might be found in a turbine cooling application. Increased use of additive manufacturing (AM) or 3D printing techniques for turbomachinery components enable the manufacture of complex features to achieve higher operational performance. Accurate modeling of flow losses and heat transfer effects are critical to designing parts which achieve optimal efficiency paired with durability. Surface finish is rougher with AM compared to more traditional manufacturing techniques; therefore enhancing the pressure loss and heat transfer effects. Proper implementation of surface roughness within the computational model and correct modeling of the near wall boundary mesh must be maintained to produce accurate results. This study focuses on the comparison of near wall mesh treatment coupled with surface roughness to determine a practice for obtaining accurate pressure loss and heat transfer within a cooling passage, as compared to measurements.
Steady-state computational fluid dynamics (CFD) models consisting of a wind tunnel inlet nozzle and outlet diffuser, along with internal cooling passages represented using micro-channels, has been run for a range of Reynolds numbers and simulated roughness levels. Analysis of a baseline configuration with aerodynamically smooth walls is first compared to the measured data to verify the assumption of aerodynamically smooth walls. Surface roughness is then added to the channel walls, from published test coupon measurements, and compared to published experimental data for a range of Reynolds numbers. The metal surrounding the passages is also included as a conjugate heat transfer model providing heat addition to the fluid. Pressure loss and heat transfer is compared to the measured data as a friction factor and Nusselt number for the range of Reynolds numbers. Since surface roughness units and measurements vary, an effect of surface roughness values on pressure loss and heat transfer will also be investigated to determine the importance of using and converting to the correct units for the numerical model. This serves as a starting point for a guideline that will help when both heat transfer and surface roughness are included in a CFD model. Further study is recommended to understand the diminishing levels of increase in friction factor and Nusselt number observed as surface roughness was continually increased in the numerical simulation.