Thermohydraulic Performance and Flow Structures of Diamond Pyramid Arrays

Abstract Surface features are a common heat transfer enhancement method used in a myriad of applications including gas turbines and heat exchangers. One such style of surface feature is diamond pyramids, which offer significant heat transfer augmentation for moderate increases in overall pressure losses. This study investigated a suite of additively manufactured pyramids in a variety of sizes and arrangements at relevant scale contained in test coupons. Designs were printed with low surface roughness relative to typical additive components (Ra < 5 μm), and pyramids were printed within 100 μm of the design intent. Experimental and computational results indicate that the pressure penalty and heat transfer increased as the pyramids increased in size with aligned pyramids on both channel walls having higher values than staggered pyramids. It was found that implementing the pyramids onto a rough surface had a lesser impact on the friction factor than implementing it on a smooth surface, but that the relative increase in heat transfer was the same regardless of the roughness of the endwall. The greatest enhancement to local heat transfer and pressure loss was offset from the location of the minimum flow area due to local acceleration around the wake regions. The vortices formed in the wake of the pyramid structures enhanced the endwall heat transfer and shear stress. The performance of the pyramids investigated in this study follows a similar trend to prior studies investigating smooth rib geometries, though certain rib designs had higher heat transfer at lower pressure losses.