Effect of Reynolds number on turbulent junction flow fluid dynamics and heat transfer

•Optically accessible test section designed for high speed junction flow measurements.•Turbulent kinetic energy increases underneath primary vortex with increasing momentum thickness Reynolds number.•Increasing randomness in primary vortex position with Reynolds number.•Symmetry plane endwall heat transfer scales with incoming momentum thickness Reynolds number. Turbulent junction flow is commonly seen in various turbomachinery components, heat exchangers, submarine appendages, and wing-fuselage attachments, where the approach boundary layer separates and rolls up into a coherent system of vortices upstream of a wall-mounted bluff body. One of the signature features of this flow is its tendency to switch randomly between two semi-stable states. The highly unsteady behavior causes high pressure fluctuations on the wall and obstacle surfaces and high heat transfer. Despite its prevalence, few studies have examined the Reynolds number dependence of the dynamic junction flow behavior. In this paper, the flow physics as well as heat transfer of the turbulent junction flow are investigated using high speed particle image velocimetry and time-average infrared thermography measurements. A wide range of approach momentum thickness Reynolds numbers are studied, ranging from 550 to 5740. Although the time-mean flowfield does not show significant Reynolds number dependency, the normalized turbulent kinetic energy in and around the vortex core increases with Reynolds number, and the high heat transfer associated with the junction flow moves closer to the junction. These effects are linked to the increasing randomness in the position of the primary junction flow vortex as the Reynolds number increases.