Unsteady heat flux measurements of turbulent junction flow with Reynolds number and freestream turbulence effects

Turbulent junction flow is a three-dimensional unsteady phenomenon occurring in the flow upstream of the leading edge of bodies attached to a surface, such as in turbine rotors and stators, heat exchangers, submarine appendages, and wing-fuselage attachments. One of the signature features of this type of flow is the presence of bimodal behavior in the probability density functions of velocity, but the bimodal phenomenon has not been observed in surface heat flux measurements. However, it is well-known that time-mean levels of heat flux are significant. In situations where the body experiences high freestream turbulence, which are common in various turbomachinery and heat exchanger applications, mean heat flux is further increased but the time-resolved behavior is unknown. In this paper, unsteady heat flux is reported for body thickness Reynolds numbers of 7,000, 25,000, and 80,000 at freestream turbulence ranging from 1 % to 21 % for several locations around a symmetric wing based on a common research model for junction flows. Time-resolved heat flux measurements from the symmetry plane of the junction region indicate that high freestream turbulence increases endwall heat transfer at low Reynolds number, but has negligible influence at high Reynolds number. The stretching of the junction vortex legs as they convect around the sides of the wing results in less sensitivity to freestream turbulence. The knowledge from the time-resolved unsteady heat flux behaviors in various Reynolds numbers and low and high freestream turbulence may be applied in the future design and instrumentation of turbomachinery endwalls and low pressure drop heat exchangers.