Unsteady Heat Flux Measurements of Junction Flow With Reynolds Number and Freestream Turbulence Effects

Abstract

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, mean heat flux is further increased, but the mechanisms of the enhancement are unclear. In this paper, a test section for simultaneous time-resolved heat flux and flowfield measurements in front of a common research wing is highlighted. Time-resolved unsteady heat flux is also reported for a range of Reynolds numbers at high freestream turbulence. Time-resolved heat flux measurements from the symmetry plane of the junction region are compared with measurements downstream of the airfoil to determine if there are correlated behaviors. Also, a comparison between the effects of baseline freestream turbulence and high freestream turbulence on junction heat transfer is presented. It is found that at the plane of symmetry, high freestream turbulence increases endwall heat transfer at low Reynolds number and has negligible influence on endwall heat transfer at high Reynolds number.

Time-resolved PIV Measurements of the Effect of Freestream Turbulence on Horseshoe Vortex Dynamics

“…and at high Reynolds number, appears to have the effect of insulating the horseshoe vortex, which is contained entirely within the boundary layer, from freestream turbulence. This observation agrees with the findings of a companion publication by Elahi, et al [21], which suggests that the effect of freestream turbulence on surface heat transfer produced by the horseshoe vortex is observed most strongly at low Reynolds number and decrease with increasing Reynolds number for a given freestream turbulence level.…”

“…A detailed table of estimations of uncertainty in the SPIV measurements of this study may be found in Elahi, et al [18]. An analysis of uncertainty in the hotwire measurements was conducted via the method described in Moffat [21], with the resulting uncertainty in velocity measurement over the range of velocities measured in this study at 2.6 percent.…”