Jets in a Crossflow: Effects of Hole Spacing to Diameter Ratio on the Spatial Distribution of Heat Transfer

Abstract

Detailed measurements of local heat transfer coefficients are presented for air injection through a row of holes into a crossflow. Pitch-to-diameter ratios of 2,4, and 6 are realized and the momentum flux ratio is varied in the range from 0.25 to 4.0. The injection angle of the jets is fixed at 90°. The experimental technique developed uses an Infrared Camera to measure the temperature distribution on the constant heat flux test surface. This measurement technique allows detailed spatial resolution of the heat transfer and gives information about the three-dimensional mixing process of the jets with the mainstream. The experimental results indicate a large influence of the hole spacing to diameter ratio, (s/d), on the heat transfer coefficient. With s/d = 2.0, the spanwise heat transfer coefficients in the vicinity of the injection holes are noticed to be highly uniform. For momentum flux ratios, J, greater than 1, two regions of high heat transfer coefficient exist. The first region occurs in the vicinity of the injection holes. The second region observed some distance downstream is due to the reattachment of the jets to the surface.