Turbulent Heat Transport in a Boundary Layer Behind a Junction of a Streamlined Cylinder and a Wall

Measurements of the turbulent velocity and temperature fields were made in a heated boundary layer 14 diameters downstream of a junction of a tapered cylinder and a wall (Re_D = 24,700). The boundary layer is strongly affected by the presence of large-scale unsteadiness arising from vortex shedding, which appears in the measurements as “turbulence” with a strong spectral component at the shedding frequency. The boundary layer exhibits three distinct spanwise regions: (1) the innerwake region, z/D<0.8, where vortex shedding effects are observed only in the spanwise component of the fluctuations; (2) the middle-wake region, 0.8<z/D<1.6, where strong vortex shedding is seen in all three components of the fluctuations; and (3) the outer-wake region, z/D>1.6, where the flow is approaching a two-dimensional boundary-layer flow. Cross-spectra of νθ indicate that vortex shedding increases the turbulent heat flux in the middle-wake region. However, peak values of the Stanton number and the eddy diffusivity are observed in the inner-wake region, where the cross-spectra of turbulent heat flux do not exhibit a peak near the shedding frequency, but do show an increase compared to a two-dimensional boundary layer over a much broader frequency range.