Flow instabilities leading to the formation of streamwise vortices in a natural convection boundary layer over a heated inclined plate submerged in a water tank are
manipulated using spanwise arrays of surface-mounted heating elements. The flow
over the plate is driven by a two-ply surface heater comprised of a uniform, constant-
heat flux heater and a mosaic of 32
×
12 individually controlled heating elements
that are used as control actuators. Surface temperature distributions are measured
using liquid crystal thermography and the fluid velocity in cross-stream planes is
measured using particle image velocimetry (PIV). Time-invariant spanwise-periodic
excitation over a range of spanwise wavelengths leads to the formation of arrays of
counter-rotating streamwise vortex pairs and to substantial modification of the surface
temperature and heat transfer. The increase in surface heat transfer is accompanied
by increased entrainment of ambient fluid and, as a consequence, higher streamwise flowrate. Subsequent spanwise-periodic merging of groups of vortices farther
downstream retards the streamwise increase of the surface heat transfer rate. Finally,
the suppression of small-amplitude spanwise disturbances by linear cancellation is
demonstrated.
Heat Transfer Enhancement in a Turbulent Natural Convection Boundary Layer
