Abstract
Horizontal convection driven by a linear temperature profile along the bottom of a twodimensional rectangular enclosure is perturbed by a small tuned synthetic (zeronetmassflux/ZNMF) jet. The jet permits instability in the horizontal convection boundary layer to be investigated in a controlled manner. At a Prandtl number Pr = 6.14 and Rayleigh number Ra = 2.5 × 10^{8}, slightly below the natural onset of instability, the boundary layer is found to be convectively unstable, exhibiting a disturbance pattern consistent with a Rayleigh–Bénard mechanism. Advection of the boundary layer disturbance gives rise to unsteadiness in the vertical endwall plume. Nusselt number is enhanced across a range of frequencies for all perturbation amplitudes, with the response dominated by two frequencies differing by approximately a factor of two: each invokes the periodic shedding of vorticity into the vertical endwall plume at the higher frequency. This suggests that there exists a natural sensitivity in this flow to disturbances convecting in the upstream boundary layer. That is, a convective instability in the horizontal convection boundary layer serves as a disturbance amplifier, with the endwall plume controlling the frequency of the resulting instability mode. The increase in Nusselt number achieved by a jet with peak speed of the same order as the horizontal convective velocity in the unperturbed flow is consistent with a greater than twofold increase in Rayleigh number.
Original language  English 

Pages (fromto)  251260 
Number of pages  10 
Journal  International Journal of Thermal Sciences 
Volume  110 
DOIs  
Publication status  Published  1 Dec 2016 
Keywords
 Boundarylayer instability
 Horizontal convection
 Nusselt number
 Synthetic jet
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