SPECTRAL ELEMENT SIMULATIONS OF UNSTEADY FORCED CONVECTIVE HEAT-TRANSFER - APPLICATION TO COMPACT HEAT-EXCHANGER GEOMETRIES

Numerical investigations of the flow pattern and forced convective heat transfer in supercritical flows, such as those encountered in compact heat exchangers, are presented. These flows exhibit laminar self-sustained oscillations at the plane channel Tollmien-Schlichting frequency for Reynolds numbers above the critical one. These studies indicate that oscillatory separated flow results in large-scale convective patterns that are responsible for significant heat transfer enhancement and leads to a reduction in the pumping power required to achieve a given Nusselt number. The hydrodynamic-heat transfer numerical results are obtained by direct simulation of the unsteady energy and Navier-Stokes equations using a spectral element method for the spatial discretization. The spectral element method is a high-order weighted-residual technique that exploits both the common features and the competitive advantages of low-order finite element methods (versatility) and spectral techniques (accuracy and rapid convergence). It is shown that computational heat transfer and, in particular, direct numerical simulation can contribute significantly to exploration of the rich physics associated with heat transfer enhancement by flow destabilization.