Thermo-Hydrodynamic Instabilities in Fluid Flow at Supercritical Thermodynamic Conditions

We investigate the hydrodynamic instabilities occurring in the thermally developing flow of a fluid at supercritical thermodynamic conditions in a channel. Fluid at these conditions is compressible, single phase, with highly varying properties, and vanishing Mach number. In the configuration considered, flow stability is affected by competing natural and forced convection. We do not use the Boussinesq approximation. Instead, we solve the full compressible Navier-Stokes equations. An advanced equation of state for supercritical water was implemented in Arbitrary Lagrangian-Eulerian multi-physics simulation tool developed at LLNL. A newly developed, robust, 5th order in space and time, fully implicit, all-speed, reconstructed discontinuous Galerkin method is used to simulate convective heat transfer with supercritical water. We find that with an increase in the driving force for natural convection, instabilities tend to become prominent earlier in the flow field and therefore affect the overall heat transfer of the system. Results demonstrate the capability of this approach to accurately capture the non-linear behavior and instabilities arising in supercritical water flow, which cannot be adequately modeled using traditional incompressible fluid dynamics methods.