Unsteady RANSCalculations of Perturbed Natural Circulating Flow Within an Experimental Test Loop

The implications of transient events can have significant influence on the cooling capabilities of a natural circulation loop, where perturbations such as cold fluid injection can hinder natural circulation flow. Comparisons have been made between unsteady Reynolds averaged Navier-Stokes (RANS) computations to high fidelity Large Eddy Simulation (LES) results for a simple natural circulation loop. Two transient types were considered; low point cold fluid injection for 2000 seconds, and zero power scenarios where the heat input was removed once a steady state was established. The results from RANS and LES were shown to be comparable in their predictions of bulk mass flow rate and temperature trends, with both transient types demonstrating a reduction in prevailing mass flow rate and heat transfer capability.