Temperature, velocity and mean turbulence structure in strongly heated internal gas flows

Fundamental Thermal Fluid Physics of High Temperature Flows in Advanced Reactor Systems - Nuclear Energy Research Initiative Program Interoffice Work Order (IWO) MSF99-0254 Final Report for Period 1 August 1999 to 31 December 2002

“…Conceptually, one can apply various commercial, "general-purpose" CFD codes to these situations. However, most turbulence models employed in these codes fail to give adequate heat transfer predictions for the simplest internal flows [Mikielewicz et al, 2002]. Direct Numerical Simulations should give reasonable predictions, particularly at low Reynolds numbers --but only recently have these techniques been extended to gas flows with property variation [Satake et al, 2000].…”

“…A number of turbulence models, developed for turbulent flows under conditions of uniform fluid properties, were applied by Mikielewicz et al [2002] for the purposes of simulating experiments with strongly-heated, variable property gas flows at low Reynolds numbers in a vertical circular tube, i.e., the conditions of Shehata and McEligot. The selection of models included a mixing length model, eddy diffusivity models, a one-equation k model and two-equation models of the k-ε type with low-Reynolds-number treatments; this selection is representative of models which have been widely used is but not all-inclusive.…”

Assessment of a common nonlinear eddy-viscosity turbulence model in capturing laminarization in mixed convection flows

“…The review papers of Jackson et al [3] and Jackson [4] provide extended discussions of heat transfer performance under mixed convection conditions. The most popular computational fluid dynamics (CFD) technique adopted in simulating mixed convection flows is based on the solution of Reynolds-averaged Navier-Stokes (RANS) equations, and among the possible turbulence models available to close these equations, eddy-viscosity models (EVMs) have been employed by the majority of researchers including Abdelmeguid and Spalding [5], Tanaka et al [6], Cotton and Jackson [7], Mikielewicz et al [8], Richards et al [9], Kim et al [10], and Keshmiri et al [11][12][13], among others. Keshmiri et al [11,12] recently tested a wide range of RANS turbulence models and found that the k-ω-SST model [14] and the nonlinear eddy-viscosity model (NLEVM) of Craft, Launder, and Suga [15] completely failed to capture the laminarization phenomenon present in ascending mixed convection flows.…”

Measurement of turbulent flow phenomena for the lower plenum of a prismatic gas-cooled reactor

“…The objectives of the NGNP Methods Program that led to performing the experiments described in this paper are (1) to build numerical calculational models of the important VHTR thermalfluids phenomena identified in the phenomenal identification and ranking tables (PIRT) to date; and (2) to demonstrate that the models have sufficient capability to calculate the important phenomena within a prescribed acceptance criteria by using high fidelity validation data. The experiment described herein was designed to deliver high-fidelity data to validate the capability of CFD software to calculate the turbulent behavior in the lower plenum of a gas-cooled reactor with a prismatic core.…”

“…Because the flow in the reactor lower plenum is turbulent and complex, the turbulence models available in CFD software will be used to calculate the expected behavior. Unfortunately, some turbulence models in general purpose CFD codes provide optimistic predictions in the sense that surface temperatures are typically underpredicted [1,2]. The U.S. Department of Energy (DOE) needs improved modeling capabilities, independent from the traditional approaches employed by reactor vendors.…”