Comparison of Natural Convection Flows Under VHTR Type Conditions Modeled by both the Conservation and Incompressible Forms of the Navier-Stokes Equations

Journal Article · Tue Jun 01 00:00:00 EDT 2010 · Nuclear Engineering and Design

DOI:https://doi.org/10.1016/j.nucengdes.2010.01.022· OSTI ID:983938

Martineau, Richard C; Berry, Ray A; Esteve, Aur´elia; Hamman, Kurt D; Knoll, Dana A; Park, Ryosuke; Taitano, William

This manuscript illustrates a comparative study to analyze the physical differences between numerical simulations obtained with both the conservation and incompressible forms of the Navier-Stokes equations for natural convection flows in simple geometries. The purpose of this study is to quantify how the incompressible flow assumption (which is based upon constant density advection, divergence-free flow, and the Boussinesq gravitational body force approximation) differs from the conservation form (which only assumes that the fluid is a continuum) when solving flows driven by gravity acting upon density variations resulting from local temperature gradients. Driving this study is the common use of the incompressible flow assumption in fluid flow simulations for nuclear power applications in natural convection flows subjected to a high heat flux (large temperature differences). A series of simulations were conducted on two-dimensional, differentially-heated rectangular geometries and modeled with both hydrodynamic formulations. From these simulations, the selected characterization parameters of maximum Nusselt number, average Nusselt number, and normalized pressure reduction were calculated. Comparisons of these parameters were made with available benchmark solutions for air with the ideal gas assumption at both low and high heat fluxes. Additionally, we generated specific force quantities and velocity and temperature distributions to provide a basis for further analysis. The simulations and analysis were then extended to include helium at the Very High Temperature gas-cooled Reactor (VHTR) normal operating conditions. Our results show that the consequences of incorporating the incompressible flow assumption in high heat flux situations may lead to unrepresentative results. The results question the use of the incompressible flow assumption for simulating fluid flow in an operating nuclear reactor, where large temperature variations are present.

• Research Organization: Idaho National Lab. (INL), Idaho Falls, ID (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: DE-AC07-05ID14517
• OSTI ID: 983938
• Report Number(s): INL/JOU-09-15688; TRN: US1005202
• Journal Information: Nuclear Engineering and Design, Vol. 240, Issue 6; ISSN 0029-5493
• Country of Publication: United States
• Language: English

Related Subjects

22 GENERAL STUDIES OF NUCLEAR REACTORS
ADVECTION
AIR
BENCHMARKS
FLUID FLOW
GAS COOLED REACTORS
HEAT FLUX
HELIUM
HYDRODYNAMICS
INCOMPRESSIBLE FLOW
NATURAL CONVECTION
NAVIER-STOKES EQUATIONS
NUCLEAR POWER
NUSSELT NUMBER
REACTORS
TEMPERATURE DISTRIBUTION
TEMPERATURE GRADIENTS
VELOCITY
Natural convection
conservative and incompressibl