The paper addresses the issue of the prediction of flow stability in heated channels containing supercritical water by the use of computational fluid-dynamics techniques. The long term aim of the research is to qualify a methodology for analyzing stability by CFD codes, basing on previous preliminary experience by the FLUENT code and making use of the present capabilities of the STAR-CCM+ code. The effect of using first and second order schemes with different time-step size for a simple thermal-hydraulic problem is firstly checked, mainly making use of the implicit transient coupled scheme available in STAR-CCM+; this step was required in order to clarify the effect of truncation error that in such implicit schemes is predicted to be quite large. Then, the analysis progresses considering a more realistic bundle slice, including the fluid and the fuel rod, with UO2, cladding and gap regions, simplified only by neglecting the effects of spacer grids and inlet throttling, to be addressed in a later phase of the research. The coupling with a point kinetics model, obtained by using an external program, developed in java, is also parametrically assessed. Conclusions are finally drawn on the observed numerical effects, sketching the lines for further research on this topic.
Studies on the adoption of CFD codes in the analysis of stability in heated channels with supercritical fluids
AMBROSINI, WALTER;FORGIONE, NICOLA;
2012-01-01
Abstract
The paper addresses the issue of the prediction of flow stability in heated channels containing supercritical water by the use of computational fluid-dynamics techniques. The long term aim of the research is to qualify a methodology for analyzing stability by CFD codes, basing on previous preliminary experience by the FLUENT code and making use of the present capabilities of the STAR-CCM+ code. The effect of using first and second order schemes with different time-step size for a simple thermal-hydraulic problem is firstly checked, mainly making use of the implicit transient coupled scheme available in STAR-CCM+; this step was required in order to clarify the effect of truncation error that in such implicit schemes is predicted to be quite large. Then, the analysis progresses considering a more realistic bundle slice, including the fluid and the fuel rod, with UO2, cladding and gap regions, simplified only by neglecting the effects of spacer grids and inlet throttling, to be addressed in a later phase of the research. The coupling with a point kinetics model, obtained by using an external program, developed in java, is also parametrically assessed. Conclusions are finally drawn on the observed numerical effects, sketching the lines for further research on this topic.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
