A Numerical Approach For ThermallyCoupled Fluid And Solid Problems In ComplexGeometries

Abstract

Thermal coupling between fluid and solid domains is widely present in industrial applications. The approach implemented relies upon the existing CFD code N3S (see Chabard [1]), which handles the averaged Navier-Stokes system with a finite element technique, and a module named Syrthes which takes care of the heat equation inside the solid using finite elements technique. An explicit scheme, has proven to be very stable to exchange information (temperature or flux) between solid and fluid domains within each time step. The numerical and geometrical de-coupling of solid and fluid domains has numerous advantages and provides good flexibility when handling complex cases. INTRODUCTION In many industrial applications, a thermal coupling exists between a fluid and the solid body by which it is surrounded. Among topics of interest, studied at EDF, thermal shocks arising in piping systems of nuclear plants can be pointed out. These shocks originate from a quick variation of the flow temperature. This may lead to mechanical damages (like cracks). Of course, other fields, like heat exchangers, electrical devices, etc... have to address the same kind of problem. Experimental approaches have been used extensively in the past, but they may become very costly (when dealing with a very hot fluid under high pressure for example). Moreover, they often lack the flexibility needed when a parametric study is desired. On the other hand, with powerful computer facilities now available at affordable cost, numerical approaches become more and more promising to accurately predict thermal phenomena and their effects. Tackling a full size problem requires to handle thermal phenomena in the fluid part, in the solid part and the strong interaction between the two regions. At EDF, sophisticated numerical tools have been developped in the past years to handle fluid problems. The software N3S relies on finite element techniques to solve the averaged Navier-Stokes equations. Unfortunately, wall effects (from the thermal point of view) could only be taken into account in N3S by imposing a wall temperature or a flux. Therefore, thermal fields within solids were not available and thermal inertia caused by the solid wall could not be accounted for. A general purpose conduction module, Syrthes, is now handling the heat equation inside the solid and the thermal coupling between fluid and solid regions. Transactions on Engineering Sciences vol 5, © 1994 WIT Press, www.witpress.com, ISSN 1743-3533