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Advanced Computing to Bridge Micro and Macro: LBM, Advanced CFD and Coupled CFD-System Codes |
Prashant K. Jain, Suneet Singh, Yizhou Yan, and Rizwan-uddin
University of Illinois Urbana-Champaign
Present state of computational power requires simulations at different levels of details, and therefore, also methods to link/bridge the results obtained at these levels. For example, Lattice Boltzmann Method (LBM) is a good candidate because of its remarkable potential to simulate single and multiphase fluids at mesoscopic levels with affordable computational expense. Most important part of this approach is that the rules governing the simulation are designed such that the motion of particles is consistent with the Navier-Stokes equations. Various boundary conditions are easily incorporated; these include not only the standard single-phase flow boundary conditions, but also boundary conditions in multi-fluid systems and bubbles, such as pressure drop across interfaces and fluid-solid-interface wetting effect, as well. However, it is hard to solve practical engineering problems with this approach alone. Many practical fluid dynamics problems are today solved using CFD. Despite significant improvement in CFD tools over the last two decades, there is still significant room for improvement, for example to simulate multi-phase flows. Thus a bridge between LBM and CFD approaches is desirable.
Due to the size and complexity of nuclear system geometry, CFD alone is not capable of solving the kind of problems currently addressed using the nuclear system codes like RELAP5. A solution to this problem is to couple a system code with a three-dimensional CFD code, and apply the CFD code to simulate the parts and components where system codes do not perform adequately, such as lower plenum, downcomer, and possibly even reactor core while taking advantage of system codes to simulate flow in components where flow can be adequately simulated by 1D flow.
Our group is focused on developing and improving the individual methods as well as in linking/bridging these simulations that cover rather different spatial scales. Our goal is to develop an approach to solve problems over rather different spatial scales using different, but self-consistent, approaches on computers that are available today and those that will become available over the next two decades. For example, a methodology has been developed to couple a CFD and a system code, and used to link the CFD code, FLUENT and system code, RELAP5-3D. This allows different parts of the domain to be modeled using FLUENT or RELAP-3D.
Contact
Rizwan-uddin
University of Illinois Urbana-Champaign
Department of Nuclear Plasma and Radiological Engineering
103 S. Goodwin Avenue
Urbana, IL 61801
rizwan@uiuc.edu