RELAP 5 3 D to Fluent CFD Software

RELAP 5 -3 D© to Fluent CFD Software Coupling Richard R. Schultz Workshop: VHTR R&D Plan Hosted by: Academic Center of Excellence for Thermal Fluids and Reactor Safety, Oregon State University September 19 -20, 2005

Project Summary & Other Considerations… • RELAP 5 -3 D© & Fluent coupling. – Importance – Benefits – How it was done – Status – Ongoing analysis of VHTR • Other considerations VHTR R&D Plan Workshop Corvallis, OR September 19 -20, 2005 2

Importance of Coupling Systems Analysis Codes to CFD Codes widely recognized … IAEA recently hosted a meeting to discuss: “…interest in the application of 3 -dimensional CFD software as a supplement to or in combination with system codes, which provide the boundary conditions for CFD codes. ” Problems under discussion include: · Evaluation of performance of passive safety features; · Local phenomena leading to cladding ruptures; · Multidimensional TH in various components; · Liquid/gas stratification and interface tracking; and · Bubble dynamics in suppression pools. ” VHTR R&D Plan Workshop Corvallis, OR September 19 -20, 2005 3

To Address Such Issues… • Fluent Corporation & INEEL embarked on project to couple Fluent CFD and RELAP 5 -3 D© • Fluent CFD was selected as collaborator by INEEL* because: – Fluent CFD demonstrated high quality—see CFD Forum results: C. J. Freitas, “Perspective: Selected Benchmarks from Commercial CFD Codes, ” Journal of Fluid Mechanics, 117, 1995, pp. 208 to 218 – Extremely cooperative – High quality standard: ISO 9001: 2000 – Largest user base and largest suite of applications (& probably largest suite of V&V cases). __________ * after contacting CFX, Fluent, and STAR-CD VHTR R&D Plan Workshop Corvallis, OR September 19 -20, 2005 4

Fluent to RELAP 5 -3 D© Coupling: Advantages • Utilize system-wide macro modeling capability of RELAP 5 -3 D • Model some components of the system in detail using the micro-modeling features of FLUENT VHTR R&D Plan Workshop Corvallis, OR September 19 -20, 2005 Courtesy of Fluent 5

Benefits of Fluent & RELAP 5 -3 D© Coupling • The performance of the system depends on the flow through each component, and vice versa • Boundary condition information is transferred back and forth between the two codes • Both the system and component behaviors are more accurately predicted Courtesy of Center for Multiphase Research, RPI 6 VHTR R&D Plan Workshop Corvallis, OR September 19 -20, 2005

An Executive program controls the coupling of RELAP 5 -3 D© to other codes using PVMEXEC PVM RELAP-3 D FLUENT CONTAIN Synchronous or Asynchronous coupling VHTR R&D Plan Workshop Corvallis, OR September 19 -20, 2005 7

Coupling Protocol has been extensively checked out. . • Most extensively by Bettis Atomic Power Laboratory • Performed calculations with up to three codes coupled to RELAP 5 -3 D© simultaneously, including the CFX CFD code. • Grind time defined by CFD code when coupled with RELAP 5 -3 D© VHTR R&D Plan Workshop Corvallis, OR September 19 -20, 2005 8

Coupling of RELAP 5 -3 D© & Fluent is Semi-Implicit • RELAP 5 -3 D© & Fluent move forward time step-by-time step to perform calculation. • Calculation only moves forward when convergent solution is achieved in both left and right computational domains. • RELAP 5 -3 D reactor physics can be coupled to Fluent (as one domain— with small additional of work). Completion of this task will create only known example of commercial CFD code with reactor physics. VHTR R&D Plan Workshop Corvallis, OR September 19 -20, 2005 9

Blowup of Fluent model linked to RELAP 5 -3 D© model VHTR R&D Plan Workshop Corvallis, OR September 19 -20, 2005 10

Validation Underway Using Gas. Cooled Reactors as Basis • Prismatic reactor is focus • Working fluid: helium • Collaborators: Fluent, General Atomics, and INEEL • Fluent model of lower plenum* will couple with RELAP 5 -3 D© model of balance-of-system. ________ * Lower plenum CFD calculations provided by Fluent Corporation. VHTR R&D Plan Workshop Corvallis, OR September 19 -20, 2005 11

RELAP 5 -3 D© coupled to enable detailed analysis of lower plenum flow patterns Upper Plenum RELAP 5 model Core Balance Of Plant RELAP 5 model Lower Plenum Fluent model VHTR R&D Plan Workshop Corvallis, OR September 19 -20, 2005 12

Fluid Behavior in Lower Plenum • Need: Preliminary evaluation of turbulent intensity and mixing characteristics likely to be present in lower plenum (LP) at rated condition. • Use existing CFD model of LP with most representative turbulence model and perform preliminary evaluation of fluid behavior as function of location in LP. Helium gas entering domain around core support posts Fluid Domain VHTR R&D Plan Workshop Corvallis, OR September 19 -20, 2005 Core support post Helium gas exiting domain via Hot 13 Duct

Validation of LP Flow Model Objective: The flow in the lower plenum of the NGNP will involve multiple jets entering from the core into a crossflow moving toward the exit duct and having to negotiate the presence of rows of support pillars. The modeling strategies (turbulence model, grid characteristics, time stepping, etc. ) for simulating this complex turbulent flow must be validated. VHTR R&D Plan Workshop Corvallis, OR September 19 -20, 2005 14

RELAP 5 -3 D© & Fluent Coupling Summary • Fluent selected as collaborator—Fluent CFD may be capable of analyzing large fraction of required problems for gas-cooled and liquid metal advanced systems • RELAP 5 -3 D© & Fluent are coupled. • The two codes will move forward time-step-by-time step after each code has converged. • Coupling software has been extensively checked. • Presently performing calculations to study mixing in prismatic lower plenum. VHTR R&D Plan Workshop Corvallis, OR September 19 -20, 2005 15

Relationship of RELAP 5 -3 D© to CFD Codes as a Group… • RELAP 5 -3 D© can be coupled with most, if not all, CFD codes. • Bettis Atomic Power Lab has coupled CFX* with RELAP 5 -3 D© using our Executive—consequently expertise to couple these codes for Gen IV use exists. • STAR-CD has offered us access to their source code—however we haven’t had the resources to pursue their offer. • No problems foreseen in coupling with non-commercial CFD codes. ___________ * A variant of CFX—source code owned and modified by Bettis VHTR R&D Plan Workshop Corvallis, OR September 19 -20, 2005 16

Potential Non-Commercial CFD Candidates… • LANL’s T-3 CFD codes. • NPhase: Rensselaer Polytechnic Institute VHTR R&D Plan Workshop Corvallis, OR September 19 -20, 2005 17