RELAP5-3D© 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

2VHTR R&D Plan Workshop Corvallis, OR September 19-20, 2005

Project Summary & Other Considerations…

• RELAP5-3D© & Fluent coupling.– Importance– Benefits– How it was done– Status– Ongoing analysis of VHTR

• Other considerations

3VHTR R&D Plan Workshop Corvallis, OR September 19-20, 2005

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.”

4VHTR R&D Plan Workshop Corvallis, OR September 19-20, 2005

To Address Such Issues…

• Fluent Corporation & INEEL embarked on project to couple Fluent CFD and RELAP5-3D©

• 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

5VHTR R&D Plan Workshop Corvallis, OR September 19-20, 2005

Fluent to RELAP5-3D© Coupling: Advantages

• Utilize system-wide macro modeling capability of RELAP5-3D

• Model some components of the system in detail using the micro-modeling features of FLUENT

Courtesy of Fluent

6VHTR R&D Plan Workshop Corvallis, OR September 19-20, 2005

• 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

Benefits of Fluent & RELAP5-3D© Coupling

Courtesy of Center for Multiphase Research, RPI

7VHTR R&D Plan Workshop Corvallis, OR September 19-20, 2005

An Executive program controls the coupling of RELAP5-3D© to other codes using PVM

PVMEXEC

PVM

RELAP-3D FLUENT CONTAIN

Synchronous or Asynchronous coupling

8VHTR R&D Plan Workshop Corvallis, OR September 19-20, 2005

Coupling Protocol has been extensively checked out..

• Most extensively by Bettis Atomic Power Laboratory

• Performed calculations with up to three codes coupled to RELAP5-3D© simultaneously, including the CFX CFD code.

• Grind time defined by CFD code when coupled with RELAP5-3D©

9VHTR R&D Plan Workshop Corvallis, OR September 19-20, 2005

Coupling of RELAP5-3D© & Fluent is Semi-Implicit

• RELAP5-3D© & 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.

• RELAP5-3D 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.

10VHTR R&D Plan Workshop Corvallis, OR September 19-20, 2005

Fluent model

Zone 2 of Fluent model

Zone 3 of Fluent model

SNGLJUN Component 115: upcrin

Blowup of Fluent model linked to RELAP5-3D© model

11VHTR R&D Plan Workshop Corvallis, OR September 19-20, 2005

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 RELAP5-3D© model of balance-of-system.

________________* Lower plenum CFD calculations provided by

Fluent Corporation.

12VHTR R&D Plan Workshop Corvallis, OR September 19-20, 2005

RELAP5-3D© coupled to enable detailed analysis of lower plenum flow patterns

Core

UpperPlenum

LowerPlenum

BalanceOf

Plant

Fluent model

RELAP5model

RELAP5model

13VHTR R&D Plan Workshop Corvallis, OR September 19-20, 2005

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

Helium gas exiting domain via Hot Duct

Fluid Domain

Core support post

14VHTR R&D Plan Workshop Corvallis, OR September 19-20, 2005

Validation of LP Flow ModelObjective: 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.

15VHTR R&D Plan Workshop Corvallis, OR September 19-20, 2005

RELAP5-3D© & Fluent CouplingSummary

• Fluent selected as collaborator—Fluent CFD may be capable of analyzing large fraction of required problems for gas-cooled and liquid metal advanced systems

• RELAP5-3D© & 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.

16VHTR R&D Plan Workshop Corvallis, OR September 19-20, 2005

Relationship of RELAP5-3D© to CFD Codes as a Group…

• RELAP5-3D© can be coupled with most, if not all, CFD codes.• Bettis Atomic Power Lab has coupled CFX* with RELAP5-3D©

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

17VHTR R&D Plan Workshop Corvallis, OR September 19-20, 2005

Potential Non-Commercial CFD Candidates…

• LANL’s T-3 CFD codes.

• NPhase: Rensselaer Polytechnic Institute