Recent applications of overset mesh technology in SC/Tetra NIA CFD Seminar October 6, 2014 Tomohiro Irie Software Cradle Co., Ltd. 1
Contents Introduction Software Cradle SC/Tetra Background of Demands for Overset Technology Overset Mesh Strategy Basic Validation Application Examples Parts replacing by overset mesh Coupling with flow-driven 6DOF motion Coupling with free surface flow (VOF method) Coupling with flow-structure interaction (FSI) analysis Special treatment for piston engine analysis 2
Software Cradle Co., Ltd. President Ichiro Komada Locations Osaka (Headquarter), Tokyo Foundation 1984 Employees 96 Subsidiary Cradle North America Inc. (Ohio, USA) France Office (Lyon, France) Affiliated company Osaka Office(HQ) Applied Thermal Fluid Analysis Center, Ltd (Taipei, Taiwan) ContraVolts Info Tech Pvt. Ltd (Bangalore, India) Tokyo Office 3
Products Unstructured CFD code Structured (Cartesian) CFD code Co-located grid Robust and less memory Auto-mesh generator Staggered grid Robust and fast Easy modeler and auto-mesh generator 4
Basic Capabilities of SC/Tetra Equations Compressible and incompressible Navier-Stokes equations RANS Discretization Unstructured mesh (Tetrahedron, pentahedron, hexahedron) Cell-vertex FVM Pressure-velocity coupling scheme Pressure-based segregated (SIMPLEC) Density-based coupled (for compressible fluid) Turbulence modeling RANS, LES, LES-RANS hybrid (DES,VLES) Parallelization MPI, Domain partitioning (ParMETIS) 5
Motivation for Overset Mesh Technology Widespread use of CFD in industries (Automotive, Electronics, etc.) Demands for analysis of real products Difficult problems for CFD Moving and contacting solid Intake/exhaust valve Gear pump Complex motion Scroll compressor Floating ball valve Introduction of overset mesh technology to SC/Tetra 6
Overset Mesh Strategy Hole cutting is processed dynamically following to mesh motion Solid objects can be in contact with Coefficient matrix on each meshes are merged to a single matrix at inter-mesh boundary and solved implicitly The field variables are interpolated at the inter-mesh boundary in order to improve smoothness Solid object on master mesh Slave mesh A Slave mesh B The situation that solid objects come in contact with 7
Basic Validation Flow around a fixed sphere (Re=118) Overset mesh Single mesh Exp. (Taneda,1956) 8
Application : Static Problem Parts replacement procedure of motorcycle 1 2 3 Base shape Added aerodynamic parts Courtesy of Yamaha Motor Co., Ltd. 9
Application : Static Problem Single mesh Overset mesh Single mesh Overset mesh 1 2 1 2 3 CD 1 2 3 3 1 2 3 1 2 3 CL 10
Application : Dynamic Motion of Close-Set Objects Flapping wing of MAV (Micro Air Vehicle) Studied by Dr. George Huang (Wright State University) 11
Application : Dynamic Motion and Thermal Analysis Cold air leaking from opening door of a refrigerator Opening door movement is represented using overset mesh Temperature distribution at a center cross section Isothermal surface of leaking air 12
Flow Driven Motion (6DOF) Coupling with flow driven motion (6DOF) and free surface analysis (VOF method) Floating ball by air jet Jumping ball through the water-surface (Ball motion driven by buoyancy) 13
Application : Flow-Structure Interaction (FSI) Reed valve for compressor Elastic deformation of the reed valve is simulated by Abaqus (Dassault Systèmes) The reed valve and the piston are represented by overset mesh 1.5 [MPa] Retainer Reed valve Piston 0.3 [MPa] 14
Piston Analysis using Overset Mesh (1) Transient analysis of the inside of the engine cylinder using overset mesh Advantages Relatively easy mesh generation and moving condition setting Disadvantages Insufficient conservation of the amount of air in the cylinder Magnitude of particle velocity 15
Piston Analysis using Overset Mesh (2) Special treatment for piston analysis Cylinder space is represented by sweep cells (prism) A part of overlapping cells of the cylinder mesh are compressed according to the piston movement The volume of the deleted (in-activated) cells is considered as the volume change of their neighboring active elements These treatments improve accuracy of mass-conservation in the cylinder to practical level 16
Piston Analysis using Overset Mesh (4) Velocity distribution and mesh configuration Courtesy of Yamaha Motor Co., Ltd. 17
Piston Analysis using Overset Mesh (3) Time variation of air, mean pressure, and mean temperature in the cylinder Total mass of air in the cylinder Average pressure in the cylinder Average temperature in the cylinder IVC EVO Relative values from atmospheric pressure (101325Pa) New: With the special treatment for piston analysis Org : Without the special treatment for piston analysis 18
Piston Analysis using Overset Mesh (5) Particle tracking (passive marker particle) Courtesy of Yamaha Motor Co., Ltd. 19
Conclusion Software Cradle has introduced overset mesh technology to SC/Tetra since 2007. Overset mesh technology has been an necessary function for flow simulation with moving components in complex geometries, which is not uncommon in real products. SC/Tetra's overset mesh technology has been improved continuously, that become possible to couple with free-surface analysis, flow-structure interaction and dynamical moving components (6DOF). In the latest version, a special treatment for flow analysis in piston engine was introduced, that achieve practical accuracy for mass conservation in the cylinder. 20
Thank you for your attention. 21