ehlen_fluent_deutschland

Dipl.-Ing. Michael EhlenFluent Deutschland GmbHCFD Konferenz 2004 in Bingen! "# ! "$A method by which the solver (FLUENT) can be instructed to moveboundaries and/or objects, and to adjust the mesh accordinglyExamples:Automotive piston moving inside a cylinderA flap moving on an airplane wing A valve opening and closingVolumetric fuel pumpAn i m a t i o n#$•Used when rigid boundaries move with respect to each other, e.g.,–Piston moving w.r.t. an engine cylinder (linear motion)–Flap moving w.r.t. an airplane wing (rotating motion)•Used when boundaries deform/deflect, e.g.,– A balloon that is being inflated– A solid propellant retreating as it is being consumed by the flame–The shrinking or extending walls of an engine cylinder as the piston moves in and out! " %• A general purpose model targeted for moving boundary problems –Aero industry: store separation, stage separation, jet engines, etc.–Auto industry: IC engines, valves, fuel injectors, etc.–Mechanical engineering: pumps, blowers, turbomachinery, etc.–Many more applications!•Can also be used for steady-state parametric studies, to vary the geometry methodically;•Compatible with all physical models in FLUENT 6., except the Eulerian multiphase models;•Compatible with all three solvers;•Compatible with any pre-processor;•Fully parallelized.! " %•Several meshing schemes are available to handle all types of boundary motion;•Boundaries/Objects may be moved based on:–In-cylinder motion (RPM, stroke length, crank angle, …);–Prescribed motion via profiles;–Prescribed motion via UDF(User-Defined Function);–Coupled motion based on hydrodynamic forces from the flow solution, via FLUENT’s 6 DOF model.%&•Fluent’s DM (Dynamic Mesh) model offers three meshing schemes:–Spring analogy (smoothing);–Local remeshing;–Layering.•Mesh motion may be applied to individual zones;•Different zones may use different schemes for mesh motion;•Connectivity between adjacent deforming zones may be non-conformal, e.g., there might be a sliding interface between two neighboring zones.&' ( ( !&' ( & ("•The nodes move as if connected viasprings, or as if they were part of asponge;•Connectivity remains unchanged;•Limited to relatively smalldeformations when used as a stand-alone meshing scheme;•Available for tri and tet meshes;•May be used with quad, hex and wedge mesh element types, but that requires a special command;Animation) (•As user-specified skewness andsize limits are exceeded, localnodes and cells are added ordeleted;•As cells are added or deleted,connectivity changes;•Available only for tri and tet meshelements;•The animation also shows smoothing (which one typically uses together with remeshing).Animation(•Cells are added or deleted as thezone grows and shrinks;•As cells are added or deleted, connectivity changes;•Available for quad, hex and wedge mesh elements.An i m a t i o n(Bottom Layeringinterior zoneTop Layeringfluid (hex)wall (bottom) Settings: - wall (bottom): rigid body Settings: - fluid (hex): rigid body - interior zone: stationary - wall (bottom): rigid body*• • Initial mesh needs proper decomposition; Layering: – Valve travel region; – Lower cylinder region. Remeshing: – Upper cylinder region. Non-conformal interface between zones.''• •Ani m at io n+ ,! +•',"Define > Dynamic Mesh > Parameters – Select “Dynamic Mesh” to enable the model, then select one or more specific mesh method: spring smoothing, layering, and/or local remeshing; – The “In-Cylinder” option is for easily defining the motion of pistons and valves.&'• The motion of certain boundaries or fluid zones is specified via Define > Dynamic Mesh > Zones The example shows a wall called “rotor_clock” that moves as a rigid body according to a UDF called “clockwise”: the example is for a gear that spins clockwise about its C.G. (center of gravity).•&'(( ! &'(&(")(( • • Split if: Collapse if:'.%/h > (1 + α S ) hideal h < α c hideal•hideal is defined later, during the definition of the dynamic zones.(• • Constant Height: – Every new cell layer has the same height; Constant Ratio: – Maintain a constant ratio of cell heights between layers (linear growth); – Useful when layering is done in curved domains (e.g. cylindrical geometry). Piston at Initially, top-most piston at position bottom-most position Edge “i” Constant Height Edges “i” and “i+1” have same shape Constant Ratio Edge “i+1” is an average of edge “i” and the piston shape(• Definition of the dynamic zone:piston (wall zone) moves as a rigid body in the y-direction(• • Definition of the ideal height of a cell layer; hideal is about the same as the height of a typical cell in the model.&'•Internal node positions are automatically calculated based on user specified boundary motion:•Prescribed mesh motion:–Position or velocity versus time, i.e., ‘profile’ text file;–UDF with expression for position or velocity versus time(independent of the flow solution).•Flow dependent motion (coupled motion):–Mesh motion is coupled with the flow solution through a UDF;–One can compute forces (pressure, gravity, viscous, etc.) on a body to arrive at its translational and rotational velocity components;–Six degree of freedom (6DOF) UDF provided;–UDF readily customized for desired mesh motion./•Mesh motion can be previewed without calculating flow variables:–Allows user to quickly check mesh quality throughout the simulation cycle;–Applicable to any dynamic mesh simulation;–Accessed via GUI: Solve > Mesh Motion;–Be careful with the time step.–Save your case before doing the preview, else the setup will be lost!! " %•Objects may not move from one fluid zone into another;•Cannot (yet) be used in conjunction with hanging node adaption (including dynamic adaption);•Constrained motion, such as a motion about a hinge, is only allowed if one uses a UDF;•Bodies may not make contact, since that implies a change in topology; one always leaves at least one layer of cells between bodies;•DPM (discrete phase model) particles cannot be released from moving surfaces (but one could vary the injection location as a function of time).012213 ) (4& (•For mapable(2.5D; extruded) geometries in particular pumps5 ) ( ) (& ) (•New in FLUENT 6.2:–Symmetric boundaries–Across multiple zones–Feature preservation(e.g., corners arepreserved)–Non-closed loops) (4& ( 'Limitation:Dynamicadaptioncannot be usedin conjunctionwith layeringor withboundaryremeshing( /Also: layeringis now possiblein fluid zoneswith mixedcell types,provided thecell type doesnot change asone crossesfrom thelayering zoneto the adjacentzone(s).* ' 607 &•6-DOF solver now built into the GUI;•GUI panels still do not provide for constraints (such as hinges), but constrained motion is possible via UDF;•The dynamic mesh UDFs contain hooks for loadforces/moments;•Transformations can be customized (although we use a transformation between local and global coordinate systems that is widely used in the aerospace and shipbuilding industries).•Events based on time (not just based on the crank angle as before), and without having to use the in-cylinder tools (where they were called in-cylinder events);•New events:–Activate/Deactivate cell zones–Change URF•You can also use events to control the time step!/ , ' 020406080100120140Fluent 6.1Fluent 6.21c y c l eF l o w R u n T i m e (h r s .)1CPU 2CPU 1CPU 2CPU - 12%- 34%5.4 days 4.5 days 4.83 days 3 days•HP-Linux machine with 2.2GHz processor speed •No need to encapsulate the interfaces •Run time reduction depending on case •Can vary between 33%-40%,* /•IC specific setup panel–Fewer inputs and more features than 6.1 panel–Automatic setup of activate/deactivate, variable time step size and URFs–Three different pistons types are also automatically set up •Pistons with enough room to put one layer to start with (1)•Flat pistons with tight squish combustion chamber (2)•Complex piston shape like GDI engines (3)–User need not specify the meshing parameters in the panel •Meshing parameters automatically calculated by the journal –Takes care of symmetry engine as well–Can read and write parameters into a file•Becomes very handy if a slightly different setup is explored.,* /Fluent 6.2 IC Panel- ', 7*/ * (/ ( *& & '6, 8。