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© Fluent Inc. 5/10/2015N1 Fluids Review TRN-1998-004 Postprocessing and Visualization
© Fluent Inc. 5/10/2015N2 Fluids Review TRN-1998-004 Outline Solution monitoring Solution data Graphical display: vectors contours pathlines XY plots, histograms 2D vs. 3D Alphanumeric reports: field data, fluxes, forces, integrals Custom Field Functions Data export
© Fluent Inc. 5/10/2015N3 Fluids Review TRN-1998-004 Solution monitoring Graphical display of the solution provides: quick visual check of solution status indication of equations that are not converging The actual solution quantity plotted depends on the software continuity equation convergence trouble affects convergence of all equations Fidap example here
© Fluent Inc. 5/10/2015N4 Fluids Review TRN-1998-004 Other Solution Monitors You can also monitor and display other quantities during calculation Value of a variable at a boundary at a point Integrals/averages on a surface Force: lift, drag, moment Another indication of convergence is when the monitored value stops changing Lift coefficient vs. iteration
© Fluent Inc. 5/10/2015N5 Fluids Review TRN-1998-004 Solution Data (1) Pressure static, dynamic, total, pressure coefficient,... Velocity magnitude, components, stream function, vorticity, helicity,... Temperature static, total, enthalpy, internal energy, entropy,... Turbulence kinetic energy, dissipation rate, effective viscosity, wall y +,... Species mass fraction, mole fraction, concentration, deposition rate,... m o2 k
© Fluent Inc. 5/10/2015N6 Fluids Review TRN-1998-004 Solution Data (2) Properties density, viscosity, conductivity, specific heat,... Wall quantities shear stress, heat flux, heat transfer coefficient,... Grid coordinates, areas, volumes, quality measures,... Derived quantities shear rate, stresses, other derivatives, … Custom quantites User-defined Functions Field Function Calculator
© Fluent Inc. 5/10/2015N7 Fluids Review TRN-1998-004 Graphical Display of Data What would “colorful fluid dynamics” (CFD) be without graphics?! Graphical display should be more than just pretty pictures The goal is visualization and understanding of the flow capture of gross features: is the flow headed the right way does it look correct? Have I done something wrong? Visualization of finer features: where does the flow separate what does the local heat transfer coefficient look like on the wall Many options: contours, vectors, path lines,...
© Fluent Inc. 5/10/2015N8 Fluids Review TRN-1998-004 Contours Color-coded contours are an effective means of visualizing scalar quantities such as pressure, velocity magnitude, stream function, … Display is essentially 2-D You can identify the min/max and gradients slide coater contours of stream functionfilled contours
© Fluent Inc. 5/10/2015N9 Fluids Review TRN-1998-004 Vector Plots Velocity vectors indicate the direction and magnitude of the flow Usually colored by velocity magnitude Usually displayed on a surface, but shows “three-dimensionality”
© Fluent Inc. 5/10/2015N10 Fluids Review TRN-1998-004 Path Lines Path lines trace the flow pattern using massless “particles” 3-D version of stream function contours Can be colored/twisted by any scalar value Be careful! You specify the starting point for the path lines, but... if the particles start outside a recirculating region, you won’t see it! particles released here nothing here?! Flow structure is actually quite complex! Particles released here
© Fluent Inc. 5/10/2015N11 Fluids Review TRN-1998-004 XY Plots “Quantitative” data can be viewed as XY plots Useful for comparing against experimental or other data Examples: heat transfer coefficient along a wall pressure distribution on lift surfaces time dependent behavior (e.g., shedding) Can be plotted on a surface, but usually along a line velocity distribution at exit of a coating die
© Fluent Inc. 5/10/2015N12 Fluids Review TRN-1998-004 Histograms Histograms are a good way to visualize distributions cell skewness other statistics (e.g., variation of density throughout flowfield) Cell skewness distribution
© Fluent Inc. 5/10/2015N13 Fluids Review TRN-1998-004 2D vs. 3D In 2D, data is normally plotted on the entire flow domain In 3D, this is not feasible — too much data!! Thus, for 3D problems, you normally plot data on: a surface or surfaces a line or lines All outer boundaries are available as plotting surfaces Most postprocessors provide tools for creating arbitrary plotting surfaces: points or lines planes, iso-surfaces, clipped surfaces
© Fluent Inc. 5/10/2015N14 Fluids Review TRN-1998-004 Alphanumeric Reports It is not practical to view “raw data” — perhaps on a small, “mapped” grid However, other alphanumeric reports are quite helpful: L D fluxes: e.g., summary of mass flux in/out of each boundary forces: e.g., summary of xyz components of forces/moments on a surface integrals: e.g., evaluate mass flow rate weighted average temperature at the outlet
© Fluent Inc. 5/10/2015N15 Fluids Review TRN-1998-004 Custom Postprocessing Values Sometimes, the value you want to plot isn’t provided What then? Some software programs provide: user-defined subroutines — calculation of “custom” quantities which then can be visualized “field function calculator” — you can enter a formula in a special GUI panel. The resulting quantity can be contoured, XY plotted, etc.
© Fluent Inc. 5/10/2015N16 Fluids Review TRN-1998-004 Data Export Most CFD codes can write out data in other formats For people who want to: view the data in another CAD program (I-DEAS, PATRAN, etc.) use a third-party postprocessor (FieldView, Ensight, Data Explorer, Tecplot, etc.) make some further calculations with the data using their own software
© Fluent Inc. 5/10/2015N17 Fluids Review TRN-1998-004 Animation CFD data lends itself nicely to animation: i.e., moving pictures of the data Examples: particles moving with the fluid fly-by’s, fly-through’s visualizations of moving geometries (e.g., mixing tanks) visualizations of other transient phenomena (e.g., movement of a shock) data on a plane passing through the domain Its very helpful if the CFD software provides animation support: composition of animation proper file output formats
© Fluent Inc. 5/10/2015N18 Fluids Review TRN-1998-004 Summary Postprocessing includes all the tools needed for interpretation and visualization of the CFD solution Postprocessing occurs at two levels: qualitative check: are b.c.’s correct, does flow look “right” extracting the quantitative results that are needed for design 2D postprocessing is fairly straightforward and trivial Effective visualization of 3D flows is assisted by: preparing appropriate plotting surfaces for viewing scalar data path line plots or particle tracks to “see” overall flow patterns animation to “bring the flow to life”
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