ansys 14.0: fluid dynamics for the industry 14.0... · fluent and cfx will continue to be developed...

© 2011 ANSYS, Inc. March 16, 20121

ANSYS 14.0: Fluid Dynamics for the Energy Industry

Madhusuden AgrawalDurai Dakshinamoorthy

© 2011 ANSYS, Inc. March 16, 20122

ANSYS Fluid Dynamics

ANSYS Fluid Dynamics Products• ANSYS FLUENT• ANSYS CFX• ANSYS CFD‐Post• ANSYS Turbo Tools• ANSYS Polyflow• FLUENT for CATIA v5• Icepak

ANSYS Fluid Dynamics at 14.0• Significant benefits for users

© 2011 ANSYS, Inc. March 16, 20123

We remain committed to developing and releasing an integrated, unified fluids product

– That will draw upon the best of both FLUENT and CFX, as well as add new functionality

– That will minimize migration hurdles for our fluids customers

The first release of this product is targeted for ANSYS R15.0

FLUENT and CFX will continue to be developed in the meantime (and actively maintained for a few releases beyond R15.0)

– To ensure smooth migration for our fluids customers

Our Fluids Strategy

© 2011 ANSYS, Inc. March 16, 20124

• Workflow & Usability

• Multiphysics and Systems Coupling

• Solver and HPC Performance

• Comprehensive CFD Capabilities

• Multiphase Flow Modeling

• Summary

Fluid Dynamics Themes

© 2011 ANSYS, Inc. March 16, 20125

Workflow & Usability

Simulation departments are looking for improved usability and the ability to glean more information from fluid dynamics simulations for all users –from occasional designers to experienced analysts – from geometry creation through post-processing.

© 2011 ANSYS, Inc. March 16, 20126

ANSYS Remote Solver Manager at R14 (FLUENT and CFX)

• Major improvements for fluids as well as general usability and robustness improvements to RSM

• Queue multiple jobs on a local machine– Overnight or other low‐usage times

• Submit jobs to remote machines– Distributed clusters– Management of files, including UDFs

• Update design points in parallel via RSM

Workflow & Usability – ANSYS RSM

© 2011 ANSYS, Inc. March 16, 20127

Workflow & Usability – ANSYS CFD

Improved workflow and usabilityin ANSYS Workbench • Extended User Preferences (FLUENT)– General options– Launcher options

• Extended parameters for Fluent– Real and profiles variables in zone and domain settings

– Examples:• Phases: Nucleation Rate, Coalescence and Breakage Kernels• Phase Interaction: Surface Tension Coefficients, Lift Coefficient, Restitution Coefficient

• Contact Angles (on wall BC)

© 2011 ANSYS, Inc. March 16, 20128


New mesh options in FLUENT

• Copy and move zones (TUI)– Copy zones and translate/rotate the copies directly in Fluent

• Preserve interior faces during conversion to polyhedral meshes (TUI) – Keep interior faces that may be needed for post‐processing

Copied and translated zones in Fluent 14

© 2011 ANSYS, Inc. March 16, 20129


Process more information per simulation (FLUENT)• Monitor more than a single lift, drag, or moment monitor– Multiple monitors for each type

• Assign any variable to a custom field function for use with unsteady statistics

Export reduced data for faster file write and reduced storage needs• FLUENT – on a per cell zone basis to CFD Post, EnSight, and FieldView

• CFX ‐ Output selected solution data only at boundaries during transient β

Multiple force monitors Custom field functions for statistics

Output control panel in CFX

© 2011 ANSYS, Inc. March 16, 201210


Optimization of transient chart creation performance (CFD‐Post)• Update only relevant objects during transient chart creation– Significant speed‐up when current state contains many un‐related objects

Enhanced ability to use ANSYS CFD with other tools• CGNS library version upgrade to 3.1• Support face‐based regions in CFD‐Post (in addition to node‐based)– Enable adoption use as common CFD post‐processor for 3rd party tools

Transient chart creation speed‐up*

FFT Chart 48 [%]

Time Chart 54 [%]* On standard test case; will vary depending on

particular case and post‐processing state

Example CGNS results from 3rd

party tool with face-based region definition

© 2011 ANSYS, Inc. March 16, 201211


Easier specification of animation resolution for high definition playback (CFD‐Post)• Extended output options to include HD standard sizes– HD Video 720p– HD Video 1080p

• Automatic internal adjustment to avoid Windows Media Player playback limitations

© 2011 ANSYS, Inc. March 16, 201212


Embedded Reference Frames: Local frame specification for sliding mesh• Local frame (origin and axis) defined with respect to moving (base) frame

• Origin and axis locations remain fixed with respect to base frame

• NO UDF required to update the origin or axis!

Local (embedded) frame

Base frame

Local frame set to revolve about an origin at center (0.1, 0.1) w.r.t. base frame

© 2011 ANSYS, Inc. March 16, 201213

Multiphysics and Systems Coupling

Engineers need to accurately predict how complex products behave in real-world environments with real world physics.

ANSYS is continuously improving the ease of use and efficiency of simulating real world interactions between fluid dynamics, structural mechanics, heat transfer, and electromagnetics within a single, unified engineering simulation environment using systems coupling.

© 2011 ANSYS, Inc. March 16, 201214

Two‐way surface force/displacement coupling between FLUENT and Mechanical via Systems Coupling• Steady/static and transient two‐way FSI• Integrated post‐processing with CFD‐Post• Workbench based setup and execution

– Windows and Linux• Alternative execution from command line

– including cross‐platform• Parallel processing with ANSYS HPC

– RSM currently not supported• Restarts for fluid‐structure interaction• Parameterization, design exploration and optimization

Multiphysics and Systems Coupling – FSI

Non‐Newtonian blood flow through a three leaf mitral valve

© 2011 ANSYS, Inc. March 16, 201215

Two‐way surface force/displacement coupling between FLUENT and Mechanical via Systems Coupling• No special licensing required

– minimum ANSYS license must be Structural• Low and high order solid/shell elements

– SOLID185/186/187, SHELL181/281, SOLSH190• Compatible with multi‐point constraints

– Springs, joints etc. can be created in WB Mechanical UI

• All triangular and quad boundary meshes in FLUENT– No support for polyhedral or cut‐cell meshes

• Compatible with all mesh motion types in FLUENT• Mapping is fully conservative

Multiphysics and Systems Coupling – FSI

Transient one‐way (displacement only) and transient two‐way analysis of roller squeezing a flexible pipe ‐ Structural loading drives the fluid flow

© 2011 ANSYS, Inc. March 16, 201216

Multiphysics – 1‐way FSI

Significantly faster surface mapping for 1‐way FSI (CFD‐Post) β• New Octree mapping method significantly faster algorithm – Need to set Option in CFD‐Post

• 1‐way FSI in ANSYS Workbench uses CFD‐Post ‘under‐the‐hood’– Will use mapping option set by user in CFD‐Post (which is stored in user preferences)

– Status message with diagnostics report indicates new mapping method is being used

© 2011 ANSYS, Inc. March 16, 201217

Multiphysics – FLUENT‐Maxwell

Complex multiphysics modeling• New: Electromagnetic‐thermal interactions inside Workbench using FLUENT with Maxwell– One‐way and two‐way β coupling

• Combine with 1‐way FSI

β

© 2011 ANSYS, Inc. March 16, 201218

Solver and HPC Performance

Companies need to make informed development decisions about their increasingly complex products in increasingly shorter time frames.

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© 2011 ANSYS, Inc. March 16, 201219

Solver and HPC PerformanceHybrid initialization• Initialization procedure based on collection of recipes and boundary interpolation methods to obtain a reasonable initial flow field

• Hybrid initialization was made the Default initialization method for Single‐phase steady‐state flows.

The Default spatial‐discretization in the Pressure‐Based solver for single phase flow is now 2nd‐Order in R14.0 for:– Momentum– Energy– Density– Species

© 2011 ANSYS, Inc. March 16, 201220

Solver and HPC Performance RAE‐2822 AirfoilM=0.73AOA=2.8 deg

Standard @ CFL=200

HOTR @ CFL=200

Standard @ CFL=100

HOTR @ CFL=100

Normalized scales residuals comparing HOTR to standard relaxation at different CFL settings

Diverges

Higher Order Terms Relaxations– Under‐relaxation applied to higher‐order discretization terms.

– Improve solution convergence behavior– Can prevent apparent convergence stalling– Improve solution startup robustness

© 2011 ANSYS, Inc. March 16, 201221


Faster convergence on stretched meshes

• Convergence Acceleration for Stretched Meshes (CASM) with the density‐based implicit solver

• Use local cell CFL value based on cell aspect ratio.

• Recommended for:– Steady‐state simulations– Anisotropic meshes with high stretching in the local flow direction

– Stretched meshes with Y+ near 1

CdStandardCASM

Convergence acceleration for stretched meshes requires nearly 10x fewer iterations in this case

(300 vs. 3000 iterations)

RAE-Wing-body 5M=0.8AOA=2.0 deg

© 2011 ANSYS, Inc. March 16, 201222

Pseudo‐Transient Method– Under‐relax the transport equations by adding pseudo‐transient term

– Provide better convergence on anisotropic meshes

– Designed mainly for PB solver

Accelerated convergence for complex calculations

– Equation specific control for pseudo‐transient calculations (FLUENT)

– Accessed in the expert panel• Adjust the pseudo time‐step for that particular equation

• Disable pseudo transient for a particular equation and vary the implicit under relaxation factor.


FlowScalar tTSFt

© 2011 ANSYS, Inc. March 16, 201223


PBCS – Pseudo Transient off PBCS – Pseudo Transient fully on PBCS – Pseudo Transient on for all equations except species and energy

244 iterations

125iterations

66iterations

Mesh at inlet

The mixture injected into the channel expands by flowing over a backward step

Pseudo-Transient Method

© 2011 ANSYS, Inc. March 16, 201224

Solver and HPC PerformanceNon‐reflecting Boundary Condition in PB solver (beta):– Remove reflection from the outgoing waves– In R14.0 transient NRBC available on pressure‐outlet boundary for PB solver as well.

– Inviscid flow Equations are solved at the faces at the boundary• Normal components obtained from solution of the Local One Dimensional Inviscidrelations (LODI)

• While tangential components are computed based on gradients from adjacent cell

NRBC Without NRBC

© 2011 ANSYS, Inc. March 16, 201225


Improved scalability (FLUENT)• Scalability to higher core counts• Simulations with monitors including plotting and printing

Faster auto‐partitioning (FLUENT)• Optimized for multi‐core clusters • More constant time required with fixed overhead

Hex‐core mesh, F1 car, 130 million cellsmonitor‐enabled

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Example data for scaling with R14 monitors

3072 cores

© 2011 ANSYS, Inc. March 16, 201226

Comprehensive CFD Capabilities

Manufacturing companies today face many challenges, ranging from increased product complexity to tightened quality requirements to yield and productivity pressures.

As product complexity increases and the margin for error decreases, CFD must rise to meet growing demands for comprehensive and advanced product capabilities.

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© 2011 ANSYS, Inc. March 16, 201227

Comprehensive CFD – Motion

Improved accuracy with simplicity of immersed solids (CFX)• Addition of boundary model for more realistic velocity forcing with immersed solids– Track nodes nearest to immersed solid– Assume constant shear (laminar) or use scalable wall function (turbulent) to modify forcing at immersed solid ‘wall’

• Can improve immersed solid predictions significantly– Continuing development for further improvements and broader applications

Boundary-fitted mesh

Immersed Solid (default)

Immersed Solid with Boundary Model

© 2011 ANSYS, Inc. March 16, 201228

Comprehensive CFD – Interfaces

Easy simulation of opening and closing (CFX)• Conditional GGIs that can open and close selectively as the solution progresses

• Define condition as CEL function of solution– e.g. After set time, based on solution values (single or integral values)

• Example applications– Membranes bursting, windows shattering, valves opening/closing

• Define as reversible (e.g. valve) or irreversible (e.g. burst membrane)

© 2011 ANSYS, Inc. March 16, 201229

Comprehensive CFD – Motion

Further user control on deforming mesh to allow retention of optimal mesh quality (CFX) β• Diffusion of boundary mesh motion can be defined to be anisotropic – i.e. preferential diffusion in different directions

Sample case: Deformation of an originally square domain xy xy

Final mesh with isotropic diffusion: skewed elements

Final mesh with anisotropic diffusion: improved mesh quality, greater range of motion possible

© 2011 ANSYS, Inc. March 16, 201230

Comprehensive CFD – Dynamic Mesh

FLUENT MDM improvements• Retain and remesh boundary layers during tetrahedral remeshing– Boundary layer settings from original mesh

– Example applications: internal combustion engines and FSI

• Improved robustness and usability for dynamic mesh – Mesh smoothing– Cut cell remeshing– Parallel efficiency– Support for dynamic mesh on meshes with polyhedral elements

T=0 T=25 T=50

Tetrahedral mesh with boundary layers after remeshing

Remeshing a tetrahedral mesh with boundary layers during a simulation

© 2011 ANSYS, Inc. March 16, 201231

Comprehensive CFD – Turbulence

Focus on wall treatment accuracy (FLUENT)• More accurate rough wall treatment for epsilon‐based models – Avoids reduction in roughness when the near‐wall mesh is refined

– New default for all simulations using rough wall treatment

• Reduced sensitivity to the near‐wall mesh density for the Spalart‐Allmaras model– New enhanced wall treatment is the default for S‐A turbulence model

Turbulent flow over a flat plate with roughness and heat transfer

R14 wall treatment R13 default treatment

Sensitivity of the skin friction coefficient to mesh density in an incompressible flat boundary layer modeled with Spalart‐Allmaras

© 2011 ANSYS, Inc. March 16, 201232


Improved accuracy for turbulent flows with strong rotation and streamline curvature with one and two‐equation models (FLUENT)• Option to apply a correction term sensitive to rotation and curvature

• Accuracy comparable with the RSM, with less computational effort, for swirl‐dominated flows

• TUI command under turbulence‐expert

Contours of curvature correction function (fr) in a curved duct (k‐omega SST turbulence model)

© 2011 ANSYS, Inc. March 16, 201233

Comprehensive CFD – Porous Media

Improved accuracy for turbulence near porous jump interfaces (FLUENT) β• Use wall functions to include the effects of solid porous material on the near‐wall turbulent flow on the fluid side of porous jump interfaces

• In the momentum equation, the wall shear stress is introduced at the interface

Contours of velocity showing the impact of a porous jump on velocity in bordering cells

© 2011 ANSYS, Inc. March 16, 201234


More accurate solution of high Re wall bounded flows using LES (FLUENT)• Algebraic Wall Modeled LES (WMLES) formulation based on Smagorinskymodel

Apply scale‐resolving turbulence models only locally, as required, to balance cost vs. accuracy (CFX) β• Zonal LES model using turbulence forcing• Forcing zone defined by logical CEL function

Flow over a wall mounted hump

Contours of Q criterion

A mixing layer with resolved turbulence using SAS initiated by the forcing model

© 2011 ANSYS, Inc. March 16, 201235


Other Turbulence Enhancements (FLUENT)• Time statistics data sampling time displayed in GUI

• Turbulence dissipation rate () variable for omega‐based turbulence models available in CFD‐Post

• Reynolds stress normal components accessible via UDF– Eliminates need to compute Reynolds stress normal components from scratch in a UDF

© 2011 ANSYS, Inc. March 16, 201236

Comprehensive CFD – Acoustics

Validations and model extensions (FLUENT)• Convective effect for FW‐H acoustics solver– Option to include the effect of far‐field velocity on the generated sound for the Ffowcs‐Williams & Hawkins solver

• Model Doppler effects due to the relative motion of acoustic sources and receivers – For example: Sound from a source moving with a constant speed (airplane, car)

M=0.2

FWH source surface,R=1m

Receivers, R=3m

2D monopole with convection

OASPL – overall sound pressure level

M=0.4Moving receiver

SourceSound pressure compared with analytic solution at approach and departure (Doppler effect different frequencies)

Acoustics directivity

© 2011 ANSYS, Inc. March 16, 201237

2x2 3x3 6x6

Serial/Old 218.63 s 269.95s 536.32s

Serial/New 202.40s 241.56s 429.40s

Parallel 2‐proc/Old

86.4s 107.4s 205.3s

Parallel 2‐proc/New

80.7s 98.4s 167.2s

Comprehensive CFD – Radiation

More Efficient Discrete Ordinates Radiation (FLUENT)• DO radiation calculations ignore solid zones not participating in radiation or participating in heat transfer by conduction only

• Avoids unnecessary CPU time and memory allocations• Performance improvement varies depending on specifics of case– Up to 20% improvement for test cases

Sample data for a 3D case with 5 solid zones

© 2011 ANSYS, Inc. March 16, 201238

Comprehensive CFD – Shell Conduction

Shell conduction: Improved accuracy and ability to include combustion (FLUENT)• Non‐premixed and partially‐premixed combustion models

Improved shell conduction usability (FLUENT)

• Updated documentation for wall temperature variables and shell zone and thin wall post‐processing

• Post‐process the external wall temperature if shell conduction is applied on a one‐sided‐wall

case where solid zone is resolved using a single layer of cells

case with shell conduction

Temperature on Mid Plane

The 300KW BERL combustor

© 2011 ANSYS, Inc. March 16, 201239

1D Reacting Channel Model (FLUENT)

• Model fluids reacting in thin tubes, which exchange heat with an external flow– Flow inside the tubes is simple (pipe profile), but the chemistry is complex

– Flow outside the tubes is complex, but the chemistry is usually simple (equilibrium)

• Example applications: cracking furnace, fuel reformers, …

Comprehensive CFD – Reacting Flows

1D reacting channel geometry in Fluent

© 2011 ANSYS, Inc. March 16, 201240

1D Reacting Channel Model (FLUENT)• Must resolve the outer‐diameter of the channels• No mesh inside the channels• Channels can be curvilinear• The channel can have variable cross‐section• Detailed chemistry in the tube (plug flow)


Bulk Mean Temperature

Channel wall Temperature

Two reacting channels with different materials with non reacting outer flow.

Results of the channel model are compared with full simulation (mesh inside Channels is resolved)

© 2011 ANSYS, Inc. March 16, 201241


Focus on Validation and Verification (FLUENT)• Real gas models:– RCM1, RCM3

• Surface chemistry model:– Kleijn CVD

• Turbulent non‐premixed flame model: – Sydney bluff body flame

• Turbulent premixed flame model:– Chen F3

Example simulation results for the Kleijn CVD verification for surface chemistry

© 2011 ANSYS, Inc. March 16, 201242


Other improvements (FLUENT)• Surface chemistry robustness• UDF hooks for PDF table• Tabulated laminar flame speeds in partially‐premixed PDF table for non‐adiabatic

• Chemically‐Activated bi‐molecular reactions

• Local diffusion for spark model• Real gas with partially‐premixed model

© 2011 ANSYS, Inc. March 16, 201243

Adjoint Solver

Adjoint Solver for FLUENT ‐ fully tested, documented, and supported at R14.0

• Provides information how you should modify your geometry to achieve your design goals in a single simulation

• Computes the derivative of an engineering quantity with respect to inputs for the system

• Engineering quantities available– Down‐force, drag, pressure drop

• Robust for large meshes– Tested up to ~15M cell

Shape sensitivity to down‐force on a F1 car

Shape sensitivity to lift on NACA 0012

Lift Force (N)Geometry Predicted ResultOriginal ‐‐‐ 555.26Mod. 1 577.7 578.3Mod. 2 600.7 599.7Mod. 3 622 621.8

© 2011 ANSYS, Inc. March 16, 201244

Adjoint Solver

Workflow• Pick an observation that is of engineering interest.

Lift, drag, total pressure drop• Set up and solve the adjoint problem

Define solution advancement controls Set convergence criteria

• Post-process the adjoint solution to get Shape sensitivity Sensitivity to boundary condition settings Contour & vector plots

Specify Observables

Define Advanced ControlsAdjointResidual Monitors

© 2011 ANSYS, Inc. March 16, 201245

Applies a geometric design change directly to the mesh in the solver

Uses a Bernstein polynomial‐based morphing scheme• Freeform mesh deformation defined on a matrix of control points leads to a smooth deformation

• Works on all mesh types (Tet/Prism, CutCell, HexaCore, Polyhedral)

User prescribes the scale and direction of deformations to control points distributed evenly through the rectilinear region.

Mesh Morpher and Optimizer

Application: L-shaped ductObjective Function: Uniform flow at the outlet

Significant Improvement in Flow Uniformity

© 2011 ANSYS, Inc. March 16, 201246

FLUENT Mesh Morpher and Optimizer• Create your own optimization functions using parameters, no need for UDF

• Faster mesh deformation• Constrain some boundaries and allow others to deform

• More easily assess the effectiveness of the optimization routine– Save and plot the value of the objective function as a function of design iteration number

• Execute TUI commands before and after the optimization loop

Objective function definition panel

Example data showing faster mesh deformation

Objective function as a function of design stage

Mesh Morpher and Optimizer

© 2011 ANSYS, Inc. March 16, 201247

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Adjoint Solver with Mesh MorpherExample Test Cases – Internal ducting U bend

Base design End design

© 2011 ANSYS, Inc. March 16, 201248

Multiphase Flow Modelling

Many industrial processes involve the simultaneous flow of multiple phases.

Most of these processes are impossible to observe directly. Therefore, engineers rely on models and experiments to gain insight into improving the efficiency, throughput, safety and reliability of their processes.

Courtesy of Petrobras

© 2011 ANSYS, Inc. March 16, 201249

→ Efficient modeling of poly‐disperse systems

→ Enhanced mixed mode (Eulerian andLagrangian) models

→ Enhancements to boiling models

→ Numerical enhancements for robustconvergence

Multiphase Drivers for R14

© 2011 ANSYS, Inc. March 16, 201250

Framework to track a dispersed phase in a Lagrangian manner• Account for the presence of the dispersed phase in the equations of motion for the primary phase

• Treat fluid‐particle interactions in an efficient manner

Particle‐particle interactions• O’Rourke collision/coalescence model for droplets• Expression for solid pressure – KTGF • Explicit particle interaction – DEM

Efficient for poly‐disperse particles

The DDPM Model

KTGF based collision

DEM based collision

© 2011 ANSYS, Inc. March 16, 201251

Model dense particulate flows with DEM (FLUENT)• DEM enabled as a collision model in the DPM model panel

• Use in combination with single phase and DDPM simulations

• Fully parallelized (insensitive to partitioning)• Particle size distributions• Prediction of the packing limit• Soft sphere collisions with P‐P and P‐walls• Better particle tracking algorithms• Works with all mesh types

Multiphase – DEM

© 2011 ANSYS, Inc. March 16, 201252

Multiphase – DEM

3% fines start‐up ‐15 sec

and 15‐30 sec

Note that channeling is observed in the 15‐30 sec animation

NETL Fluidized Bed Simulations using DEM with DDPM

12% fines0‐25 sec

A blind challenge problem on modeling a bubbling fluidized bed of FCC particles with a Particle Size Distribution

We present results here with the DDPM + DEM model with the R14 enhancements.

Able to simulate 16s of flow time in a day on 12 processors with a complete PSD

© 2011 ANSYS, Inc. March 16, 201253

Other DDPM‐DEM Examples

Settling regime of a liquid particulate flow

Fluidization in a bedcontaining internal walls

Flow of particles in a hopper

Flow rate of particles in a hopper independent of material head

© 2011 ANSYS, Inc. March 16, 201254

0.00E+00

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Diffusion‐controlledConvection Diffusion‐controlledExperimental Data – symbols

Multiphase – DPMAccuracy and robustness improvements

• Accurate heat and mass transfer for low and high evaporation rates in the same simulation (FLUENT)– Convection/Diffusion controlled vaporization

• More accurate modeling for high Weber number sprays (FLUENT)– Stochastic Secondary Droplet Breakup Model (SSD)

• Improved tracking for DPM with moving and deforming meshes (FLUENT)– Particles are tracked in the cells deformed/moved each time step

Single droplet experiment of Wong‐Lin

Hiroyasu spray bomb, p = 5 MPaspray penetration of 95% mass content

© 2011 ANSYS, Inc. March 16, 201255

Multiphase – DPM

Node based averaging of DPM source terms and DDPM volume fraction (FLUENT)• Standard averaging dumps all volume fraction into one cell

• Node based averaging distributes volume fraction over several cells by collecting data on mesh nodes

• Reduces grid dependency• Improves convergence behavior for steady simulations

• Allows for larger time steps in transient simulations

• Requires more memory

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volume fractionnode based average

© 2011 ANSYS, Inc. March 16, 201256

Multiphase – DPM

Easily replicate particle or droplet injection at different locations or in different directions (CFX)• Specify local coordinate frame for each Particle Injection Regions (PIR)

• Much more convenient for set‐up of large numbers of PIRs– Applications with multi‐port fuel injection, spray dryers, scrubbers, etc.

Directly specify swirling injection at PIRs (CFX)• Use CEL to flexibly define cylindrical components as f(position, time, …)

• Includes extension to LISA model for pressure‐swirl atomizers

© 2011 ANSYS, Inc. March 16, 201257

Multiphase – DPM

Generate additional particle data output for further analysis (CFX) β• Frequency distributions of particle quantities at boundaries to *.csv for histograms in CFD‐Post or elsewhere

• Wall particle monitoring per patch– Instantaneous and time‐integrated

Extend models with algebraic Additional Variables for particles (CFX) β• Analogous to fluid AVs

Time-integrated mass of particles

hitting a wall

Histogram of particle size distribution at an outlet

© 2011 ANSYS, Inc. March 16, 201258

Multiphase – DPM

Easier analysis and visualization of particle data (FLUENT)• Display sizing by diameter• Display vectors/cylinders on particles to indicate a direction of velocities, forces, etc.

• Filter particle display to view only a small part of particle tracks

Enhanced FLUENT particle track post‐processing (CFD‐Post)• Vector variables and sizing by diameter

Particles where sphere size changes with diameter and particle velocity vectors

Particles filtered by flow velocity between 10 and 11 m/s

© 2011 ANSYS, Inc. March 16, 201259

Multiphase – Free Surfaces

Better robustness and faster convergence for free surface steady‐state cases using coupled VOF (FLUENT)• Solves the momentum, pressure based continuity and volume fraction equations together through implicit coupling

• Aims to achieve faster steady state solution compared to segregated method of solving equations

Coupled VOF after 500 iterations

Coupled P‐V, Segregated VOF after 1400 iterations

Wigley Hull example

© 2011 ANSYS, Inc. March 16, 201260

•Select “Coupled” scheme as Pressure-velocity Coupling• Enable “Coupled with Volume Fraction” option

“Volume Fraction Courant Number ” provides the additional implicit under-relaxation for VOF equation.

TUIBody force linearization

Coupled VOF Solver

Options for trade-off between stability and accuracy (FLUENT)

Hybrid treatment of Rhie-Chow face flux interpolation with special treatment near free surfaces

© 2011 ANSYS, Inc. March 16, 201261

Multiphase – Free Surfaces

Continuum surface stress method for surface tension flexibility (FLUENT)• Surface tension as a function of any variable• Alternative to existing CSF model in some difficult cases– For example: cases with sharp interface discontinuities Sample data: surface tension and viscosity

as a function of temperature

Experiment image compared to Fluent results. Image from: Thermally Induced MarangoniInstability of Liquid Microjets with Application to Continuous Inkjet Printing by Furlani et al.

Movement of free surface due to contact angle is consistent with CSS method compared to CSF method.

Capillary Flow - Grid independent study

© 2011 ANSYS, Inc. March 16, 201262

Overview of boiling models available in FLUENT14

We have three different models available in R14

RPI Boiling model• Applicable to subcoolednucleate boiling

Non‐equilibrium Boiling• Extension of RPI to take care of saturated boiling

Critical Heat Flux• Extension of RPI to take care of boiling crisis

© 2011 ANSYS, Inc. March 16, 201263

Boiling Model Enhancements

Critical Heat Flux (CHF) modeling• Boiling in a vertical pipe with large heat fluxes• Causes burn out of the liquid film next to the wall• Flow transitions from bubbly to mist flow

The CHF model• Accounts for correct heat transfer partitioning at CHF conditions

• Accounts for the variations of drag and interfacial quantities to move from bubbly to droplet regime

Axial Position (m)

Wal

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Inlet mass flux 1495 kg/m2sQwall = 797kw/m2

Hoyer’s et. al

© 2011 ANSYS, Inc. March 16, 201264

Multiphase – Eulerian

Boiling model extensions, and testing (FLUENT)• Boiling with bubble size distributions using interfacial area concentration (IAC) models (FLUENT)• Accurate interfacial areas for heat and mass transfer calculations in non‐equilibrium boiling conditions

• Extensions to MuSiG model in CFX (β)– Homogeneous and inhomogeneous MuSiG in combination with phase change and RPI wall boiling model

• Example applications: Nuclear industry, engine jacket cooling

IAC gives variation of bubble diameter

Bubble diameter at different stations along the pipe

Simulation and comparison with experimental results from TOPFLOW Test Facility, courtesy of HZDR (formerly FZD)

© 2011 ANSYS, Inc. March 16, 201265

Multiphase – Eulerian

Improved numerical stability for user‐defined mass transfer with compressible phases (FLUENT) • Linearized option for user defined mass transfer also allows larger timesteps

New Hulin‐Gidaspow and Gibilaro drag laws for granular flows (FLUENT)• Modified Huilin‐Gidaspow drag allows smooth transition from dilute to dense limit, improving numerical behavior

• Gibilaro drag law for fluidized beds provides a better representation of physics in these cases

Cavitation in a nozzle using linearized mass transfer

vof of liquid

Absolute pressure

The problem does not converge without linearization

© 2011 ANSYS, Inc. March 16, 201266

Multiphase – Eulerian Wall Film

Eulerian Wall Film Model for rain water management, deicing and other applications • Available models:– Momentum coupling– DPM coupling

• Particle collection, splashing and shearing

– Heat transfer

Contours of temperature in an Eulerian Wall Film with heat transfer case

film

Q = 3000 W

airsolid

liquid water injected

KCmQT

Pfilm 75

400001.03000

The wall film on a car mirror withdroplets released due to wind shear

© 2011 ANSYS, Inc. March 16, 201267

Multiphase – Population Balance

DQMOM Population Balance captures the segregation of poly‐dispersed phases due to differential coupling with the continuous phase (FLUENT) • Faster solution time than the inhomogeneous discrete model

• Multi‐fluid model convects different dispersed phase sizes using different velocities

• Example applications: Fluidized beds, gas solid flows, spray modeling, bubble columns

Velocity big bubbles > velocity small bubbles

All bubbles move with same velocity

DQMOM QMOMg

Bubble diameters for DQMOM (white) compared to QMOM (red)

Contours of volume fraction of the phase with the largest diameters in a bubble column.

© 2011 ANSYS, Inc. March 16, 201268


Model diameter and other variable changes (bin fraction, moments) due to density changes in the dispersed phase (FLUENT)• Compressible dispersed phase• Example applications: Geophysical flows, oil and gas flows, compressible flows with population balance

Model growth and nucleation with the inhomogeneous discrete model (FLUENT)• Example applications: Crystallization, bubble columns with mass transfer

Effect of expansion on bubble diameter in bubble column with discrete method: Monodispersedbubbles injected at bottom and results compared with analytical diameter (in white)

© 2011 ANSYS, Inc. March 16, 201269


Ease of use for DQMOM problems• Cumulative size distribution of droplets at inlet available

• It is desired to convert the size distribution into inputs required by DQMOM (volume fraction and moment values)

• Use the “Generate DQMOM Values” to obtain relevant inputs for DQMOM

Modeling spray injection using DQMOM

Shape of the spray

© 2011 ANSYS, Inc. March 16, 201270

• Hydrodynamic Time Response system enhancements include– Fenders (similar to contact)

• Allows connections between 2 structures or between a structure and a fixed point

– Articulations (similar to joints)– Connection points on structures now defined in AQWA, not in original geometry

Enhanced Productivity with Continuing AQWA Integration in Workbench

Offloading arm represented with series of typical articulations

© 2011 ANSYS, Inc. March 16, 201271

AQWA Enhanced Environmental Conditions

• Introduction of multi‐directional wave spectra allows more realistic modelling of real wave conditions, and is important for the accurate simulation of moored vessels and offshore platforms– Almost any combination of wave spectra to be modelled in the solver modules LIBRIUM, DRIFT and the Hydrodynamic Time Response system in Workbench

• Gaussian formulated wave spectrum now available in the core solver and the Hydrodynamic Time Response system

© 2011 ANSYS, Inc. March 16, 201272

• Inclusion of linearized drag on Morison elements in Diffraction/Radiation analysis– Determined using a user specified wave spectrum.

– Computation of modified RAOs using the additional drag.

– SF/BM plots can now be made on models including Morison elements (and not just ship shaped).

– Used in design wave calculations for mixed models e.g. truss spar.

AQWA Frequency Domain Drag Linearization

Courtesy of Technip Offshore Finland

© 2011 ANSYS, Inc. March 16, 201273

ANSYS Fluid Dynamics 14 contains enhancements in all products…• ANSYS FLUENT• ANSYS CFX• ANSYS CFD‐Post

… for workflow and usability, HPC and solver speed, systems coupling and multiphase applications as well as to provide comprehensive CFD.

Summary

ansys 14.0: fluid dynamics for the industry 14.0... · fluent and cfx will continue to be developed...

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