2.1 CFD PROJECT PLANNINGusers.abo.fi/rzevenho/CFD_Mgrs_02_Proj_Man.pdf · Import / build geometry...
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© 2006 ANSYS, Inc. All rights reserved. ANSYS, Inc. Proprietary 2.1 CFD PROJECT PLANNING
Transcript of 2.1 CFD PROJECT PLANNINGusers.abo.fi/rzevenho/CFD_Mgrs_02_Proj_Man.pdf · Import / build geometry...
© 2006 ANSYS, Inc. All rights reserved. ANSYS, Inc. Proprietary
2.1
CFD PROJECT PLANNING
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Fluent User Services Center
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CFD for Managers
February 2008
CFD PROJECT PLANNING
Task definition
Resources
Timing and deliverables
Design review
Assumed part of bigger engineering project, but same
principles apply to stand-alone consultancy
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Fluent User Services Center
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CFD for Managers
February 2008
TASK DEFINITION
How can we break a CFD job into activities?
How can work be shared?
How do we measure progress?
What are the inputs and outputs for each task?
Where can bottlenecks occur?
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CFD for Managers
February 2008
Generic CFD project plan
CFD project activities are serial in nature
Not all activities are full-time: share time across projects
TASK RESOURCE TIME
Define objectives Consultative
Define model features / physics Modeler
Define geometry Engineer / consultative
Define inputs (prelim calcs) Engineer / modeler
Import / build geometry CAD op / modeler
Build mesh Modeler
Specify physical model Modeler
Specify boundary conditions Modeler
Solve equations Modeler, part-time
Post-process / export data Modeler / consultative
Review results Eng / mod / cons
Write report Modeler
Store / archive Modeler
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February 2008
Objectives - 1
Objective should never be “to do a CFD model” -
unless you just want some colour pictures!
Discuss the objectives with the modeler, explaining
the engineering context and the accuracy required
Get the modeler’s agreement to provide the specific
information that you need
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February 2008
Objectives - 2
Clear and precise quantitative questions:
What is the pressure change from A to B?
What are the heat transfer coefficients on surface C?
What are the forces acting on body D?
What is the air-fuel unmixedness at plane E?
Qualitative studies are OK, if you know what to do
with the results!
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February 2008
Define model features/physics
Many physical modelling options provided in Fluent
Selection by default adequate for many users
Adopt “cook-book” approach for similar jobs
Turbulence model, fluid properties should always be considered
Non-standard physical models require UDFs - add
greatly to project workload
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CFD for Managers
February 2008
Geometric information
Identify source of geometry to be modeled
Select an appropriate calculation domain
Omit irrelevant geometrical detail
Do not omit details which you know to have an
important effect in reality
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CFD for Managers
February 2008
Inputs and preliminary calcs
Good input data for CFD calculation are vital to success
Flow rates, velocity distributions, boundary pressures, temperatures
Usually necessary to make estimates or “hand calculations” for
some quantities
Turbulence data hardly ever known
Discuss source of input data with modeler
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CFD for Managers
February 2008
Geometry building
Maybe the biggest single task in a CFD job
CAD import can be effective, but clean-up can be time-
consuming
Ask the CFD modeller to explain his requirements to the CAD
operator before the CAD model is created
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CFD for Managers
February 2008
Mesh generation
Often the biggest single task, but increasingly automated
Plan the mesh - type, overall structure, size requirements
Decide how mesh is to be built up from geometry, and required
sequence of operations
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February 2008
Physics and boundary conditions
Menu selection and data input process
The most common source of errors in carrying out a job
Good preparation essential - prepare data and do preliminary
calculations before starting to input boundary conditions
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CFD for Managers
February 2008
Solution
Can be easy or time-consuming, but not normally a full-time job
Solver optimised for standard flow equations on good quality mesh
Large source terms in equations tend to make solution more difficult:
eg. buoyancy, chemical heat release, radiation
Resist temptation to tweak solver controls (under-relaxation) unless
necessary
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CFD for Managers
February 2008
Post-processing and data export
Post-processing necessary to
verify solution quality
understand qualitative aspects of flow
determine answers to objective questions
produce material for reports
Data can sometimes be exported directly for further analysis
eg. boundary conditions for stress analysis
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CFD for Managers
February 2008
Reporting
Conform to requirements of QA system
State objectives
Identify source of data and preliminary calculations
Identify code, version, modelling options selected and reasons
why
State important results
Provide details of archive/data storage
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CFD for Managers
February 2008
Storage/archive
Media incompatibility a major challenge
Magnetic media (tapes, disks, cartridges) have life limitations
CD or DVD-ROM recommended current option
Store one copy with project file
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CFD for Managers
February 2008
Resources
Human resources
CFD skills and experience
Management
Computers
Software
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CFD for Managers
February 2008
What makes a good CFD modeler?
Good fluids engineering background
recognises and understands fluid behaviour
relates to engineering objectives and context
able to read and interpret drawings/CAD!
Basic understanding of CFD principles
Able to think and work in 3D
Trained and experienced in use of software
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February 2008
Who can do CFD?
Many activities do not require specialist
Software improvements and on-line support are aimed at “de-skilling” CFD
Definition of problem and analysis of results requires fluid dynamics
know-how
Use of CAD operators and stress analysts is feasible, but close
supervision by fluid dynamicist is almost essential
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February 2008
Management of CFD
CFD is not an exact science:
Basic equations correct, but turbulence modelling approximate
Finite mesh size limits accuracy of solution
Experience and know-how needed to interpret solution and judge
quality
Important role for technical management
Make effective use of Fluent Support and other external resources
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February 2008
Computers
Affordable computer hardware now up to the job
Clusters, workstations, top end PCs (Win-32, Win-64, Linux)
1M+ computational cells the norm
Typical need is 1Gb RAM for 1M cells
BUT REMEMBER
Design the job to fit the computer!
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February 2008
Software
The choice is obvious . . .
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February 2008
Timing and Deliverables
Time estimation
Milestones
Managing the processes
The unforeseen
Job completion
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February 2008
Time estimation
Time-consuming activities are skills-based
plan according to the individual
Base estimates on experience of similar job
Uncertainties usually occur due to geometry creation and mesh
generation
Slippage most frequently results from rework due to inadequate,
incomplete or changing data
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February 2008
Milestones
Major milestones used to measure progress
Data and geometry complete
Mesh complete
Solution converged
Project complete
Final deliverables
Fluent data files
Answers to objective questions
Report
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February 2008
Managing the processes - 1
Attempt to define standard approach
QA procedure, best practice guidelines
Resist temptation for modeler to try the effects of different
options!
“Data matching” encourages this tendency
Grid refinement, validation and calibration should be carried
out separately, not as a normal part of an engineering project
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February 2008
Managing the process - 2
Get the modeler talking to the engineers
explanation uncovers errors
Manage data exchange between the modeler and other team
members
use engineering co-ordination memo or similar configuration control
system
Don’t get blinded by science!
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February 2008
The unforeseen
Turbulence models are inexact
Fluid dynamics is non-linear
chaotic behaviour can result!
Even the best software can contain bugs
impossible to test all combinations of options
Critical changes can occur at a late stage
…… so allow reasonable contingency - it is often necessary to repeat
parts of work
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February 2008
Job completion
Reporting and archiving essential tasks
generally high turnover of CFD staff
difficult to pick up someone else’s model without notes
Typically 20% of project remains after converged solution obtained
post-processing, report, review, presentation
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February 2008
DESIGN REVIEW
Purpose
Content
Reviewers
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February 2008
Purpose of Design Review
To verify that:
calculations were fit for purpose (ie. appropriate to original objectives)
model conforms to intent, and free from obvious errors
results have been interpreted correctly
To review and ratify engineering implications of results
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February 2008
Design review content
Presentation of model
Physical models, critical areas of mesh, boundary conditions
Presentation of results
Overall fluid behaviour, key objective results
Summary of engineering implications
Critical discussion
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February 2008
Reviewers
Engineering and CFD know-how required
hard in many organisations to provide both
key questions relate to quality, uncertainty, and best practice
“engineering judgement” has important role
ANSYS Fluent can provide resource to contribute to either side
of review process
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CFD for Managers
February 2008
Summary
Guidelines offered for project managers in handling CFD tasks
CFD is not fundamentally different from many other technically
challenging tasks
beware of the specialist!
ANSYS support and consultancy services are available to help
