This viewgraph presentation gives a profile of Advanced Scientific Computing (ASC) Ltd., applications, clients and clients' needs, ASC's directions, and how the Center for Modeling of Turbulence and Transition (CMOTT) can help

Mueller, C. M.

Raw, M. J.

Vandoormaal, J. P.

English

NASA Technical Reports Server

TURBULENCE REQUIREMENTS OF A COMMERCIAL CFD CODE
J.P. Van Doormaal, C.M. Mueller, and M.J. Raw
Advanced Scientific Computing Ltd.
Waterloo, Ontario, Canada
N95- 27897
Outline
• Profiles
- ASC
- Application
- Client
• Needs
Clients'
ASC's
• ASC Directions
- Research
- Development
- Products
• How Can CMOI-I- Help?
193
https://ntrs.nasa.gov/search.jsp?R=19950021476 2020-06-16T08:03:51+00:00Z
Profile of ASC
• Established in 1985
• Components of business
- development
- applications
licensing and service
• Geographic markets
- North America
- Europe
- Pacific rim countries
Application Profile
Rotating machinery components
hydraulic turbines
pump
- compressors
- turbines
- stators
wicket gates
scrolls
- volutes
- inlets and diffusers
- seals
- stage
rotor stator
194
Application Profile cont'd
• Combustion
- gas turbine combustor
coal fired boilers
gasification
- fire suppression
- emissions reduction
- safety
• High speed external- ballistics
- explosively formed projectiles
- finned projectiles
sabot discard
Heat transfer
- turbine cooling
- nuclear reactors
heat exchangers
electronics system cooling
Typical uncertainties
- geometry
- initial and boundary conditions
- transient effects
- transition
- limitations of physical models
- numerical error
195
Client Profile
o Companies or divisions
-industrial/manufacturing/research
- 10 - 200 employees
- limited or no access to high
performance computing
o Users
design and/or analysis
- < 3 people
- network of engineering workstations
- turnaround time in less than a day
for analysis, hours for design
Clients' Needs
Needs are most readily identified through typical
questions from clients.
o General
- I am using k-E or two-layer or k-e), or RNG .... what does it
mean to my calculation? Tell me in words what the deficiencies
of the model means for my application?
- What is the relative price/performance of the various turbulence
models?
- Has the model I am using been validated for type of flows I am
trying to model? If so, when, where, how ... ?
How well does the model handle the interaction between
turbulence and rotation, curvature, adverse pressure gradients,
separation, swirl, bouyancy, extinction, droplets and particles,
anisotropies ...?
- How can I use Navier-Stokes solvers for design? Can I tune the-
turbulence model to suit my needs? If so, what are the
appropriate settings for my application?
196
Clients' Needs cont'd
• Grid
- I don't have access to high performance computing, I
don't have any more time, i have a coarse non-
orthogonal mesh, is my CFD result useful?
I have just made my grid finer, why should I have to
worry about whether y+ is in a given range?
• High speed flows
I am solving a flow with many speed regimes including
low speed separations and shocks, why do turbulence
levels become unp.hysical as the grid is refined through
shocks?
- How should experimental data be compared to results
from time or Favre averaged calculations?
Clients' Needs cont'd
Combustion
Which of the many different combustion models in
combination with which turbulence model works best for
my application?
How appropriate is the single scale implicit in the
turbulence model for the combustion model?
How can the Bousinesq assumption be valid in the
presence of counter-gradient diffusion?
How important are turbulent fluctuations to my problem?
If I had all the mean flow and fluctuating components of
the the turbulent flow, how can the effects of stretch and
curvature on the instantaneous flame front be modelled.
Can extinction due to vortex stretching be modelled?
What is the influence of the flame front on the turbulence?
197
Clients' Needs cont'd
Calculated pdf models
If I use a more detailed chemistry model - like a pdf
transport model - how much lmprovementcan I expect in
the results for my application? How can I measure that?
- Is it the case that the results for my application will not be
sensitive to the shape of the pdf? If not, then why should I
incur the costs associated with a pdf transport equation.
- i am solving a pdf transport equation, how much are the
results dominated by the limitations of modelling of the
diffusion transport term?
Clients' Needs cont'd
Flamelet models
- I am using a flamelet model in modelling my gas turbine
combustor, but in some regions of the combustor the
model is not strictly appropriate - can any of the results
be used? If so, how much?
In some models like the flamelet model, it is assumed
that the turbulent time scale is inversely proportional to
the velocity gradient of a "laminar" model flame. What is
the validity of this assumption?
How sensitive are my results to the assumption of
statistical independence of the quantities in a joint pdf?
198
ASC's Directions
• Develop in-house model expertise
two-layer model
- alternative two-equation models
- second moment closure models
- expanded EBU models
flamelet model
• Develop in-house expertise applying models
turbomachinery
combustion
heat transfer .
• Promote high performance computing
parallel computing
How Can CMOTT Help?
Model improvements to
address between
turbulence and
rotation
curvature
adverse pressure
gradients
separation
swirl
bouyancy
- droplets and particles
- anisotropies ...
as well issues related to
extinction
trace species
vortex stretching
flame fronts
time and length
scales
,,.
• Great, but is this what
users really want?
199
How Can CMOTT Help? cont'd
• Curator of information on existing
models
- define
- validate
- process
- educate
as an independent agency
How Can CMOTT Help? cont'd
Define models
- unified conceptual framework
- establish baseline for various
models
- set context for model improvements
- for each model
> document derivation
> identify assumptions
> clearly state implications of assumptions
> separate physics from numerics
2OO
How Can CMOTT Help? cont'd
Validate models
- fundamental flows
> validate assumptions
- benchmark problems
> select real engineering problems
relevant to identified applications (in
propulsion)
> review selection of benchmark on
regular basis
- experimental data
> collect and review existing data
> define new experiments
> review quality of resulting data for
validation of models
How Can CMOTT Help? cont'd
Process data
- collect
- distil
- review
-interpret
- describe
- compile
201
How Can CMOTT Help? cont'd
Educate
- document
- publish
- workshops
- seminars
- short courses
- market
Summary
Provide information so users, for their
applications can:
• make an educated choice of model
• understand how to appropriately use
existing models
• move forward with existing models and
technology
• understand implications of
improvements to existing models
202


Turbulence requirements of a commerical CFD code

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