CFD’s Expanding Role

By Pamela J. Waterman

A  simple yet critical explanation for the increased use of CFD  software lies in the fact that computer systems continue to become  faster and cheaper. Five years ago, we devoured Pentium 4s at 2GHz with  256MBmemory and some parallel-processing capabilities. Now it’s easy to  tap the resources of 64-bit dual and quad processors humming at  2.66GHz.Desktop systems boast 1GB memory along with multi-threading  and distributed processing, while analysis programs “farm” their tasks  out simultaneously to Unix, Linux, and Windows platforms.

Why is this  increased power so important? All CFD problems are nonlinear, which  immediately makes their solutions more processor and memory intensive  than basic FEA computations. Fully defining the problem means defining  data sets that include not only the object (to capture details of the  interaction), but its “reverse volume,” either internally or to some  distance around it. Add turbulence and unsteady conditions, and any  advances in computing offer immediate benefits in CFD speed, efficiency,  and overall performance.
 
Bob Williams, ALGOR’s product manager,  explains typical expectations.“Designers and engineers have gotten used  to the fact that most linear static stress and heat transfer analyses  run in minutes,” he says,“even with large complex models. They also  understand that moving into complex analyses like CFD would often take  longer. But now, analyses that used to take one week, run overnight; and  analyses that used to take eight hours, run in two hours.”

< < This Fluent simulation of the flow of air through the under hood  region of a pickup truck is used to identify hot regions so that the  cooling fan can be designed accordingly. The complexity of the geometry  is indicative of the models being solved by engineers today.  Parallel computing has made it possible to simulate problems like this  that involve complicated geometry and a range of physical  models.Post-processed by FIELDVIEW from Intelligent Light.

Meshing  tools have also changed. Dennis Nagy, CD-adapco vice president of  marketing and business development, says that meshers have  improved across the board, making them accessible to a broader range  of engineers.
 
“What was trail-blazing 10 years ago is now  routine,” says Nagy. “Right now we might be able, with a 100  million-cell polyhedral model, to get an answer that’s as accurate as a  billion-cell tetrahedral model.”
 
Other options that have arrived  due to increased computing power include online subscription-based  access to CFD services from such companies as ANSYS, CHAM, and Fluent,  and the opportunity to harness the power of supercomputing resources  (see sidebar “Super Power for Everyone"below).

TurboTax for Designers   

Just  as you don’t need to be an accountant to use TurboTax software,you  don’t need to be an analyst with a Ph.D. to use many of today’s  CFD packages. Ed Fontes, COMSOL vice president of applications, points  out that CFD used to be done at a central research facility by  specialists versed in a particular software package. He notes that now,  “CFD is reaching all levels of product and process design and control,  and is becoming popular even for freshmen at engineering schools.”

> > Water flow and mixing in a Grohe faucet simulated with EFD.Lab.

Making  this capability usable for a non-expert population still depends on  vendor support of the fundamentals, starting with the way MCAD models  are handled. Jim Spann, vice president for North American marketing at  Blue Ridge Numerics, says his company focuses on the needs of product  development engineers, the over-worked multitaskers who say,“I don’t  have time to learn a new geometry system.” The company’s CFdesign  software actually goes into the MCAD system, and interrogates and  “reads” the MCAD model, meaning the model the user sees in CFdesign is  the MCAD model itself, not an import.
 
”]Product development  engineers] don’t want CAE to change their processor to become their  process,” says Spann. “They want it to fit their current process, and  are intrigued by the possibility of saving time by getting information  faster.” Blue Ridge’s CFdesign software connects MCAD and CAE using  “integrated intelligence,” whereby CFdesign algorithms make meshing and  analysis set-up decisions for the user —yet let the designer make the  engineering decisions.

< < This is a diagram showing how an engineer can use ALGOR CFD to set up  a model at his desktop then perform an analysis using a cluster  of computers. This scenario is ideal for models that are too large  to analyze on a single computer or to obtain fast solution times.

Flomerics also  acknowledges the important CFD-and-MCAD connection,preferring direct  interaction with native MCAD data to any geometry translation, copy, or  “analysis version.” Mike Reynell, Flomerics director of marketing, says  a major problem in translating a solid model is that the (empty) fluid  space does not exist as a discrete object in the MCAD system. Managing  this issue, Flomerics’ EFD software analyzes the MCAD model,  automatically identifies fluid and solid regions, and defines and meshes  the entire flow space in a single step.
 
COSMOS FloWorks takes the  MCAD issue one step further, being fully embedded within SolidWorks 3D  design software. It, too, automatically generates the fluid volume and  updates all flow parameters based on changes to the associative  SolidWorks geometry.
 
Other examples of CFD software directed at  the MCAD user include Fluent for CATIA and FloWizard, both from  ANSYS/Fluent, CFD-CADalyzer from ESI Group, and SC/Tetra from Software  Cradle. Fluent’s software (again with automatic fluid domain creation)  aims directly at design engineers,helping to eliminate ideas that won’t  work, and optimizing the ones that will. CFD-CADalyzer, with built-in  pre- and post-processors,simulates flow and heat transfer, and compares  results over a range of geometries and operational conditions. SC/Tetra  also offers a complete package that offers adaptive meshing and  wizard-guidance.

Wider Markets   

Paul Bemis, Fluent’s vice  president of product management, offers this straightforward  perspectives. “In the past, CFD was used by people who had no choice,  working on jets, rockets, and overheated car engines,“he says. “They  used CFD primarily as a forensic tool to understand failure. Now, with  better predictability (results), people use CFD to help with the design  decision process, hoping to optimize at the beginning.”

> > View of a transient fluid-structure interaction (FSI) in  ABAQUS/CAE,analyzing the effects of blood flow on a diseased artery  with an aneurysm. The contour plot in the top image shows static  pressures in the fluid domain and a vector plot of these forces acting  on the surrounding arterial wall. The middle image shows  resulting displacement forces on the arterial wall. The contour plot in  the bottom image shows fluid velocities within the artery and the  Misesstresses on the wall structure. The analysis was performed with  ABAQUS and Fluent software, with the FSI coupling managed by MpCCI.  

Sheer numbers are  behind some of the increased usage in CFD analyses.For example,  electronics cooling has always represented a large portion of  applications; nowadays, particularly in the automotive world,  this percentage is rapidly increasing. According to Richard Bush,  marketing director for NX digital simulation at UGS, a recent study  showed that while the growth rate, say, for suppliers of chassis parts  will increase at $13 billion per year for the next 10 years or so,  the comparable yearly value for electronics modules will be $157 billion.

< < Radiation analysis of headlamps allows for bi-spectral heat  sources including visible and IR spectrum radiation.

Even when compared to the  general CAE market, the numbers are soaring. Chris Reid, vice president  and general manager of the fluids business unit at ANSYS, notes that a  Daratech study predicts an 18% growth rate for the CFD market through  2010, compared to 11-12% for CAE.
 
Besides the numbers, just the  variety in CFD applications makes for a fun and mind-boggling read.  CD-adapco has shown NASCAR designers that it’s not too complicated to  run large-scale simulations of the airflow around a number of closely  spaced, high-speed vehicles. Another customer modeled ductwork for power  plants that must retrofit pollution-abatement systems (the analysis paid  for itself in one hour).

> > Empowering engineers with CFD during the up front design phase means  the software must deliver the know-how required to generate a mesh  on complex MCAD assemblies. CFdesign uses integrated intelligence  that automatically determines optimal mesh sizes for flow volumes and  solids(see top image) before automatically generating a high-quality FE  mesh for the user. 

Peter  Spalding, sales manager at CHAM, points out that CFD is also being  applied to very topical issues such as fuel-cell design and global  warming, with analyses of various pollution control approaches and wind  and wave energy systems. For example, CHAM’s PHOENICS product can handle  complex multi-phase and multi-fluid flows, such as modeling discharge of  pollutants into rivers.

Multiphysics Now the Norm   

“People  like to look at problems in a multiphysics manner,” says ANSYS’ Reid,  “because it gives them real-world results. As problems get bigger and  more complicated you want better fidelity and to allow for  more flexibility.” Reid says that multiphysics has always been at  the forefront of ANSYS’ strategy and is one of the areas where the  company continues to make investments, with fluid-structural  interactions (FSI)being perhaps one of the most visible categories.
 

< < On  the left, STAR-CCM+ from CD-adapco was used to analyze the wave  pressures resulting from a giant wave slamming into an oil platform.

ALGOR  also notes that the same engineers who used to only do FEA are now using  CFD features. Williams explains, “It used to be that people thought CFD  is much different than FEA. Now most FEA companies have some subset of  CFD. We don’t even refer just to fluid flow any more.For example,  there’s the coupling of heat transfer and fluid flow, and the direct  effect on structures.”
 
COMSOL’s Fontes echoes these thoughts,  describing two applications. “If you want to simulate the blood flow in  a vein,” he says, “multiphysics is the only way to simulate, in a  realistic fashion, the effect of FSI in the one-way venous valves.  ]Then] in biotech and micro fluidics you often need to model the  influence of electric fields on the flow pattern.” Fontes adds, “Ten  years ago only a few engineers were doing thermal-fluid analysis in  electronics — now it is pretty standard.” One COMSOL user is modeling  MEMS structures for isolating individual DNA strands, a task that  incorporates six different types of physics.
 
ABAQUS software  from Simulia, Dassault’s umbrella name for its simulation solutions,  draws on its long-standing strength in multiphysics in several ways.  Simulia has created interfaces to such CFD packages as CD-adapco’s  STAR-CD, letting structural designers work in a familiar environment.  All kinds of nonlinear materials can be handled along with such  conditions as partially shut-off flows. The ABAQUS scripting capability  then lets users view results from both the FEA and CFD analyses in a  single system.

> > When  performing a CFD analysis, engineers set up a virtual model to predict  how fluids will flow and the effects they will have on the structures  with which they come into contact. Shown here is a valve assembly that  was modeled in SolidWorks (left); then the user specified the surfaces  for modeling the fluid medium in FEMPRO (center); and anew part was  automatically created where fluid flow analysis will be performed  (right). ALGOR automatically creates new parts where fluid flow analysis  will be performed, which makes modeling fluid flow systems easier and  faster.

High-end  users reaping the benefits of this power include those dealing with  complex FSI problems, such as UGS’ partner in fluid-thermal analyses,  Maya HTT. One area of its expertise helps designers of headlamps, fog  lamps, and other exotic lighting systems manage the strong coupling  between radiative heating and 3D fluid flow. Maya software answers  questions like, How does shadowing affect cooling,What about behavior  at different wavelengths, and Will different kinds of plastic housings  have different hot spots?
 

< < Multiphysics model of a micro-fluidic, 40 micron-diameter microchannel  surface for analyzing single-strand DNA. Dr. Carl Meinhart, University  of California Santa Barbara, used COMSOL Multiphysics software to model  improving flow near the reaction surface using electro kinetic flow from  two electrodes. Analysis involved modeling steady-state and transient  cases of dielectrophoresis, electro thermal stirring, and an  electro osmoticforce. 

ESI  Group also offers a multiphysics oriented product, the general,  PDE(partial-differential equation) solver, CFD-ACE+, along with  an automatic shrink-wrapping volume grid generator. An example where  its FSI simulations quickly take on complicated physics involves  automotive engine-compartment temperatures; CFD-ACE+ couples a turbulent  flow module with convective and radiative heat transfer, providing  answers in just days with accuracy within 3% of real-life tests.

Valuable Tool for Time and Money   

Cheaper,  faster, CFD is now affordable for many applications, and gives an  understanding that would otherwise take expensive experiments  to acquire. As Blue Ridge’s Spann puts it, “You can’t improve what  you can’t see.” CFD analyses supply the “look inside” that many  physical tests simply can’t provide. And that look inside can bring  added insight, efficiency, and performance to product and system design.
   
Contributing Editor Pamela J. Waterman is an electrical engineer and freelance technical writer based in  Arizona. Send your comments about this article through e-mail by  clicking here. Please reference “CFD’s Expanding Role” in your message.

You may not have heard of the Council on Competitiveness,  but its low-key work may enable you to become a supercomputer user  without leaving your office or investing a million dollars. For example,  this nonprofit D.C.-based group helped create an initiative connecting  companies in need of high-performance computer power with CPU time  available at government national laboratories such as Oak Ridge and  Lawrence Berkeley.
   
Paul Bemis, vice president at Fluent, who  sits on this council’s HPC Advisory Committee, explains that his company  has now partitioned its software to run across 512 processors (with a  1024-processor version in the works) to help customers take advantage of  this national computing-grid resource. This way, designers who have  “never ever done simulation, and never ever used a supercomputer” will  be guided in the process.—P.W.

ABAQUS, Inc.
  Providence, RI
 
ALGOR, Inc.
  Pittsburgh, PA
 
ANSYS, Inc.
  Canonsburg, PA
 
Blue Ridge Numerics, Inc.
  Charlottesville, VA
 
CD-adapco
  Melville, NY
 
CHAM
  London, UK
 
COMSOL, Inc.
  Burlington, MA
 
COSMOS—SolidWorks Corp.
  Santa Monica, CA
 
ESI Group
  Huntsville, AL
 
Flomerics, Inc.
  Marlborough, MA
 
Fluent, Inc.
  Lebanon, NH
 
Intelligent Light
  Rutherford, NJ
 
Software Cradle Co., Ltd.
  Sterling Heights, MI
 
UGS/Maya HTT
  Plano, TX