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Volume 9 Issue 2 Fall 2005

Computing High-Speed Flows 1

QinetiQ Haslar 1

Gridgen User Group Meeting 4

Gridgen Product News 5

Gridgen Support 6

INSIDE THIS ISSUE

The ability of computational analyses to inform the aerodynamic design process at an early stage in the design cycle requires rapid, robust and credible productivity oriented analysis tools. At Cranfi eld University, we have sought to meet this challenge for the United Kingdom weapon aerodynamics community through the development and demonstration of four key competencies; a computationally effi cient high-fi delity fl ow solver based upon the solution of the parabolized Navier-Stokes equations; a detailed appreciation of error and uncertainty obtained from a continu-

Computing High-Speed Flows Using IMPNS and Gridgen

Article by Scott Shaw and Bernd Wagner, School of Engineering, Cranfi eld University, United Kingdom

ous and rigorous verifi cation and validation regime; effective use of analysis data through reduced order modelling; and robust, reliable and effi cient mesh generation. The latter is provided by Pointwise’s Gridgen software.

To demonstrate the effi cacy of this approach to our industrial partners for a complex geometry, Cranfi eld University has recently undertaken computations of the X-15 aircraft. The X-15 was the world’s fi rst manned hypersonic research aircraft setting a

Surface model of the X-15 aircraft vehicle.

Mesh Automation at QinetiQ Haslar

Article Courtesy of Dr. Ben Raylor, QinetiQ Haslar

QinetiQ Haslar is a research organization focusing on the ma-rine industry. As the former Defence Research Agency for the United Kingdom, it has a unique combination of experimental and computational facilities. Many of its researchers are well versed in both experimental and computational techniques of analyzing fl uid fl ow around ships and their propulsors. The range of problems they analyze includes comparisons of full-scale and

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Flow around a surface ship hull with appendages

2Pointwise® FocalPoint Fall 2005

Interested in our Gridgen Teaching Partnership?Recognized academic institutions already having at least two Gridgen academic licenses can add ten additional licenses for the duration of a class at no additional charge. For more information about our teaching licenses, please contact Heather McCoy at hlmccoy@pointwise.com.

series of speed records in the Mach 4-6 range between 1959 and 1967. Uniquely, the aircraft was extensively instrumented providing a wealth of data on supersonic and hypersonic air fl ows, aerodynamic heating and stability and control. The geo-metric complexity of the aircraft coupled with the availability of extensive fl ight and wind tunnel test data provide an ideal opportunity to demonstrate credible, rapid CFD.

To construct the grids used in the project, extensive use was made of the tools available within Gridgen to manipulate CAD data-bases for the individual aircraft elements (nose, fuselage, wings and fi ns) into a watertight surface model of the X-15 aircraft.

Multi-block grid over the forward fuselage.

High-Speed Flow(Continued from page 1)

The IMPNS solver employs an effi cient space marching solution algorithm requiring that grid points should lie in a sequence of planes normal to the marching (fl ow) direction. Fortunately, the fl exibility of the structured multi-block grid generation tools within Gridgen means that such constraints posed no signifi cant challenge for the experienced analyst. The fi nal grids around the complete confi guration contained 20 blocks and between 2 - 3 million grid cells. In addition to the full aircraft, 12 supporting confi gurations exhibiting a range of geometric and physical complexity were also considered in the fi nal study requiring the generation of more than 60 high-quality grids and analyses within a 13 week period.

Initial comparisons of computations with fl ight test data are fa-vourable demonstrating the credibility of Cranfi eld’s approach to the prediction of aerodynamic fl ows involving complex geometry and physics. The ability of Gridgen to provide reliable, robust mesh generation in a timely fashion lies at the heart of this suc-cess and work has now begun on a more extensive programme of work to evaluate the IMPNS software for the prediction of stability and control derivatives using a CAD model provided by NASA’s Geolab.

Flow Visualization at M∞=4.2, α = 0°. Left - wind tunnel. Right - CFD.

Pointwise Consulting ServicesHere’s something you may not have known about the Pointwise Support Group - we can provide consulting services. If you need help with a diffi cult grid, extra hands during a peak workload, or Gridgen customized for your computing environment, we can assist. Starting this fall, we’re adding complete CFD solutions with codes like FLUENT and STAR-CD. For more information, please visit: www.pointwise.com/products/services.shtml.

3Pointwise® FocalPoint Fall 2005

QinetiQ Haslar

model-scale propeller performance, rotor-stator propulsors, submarine wake fl ows, and fl ow around surface vessels with appendages, as shown in the picture on the fi rst page.

QinetiQ Haslar has been using Gridgen for several years, and they have become heavily involved in using the GridgenGlyph scripting language (based on Tcl) to automate some of their mesh generation processes. This can be a big time-saver, particularly for parametric studies where many variations of geometry must be gridded and fl ow-solved.

One example of this is a parametric study of the effect of ducted rotor tip gap clearance performed last year. A representative surface grid for the hub and rotor of this geometry is shown below. A script was developed that automatically generates grids for different tip gap clearances. It is able to generate a new grid in about 10 minutes, compared to the 2-3 days it takes to generate a grid by hand.

Many of the grids and solutions for this parametric study were completed automatically during a holiday period when computer resources were readily available. If the grids had to be made interactively, an engineer would have been required to come in over the holiday period, or the project would have taken signifi cantly more time.

QinetiQ engineers have found their Glyph scripting can be classifi ed as one of three techniques, which they call novice, experienced, and brilliant.

In the novice approach, engineers create scripts using Gridgen’s journaling feature to capture a script as the engineer generates the grid by hand. This approach has the advantage that it is very easy to create the initial script. The drawbacks to this ap-proach are that it does not allow much fl exibility in the types of variations that can be made on a grid, and more importantly, it produces scripts that can be sensitive to the geometry, meshing parameters, or even the Gridgen version.

In the experienced approach, the topology for the grid is designed in advance and the script is written manually by an engineer in a more structured fashion. The disadvantage of this approach is it takes a bit longer to develop the initial script and the script writer has to be more familiar with Glyph. The advantage of this approach is it produces more robust and con-cise scripts. Repetitive tasks can be encapsulated in procedures that are more effi cient and easier to debug. As a result, the script is easier to maintain and can be made to function for a wider variety of geometries and grids.

The brilliant approach is similar to the experienced approach, but uses Tcl’s graphical interface toolkit, Tk, to add a graphical inter-face to the script. This makes it easier for engineers not involved in development of the original script to make use of it without expert assistance. Using the brilliant approach, the effort and knowledge that went into developing the script are disseminated and preserved for others in the organization to use.

QinetiQ engineers also take advantage of Glyph scripting to col-laborate with engineers in other organizations, even when they are located an ocean away. They have an ongoing project with Defence Research & Development Canada – Atlantic and the University of New Brunswick to study fundamental fl ow phys-ics associated with maneuvering submarines. By trading Glyph scripts with each other they are able to divide up the work of grid generation and ensure they are using consistent grids.

In a short time, QinetiQ has used Glyph to integrate Gridgen into their design process, save mesh generation time, and collaborate with others. Who knows what the future holds.

For more information, please contact Dr. Raylor at braylor@qinetiq.com.

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Rotor and hub surface grids created automatically by Glyph script.

Meet Our Newest Employee...Dawn Dickinson, Administrative AssistantIf you have phoned the Pointwise offi ce recently, you may heard a new voice on the line. Dawn Dickinson joined the Pointwise staff in July 2005 and is responsible for administrative and fi nancial matters. Next time you phone, be sure to say “Hi.”

4Pointwise® FocalPoint Fall 2005

Vrooom, vroom. Are you ready to get behind the wheel of a high performance, exciting new grid generator? Then come to the Gridgen User Group Meeting 2006 and take part in our Gridgen V16 Test Drive. This will be the fi rst time we let anyone outside Pointwise get their hands on this baby, and it promises to be an exciting time. Not only will you be the fi rst to see this next-generation grid generation product with all its productivity enhancements, we also want to hear your feedback so we can do any needed last minute fi ne-tuning before it goes out to the general public.

Gridgen User Group Meeting 2006 will be hosted by Pointwise at the Sheraton Grand Hotel at Dallas/Fort Worth Airport in Irving, Texas on April 24-25, 2006. You will see special Gridgen training seminars, presentations by Pointwise staff on new Gridgen developments, exhibits by our partners, and user presentations so you can learn about the latest Gridgen features, get a glimpse of future developments, and network with other CFD experts.

Delivering the keynote address at this year’s meeting is Dr. Dipankar Choudhury, Chief Technology Offi cer at Fluent Incorporated, a leading Computational Fluid Dynamics software and solutions provider. Dr. Choudhury has been on the leading edge of the CFD industry since its infancy. He will provide his perspectives on the industry and where it might be heading.

Users interested in learning more about the hands-on use of Gridgen are invited to the Gridgen Seminars on Monday, April 24. The topic of both seminars will be Gridgen’s hybrid meshing capability. The fi rst seminar will provide an intro-duction to the basics of hybrid meshing for the new user. The second seminar delves deeper into the topic including advanced features and tricks to get the most out of the hybrid meshing.

In addition to training sessions, the Gridgen Support Team encourages you to join a support engineer in one-on-one consultation. Bring your own geometry or meshing problem with you so you can sit down and receive face-to-face help from one of our meshing experts. This has been very popular

at our past meetings, so you will want to sign up early to reserve a meeting time with a support engineer.

We would also like you to present your interesting, unique meshing and CFD projects at the Gridgen User Group Meet-ing on Tuesday, April 25. Presentations will be 30 minutes total: 20 minutes for the presentation and 10 minutes for Q&A. Presenters will not be required to submit a formal paper but instead will be asked to provide a copy of their presentation materials for inclusion in the meeting’s proceed-ings. If you are interested in presenting, please view the Call For Papers at www.pointwise.com/ugm/cfp/shtml.

The V16 Test Drive is scheduled for Tuesday afternoon. After Pointwise’s presentation about The Future of Gridgen, work-stations will be available for attendees to use and comment on a pre-release version of V16.

Still not sure if you should attend? Read the list below, and you will have no choice but to join us for this fun learning and networking experience.

10 Random Reasons (to avoid copyright infringement) to Attend the Gridgen User Group Meeting

Network with other CFD and meshing experts.Attend Gridgen training.Attend sessions to hear what others are doing in the industry.Work one-on-one with a Gridgen support expert.Meet with CFD vendors to see what is new. Experience Pointwise hospitality.Tell Pointwise face-to-face what new features you want in Gridgen.Find out what Gridgen tricks others are using to get their jobs done faster and better. Get an update on the latest new features in Gridgen and how you can use them to make grids better and faster.Be the fi rst to test drive V16.

Register now at www.pointwise.com/ugm

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Test Drive V16 at the Gridgen User Group Meeting - North America

213 South Jennings Avenue Fort Worth, Texas 76104-1107 Toll-free 888-GRIDGENTel (817) 377-2807 Fax (817) 377-2799 news@pointwise.com www.pointwise.com

FocalPoint is a publication of Pointwise, Inc. It is for Gridgen users and people interested in learning more about Gridgen and numerical grid generation. It includes information about the latest release of Gridgen, future development plans, and tips on how to get the most out of Gridgen while saving time in grid generation. Pointwise and Gridgen are registered trademarks and GridgenGlyph is a trademark of Pointwise, Inc. All other trademarks are property of their respective owner. Copyright © 2005 Pointwise, Inc. All rights reserved

5Pointwise® FocalPoint Fall 2005

G r i d g e n P r o d u c t N e w s

The next major Gridgen maintenance release will have a new suite of features collectively known as solid meshing. Solid meshing involves generating a surface mesh on a solid model and represents an approach to CAD surface meshing that complements Gridgen’s current technique called fault tolerant meshing. A solid model is simply an assembly of trimmed surfaces similar to how domains are assembled into a block’s face. The benefi ts of solid meshing relative to fault tolerant meshing are:

By using solid modeling entities, the database is simplifi ed. Instead of working with hundreds of entities for a single component (for example, a patchwork of surfaces for a wing), the component can be represented by a single entity.Solid meshing reuses the solid model topology whereas fault tolerant meshing recomputes the proximity of two meshes each time the mesh is regenerated.Solid models may exist in the CAD fi le but fault tolerant meshing currently ignores them. With fault tolerant meshing, it’s often not clear what values should be used for the tolerances (for Auto Merge) and the angles (for Auto Join). In solid meshing, all this information is unambiguously stored in the solid model.

Several new features are being added to Gridgen to support solid meshing. They are:The ability to import solid models from IGES (Entity 186) and the Native CAD Readers.The ability to create solid models in Gridgen.The ability to generate a surface mesh on a solid.The ability to export a solid model to Gridgen’s composite database fi le (.dba) and IGES.

Gridgen’s implementation of solid meshing goes beyond simple solid modeling. Gridgen will support two types of solid modeling database entities: quilts and models. Models exist so that the database can be formed into a solid; they are ex-actly what you have in the CAD system. Quilts are created to identify components within a solid that should be meshed as a single unit. As an example, consider a Rubik’s Cube. Its model entity would consist of 54 trimmed surfaces (9 on each of its 6 faces). If you meshed the model directly, you’d end up with 54 domains. This probably isn’t what you want; you probably want only 6 domains, one for each face of the cube. This is where quilts would be used. By creating 6 Quilts (one for each face) and then assembling the quilts into a model you get both the ability to easily mesh the solid while at the same time preserving the meshing intent. In other words, models handle the Auto Merge function while Quilts handle the Auto Join function.

On the hardware side of things, the next major Gridgen V15 release will include support for two new platforms: Linux on the SGI Prism and Linux and Windows on AMD Opteron. We worked very closely with our partners at SGI and AMD to ensure that Gridgen was fully functional on their respective platforms.

Other new features to be released are an option to export Cobalt fi les unformatted, a new native interface to the FrontFlow CFD solver, support for the FV-UNS v3 fi le format, and addition of the “bread” command to STAR-CD fi les.

Since the last issue of Focal Point, we also released Gridgen Version 15.08. It contained a great new feature for structured grid users: the addition of a multigrid solution algorithm to the elliptic PDE solver. The new multigrid algorithm (which is now the default) converges to the same grid as the original successive over-relaxation algorithm but does so up to 15 times faster, especially for large grids. V15.08 also featured Native CAD Reader support for Unigraphics NX 3, and an upgrade of Gridgen’s support for HP PA-RISC workstations to HP-UX 11.

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213 South Jennings AvenueFort Worth, Texas 76104-1107

Volume 9 Issue 2 Fall 2005

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Have you ever encountered a problem in Gridgen that you didn’t know how to tackle? Ever seen something in Gridgen that you thought might be a bug? If you answered yes to either of these questions, then you need to know about the many resources Pointwise provides to help you in these situations.

The best place to get started is the Support area of our website where you can browse through our Frequently Asked Questions (FAQ) and Library web pages for the answers you need. The FAQ covers common user questions ranging from installation issues to structured and unstructured solver usage. Our Library goes a step further and provides detailed reference material in the form of complete installation instructions, back issues of The Connector announcements, and past issues of the Pointwise Pointer.

If the answers you seek cannot be found in the FAQ or the Library, then you probably need to work with one of our dedicated Sup-port engineers. There are several easy ways to start a dialogue with us about your questions or issues, but fi rst you will want to gather a few pieces of information that will help our staff to better help you:

Customer ID

Gridgen Version Number

Machine Platform and Operating System

Error Messages (if any)

Problem Description

Once you have this information, there are three ways you can contact us:

Email us at: support@pointwise.com

Call us Toll-Free: 1-888-GRIDGEN

Go online to www.pointwise.com/gethelp

Our Support engineers will then quickly and effi ciently work with you directly to address all your questions and concerns. Getting help has never been easier!

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Need Support?