The way the audience was looking at me, you’d have thought I had just offered a previously unknown antidote for some long suffering pain. For a brief moment, I thought someone might come up and give me a hug. The amount of pre-processing suffering experienced by the infrared modeling community was apparent by their reaction to my recent talk at the International IR Target and Background Modeling & Simulation Workshop (www.itbms.de) in Ettlingen, Germany.
This annual workshop, alternately hosted by Onera and Franhoufer IOSB, is a forum for engineers concerned with the development and application of infrared modeling techniques. Pointwise attended this workshop along with W.R. Davis as the result of a recent collaboration between our respective companies. W.R. Davis develops an IR modeling package called ShipIR. Here is The Connector article from last May discussing the collaboration with W.R. Davis in more detail.
It also was apparent that the infrared modeling community generally is not aware that preprocessing tools available in other disciplines can alleviate the pain they are experiencing.
The obvious question is how can the infrared modeling community benefit from using a computational fluid dynamics (CFD) meshing tool such as Pointwise? First, although Pointwise is generally known as a mesh generator for CFD, it’s not strictly limited to CFD applications. One of the fundamental tenets we strive for in Pointwise is flexibility. To achieve this, we need to accommodate more preprocessing duties than meshing: CAD import, geometry clean-up, CAD export, CAE export, scripting. Being flexible also means not locking you into a process we believe is best for you, but adapting to your needs, processes and applications. W.R. Davis’ use of Pointwise for IR modeling is a perfect example of Pointwise’s flexibility.
Infrared modeling requires only surface meshes on the solid surfaces, but it has a couple of strict requirements. First, the element count should be as kept as low as possible. Calculations with only several thousand elements can take several hours to run and use several gigabytes of memory. The second requirement is that quadrilateral elements have right angle (or very close to) corners and have minimal warpage, otherwise ShipIR will diagonalize the quad element, increasing element count. The preprocessing tool most commonly used with ShipIR is a CAD package and would require several weeks to a month to mesh a geometry like the one in the left image of Figure 1. The shortcomings and inflexibility of the meshing features the CAD tool provided was the biggest source of grief.
After one week of training, W.R. Davis engineers were able to create a suitable surface mesh for ShipIR analysis (right image in Figure 1) on their own in about one day. They felt the time savings were three to 10 times faster than their current preprocessing tool, depending on the application.
In addition to the time saved creating surface meshes for ShipIR analysis, Pointwise was able to provide W.R. Davis a completely new capability. While ShipIR has significantly more radiation modeling capabilities than a general purpose CFD solver, it must use empirically determined convective heat transfer coefficients because it does not solve the Navier-Stokes equations. I was told that empirical heat transfer coefficients give surprisingly good results for a wide range of applications but do not work when the convective heat transfer mode notably modifies the surface temperatures. A good example is a naval ship when the hot exhaust plume from the gas turbine is blown onto adjacent surfaces, for example, due to an apparent wind direction different than the ship heading (Figure 2).
The obvious solution is to couple ShipIR with CFD. To be able to do this with some reliability, the mesh points in the ShipIR mesh must also exist in the CFD surface mesh. This is necessary to reduce the interpolation errors when ShipIR passes heat fluxes to the CFD solver. David Vaitekunas of W.R. Davis and I collaborated this past year to accomplish a ShipIR/ANSYS Fluent coupling using Pointwise, as described in the previously mentioned The Connector article. The ability to couple ShipIR and CFD is a new capability to both W.R. Davis and to the infrared modeling community.
CAE not just CFD
The infrared community and our collaboration with W.R. Davis is only one example of Pointwise’s flexibility. While most of our customers use it for CFD and our own expertise lies there, this does not preclude your applying Pointwise to your non-CFD, CAE application. Figure 3 describes Pointwise’s versatility very clearly.
I’ll entice you by saying we plan to demonstrate another example of Pointwise’s flexibility in an upcoming article on high-order, curvilinear meshing. In the meantime, don’t be afraid to explore Pointwise for your non-CFD applications. If you are unsure if it will work, give us a call and we can discuss it in more detail.
If you’re interested in the full details of the ShipIR-CFD coupling with Pointwise, the initial results of this work was presented at the SPIE Defence, Security, and Sensing conference in Orlando, FL, USA, in April 2011. I will send copies of the paper upon request.