I’m Rajib Roy and This Is How I Mesh

Rajib Roy, Intern on the Sales & Marketing Team.

Rajib Roy, Intern on the Sales & Marketing Team.

I was born in a rural village in southern Bangladesh and raised in Chittagong Hill Tracts in the southeastern part of the country. The Hill Tracts is a mountainous region with a diverse demography and vibrant culture.

I loved math and physics in school and in college I choose to study mechanical engineering. For my senior year thesis research I experimented with phase change heat transfer device prototypes for power electronics cooling. In search of an optimum design, I found that experimental measurements are indispensable. However, because of resource limitations, I was only able to go through a few design iterations. Alas, in the eleventh hour, I learned about use of CFD to conduct virtual experiments.

After graduation, I received training on HVAC system design and was appointed as a project engineer for building a pharmaceutical “Clean Room”. Clean rooms are a particular type of controlled environment that maintain ultra-clean air for sensitive processes such as drug preparation and microchip manufacturing. Such facilities use very high air exchange rates to filter out environmental pollutants which eventually lead to turbulent flow (very high Reynolds number) through the air-ducts. However, to deter pollutant mixing within the room, flow turbulence number are kept very low. The only exception is the use of “Laminar Flow Hoods” which provides very low-speed laminar flow for inhibiting mixing of pollutants. There I learned about the application of CFD to simulate air and pollutant flow to ensure desired environment quality. This work motivated me most to learn and apply CFD to solve engineering problems.

At the University of Wyoming, my master’s work focused on turbulence modeling for bluff body flows. Currently, I’m working on the CFD simulation of wind turbine aerodynamics for my Ph.D. research.

While performing CFD for my research, I found that grid generation can require significant user input, and being upstream in the CFD workflow, high quality grid generation is essential for high quality results. Before using Pointwise, I was using a few open source meshing tools. Three factors made me a Pointwise user:

  1. I received a free evaluation of the complete software for one month.
  2. I received excellent technical support throughout the evaluation.
  3. Pointwise was superior to the tools that I was using.

When I started writing Glyph scripts to automate my meshing process, meshing became more enjoyable and productive.

  • Location: Fort Worth, Texas
  • Current position: Sales & Marketing Intern
  • Current computer:  Lenovo W530, 16 GB RAM, Windows 8
  • One word that best describes how you work: Focused

What software or tools do you use every day?

My workstation at the University of Wyoming runs Ubuntu 14.04 LTS and I use a range of Ubuntu/Linux tools (bash shell for terminal, Kate & gedit for text editing and code development). I use Outlook heavily to keep up with emails, OneDrive to backup documents, and Tweetdeck for Twitter. A few of the other tools I use include:

What does your workspace look like?

Rajib's current workspace.

Rajib’s current workspace.

My desk is in room 101 (perfect number for an intern!) which is fortunately between the offices of two meshing gurus: Dr. Steve Karman and Dr. John Steinbrenner. I like the brick walls of the century old Bicocchi Building (Pointwise headquarters in Fort Worth, TX) and a nearby window helps me keep track of the summer weather. I keep hard copies of the tutorial workbook, V17 training notes and Glyph scripting notes handy and use the Pointwise Accelerators mousepad for reference.

What are you currently working on?

I am very excited about the meshing projects that I have been working on during my internship here. I am currently applying the new Advancing Front-Ortho algorithm (a new feature to be released in Pointwise V18) to generate quad dominant unstructured surface meshes. Hence, a boundary layer volume mesh generated using T-Rex will be hex-dominant which reduces the cell count significantly compared with prism/tet meshes. My first meshing project was to generate a hybrid, viscous mesh for a glider geometry. The figure below illustrates the quad dominant surface mesh and hexahedral elements in the boundary layer.

NidaGlider-QuadDominant

Representing a geometry with high surface curvature (e.g. leading and trailing edges of a glider wing) was a challenge. Application of 2D T-Rex in such areas can reduce the surface-cell count significantly compared to pure isotropic triangle refinement by using anisotropic triangles normal to the boundary. When using 2D T-Rex, connectors designated as “match” type boundary conditions receive a growth distribution that is defined by an initial spacing and growth rate. Therefore, curvature based refinement (e.g. turning angle or surface deviation) is not automatically enforced.

To properly resolve the curvature for the glider project, I wanted to specify an initial spacing for 2D T-Rex that resulted in a lower turning angle between adjacent facets. Using Glyph, I wrote a script called Turning Angle Calculator to compute the turning angle between adjacent grid points along connectors so that I could more appropriately define connector grid point spacing. Moreover, the script can also calculate maximum and minimum turning angles for a batch of selected connectors which is helpful to examine the overall grid tuning angle quality metric.

I have also prepared a hybrid mesh for the Potsdam Propeller Test Case. The Advancing Front-Ortho algorithm was applied on the propeller surface to generate a quad dominant surface mesh which ultimately resulted in a hexahedral element dominant boundary layer.  Since the five propeller blades are identical, the surface mesh was prepared for a single blade and copy, pasted using Pointwise “copy and rotate” tool. The figure below depicts the quad dominant surface mesh on the propeller geometry and hexahedral (cyan) and prism (blue) cells in the boundary layer region of the mesh.

A hybrid viscous mesh generated with Pointwise for the Potsdam Propeller Test Case.

A hybrid viscous mesh generated with Pointwise for the Potsdam Propeller Test Case.

What would you say is your meshing specialty?

Well, I am still learning different meshing techniques and best practices here at Pointwise. But, in our research group at University of Wyoming, we perform a lot of parametric CFD simulation studies and I enjoy writing Glyph scripts for automating the meshing process. I frequently use OpenFOAM which is an unstructured CFD solver and prefer to use hybrid meshes and apply T-Rex when working with complex geometry, and will resort to multi-block structured meshing in geometrically simple regions of the domain.

Any tips for our users?

  1. Pointwise technical support is just an email (support@pointwise.com) or a phone call (800-4PTWISE) away. Don’t hesitate to contact us to discuss your meshing issues.
  2. The Glyph Script Exchange on GitHub has a great collection of meshing scripts which are open and distributed for free. The scripts can be used right away, or modified for a slightly different application without the need to start from scratch.
  3. Subscribe to #TutorialTuesday on YouTube where a Pointwise feature is discussed every Tuesday. The features discussed range from explanation of a particular tool, meshing parameters, as well as tips, tricks and best practices from Pointwise meshing experts.

What CFD solver and postprocessor do you use most often?

I mostly use OpenFOAM as my CFD solver and ParaView for visualization.

Are you reading any interesting technical papers we should know about?

Unlike RANS, LES and hybrid models require time-varying inflow with large scale turbulent structures. I am reading a review paper titled Inlet conditions for LES using mapping and feedback control. I’m also reading Wind Farm Simulations Using a Full Rotor Model for Wind Turbines where the authors coupled a weather model (mesoscale) with wind farm flow in addition to a boundary layer resolved full rotor model (microscale) in a massively parallel manner.

What do you do when you’re not generating meshes?

The Pointwise kitchen is filled with a variety of healthy snacks. I never restrain myself from trying something new. In Wyoming, I like to hike and travel during the summer months, and snowshoe and visit the movie theater during the long winter. On weekends, I usually play Badminton.

What is some of the best CFD advice you’ve ever received?

“Before running a simulation, try to always get a good quality mesh. Remember, garbage in – garbage out. Or in a positive way, good mesh – good results.” –Joel Guerrero in a lecture titled tips and tricks in OpenFOAM, for CFD simulation in general.

If you had to pick a place to have dinner, where would you go?

My wife has a passion for cooking and trying new recipes. I am her reluctant but obedient assistant. Most of the time we cook. When we do eat out, we like to go to Bunkhouse Bar and Grill in Cheyenne, Wyoming for steak, and HuHot, a Mongolian grill in Fort Collins, Colorado.

About Travis Carrigan

A Pointwise engineer helping other engineers solve their meshing problems.
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One Response to I’m Rajib Roy and This Is How I Mesh

  1. Pingback: Summer Internships at Pointwise | Another Fine Mesh

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