Case Studies

Paricle Image Velocimetry (PIV)
St. Paul, MN - February 2001

Contributed by: http://www.tsi.com

Animated vector field from particle image velocimetry measurements of a hovering helicopter rotor wake

TSI, Inc., the leading supplier of flow and particle diagnostics instrumentation, developed a Tecplot add-on to post-process the vector field data collected by their Particle Image Velocimetry (PIV) system. Pioneered by TSI, PIV is one of the most prominent non-invasive diagnostic techniques. PIV measures the instantaneous velocity field and the associated flow properties. A laser light sheet illuminates the flow field of interest and two images, separated by a very short interval in time, created by pulsing the laser light are captured. Cross-correlating the images provides the velocity vector fields and associated statistical properties. TSI’s PowerView PIV systems use Tecplot as part of the INSIGHT image capture, analysis and display package.

Q&A Session with TSI, Inc.

1. How is Tecplot and your add-on integrated into the PIV solution?
2. Why is Tecplot the best choice for visualising your PIV results?
3. How has Tecplot ADK enabled your solution?
4. Compare TSI's original Tecplot macro panel solution vs. the ADK solution.
5. How did you go about developing your ADK add-on?
6. What was the development time of TSI's solution?
7. What advice would you give to someone developing an ADK add-on for Tecplot?
8. How have your customers reacted to Tecplot and the TSI Add-on?

1. How is Tecplot and your add-on integrated into the PIV solution?

The TSI PowerView PIV systems include PIV hardware – Laser, CCD Camera, light sheet optics, Synchroniser system, Computer – and INSIGHT software. INSIGHT sets up the system parameters, controls the hardware, acquires images using a camera, processes the images and displays the vector field. INSIGHT overlays the vector field as arrows on the image field. For post-processing the vector field data we use Tecplot. Using Tecplot, we can compute and display the global distribution of various flow properties such as mean velocity, turbulence intensity, vorticity and strain rates. The results are displayed using color-coded arrows, line or filled contours or both and stream tubes. With the TSI Add-on, Tecplot automatically displays, online, each vector field and associated properties according to the user configuration of the properties display. The communication is done by INSIGHT writing the vector files and Tecplot reading the vector files. We also generate animated displays of the vector field and/or flow field properties.

Image courtesy of Preston B. Martin, University of Maryland

2. Why is Tecplot the best choice for visualising your PIV results?

We chose Tecplot because of its ability to display the data in ways that are of interest to the people in the fluid mechanics community. We use arrow, contour and streamtrace plots. Tecplot presents the results and switches from one type of plot to another in an easy fashion. We also use Tecplot to compute different flow properties (vorticity). The equation feature in Tecplot makes programming these parameters easy. We present the various global distributions using the 2-D and 3-D displays.

3. How has Tecplot ADK enabled your solution?

ADK allows us to undertake more complex calculations on the vector field data. With the add-on we can use Tecplot to read and display a sequence of vector fields, average the vector fields point-by-point and compute the turbulence intensity at each point in the flow field. We created a tabbed dialog that allows the add-on display options to be presented in an organised and compact way. We were also able to use our add-on to communicate with INSIGHT so that Tecplot can display a new vector field with the specified parameter (for example, as a contour) automatically.

Han. D., Su, L. K., Mungal, M. G., and Menon, R. K., "Study of a lifted-jet flame using a stereoscopic PIV system", Tenth Symposium on Applications of Laser Techniques to Fluid Mechanics, Lisbon, 2000.

4. Compare TSI's original Tecplot macro panel solution vs. the ADK solution.

In addition to all the features of the Macro Panel, new features such as vector field averaging and online communication with Insight were included in the add-on interface. Nine tabs in the add-on interface replaced many pages of the Macro Panel controls. The add-on approach also made the access and navigation to the quicker and easier. With the Macro Panel approach we computed flow parameters with a kernel on a single vector field. With the add-on we have complete access to all the data so that we can compute properties across vector fields to generate the various statistical properties. We also could put more logic in the add-on than that in the Macro Panel. This allows us to have a single add-on for displaying 2-D and 3-D data. With the Macro Panel we had separate panels for 2-D and 3-D vector fields.

5. How did you go about developing your ADK add-on?

Mechanical Engineer Dan Bjorkquist wrote the add-on using Microsoft Visual C++ 6.0. He attended a class on writing add-ons at Amtec, where Byron Ponten and Dave Smith gave him several suggestions on having the add-on do average vector fields and communicate with INSIGHT. Since most of the functions for the add-on were in our Macro Panel, many controls in the add-on were created by translating the macro into ADK calls.

6. What was the development time of TSI's solution?

TSI introduced the first PIV system in 1988 and we incorporated the add-ons in a few months.

7. What advice would you give to someone developing an ADK add-on for Tecplot?

Dan Bjorkquist found taking the add-on development class at Amtec very helpful. Learning how to use the SetLowLevel()methods was also very helpful. This is a very powerful method that can set most Tecplot parameters.

8. How have your customers reacted to Tecplot and the TSI Add-on?

They have reacted very positively to this capability and are finding it easier to use. They especially like the vector field averaging capability that the add-on enabled. With the add-on we provided a seamless interface between our processing and display software. This lets our customers focus more on the results and on arriving at the solutions to flow and particle diagnostics problems.

Tecplot add-ons enable you to modify, customise, and extend the capabilities of Tecplot to address specific visualisation needs. With Tecplot's application programming interface you can add a wide variety of new functionality and capabilities to Tecplot. For example, you can create add-ons to generate plots, load and format data, do specialised preprocessing, manipulate and analyse data and extend Tecplot's visualisation capabilities. The roster of ADK (Add-on Developer's Kit) functions serves a broad spectrum of users' demands. Amtec's CFD Analyser demonstrates these add-on capabilities by adding CFD-specific analysis tools to Tecplot.

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