Real-Time Visualisation of Pressures in a Vehicular Wind Tunnel Using LabVIEW

"The measurements that we have obtained as a result of this acquisition chain developed in LabVIEW have provided a better understanding of certain phenomena in vehicle aerodynamics."

- Guillaume Bonnavion, ENSTA ParisTech

The Challenge:

Our team needed to develop a tool to visualise, in real time, unsteady pressure data measured during wind tunnel test campaigns.

The Solution:

We used LabVIEW to create an acquisition interface that we can adapt to the needs of multiple projects.

Author(s):

Guillaume Bonnavion - ENSTA ParisTech
Aurélien Joly - ENSTA ParisTech
Olivier Cadot - University of Liverpool
Vincent Herbert - PSA Group
Sylvain Parpais - Renault Group
Rémi Vigneron - GIE-S2A
Jean Délery - CNRT R2A

Pressure Measurements and Industrial Needs

Our team developed this application in an engineering laboratory equipped with various wind tunnels dedicated to teaching and research. Our members are also involved in industrial wind tunnels. Their projects are in the fields of vehicle aerodynamics and energy and include:

Study of vehicular slipstreams and their impact on fuel consumption
Fluid forces on nuclear power plant components subjected to water flow
Stress caused by wind on solar farms

These studies, which have been carried out in collaboration with industry, require field measurements of unsteady pressures. We need to use a real-time visualisation tool to attain reliable measurements and make changes to the test program based on the results. This tool must be easily adaptable for different laboratory applications.

LabVIEW for Increased Modularity

Existing Solution

We used a pressure scanner with 32 (Scanivalve ZOC22b) or 64 (Scanivalve ZOC33) measurement channels with conditioning electronics (GLE/SmartZOC200-201) for measurements. We use a USB port for communication. The entire acquisition system is compact and easily transportable. Its software can adjust acquisition parameters and record data in engineering units but does not allow their usage in real time (export at the end of the acquisition).

Requirements

We must be able to use the program (See Figure 2) with different scanners and for different projects in which the displayed data is not the same. We limited our use to existing acquisition equipment to comply with the manufacturer’s communication protocol. Its interface must allow configuring conditioning electronics (frequency up to 200 Hz, number of channels, data format). We must be able to use it intuitively in test campaigns to reduce user fatigue.

Solution

Communication

We established communication with the conditioning electronics with LabVIEW using Virtual Instrument Software Architecture (VISA). We used character strings for settings, which comply with the communications protocol. The user types these and converts to hexadecimal format in LabVIEW. Start and stop acquisition commands are on front panel buttons and are sent using the formula described above.

Acquisition

During acquisition, the information is continuously received and cut into frames, each containing an identifier as well as the pressure data at the time. The length of these frames depends on the number of measurement channels. Another VISA reads them, one by one, within a loop. The individual frame elements are then interpreted separately using their coding (2-byte identifier, 4-byte for each measurement loop). We use a native VI byte permutation to format the frame data to make it readable by LabVIEW (inversion of low and high weight bits). The program then converts the data received from hexadecimal to decimal format. Then it checks the frame identifier to ensure correct splitting and data reception. The increment between two successive identifiers must be one. In the event of an error, the acquisition stops and the user is informed.

The program exports raw data to a text file for further processing. The program undergoes specific processing for real-time analysis (filtering, pressure gradient calculations, and pressure distribution display).

Progress in Vehicle Aerodynamics

We have tested and validated the solution in the laboratory. To date, it has accumulated 40 hours of use in teaching activities and 180 hours of acquisition in industrial wind tunnels, including approximately 20 hours on actual vehicles. Measurements obtained in this acquisition chain developed in LabVIEW have supported significant progress in terms of understanding certain phenomena involved in vehicle aerodynamics over the course of a doctoral thesis conducted in partnership with the National Centre for Technological Research in Aerodynamics and Aeroacoustics of Land Vehicles (CNRT R2A). In addition, operators are currently deploying the solution on a test bench dedicated to energy sector applications.

In addition, raw data export permits regular verification of acquisition system calibration without the need to return it to the manufacturer, which minimises downtime. We have kept the LabVIEW program open source to allow for use in new projects. We gave a version of our system to GIE S2A industrial wind tunnels as they have expressed interest in real-time visualisation possibilities.