Wind tunnel research gathers speed with NATO partnership

For aerospace and naval engineers developing the next generation of civilian and military vehicles, physical experiments and computational fluid dynamics (CFD) simulations are both essential to the design process. A critical part of this is enhancing the accuracy of the computational fluid dynamics using experiments conducted in wind and water tunnels.  

Virginia Tech is leading a NATO Research Task Group on Common Research Wind Tunnels for CFD Validation that involves over 60 international collaborators from nine NATO nations, including the United States, United Kingdom, Germany, France, Canada, and Turkey. The group is tackling the issue of how to apply computational fluid dynamics to predict the flow over test models, including the details of the wind or water tunnels in which they are being tested. 

This way of comparing computational fluid dynamics with physical experiments is the most direct and precise way of assessing and improving computational accuracy. The team is developing recommendations that can be used at national-scale facilities that are directly engaged in vehicle development. 

The four facilities chosen for the Common Research Wind Tunnel project are:

• Virginia Tech’s Stability Wind Tunnel, representing low-speed wind tunnels
• The ONERA S3Ch Tunnel in Meudon, France, representing flexible-wall transonic facilities 
• The DNW-TWG Tunnel in Göttingen, Germany, representing perforated wall transonic facilities
• The U.S. Navy’s William B. Morgan Large Cavitation Channel in Memphis, Tennessee, representing water-tunnel facilities

Over the course of the four-year initiative, researchers will document the precise details of these facilities in order to provide boundary conditions for the computational fluid dynamics and performing exploratory calculations to assess what details really matter. There is feedback from the computational fluid dynamics to the facilities too, where computational fluid dynamics insights provide reasons to adjust facility components to simplify computational modeling.

Enter the experimentalists

To date, the Virginia Tech team — led by Professor William Devenport, Research Associate Professor Aurelien Borgoltz, and Research Assistant Nanya Intaratep — have conducted high-resolution optical scans and detailed flow measurements of the high-speed leg of Stability Wind Tunnel. The scans provide detailed information on the geometry of the facility, including the exact shape of its walls in the section where model testing and flow studies are performed. Focus of the flow measurements has been on inflow boundary conditions, the development of flow in corner regions, and frictional effects near the test walls.

Undergraduates in the aerospace and ocean engineering department’s laboratory courses conducted a large portion of the flow measurements, giving  practical experience in an ongoing research effort to hundreds of students.

Just past the midpoint of the project, Virginia Tech has become the “pace setter” for experimental data collection and computational fluid dynamics modeling amongst the four facilities. As the only tunnel sited at an educational institution, the Stability Wind Tunnel has an advantage in having more flexibility to schedule its tunnel. The university team has been able to complete the work at a faster pace, developing a road map for the other facilities involved. 

The computational fluid dynamics experts 

Comparing solutions provides an understanding of the strengths and weaknesses of different computational fluid dynamics software tools and allows the most accurate turbulence models to be identified. Comparing as-built and as-designed solutions provides an avenue for deciding which geometric features of the tunnel should be included. 

Professor Chris Roy and Ph.D. student Adwait Hoge-Patil have been leading a team of international computer scientists from across NATO to calculate the flow in the Stability Wind Tunnel. They have developed detailed sets of computational grids that reflect the idealized form of the tunnel — termed "as designed" — and the actual form as revealed from the measured scans — "as built." These grids have been used to establish a series of blind validation test cases, where different computational groups using a variety of computational fluid dynamics software and turbulence models attempt to compute the measured flow properties.

This NATO activity is set to continue through the end of 2026, with upcoming workshop meetings in Latvia, France, and Turkey. Work in the Stability Wind Tunnel in the coming months will focus on the characterization of the facility and the flow when aircraft and hydrofoil models are introduced.