The wind-tunnel is a vital engineering equipment to conduct different fluid mechanics/aerodynamics experiments and tests. Wind tunnels are commercially available but expensive for some small engineering programs. Considering its fairly simple structure, it can be an attractive design project for senior undergraduate engineering students. It provides sufficient technical challenges and ample enlightening examples to allow students to apply their knowledge in fluids, materials and manufacturing, CAD/CAM, and economics.
The college of engineering at California Baptist University decided to design and manufacture a subsonic wind tunnel. It was planned as a two-year senior capstone design project. The first-year team finished the design based on the constraints of budget, space, power supply, and specific function needs, manufactured some parts of the wind tunnel if time allows. The second-year team checked the design of the previous team and made appropriate adjustments/improvements. Following approval of the final design, fans, motors, and other necessary materials were ordered to assemble the tunnel.
The first team studied and compared the closed and open-circuit wind-tunnels. The closed design was selected for its compact size and relatively low noise level, as the tunnel will be installed in a small room. The team made its design based on the size of the test section. No fluid flow simulation of the whole wind tunnel was done. To accelerate their progress, they ordered the motor, the fan, and manufactured all major parts except for the test section.
The second-year team started with a simulation of the flows within the tunnel using CFD software Comsol Multiphysics and Solidworks Fluid mechanics to check the design of the first team. The simulation results showed that the design of the closed-circuit tunnel wouldn’t function as their designed aim; guiding panes in the four tunnel corners were needed to generate uniform flows in the test section and to reduce power loss and noise. However, manufacturing the guiding panes was beyond the capability of the university machine shop. Outsource the manufacturing to other companies will make the cost higher than the budget and delay the project. Consequently, the alternative open-loop design was chosen by the team. The test section size was kept the same, and the fan purchased by the first team was also used.
Simulations of the fluid flow and the generated noise levels of the open-loop design were conducted again. The simulation results showed that the flow in the test section was sufficiently uniform, and the sound level with the highest flow speed was within an acceptable indoor volume.
After the open-loop wind tunnel design was finalized based on the simulation results, the parts were manufactured and assembled. The smoke tests demonstrated that the flow in the test section was uniform, and the sound volume with the highest speed was lower than the simulation results.
In conclusion, CFD simulation was used to check the design before manufacturing significantly reduced the cost and time. The second team successfully designed the wind-tunnel with the help of the CFD simulation.
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