CLOSED CIRCUIT TUNNELS

AEROLAB specializes in custom-built closed circuit wind tunnels (CCT). Working in steel, we have complete design freedom to meet your unique needs (ex. low overhead clearance or building support columns) and specifications. Most of our CCT designs are single-return; however, any configuration is possible. As with all AEROLAB tunnels, they provide an exceptionally steady test section flow with close uniformity of velocity. Turbulence level is typically below 0.25 percent throughout the full tunnel speed range. Contact us with your ideas (size, speed, shape) and we’ll be happy to generate a quotation.

24x24-inch Closed Circuit Wind Tunnel Undergoing Final Testing at Our Facility

Design

4 Contraction – Contraction ratio is a major driver in the overall size and complexity of a closed circuit tunnel. Power requirements, accordingly, follow. AEROLAB uses either a fifth, or, ninth-order polynomial to define a smooth transition between the settling chamber and the test section entrance. If ample space is available, ratios in excess of 9:1 offer diminishing returns in test section flow quality.

4 Honeycomb Flow Straightener – High quality, aluminum high-aspect-ratio honeycomb flow straightener supplied with all AEROLAB closed circuit tunnels.

4 Anti-turbulence Screens – All AEROLAB tunnels are supplied with two 20 x 20 stainless steel anti-turbulence screens. Also, sufficient space is provided in the settling chamber to fit two additional screens at a later date should the customer need extremely smooth flow for sensitive experiments. A full-length door allows removal for cleaning.

4 Static Pressure “Rings” – A s tatic pressure ring is fitted immediately down stream of the anti-turbulence screens . An additional ring is fitted at the entrance of the test section. Both rings consist of at least four pressure taps – one centered on each wall. Depending upon tunnel size, additional taps may be installed.

4 Test Section – Anodized 6061 aluminum is used to construct the load-bearing frame and flanges of our AEROLAB test sections. Typically, three standard Plexiglas ® windows are installed– top and two hinged sides. To compensate for boundary layer growth, the walls of the test section diverge slightly. If parallel test section walls are desired, fillets can be added to the contraction, test section, and diffuser, instead.

4 Breathers – “Breathers” are installed at the beginning of the first diffuser. These breathers increase test section static pressure to atmospheric and prevent unwanted pressure oscillations in the tunnel circuit.

4 Diffusers - To prevent separation in the diffusers, and hence diffuser-related effects in the test section, AEROLAB restricts included diffuser divergence angles to 6º. An exception to this rule would be the need for high-angle diffusers when overall space is limited.

4 Cooling – Due to friction with the walls and because air re-circulates in a CCT, temperatures can rise considerably. This is undesirable for most testing. AEROLAB has three standard treatments for the problem; cooled hollow turning vanes (as mentioned above), large radiators in the slowest section of the tunnel circuit and a cooling air “jacket” for the motor. Other solutions are available depending upon circumstances.

4 Fan/Blower – Combined with modern fans, AEROLAB uses efficient, high-quality, low-maintenance electric motors and state-of-the-art solid-state variable frequency drivers to consistently and accurately set wind tunnel speed.

4 Modular Design – For ease of shipment and installation, tunnel sections are flanged.

4 Steel Support Structure – Tubular steel legs and cross members support the tunnel in key locations.

4 Access – Hatches provide internal access to every section of the tunnel.

Advantages of the Closed Circuit Tunnel with comparison to the Open Circuit Tunnel:

4Power requirement for a given speed is lower.
4Particulate matter can be contained within the circuit.
4Noise is significantly lower.
4Laboratory air movement (air vents, doors, windows, etc.) does not affect wind tunnel flow.
4Air entering the test section is free of laboratory dust.
4Fan blades are not as vulnerable to damage from model failure.

Disadvantages of the Closed Circuit Tunnel with comparison to the Open Circuit Tunnel:

4Cost is generally three times greater.
4Air supply is recycled which can be prohibitive when working with combustion engines.
4Footprint is much larger and requires more overall space.
4Temperature can become an issue during prolonged runs.

Cross Section of Turning Vane