Blow-down Wind Tunnels
Blow-down wind tunnels are a special type of "Open Circuit" wind tunnel. For most Open Circuit tunnels, fan assemblies are located downstream of the test section and air is drawn through the wind tunnel with suction. For Blow-down wind tunnels, however, air is blown down into the wind tunnel by a fan (or centrifugal blower) located upstream of the test section, as the name implies. Compared to standard Open Circuit wind tunnel configuration, AEROLAB blow-down style tunnels provide an extra degree of testing flexibility. Most commonly, these tunnels are used for tests requiring liquid or particulate injection. Because all AEROLAB tunnels are made to fit the customer’s needs, there is no limitation to the options available. All blow-down style tunnels have custom test sections and many are requested to include built-in test article mounting arrangements.
Common Applications:
Wind tunnel testing requiring liquid or particulate injection into the airstream, Ram-air Turbine (RAT) testing
Performance Specifications:
- Airspeed Range: customer-defined
- Turbulence Level: Because the blower is upstream of the test section, flow quality tends to be lower for blow-down tunnels as compared to traditional open circuit or closed circuit tunnels. Still, every effort is made to provide smooth, consistent test section flow.
Detailed Description:
- Blower –Blow-down wind tunnels typically employ a centrifugal blower. 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.
- Wide-angle Diffuser – In order to generate smooth airflow in the test section, the blower-supplied airstream must be slowed and conditioned. The first step in this process occurs in the wide-angle diffuser.
- Honeycomb Flow Straightener – To straighten incoming airflow, a "honeycomb" of long narrow tubes is employed. Every AEROLAB wind tunnel is supplied with a high-quality, aluminum, high-aspect-ratio honeycomb flow straightener.
- Turbulence-reducing Screens – All AEROLAB tunnels are supplied with two stainless steel turbulence-reducing screens. Also, sufficient space is provided in the wind tunnel framework to fit an additional two screens at a later date should the customer need extremely smooth flow for sensitive experiments.
- Contraction – The contraction is the bell-shaped inlet. Aerodynamicist use the term "contraction ratio" to refer to the inlet-to-outlet area ratio. Although any contraction ratio is possible, 9:1 is a good compromise between physical size and test section turbulence levels. AEROLAB uses either a fifth, or, ninth-order polynomial to define a smooth transition between the tunnel inlet and the test section entrance. For test requiring a cylindrical test section (ram-air turbine testing, for example), hexagonally shaped contractions are designed.
- Static Pressure Rings – All AEROLAB blow-down wind tunnels are fitted with two static pressure “rings”: one at the entrance of the contraction and one at the entrance of the test section. Each ring consists of four pressure taps (one centered on each wall) sharing a common manifold. The pressure measured within the "rings" is used to calculate airspeed without the need of an invasive probe or sensor.
- Test Section – Anodized 6061 aluminum is used to construct the load-bearing frame and flanges of AEROLAB test sections. The three standard windows – top and two hinged sides – are made of Plexiglas ®. To compensate for boundary layer growth within the test section, the side walls diverge slightly. However, if parallel test section walls are desired (for photographic or laser work), fillets can be added to the contraction, test section, and diffuser, instead. Cylindrical test sections are made of Plexiglas ®.
- Diffuser – In order to ensure smooth airflow within the test section and to make the wind tunnel as efficient as possible, a diffuser duct is employed. The diffuser gently slows the airflow so the fan does not have to work as hard. To prevent airflow from "separating" within the diffuser, and hence undesirable diffuser effects in the test section, AEROLAB restricts included diffuser divergence angle to 6º.
Optional Features:
- Data Acquisition, Display and Control System
- Sting Force/Moment Balance
- Pyramidal Force/Moment Balance
- Traverse System
- Smoke Generator
- Wind Tunnel Models and Probes
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