1. Slides for ME 115 Laboratory Wind tunnels Purposes –To provide a uniform velocity field (e.g. aeronautic, automotive testing) and low turbulence intensity –To provide suction or blowing and measure flow rate (e.g. airflow impedance testing, AC experiment, heat exchanger testing)

2. Slides for ME 115 Laboratory Wind Tunnel Design Proper shape of the inlet is important – several journal papers offer guidance. Flow straighteners (honeycomb) and screens used to straighten flow and provide minimal turbulence intensity. Test section should not be too far downstream from inlet – otherwise boundary layers will be large for slow flows. If used, orifice plate or venturi tube must be design per strict ASME standards.

3. Slides for ME 115 Laboratory Wind tunnel Examples Test section: Uniform velocity Inlet: Designed for uniform inlet flow and minimal boundary layer formation blower Wind tunnel and test section model at NASA-Ames Source: Electronic Laboratory Design

4. Slides for ME 115 Laboratory More Wind tunnels

5. Slides for ME 115 Laboratory Velocity Measurement Pitot-static tubeHot-wire anemometer Senses stagnation pressure (at tip) and static pressure (at holes on periphery); Po – P can be measured. Velocity calculated from Bernoulli’s equation. Uses electricity to heat wire connecting two prongs to a constant temperature. Required current and/or voltage is calibrated to velocity. Orifice plates and venturi tubes are often used as well (discussed during AC experiment).

6. Slides for ME 115 Laboratory Hot Dog Anemometer Using a cylinder of known properties, a thermocouple, and stopwatch, fluid velocity can be determined. If a warm cylinder is placed in a wind tunnel, the faster the air flows around the cylinder the faster the temperature of the cylinder changes. You will use the concepts of transient heat conduction and convection around a cylinder in this lab to calculate the air temperature. In the past, a hot dog was used as the warm cylinder. However, a thermocouple must be placed right in the center, and it’s tough to make sure of that with a hot dog, so a plastic cylinder is now used.