AE301PressureInstrumentsLaboratoryManual

AE301PressureInstrumentsLaboratoryManual - 2. Pressure...

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2. Pressure Transducers 2.1. Purposes To learn about the software and hardware necessary to acquire pressure data using pressure transducers. Use a micromanometer pressure standard to calibrate a single channel and multiple channel piezo-electric pressure transducers. Learn to account for calibration errors. 2.2. Background Pressure measurement is very important for aerodynamic experimentation. Pressure taps on a surface yield surface pressure distributions that contribute directly to aerodynamic forces on a body such as lift and drag. The surface pressure distributions are boundary conditions that interact with the flow near the surface, therefore, the local flow field can be inferred from the surface pressure distribution. The measurement of the pressure distribution over the surface of a body in an air flow provides valuable information that can be used for verification of computational fluid dynamics (CFD) codes or measurement of a surface’s performance. Then improved designs can be developed based on the pressure measurements. For example, the intake manifold of an engine is a complicated branched flow that is a challenge to design. Surface pressure measurements can indicate where detrimental flow separations have occurred or where flow is accelerating beyond design targets. These type of measurements are common when investigating air flow over other surfaces such as fairings, automobiles and air conditioning ducts. Pressure out in the flow also plays a role in the flow velocity distribution. The total pressure is the sum of the dynamic pressure (due to motion) and static pressure. When total pressure is fixed, the changes in measured static pressure correlated directly to changes in flow velocity. Small metallic probes have pressure taps that are plumbed to pressure transducers. This allows the measurement of pressures out in the flow rather than at the surface of a body. There are a variety of instruments used to measure pressure but we will focus on the following, for low air speed (M<0.2) measurements. 1. Manometers (U-tube, inclined, micro) 2. Piezo-electric pressure transducer 3. Multi-channel pressure transducer
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To accomplish pressure distribution measurement over time, a surface is instrumented by using static pressure taps that are small in diameter and polished to be flush with the surface for minimal flow disturbance (we want to measure the flow as it would be without the pressure taps). Each tap is plumbed to a pressure transducer using flexible tubing. Sometimes multi-channel quick-release jacks are use to change tubing connections without having to work with each individual tubing run. The size of the pressure tap and the length and diameter of the tubing determine the dynamic response of the pressure measurement. Usually, only slow pressure variations can be detected by this method.
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This note was uploaded on 02/07/2011 for the course AE/ME 301 taught by Professor Lafleur during the Spring '11 term at Clarkson University .

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AE301PressureInstrumentsLaboratoryManual - 2. Pressure...

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