lecture 11 pressure measurements techniques to measure pressure
TRANSCRIPT
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Lecture 11
Pressure Measurements
Techniques to measure pressure.
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Pressure Measurement
• PressurePressure = Force/Area
Units of force per unit area
• Pressure measurements.– All pressure measurements are relative
measurements.– The measurement of a pressure at a point is relative
to, or referred to, a reference pressure.
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Pressure References
• Absolute Pressure:– Measured relative to a zero pressure or a
perfect vacuum.
• Gauge Pressure:– Measured relative to the local ambient
pressure.
• Differential Pressure:– Measured pressure between two point.
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Barometer
• Aneroid from Greek aneros – “not wet”
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Mercury Barometer
• Measurement of Atmospheric Pressure
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Manometers
• Manometers are one of the oldest pressure measuring devices.
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How could you make a U-tube manometer more sensitive?
• Change Manometer fluid.
• Incline the manometer.
• Combine inclined and straight sections.
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Inclined Manometer
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Pressure Transducers
• What is a pressure transducer?– A pressure transducer is a device that
converts a pressure signal to an electric signal.
• What type of devices can be used to create a pressure transducer?
• Strain gage devices• Capacitance devices• Piezoelectric devices
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Pressure TransducerStrain gage device
Strain gage is attached to a flexible membrane. When the membrane is deflected the resistance in the strain gage changes.
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Pressure Transducer Capacitance device
The capacitance between two plates changes with the distance between the plates.
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Pressure Transducer Piezoelectric device
Piezoelectric device take advantage of the electrical properties of crystals such as quartz. These crystals generate an electrical charge when they are strained.
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Pressure Sensitive Paint
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Pressure Probes to Measure Velocity
• Pitot Static Probe
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Measuring Velocity Components
• Five hole Pressure Probe
How would you calibrate this probe?
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Pressure Models
• Airfoils, wings and complete airplane models equipped with pressure ports can be used to determine model loads and load distribution.
• Pressure models provide more detail on how the loads are generated than a force balance.
• Disadvantage is pressure measurement of model forces is more time consuming.
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How to you create a pressure model?
• Suppose you have designed a new airfoil section and you want to determine its aerodynamic performance and its pressure distribution, how would make such a model?