Transcript Manometer
Lecture 11 Pressure Measurements Techniques to measure pressure. Pressure Measurement • Pressure Pressure = 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. 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. Barometer • Aneroid from Greek aneros – “not wet” Mercury Barometer • Measurement of Atmospheric Pressure Manometers • Manometers are one of the oldest pressure measuring devices. How could you make a U-tube manometer more sensitive? • Change Manometer fluid. • Incline the manometer. • Combine inclined and straight sections. Inclined Manometer 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 Pressure Transducer Strain gage device Strain gage is attached to a flexible membrane. When the membrane is deflected the resistance in the strain gage changes. Pressure Transducer Capacitance device The capacitance between two plates changes with the distance between the plates. 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. Pressure Sensitive Paint Pressure Probes to Measure Velocity • Pitot Static Probe Measuring Velocity Components • Five hole Pressure Probe How would you calibrate this probe? 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. 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?