Chapter 7 Flow Measurement by Yixin Ma 17/04/2013 2/48 Contents I.Introduction ll.Local Flow Velocity,Magnitude and Direction Ill.Gross Volume Flow Rate IV.Gross Mass Flow Rate
Chapter 7 Flow Measurement by Yixin Ma 17/04/2013 Contents I. Introduction II. Local Flow Velocity, Magnitude and Direction III. Gross Volume Flow Rate IV. Gross Mass Flow Rate 2/48
3/48 7.1 Local Flow Velocity,Magnitude and Direction 1.Flow Visualization gives an overall view of flow patterns 2.Velocity Magnitude from Pitot-Static Tube(皮托静压管) 3.Velocity Direction from Yaw Tube(偏航管)，Pivoted Vane(叶轮)and Servoed Sphere 4.Dynamic Wind-Vector(风矢量)Indicator 5.Hot-Vire and Hot-Film Anemometers(风速计) 6.Hot-Film Shock-Tube激波管)Velocity Sensors 7.Laser Doppler Anemometer 4/48 7.1.0 Flow Classifications ◆Classifications: Single-phase flow Two-phase flow Multi-phase flow ◆Flow Patterns: 2. (a)Two-phase Flow Patterns in Vertical Upflow Bubby Slug Churn Wispy-Annular Annular Bubbly Slug (b)Two-phase Flow Patterns in 0 Horizontal Flow Plug Annular 0 Stratified Annular with Mist Flow Figure 7.0 Gas/Liquid Flow Patterns Wave
7.1 Local Flow Velocity, Magnitude and Direction 1. Flow Visualization gives an overall view of flow patterns 2. Velocity Magnitude from Pitot-Static Tube (皮托静压管) 3. Velocity Direction from Yaw Tube (偏航管), Pivoted Vane(叶轮) and Servoed Sphere 4. Dynamic Wind-Vector(风矢量) Indicator 5. Hot-Wire and Hot-Film Anemometers(风速计) 6. Hot-Film Shock-Tube(激波管) Velocity Sensors 7. Laser Doppler Anemometer 3/48 7.1.0 Flow Classifications Classifications: − Single-phase flow − Two-phase flow − Multi-phase flow Flow Patterns: Figure 7.0 Gas/Liquid Flow Patterns (a) Two-phase Flow Patterns in Vertical Upflow (b) Two-phase Flow Patterns in Horizontal Flow 4/48
5/48 7.1.1 Flow Visualization -Methods Way 1:Introduction of tracer particles: ●In Liquid Flows: en Colored Dyes; n Hydrogen()bubbles formed in water by applying electric pulses. ●In Gas Flows: Smoke: Helium(氦气)-filled“soap”bubbles; n Gas molecules made luminous()by an ionizing electric spark. Way 2:Detection of flow related changes in fluid optical properties. ●Qualitative Method-Shadowgraph(阴影图)and Schilieren(纹影仪)methods: light and dark patterns related to flow conditions are produced by the bending of light rays as they pass through a region of varying density. Quantitative Technique: Interferometer:light/dark pattems are formed by interference effects resulting from phase shifts between a reference beam and the measuring beam. Particle Image Velocimetry (PIV):the liquid or gas flow must be seeded with near- neutrally-buoyant particles;the velocity of these particles is what is actually measured. Other Methods:Tomographic Techniques,Molecular Tagging Velocimetry, Holographic Techniques,etc. 6/48 7.1.1 Flow Visualization -Shadowgraph ◆Shadowgraph For compressible flow (Mach Number >0.3),density varies with velocity sufficiently to produce measurable effects; In principle,we cannot directly see a difference in temperature,a different gas, or a shock wave in the transparent air; ●However,,all these disturbances refract(折射)light rays,so they can cast(投射) shadows. Collimated light bea is used as light source. "Edgerton"shadowgram of the firing of an AK-47 assault rifle Images and artwork by Gary S.Settles,Penn State Gas Dynamics Lab
7.1.1 Flow Visualization - Methods Way 1: Introduction of tracer particles: z In Liquid Flows: Colored Dyes; Hydrogen(氢气) bubbles formed in water by applying electric pulses. z In Gas Flows: Smoke; Helium(氦气)-filled “soap” bubbles; Gas molecules made luminous(发光) by an ionizing electric spark. Way 2: Detection of flow related changes in fluid optical properties. z Qualitative Method - Shadowgraph(阴影图) and Schilieren(纹影仪) methods: light and dark patterns related to flow conditions are produced by the bending of light rays as they pass through a region of varying density. z Quantitative Technique: Interferometer: light/dark patterns are formed by interference effects resulting from phase shifts between a reference beam and the measuring beam. Particle Image Velocimetry (PIV): the liquid or gas flow must be seeded with nearneutrally-buoyant particles; the velocity of these particles is what is actually measured. Other Methods: Tomographic Techniques, Molecular Tagging Velocimetry, Holographic Techniques, etc. 5/48 7.1.1 Flow Visualization - Shadowgraph "focused" shadowgram of a common firecracker explosion Sunlight shadowgram of a martini glass A prehistoric shadowgraphy "Edgerton" shadowgram of the firing of an AK-47 assault rifle Images and artwork by Gary S. Settles, Penn State Gas Dynamics Lab Shadowgraph z For compressible flow (Mach Number >0.3), density varies with velocity sufficiently to produce measurable effects; z In principle, we cannot directly see a difference in temperature, a different gas, or a shock wave in the transparent air; z However, all these disturbances refract(折射) light rays, so they can cast (投射) shadows. z Collimated light beam is used as light source. 6/48
7/48 7.1.1 Flow Visualization -Schlieren ◆Schlieren Similar physics bases as shadowgraphy; The collimated light is focused with a lens,and a knife-edge is placed at the focal point,positioned to block about half the light. It Measures the first derivative of density in the direction of the knife-edge; Schlieren imaging of a focusing ultrasonic transducer http://en.wikipedia.org/wiki/Schlieren_photograph 8/48 7.1.1 Flow Visualization -PIV Principle Laser light sheet △y Flow plane At time between two pulses Velocity at A Ax particle displacement in x direction Ux=Ax/ras△f+0 Ay particle displacement in y direction Uy=△y/△t as At+0 Fig.7.1(a)Particle Image Velocimetry. Using multiple-exposure method,the location of particles at two times separated by a known time interval are used to compute the magnitude and direction of the particle's velocity
7.1.1 Flow Visualization - Schlieren Color schlieren image of the thermal plume from a burning candle, disturbed by a breeze from the right. Photographed by Gary S. Settles, Penn State University http://en.wikipedia.org/wiki/Schlieren_photograph Schlieren z Similar physics bases as shadowgraphy; z The collimated light is focused with a lens, and a knife-edge is placed at the focal point, positioned to block about half the light. z It Measures the first derivative of density in the direction of the knife-edge; Shock waves produced by a T-38 Talon during flight Schlieren imaging system setup: linear lens-based configuration Schlieren imaging of a focusing ultrasonic transducer 7/48 7.1.1 Flow Visualization – PIV Principle Fig. 7.1(a) Particle Image Velocimetry. Using multiple-exposure method, the location of particles at two times separated by a known time interval are used to compute the magnitude and direction of the particle’s velocity. 8/48
9/48 7.1.1 Flow Visualization -PIV Principle Universal mount and shutter Laser light Fiber manipulator sheet optics Laser Fiber optic cable Shutter drive unit CCD camera Computer with two monitors Timing box Fig.7.1(b)Particle Image Velocimetry.Using CCD camera to record images A complete system consists of a laser light source with optics,an image recording medium,a programmable time delay and sequence generator,camera interface,computer,and image acquisition/analysis software. 10/48 7.1.1 Flow Visualization -PIV Principle Fig.7.2 PIV Image of Transient Vortex(Structure in a Circular Jet Under good conditions and with proper equipment and technique,the accuracy of PIV technique is adequate for many applications Demonstration webpage:http://www.piv.de/piv/index.php
7.1.1 Flow Visualization – PIV Principle Fig. 7.1(b) Particle Image Velocimetry. Using CCD camera to record images A complete system consists of a laser light source with optics, an image recording medium, a programmable time delay and sequence generator, camera interface, computer, and image acquisition/analysis software. 9/48 7.1.1 Flow Visualization – PIV Principle Fig. 7.2 PIV Image of Transient Vortex (漩涡) Structure in a Circular Jet Under good conditions and with proper equipment and technique, the accuracy of PIV technique is adequate for many applications Demonstration webpage: http://www.piv.de/piv/index.php 10/48