Flow Visualization and Measurement Techniques in Fluid Flows

1. Flow Visualization and Measurement Techniques in Fluid Flows CAOS Presentation L.Kiranmayi

2. Understanding Fluid Flows • Dynamics causing the flow (forces) • Pressure, buoyancy, inertia, viscous forces, surface forces…. Etc. • Effects of these forces on the flow (Flow and fluid properties) • Velocity, acceleration, vorticity • Viscosity, temperature, scalar concentration, density …. Etc.

3. Why Flow Visualization • Understanding flow phenomenon • Verifying model or theory results • Easier measurements for designing • To get a priori knowledge of solution

4. What we need to visualize? • Stream lines • a line, tangent to which at any given instant is the velocity vector at that point • Streak lines • locus of particles which have passed through a prescribed point during a specified time interval • Path lines • locus of points traversed by a given fluid particle during some specified time interval • Time lines • line joining different adjacent points at any instant of time

6. Flow visualization Leonardo Da Vinci’s Hand drawings Naturally occurring flow visualization

7. Flow Past a Cylinder Clouds past a mountain

8. Methods of flow visualization • Gas flows • Smoke visualization • Particle • Shadowgraphs and Schlieren • Liquid flows • Dye • Shadowgraphs and Schlieren • Particles • Bubbles • Fluorescence, phosphorescence

9. Some gas flow visualization images Smoke visualization Top- flow past aerofoil Side- laminar smoke jet

10. Shadowgraph Schlieren flow visualization Bullet at supersonic speed

11. Liquid flows Flow over Aerofoil Side –particle visualization Below –dye visualization

12. Insects walking on water

13. Drop falling on liquid surface Normal laminar flow chain

14. Jets and Plumes • Top left- flow below an ice cube in water • Top right- near field of a jet • Side- jet and flame jet

15. Buoyant jet in stratified fluid Tear ducts in wine glass

16. Vortex Interactions Head on collision of vortex rings Leap-frog movement of vortex rings

17. Measurements in Flows • Velocity • Conventional methods • Pitot tubes • Hotwire anemometers • Local steady state measurements • Vane anemometers • Non intrusive methods • Laser Doppler Velocimetry • Particle Image Velocimetry • Particle Tracking Velocimetry

18. Orifice meter for velocity in pipes Pitot Static tube Hot wire Anemometer

19. Optical Methods Laser Doppler Velocimetry

21. Particle Image Velocimetry

23. Concentration • Conventional • Sample analyzers • Collecting samples by introducing samplers in the flow • Conductivity probes • Depends on the conductivity of the scalar being used • Optical methods • PH Sensitive dyes • Light extinction • Scattering • Fluorescence methods.

24. If = IeCL, Where  = Quantum efficiency of the dye  = Attenuation coefficient L =Spatial extent of illuminated volume under consideration

25. Buoyant jet from GFDL, CAOS

26. Pressure • Pressure transducers • Pressure Sensitive Paints

27. Temperature • Thermister probes • Change in resistance with temperature • Thermocouples • Voltage produced at junction of two metals depends on temperature • Temperature Sensitive Paints • Density • From Absorption/ scattering/refractive index • Capacitance/vibrations

28. Thank you