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

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.

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

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

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

Flow Past a Cylinder Clouds past a mountain

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

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

Schlieren flow visualizationShadowgraph Bullet at supersonic speed

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

Insects walking on water

Drop falling on liquid surface Normal laminar flow chain

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

Buoyant jet in stratified fluid Tear ducts in wine glass

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

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

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

Laser Doppler Velocimetry Optical Methods

Particle Image Velocimetry

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 P H Sensitive dyes Light extinction Scattering Fluorescence methods.

I f = I e  CL, Where  = Quantum efficiency of the dye  = Attenuation coefficient L =Spatial extent of illuminated volume under consideration

Buoyant jet from GFDL, CAOS

Pressure –Pressure transducers –Pressure Sensitive Paints

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

Thank you