Flow Visualization and Measurement Techniques in Fluid Flows

CAOS PresentationL.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 visualizationLeonardo 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 aerofoilSide- laminar smoke jet

Schlieren flow visualizationShadowgraph

Bullet at supersonic speed

Flow over AerofoilSide –particle visualizationBelow –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• PH Sensitive dyes• Light extinction• Scattering• Fluorescence methods.

If = IeCL,

Where = Quantum efficiency of the dye = Attenuation coefficientL =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