Flow Visualization and Measurement Techniques in Fluid Flows

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24 Οκτ 2013 (πριν από 3 χρόνια και 9 μήνες)

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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 visualization

Shadowgraph

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