Flow Flow VisualizationVisualization

By: Jagpal Singh PawarRoll NO:2007/12

Flow VisualizationFlow VisualizationFlow visualization plays an important role in the understanding of fluid mechanics since “seeing is believing” and most of the fluids and their motions are invisible to human eyes.

There are many techniques have been developed over the years to provide an “eye-catching” way to allow us to visualize the motions of fluids and their interactions with the surroundings.

Flow VisualizationFlow Visualization

Flow visualization in fluid dynamics is used to make the flow patterns visible,

In order to get a qualitative or quantitative information on them.

Most fluids (air, water, etc.) are transparent, thus their flow patterns are invisible to us without some special methods to make them visible.

Methods of visualizationMethods of visualization

Surface flow

visualization

Particle tracer methods

Optical methods

Surface flow visualizationSurface flow visualization

The interaction of a fluid with the surface of a solid body is subjected to a shear forces , pressure forces and heating loads.

For estimating the rates of momentum, mass, and heat transfer rate is to visualize the flow pattern very close to body surface

Surface flow visualizationSurface flow visualization

In this technique the surface can be coated with the thin layer of a material/ oil , which the interaction with the fluid flow, develops a certain visible pattern.

Texture-based flow visualization on a curved surface for an automotive CFD simulation.

Surface flow visualizationSurface flow visualizationF-18 HARV fore body surface flow visualization at 26 degree angle of attack

A glycol-based liquid, released through very small holes around the nose of an FA-18

Particle tracer methodsParticle tracer methodsParticles, such as smoke or ink, can

be added to a flow to trace the fluid motion.

We can illuminate the particles with a sheet of laser light.

Particles Smoke

ChimneyPositive Jet

Optical Techniques for Optical Techniques for Flow VisualizationFlow Visualization

Schlieren photographyShadowgraphInterferometry

All depend of the fact that the speed of light and the index of refraction varies with the density of fluid flow.

Schlieren PhotographySchlieren Photography

Schlieren photography is a visual process that is used to photograph the flow of fluids of varying density.

Invented by the German physicist August Toepler in 1864 to study supersonic motion.

It is widely used in aeronautical engineering

Schematics view of Schlieren flow visualizationSchematics view of Schlieren flow visualization

Light rays from light source are collimated by a lens 1. It produce a parallel beam of light which passes through the test section. The rays then pass through lens2 and produce an image. Then image is cut off by knife edge and block half the light at the focal point Beyond the cut off is a lens3 which forms an image of the flow on the screen.

Screen record this image

Schlieren PhotographySchlieren Photography

A Schlieren photograph showing the compression in front of an upswept wing at Mach 1.2

Shock waves produced by a T-38 Talon during flight

Schlieren PhotographySchlieren Photography

Schlieren Imaging Photography – Supersonic Wind Tunnel (Shape-sphere)

Schlieren Imaging Photography – Supersonic Wind Tunnel (Shape-Cone)

ShadowgraphShadowgraph

Shadowgraph is a type of flow visualization.

Shadowgraph is an optical method that use in transparent media like air, water.

It is related to Schlieren photography methods , but simpler than it.

Simple Concept Visible with naked eye

Schematics of shadowgraph flow visualisationSchematics of shadowgraph flow visualisation

Light rays from a source are collimated by a lens; Producing a parallel beam of light which passes through the test-

section. In the absence of flow, intensity distribution will be uniform at

screen. When flow is on, light rays are deflected resulting in the non-

uniform intensity distribution at display screen.

Simple phenomena of Simple phenomena of ShadowgraphShadowgraph

Shadowgraph ImagesShadowgraph Images

Bullet ShadowgraphBullet Shadowgraph

Shadowgraph ImagesShadowgraph Images

Shadowgraph ImagesShadowgraph Images

Shadowgraph image of supersonic bullet

InterferometryInterferometryInterferometry is a techniques in which

waves, usually electromagnetic, are superimposed in order to take information about the waves.

Interferometry is an important investigative technique in the fields of fiber optics, engineering metrology, chemistry, quantum mechanics, nuclear physics.

Interferometers are widely used in science and industry for the measurement of small displacements, refractive index changes.

Schematics of InterferometerSchematics of Interferometer

Light rays from a source are collimated by a lens 1 and split into two streams One stream to the mirror 1 which reflect s a parallel beam of light rays to the test section,

and there after projected on screen. And the second stream which passes trough the splitter 1 projected on Mirror 2 which

reflect the light to splitter 2 and reunites with first beam coming from mirror M 1 and the moves to the screen.

In the absence of flow, both the beams give the same pattern of illumination on screen But when flow is on , various shades of pattern are made up on screen

Interferometer Interferometer Images

Shock wave from a gun seen with flow Shock wave from a gun seen with flow visualization technique visualization technique

Interferometer Images of Interferometer Images of Turbine Turbine

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