AIRFLOW AND COMPRESSIBLE FLOW VISUALIZATION Flashcards
This technique simply consists in introducing into the working section
of a wind tunnel a number of fine smoke filaments, usually in the
plane of a section of the model wing under test.
Smoke Technique
_____________ is needed if the smoke filaments are to be clearly seen,
and an open circuit tunnel is required in order to get rid of the smoke
Good lighting
The main disadvantage os Smoke Technique
usually only isolated spanwise
positions can be examined, and not the flow over the whole wing.
The speed must not be _______, or ___________ will affect the paths of the smoke particles, curving these paths __________.
too low; gravity; downwards
If the speed is too high, the smoke filaments may become ________,
even when large quantities of smoke are introduced.
attenuated
If this is not achieved, the smoke will quickly become _____________.
diffused
The principal requirement of a smoke tunnel is for ____________
uniform flow with low turbulence.
This technique involves using a heated wire inserted into the airstream to produce a filament of air of different density from the mainstream.
Hot Wire Technique
Small volumes of air are heated by the discharge of a ______________.
series of
electric sparks
Similar to the hot wire in principle is the _______________
spark technique
Several methods of flow visualization consist in utilizing the changes in
the refractive index of air caused by changes in density.
Optical Methods
They may be used to investigate the flow in boundary layers, but their
main application is to the visualization of high-speed flow.
Optical Methods
When light passes through a region of a gas in which the density varies,
the changes in the refractive index of the gas associated with these
density changes cause the ____________
direction of the rays to be altered.
The amount of the deflection is proportional to the ___________
density gradient.
optical methods
There are three commonly used methods:
the shadowgraph, schlieren
and interferometer systems
The ___________ is the simplest, but the _____________ is more effective, and is the most commonly used of all three methods. ___________ is more difficult to interpret.
shadowgraph system; schlieren system; Interferometer
They are all based on the same principle, but, shadowgraph and schlieren are mainly useful simply for _________, and interferometer may also be used for ____________.
flow visualization; quantitative measurement
SHADOWGRAPH SYSTEM
Light from a point source is collimated by a lens, so that a parallel beam passes through the working section of the wind
tunnel on to ________, where an image of the working section then appears.
a screen
SHADOWGRAPH
If there is no model in the tunnel, the screen will be ____________.
uniformly illuminated
SHADOWGRAPH
If a model is introduced, its ___________ on the screen.
shadow will appear
SHADOWGRAPH
If light passes through a region of
_______________, the rays will diverge more and more, and the corresponding region on
the screen will be ___________.
increasing density gradient; lightened
Conversely, the area on the
screen corresponding to regions of
reducing density gradient in the
working section will be darkened.
Schlieren System
Light from a source is collimated by a lens, so that a parallel beam passes through the working section of the wind tunnel, is collected by __________, then passes through yet ___________ to project an image of the working section on to a screen.
another lens and brought to a focus; another lens
Schlieren System
At the focus position, a __________ is introduced, which can be moved into or out of the beam to cut out some or all of the light.
knife edge
Schlieren System
When the tunnel is empty, the intensity of illumination on the screen may be ______________, but it remains _____________ over the whole image area.
varied by moving the knife edge; uniform
