Module 3 - Airflow and Compressible Flow Visualization Flashcards
Methods that have been developed for visualizing the nature of fluid flow, inside and outside the boundary layer, past wind tunnel models.
flow visualization techniques
Two types of flow visualization techniques
- smoke technique
- hot wire technique
The smoke technique simply consists in introducing into the ______________ of a wind tunnel a number of _________________, usually in the _____________ of the model wing under test.
working section, fine smoke filaments, plane of a section
As the particles of smoke move ______________, the filaments define the ______________ which, in steady flow, are the same as the ______________.
downstream, particle paths, streamlines
Allows the observation of streamline pattern
Smoke technique
Phenomena that may be demonstrated using the smoke technique
- trailing vortices
- breakdown of streamline flow in a region of separated flow
- unsteady nature of the flow in the wake of a wing or other obstacle
The principle requirement of a smoke tunnel is for _____________ with ________________. If this is not achieved, the smoke will quickly become ____________.
uniform flow, low turbulence, diffused
Smoke Tunnel: The speed must not be too low, or ___________________ of the smoke particles, curving these paths ____________. On the other hand, if the speed is too high, the smoke filaments may become ____________, even when ______________ of smoke are introduced.
gravity will affect the paths, downwards, attenuated, large quantities
_______________ is needed if the smoke
filaments are to be clearly seen, and an _______________ is required in order
to get rid of the smoke.
Good lighting, open circuit tunnel
Three types of light used in an experiment in order to determine the best light to be used for smoke tunnels and which of these is the best?
- fluorescent
- led
- halogen/cold light (best)
From a smoke generator, how is smoke being introduced into the smoke tunnel?
probes or rakes
Explain the basic workings of a smoke-wire tunnel
A smoke wire is suspended in the test section, using a mass to straighten/strengthen the wire with a DC power supply for the smoke generator. It also uses a cold light for better visualization.
What is the main disadvantage of using a smoke visualization technique?
usually only isolated spanwise positions can be examined, and not the flow over the whole wing, in other words, only 2D examinations can be observed
factors to consider before performing smoke visualization technique
- wind tunnel should be fixed
- check the oil
- check the pressure
- check the mounting of the model
- flow should be stabilized
- turn on the lights
- set the smoke generator
The hot wire technique involves using a _____________ inserted into the ___________ to produce a filament of air of _______________ from the mainstream.
heated wire, airstream, different density
Hot Wire: The path of this filament can then be followed by using ___________________, in the context of their use with _____________________.
one of several optical systems, high speed wind tunnels
A technique similar in theory to the hot wire technique
spark technique
Spark Technique: Small volumes of air are heated by the discharge of a __________________. An _____________ is used to trace paths of such ‘_____________.’
series of electric sparks, optical system, particles
Optical systems have been used to photograph _________________ in ________________________.
velocity distributions, boundary layers
For many studies of fluid flow, the main information required about the boundary layer consists of:
- knowledge of the nature of the layer, whether laminar or turbulent
- the position of the transition point
- the position of the separation point, if any
Which type of methods are beneficial in acquiring the main information required about the boundary layer?
visual methods
Methods used in boundary layer investigation
- use of smoke
- gas filament method
- china clay method
- liquid film method
- use of wool tufts
Use of Smoke: A __________________ is introduced ________________ of the model.
very thin filament of smoke, very close to the surface
Use of Smoke: The main difficulty is to ensure that there are _____________ at the point where the smoke is ______________________.
no disturbances, introduced into the boundary layer