‫ كلية الهندسة‬- ‫جامعة القصيم‬
Al-Qassim University
‫قسم الهندسة الميكانيكية‬
College of Engineering
Department of Mechanical Engineering
Experiment-1
Flow visualization
Thermo-fluid lab-1
Introduction
Flow visualization is the art of making flow patterns visible. Flow visualization can
be appreciated on several levels. Most fluids (air, water, etc.) are transparent,
thus their flow patterns are invisible to us without some special methods to make
them visible. On another level, we know the governing equations of fluid motion
(the Navier-Stokes equations), but they are nonlinear partial differential equations
with very few general solutions of practical utility. We can solve them numerically
with modern computer methods, but these solutions may not correspond to
nature unless verified by experimental results. On still another level the NavierStokes equations are pattern generators, and natural fluid flows display
corresponding patterns that can recur on scales differing by many orders of
magnitude. Such fluid patterns are familiar to almost everyone: the bathtub
vortex and the tornado, the smoke ring and the mushroom cloud, the swinging of
wires in the wind and the collapse of a historic bridge due to forced oscillations
from vortex shedding.
The following topics are covered by the flow visualization wind tunnel:
- flow patterns of real fluids around bodies
- separation phenomena on bodies
- demonstration of turbulent and laminar flow influence of the angle of
incidence of a body
- air flow around a symmetric wing
- air flow through a slit diaphragm
- air flow around a cylinder
The following topics are covered by the flow visualization apparatus:
- definition of flow and path lines in the field of fluid mechanics
- representation of parallel flow lines around obstacles
- influence of various obstacles shapes on the flow
- test of the influences of sources and negative sources on flow lines
Objective
-
Flow diagrams for a real fluid when flowing around bodies
Onset of boundary layer separation on bodies
Demonstration of turbulent and laminar flow
Influence of angle of incidence
Flow around a symmetrical and an asymmetrical wing
Flow around the cylinder
- Depiction of streamlines in the flow around bodies
- Effect of bodies of different shape on the flow
Apparatus
Flow visualization wind tunnel
The bench top unit contains a narrow flow chamber with viewing window in which
the drag model is placed. The airflow is generated using a blower. To obtain a flow
with low turbulence, the air passes through a settling chamber, a fine sieve and a
flow straightener. Smoke is used to make the streamlines visible. The smoke is
generated by vaporizing a glycol mixture and enters the tunnel via a manifold with
a large number of outlet holes. The flow patterns can be clearly seen due to the
black background of the flow chamber and additional lighting. Four different
models (cylinder, orifice and two wing sections) are supplied. They can be
interchanged and have an adjustable angle of attack.
Specification
[1] Bench top unit for visualization of stream lines around different bodies
[2] Illuminated experimental area with transparent panel and black background
[3] Wind tunnel with radial fan and smoke generator
[4] Low-turbulence flow due to stabilization chamber and flow straightener
[5] 4 different models, adjustable angle of incidence
[6] Graduated scale indicates angle of incidence of model
[7] 230V, 50Hz, 1 phase
Theory
The flow of a fluid, e.g. air, around a body can be observed by rendering the
streamlines visible. In the case of stationary flows, these streamlines coincide with
the trajectories of the individual fluid particles.
The smoke tunnel recording of the cylinder in an air flow is shown in Fig. 5.1 as is
evident, the flow around the upper part of the body is smooth but becomes
turbulent from a certain point on ward where the streamlines start to separate from
the body.
In the case of the air flow around the wing profile Fig. 5.2, the separation is not
nearly as pronounced. However, the turbulence increases as Reynolds’s number Re
decreases:
Re = ρuL/ν
Where:
u: air speed
L: length of the wing profile
ρ: Density of air (20C˚, ρ=1.29kg/m³)
ν: Dynamic viscosity of air
Fig. (1.1)
Fig. (1.2)
Experimental procedure
- Connect of the exhaust-air hose to the end piece.
- Loosen the knurled screws on the front panel.
- Remove the front panel.
- Change the flow model.
- Connect the smoke generator electrically with the control unit and turn on.
- Turn on the lamp on the remote trigger.
- To achieve good result, perform the experiment at low wind speed.
Report
In the Report:
- Use your mobile to take a picture for the flow of a fluid around a body.
- Use several shapes of bodies with different speed of wind to see the behavior of
the flow around these bodies and show the region of laminar and turbulent and
take a picture for each body.
- Discuss your result and write your conclusion.