Chapter 7
Flow Visualisation Techniques
7.1 Earlier Contribution to Visualisation Techniques
In aerodynamics and more generally fluid mechanics one has the invaluable advantage of being interested in the physical phenomena that can be visualised directly,
unlike other disciplines where only the consequences of the phenomena can be
observed. While studying fluid flows, engineers and researchers have developed
more or less sophisticated visualisation techniques to help them in their approach.
Among the forerunners of aerodynamics, it is worth mentioning Étienne-Jules Marey
(1830–1904) whose visualisations served as a starting point for the first modern wind
tunnel, designed by Gustave Eiffel and installed at the foot of the tower in 1909. The
device developed by Marey consisted of producing very thin and parallel smoke
streams flowing vertically and sucked downwards by a fan (see Fig. 7.1). Then by
placing an obstacle in the flow, the deviation in the path of the smoke while passing around the obstacle can be studied. Marey developed several devices, the latest
version showing the speed of the flow of the smoke by taking a series of snapshots
which is in fact a predecessor of the PIV. Smoke visualisations are still used to detect
flow separations or vortices generated by the vehicle or models (see below).
Another very old visualisation method is to use tufts (silk, woollen or any other
fibre) whose ends are glued to the surface of the model. Like a boat sail, the free
end is aligned or flapping in the flow, thus indicating the direction of the flow and its
fluctuations respectively, confirming the existence of unsteadiness. This technique is
very economical and easy to implement and is still used to detect regions of separated
flow (see Fig. 7.2).
Optical techniques are of primary interest for the visualisation of shock phenomena in high-speed flows showing zones of rapid expansion and compressions,
boundary layers and wakes. There are many visualisation methods that have emerged
in aerodynamics, but will be not all treated here. In the following, we limit ourselves
to the visualisation techniques mostly used in today’s applications.
© Springer Nature Switzerland AG 2020
B. Chanetz et al., Experimental Aerodynamics,
Springer Tracts in Mechanical Engineering,
https://doi.org/10.1007/978-3-030-35562-3_7
165
Flow Visualisation Techniques
7.1 Earlier Contribution to Visualisation Techniques
In aerodynamics and more generally fluid mechanics one has the invaluable advantage of being interested in the physical phenomena that can be visualised directly,
unlike other disciplines where only the consequences of the phenomena can be
observed. While studying fluid flows, engineers and researchers have developed
more or less sophisticated visualisation techniques to help them in their approach.
Among the forerunners of aerodynamics, it is worth mentioning Étienne-Jules Marey
(1830–1904) whose visualisations served as a starting point for the first modern wind
tunnel, designed by Gustave Eiffel and installed at the foot of the tower in 1909. The
device developed by Marey consisted of producing very thin and parallel smoke
streams flowing vertically and sucked downwards by a fan (see Fig. 7.1). Then by
placing an obstacle in the flow, the deviation in the path of the smoke while passing around the obstacle can be studied. Marey developed several devices, the latest
version showing the speed of the flow of the smoke by taking a series of snapshots
which is in fact a predecessor of the PIV. Smoke visualisations are still used to detect
flow separations or vortices generated by the vehicle or models (see below).
Another very old visualisation method is to use tufts (silk, woollen or any other
fibre) whose ends are glued to the surface of the model. Like a boat sail, the free
end is aligned or flapping in the flow, thus indicating the direction of the flow and its
fluctuations respectively, confirming the existence of unsteadiness. This technique is
very economical and easy to implement and is still used to detect regions of separated
flow (see Fig. 7.2).
Optical techniques are of primary interest for the visualisation of shock phenomena in high-speed flows showing zones of rapid expansion and compressions,
boundary layers and wakes. There are many visualisation methods that have emerged
in aerodynamics, but will be not all treated here. In the following, we limit ourselves
to the visualisation techniques mostly used in today’s applications.
© Springer Nature Switzerland AG 2020
B. Chanetz et al., Experimental Aerodynamics,
Springer Tracts in Mechanical Engineering,
https://doi.org/10.1007/978-3-030-35562-3_7
165