7.5 Visualisation by Optical Imaging
179
Such an interferometer has significant advantages over other visualisation
techniques:
– it is relatively insensitive to vibrations and imperfections of the optics
– it offers a great flexibility in the visualisation of different phenomena, in particular
in very low-density gases, the sensitivity being adjustable by the choice of the
Wollaston prism angle.
Figure 7.20 shows a false-colour image, obtained by differential interferometry
of the separation of two half-cylinders surrounding a sting which produced a shock
in the tunnel at Mach 4.5, for altitude conditions of 13.9 km.
To highlight the differences in sensitivity between the methods, Fig. 7.21 compares
the three visualisation techniques used in the ISL shock tunnel. The case presented
corresponds to the flow past a sphere for the Mach number of 10 at altitude conditions
of 50 km.
Fig. 7.20 Image obtained by
differential interferometry of
the separation of two
half-cylinders (© ISL)
(a) Shadowgraph
(b) Schlieren
(c) Differential interferometry
Fig. 7.21 Visualisations of the flow past a sphere at Mach 10 for an altitude of 50 km (© ISL)
179
Such an interferometer has significant advantages over other visualisation
techniques:
– it is relatively insensitive to vibrations and imperfections of the optics
– it offers a great flexibility in the visualisation of different phenomena, in particular
in very low-density gases, the sensitivity being adjustable by the choice of the
Wollaston prism angle.
Figure 7.20 shows a false-colour image, obtained by differential interferometry
of the separation of two half-cylinders surrounding a sting which produced a shock
in the tunnel at Mach 4.5, for altitude conditions of 13.9 km.
To highlight the differences in sensitivity between the methods, Fig. 7.21 compares
the three visualisation techniques used in the ISL shock tunnel. The case presented
corresponds to the flow past a sphere for the Mach number of 10 at altitude conditions
of 50 km.
Fig. 7.20 Image obtained by
differential interferometry of
the separation of two
half-cylinders (© ISL)
(a) Shadowgraph
(b) Schlieren
(c) Differential interferometry
Fig. 7.21 Visualisations of the flow past a sphere at Mach 10 for an altitude of 50 km (© ISL)