174
7 Flow Visualisation Techniques
Fig. 7.12 Principle of a shadowgraph optical bench
Fig. 7.13 Shadowgraph of a space probe model fired in the ISL aeroballistic tunnel (© ISL)
Schlieren technique: this technique is slightly different; the light which is not
deflected by the gradient of the refractive index of the flow is suppressed by the use
of a knife (see Fig. 7.15). The method highlights the first derivative of the refractive
index of light, directly related to the density gradient. The Schlieren technique is
more sensitive than the shadowgraph because it offers greater dynamics of the grey
7 Flow Visualisation Techniques
Fig. 7.12 Principle of a shadowgraph optical bench
Fig. 7.13 Shadowgraph of a space probe model fired in the ISL aeroballistic tunnel (© ISL)
Schlieren technique: this technique is slightly different; the light which is not
deflected by the gradient of the refractive index of the flow is suppressed by the use
of a knife (see Fig. 7.15). The method highlights the first derivative of the refractive
index of light, directly related to the density gradient. The Schlieren technique is
more sensitive than the shadowgraph because it offers greater dynamics of the grey