7. Conclusion

Optical methods for visualizing flows are most often used for the qualitative understanding of phenomena encountered in fluid mechanics. In the general case of three-dimensional flows, it is not at all easy to trace variations in light intensity measured on the detector (photograph, electronic camera) back to variations in the refractive index of the transparent object under study, and then to variations in density, for example. As we have seen, we have access to variations in the optical path of light after it has passed through the flow. As a result, tracing local information back to a given point in the fluid is only possible in special cases of two-dimensional phenomena or those possessing symmetry (e.g. objects of revolution). In the general case, it is necessary to take n images of the flow in n different directions (the principle of tomography or tomoscopy) and then compute the information...