ABSTRACT
Gaseous flows are important parts of many industrial processes. They are important in machines such as fans, pumps and ventilators, which are major components of many factory systems, and in aviation, which has become remarkably widespread in recent years. A large amount of research is aimed at improving the efficiency of these machines, and, to a great extent, this research involves understanding basic hydro-or fluid-dynamic mechanisms that occur in these devices. Experimental methods for measuring quantities associated with the flow include measurement of the pressure at the walls around the flow and measurement of flow properties such as temperature using instruments inserted into the flow. These instruments, however, often perturb the flow or have poor temporal and spatial resolution. When such measurements can be made, it is sometimes difficult to analyse the measured data to obtain accurate information about the flow. For these reasons, accurate non-perturbing measurement techniques are desired. Optical diagnostic techniques are well suited for these measurements, but practical methods became possible only with the development of lasers and their associated optical technology.
