On the use of colour in experimental fluid mechanics

Abstract

This paper discusses how colour is used in experimental fl uid fl ow studies. Firstly, colour (defi ned scientifi cally by the wavelength of the light) can be used to discriminate between different channels in optical instrumentation, making it possible to measure several fl ow properties, simultaneously, and without any intrusion into the fl ow. These aspects of modern fl ow measurement are discussed in terms of some examples. Alternatively, the results of the fl ow measurement may be represented in the form of images, graphs and three-dimensional schematics with colour being used to identify and emphasise particular features that might otherwise remain concealed. The experimental results presented in the paper confi rm that using colour to discriminate between sets of data has several important advantages over the older black and white or grey scale forms of representation. Not only do colours provide an excellent basis for communication through graphical and three-dimensional presentations, but the resulting clarity may also help to reveal complex forms of flfl ow behaviour. Moreover, the inherent artistic appeal of some colour representations can draw the viewer into the technical detail, helping to simplify physical phenomena in ways that would not otherwise be possible. Although the observations made on the presentation of data are illustrated with reference to a number of experimental fl uid fl ow problems, many of the methods and observations would be applicable in other situations, where scientifi c or technological data needs to be presented.