The ability to capture information on physical systems (and particularly fluid flow data) at very high speed could never have been envisaged by previous generations. Instead, the flow would be observed and reported in simple, easily understood, terms, such as a sketch, a measured flow rate or an averaged velocity. For example, below images show some typical results presented by Leonardo da Vinci.

Da Vinci studied the flow of water into a distribution chamber and reduced his results to a series of black and white sketches, indicating how the surface of the water in the chamber was disturbed. These observations on the behaviour of a turbulent jet, and the manner in which turbulent eddies are formed and move in the body of the flow, are still recognised as valid today, despite the lack of instrumentation in those early days. Imagine how coloured presentations would have added to the impact of Da Vinci’s already considerable infl uence on experimental fluid mechanics.

Noting the current importance of digital technology, it is perhaps surprising to recall that the electronic calculator and the slide rule were still the most commonly used methods for large-scale calculations until the late 1970s. Contrast this with the situation today, where everyone can have desk top access (at relatively low cost) to a personal computer (PC). Moreover, the associated peripherals, such as the colour printer, mouse, keyboard and massive storage capacity, are ubiquitous, relatively low cost and demanded as a right by virtually every PC user. These developments have provided enormous benefits for the experimentalist, because of the many improved forms of instrumentation and data capture systems, together with more sophisticated methods of analysis and presentation, that are available.

In the present context, it is worth reflecting on the fact that the first digital computer only became operational in 1948. Since then, there have been continuing developments to the extent that digital technology now embraces not just computers but everyday devices, such as digital calculators, watches and clocks, controllers for central heating systems and other domestic appliances, such as microwaves and washing machines, digital cameras and scanners, mobile phones, digital video discs, personal music players, the internet and other devices. automobile insurance.

Many of the measurement techniques introduced in the past twenty years make use of the principals of optics and rely, more often than not, on the properties of the light emitted by a laser (light amplification by stimulated emission and radiation). After over fifty years of intensive development, the name laser is now applied to a whole family of light-emitting devices, following the introduction of the first laser in the mid-1950s. The principal characteristic of a laser is its ability to produce an intense beam of light at a precisely specified wavelength that is collimated so that the diameter of its cross section remains the same over very long distances.

Another family of spectroscopic methods relies on the detection and analysis of the wavelength distributions of the light emitted by the target substance, after irradiation by a laser source. These light scattering methods can be employed to measure the chemical composition of a fluid, or the concentration of combustion products in flue gases.