Tosurvive,every employee inBritishAerospace must recover or earn in the market place, each and every year:

(These figures are the approximate actual figures for every employee in the British Aerospace Corporation in the year 1977.)

Presentation of the Daniel and Florence Guggenheim International Memorial Lecture is both a high honour and a challenge. The challenge is implicit in the final two words—to present to you both a lecture and a fitting memorial to the remarkable Guggenheim family. I believe that the subject which I have chosen is particularly appropriate for this task. As many of you know, Daniel Guggenheim, in the years from 1925 to his death in 1930, sponsored and endowed the now famous Guggenheim Aeronautical Laboratories in major universities across the USA. It is clear from his writing that these were not simply gifts to the universities—conventional endowments—but that they reflected Daniel Guggenheim's vision of a future in which the aircraft would link cities and countries in a safe, efficient civil transport system surpassing all other modes of travel.

The aerodynamics of aeronautics to most people is prob-ably synonymous with the aerodynamics of streamlined shapes. By contrast aerodynamics outside of aeronautics may well conjure up a picture of a non-uniform airstream approaching a building, creating an unsteady, separated flow. That these pictures are misleading would be known to most of those connected with aeronautics—aircraft do develop separated, unsteady flows, and outside of aero-nautics there is interest in aerodynamic efficiency and smooth attached flows. Until comparatively recently, however, the need in aeronautics has been to increase aerodynamic efficiency, and virtually all major research topics seem to have been related to steady, smooth flows; the problems connected with separated and unsteady flows (e.g. wing stall, or buffeting in bomb bays) have, by contrast, usually been tackled on an ad hocbasis, without very much emphasis being given to understanding whythe flow was as it was.

In recent years the need for high Reynolds number wind tunnel facilities has led to the development of the Cryo-genic Wind Tunnel. In this type of tunnel, the flow is cooled to extremely low temperatures, with the result that at constant Mach number the Reynolds number is greatly increased whilst the power required to drive the tunnel is reduced. The cryogenic tunnel incorporates a means of injecting liquid nitrogen into the free stream. The evaporation of this liquid cools the flow and some or all of the tunnel structure. Once the required low temperature has been reached a steady flow of liquid nitrogen into the tunnel and gaseous nitrogen out balances the heat input through the walls and from the fan and maintains constant pressure in the circuit. In addition to providing increased Reynolds numbers at reduced drive power, the cryogenic wind tunnel possesses numerous other advantages over its ambient temperature counterpart. For a detailed theory see Ref. 1.