LASER VELOCIMETRY FOR AERODYNAMIC FLOW CHARACTERIZATION

Laser velocimetry is a nonintrusive method which gives the velocity of air flows around or inside models installed in wind tunnels. The mean and turbulent fields are easily available, with very good accuracy an d reliability. ONERA has been working in the field of velocity measure ment since 1970, and has developed operational three-dimensional laser velocimeters, a mosaic laser velocimeter for large facilities, and PI V (Particle Image Velocimetry) and DGV (Doppler Global Velocimetry) se tups. These two last techniques provide instantaneous images of the ve locity flow field. In the past and up to now, point methods as fringe velocimeters and laser two-focus velocimeters were mostly used. They h ave given a tremendous amount of valuable data which improved understa nding of complex flows and allowed CFD code validation and resolution of problems raised by recirculation regions, mixing layers, cyclic phe nomena, highly turbulent flows, etc. Some examples are given. Point me thods lack the capability to show the instantaneous pattern of unstabl e flows such as moving vortices. New methods are now available which p rovide instantaneous maps of the velocity field such as PIV, already o perational, or DGV, still in development, In conclusion the techniques each have their own specificities and must be considered as complemen tary.