The development of Particle Image Velocimetry towards a versatile experimental tool for turbulence research

Abstract

The particle image velocimetry technique (PIV) allows to measure instantaneous flow velocity fields within a thin sheet or a small volume illuminated by laser light by determining the velocity of tracer particles following the flow faithfully. PIV is under development for more than 25 years. Due to the fast progress made in the field of computers, lasers, electronics, video technique etc. in the past decade it was possible to set up reliable, modular and mobile advanced measurement systems which cannot only be used for fundamental research such as turbulent flows but also in industrial test facilities such as in large wind tunnels. The latter being one of DLR’s primary objectives, teams of the University of Oldenburg and DLR carried out measurements of the instantaneous flow field by means of Particle Image Velocimetry for the first time in a wind tunnel of DLR Göttingen back in 1984. In those days the recording of the PIV images had to be done photographically. Also, the evaluation of the recordings to obtain the displacement of the images of the tracer particles, added to the flow, had to be performed optically. A few months later DLR had the first double oscillator Nd:YAG laser at its disposal and started the development of a PIV system applicable for aerodynamic research in large industrial wind tunnels. Around 1995 a major breakthrough in the development of PIV, which has been a prerequisite to bring this technique out of the laboratory, has been made. Then, digital video cameras, allowing capturing the two frames of a PIV recording within a short time interval and with full spatial resolution became available. In the following decade the PIV technique has been widely spread and differentiated into many distinct applications ranging from micro flows to combustion and supersonic flows, both for research and industrial needs. Nowadays the PIV technique is considered a ‘validated tool’ by the aeronautical industry and used in large industrial wind tunnels to support the design of new aircraft to reduce drag, noise etc. to meet the challenges of VISION 2020. The presentation will give a short historical overview of the development of the PIV technique from photographical PIV recording and evaluation to high speed PIV and tomographic PIV, which became important tools for turbulence research.