Industrial applications of image based measurement techniques in aerodynamics – Problems, progress and future needs

Abstract

Since two decades technological progress at lasers, video techniques, optoelectronics, computers and evaluation algorithms allow to extract quantitative information from images of flows, mostly for those of technical interest. Continuous improvement of such image based measurement techniques and decreasing costs of equipment enabled many research groups to exploit these techniques for extraction of 2 dimensional or even 3-dimensional data mainly for fundamental research. Since a decade ago many image based measurement techniques have found interest in aerodynamics and are even used as a matter of routine in industrial applications, especially in large wind tunnels or at in-flight testing. Quantitatively measurable values of interest for aerodynamics are pressure (Pressure Sensitive Paint, PSP), velocity (Particle Image Velocimetry, PIV), location of transition lines (Temperature Sensitive Paint, TSP), density (Background Oriented Schlieren Method, BOS), and sound pressure (Acoustic Microphone Array Technique), in parallel with the determination of deformation (Image Pattern Correlation Technique, IPCT) and position of the model in the wind tunnel or of the wing of an airplane in flight (Position and Deformation Measurement System, PDMS) ; Kompenhans et al., 2006a, 2006b. Application is mainly performed in the scope of large industrial projects in European co-operation. For this purpose mobile measurement systems have been developed by the department, which can be flexibly adjusted to particular testing environments. All data is acquired non-intrusively so that no interference of the flow field by the measurement is to occur. In consequence, the methods developed are particularly suited for the aero-dynamical and aero-acoustical analysis of complex, unsteady three-dimensional flow fields. The paper will report on the state-of-the-art of the application of image based measurement techniques by the Department of Experimental Methods in aerodynamics and will describe current problems and future needs, in particular with respect to optics.