Advanced synchronization techniques for complex flow field investigations by means of PIV

1 Introduction Since PIV became a mature technology for flow field investigations in industrial research, see for instance Kompenhans et al. (1998), it has been increasingly challenged by more complicate applications. As far as static models in wind tunnels are concerned, the experiment does not need to be synchronized with the measuring instrument. However, for the examination of dynamic systems synchronization becomes crucial. Recently, the continuous but alternating and, with regard to the measurement system, asynchronous wake flow of a helicopter's rotor blade was interfaced with a PIV system in order to investigate defined planes in the rotor blade's frame of reference, see Raffel et al. (1998). This test is the first of two examples which are described in this paper. Within the framework of the European research program WAVENC (WAke Vortex evolution and wake vortex ENCounter, Brite/EuRam project BE97-4112) PIV has been applied to a discontinuous experiment, i.e. the wake flow of a free flying airliner model in the catapult facility of ONERA, Lille. The goal was to provide an experimental database for the far-wake evolution of the trailing vortices. The data base will be used to validate CFD calculations. First results of the PIV measurements as well as a comparison with smoke visualization tests have already been presented by Dieterle et al. (1999a). A general description of the PIV experiments is given by Dieterle et al. (1999b). Beside this two applications a technical description of the synchronization hard-and software which has been developed in cooperation DLR in Göttingen and HARDsoft and which is distributed in license by PIVTEC will be presented. 2 The sequencer The sequencer is a completely microprocessor-controlled pulse generator. It enables the generation of complex patterns of TTL pulse trains on multiple channels. The pulse width, the time interval, the number of pulses and the output channel number are software programmable. The first sequencer was developed some years ago as a part of a ultra high-speed video camera system (Stasicki et al. 1995) to synchronize the recorded event with the eight independent camera shutters and the eight light pulse generators in the Cranz-Schardin configuration. Since that time, a whole sequencer family has been designed and manufactured. Due to their flexibility, sequencers have been integrated into several demanding scientific systems for triggering and synchronizing of their components. 3 The principle of the operation The block circuit of the sequencer is displayed in Fig. 1. It has …