Novel Processing Tools for Automated Doppler Picture Velocimetry (DPV) evaluation

Article type: Research Article

Authors: Seiler, F. | Pichler, A. | Pfaff, R. | Srulijes, J.

Affiliations: French-German Research Institute of Saint-Louis (ISL) 5, rue du Général Cassagnou, 68301 Saint-Louis, France | Control Theory and Application Centre, Coventry University, Priory Street, Coventry, Great Britain

Abstract: A unique technique, the Doppler Picture Velocimetry (DPV), for measuring and visualizing velocities especially in hypersonic gas flows is presented. By means of a Michelson interferometer (MI) the Doppler shifted light scattered by tracers is transformed into an image showing Fizeau fringes. The image fringe distribution provides information on the Doppler frequency shift which is related to the velocity of the particles crossing a light sheet plane. To overcome former disadvantages of DPV, the optical set-up as well as the processing scheme have been improved significantly. Two schemes have been tested in recent times for fringe processing: 1) an alternative process, the Least Square Estimators (LES) and 2) an algorithm based on a technique using Fast Fourier Transformations (FFT) to examine the DPV images in the frequency domain. The new DPV algorithms now allow an automated calculation of the velocity profiles from the Doppler pictures without manual fringe tracing as it had to be done in the past. Both methods are compared by means of Mach 6 flows around a wedge and a sphere produced in the ISL high energy shock tunnel STA. TiO_2 particles are illuminated by a laser light sheet which was perpendicularly arranged to the main flow direction. Light observation via the MI from the side (90° to illumination) informs on the vertically oriented velocity through the DPV images.

Keywords: 2D Doppler velocity measurements, hypersonic flow, light sheet, tracer, velocity visualization, Michelson interferometer, sphere and wedge flow velocity visualization

Journal: Journal of Visualization, vol. 12, no. 4, pp. 323-337, 2009