Evaluation and Optimization of a Multi-component Planar Doppler Velocimetry System

Abstract

A Planar Doppler Velocimetry system has been developed for multi-component velocity measurements in large scale subsonic wind tunnel facilities. System components, methodologies and improvements are evaluated and discussed. Data is presented on two component measurements conducted in the flow field above a 70 degree delta wing at an angle of attack of 23 degrees in a Mach 0.2 (69 m/s) free stream. Although only two components of velocity could be resolved, axial and spanwise measurements were made characterizing the velocity field associated with the vortex cores as they developed downstream. Detector placement and system performance was improved in a second test to measure the three dimensional velocity field above a Boeing UCAV model again at 20 degrees angle of attack operated in a Mach 0.2 free stream. The evolution of the three dimensional velocity field created by vortices from the sharp leading edge of the body and the outboard vortex above the wing was characterized. Further optimization of the current system indicated that current levels of uncertainty can be improved by proper camera placement to reduce the sensitivity to laser frequency fluctuations and by improving the linear independence of the measured velocity components as characterized by the condition number of the coefficient matrix. Other considerations of camera placement and considerations to make measurements are also discussed.

Investigation into the selection of viewing configurations for three-component planar Doppler velocimetry measurements

“…In our previous publications 9 and those of others 8,[10][11][12][13][14] assessments of the level of errors, and their causes, have been investigated. However, these investigations have focussed on determining the level of error in the measured components and there has only been limited investigation 8,15,16 into how these errors propagate through the transformation matrix used to map data from the nonorthogonal to the orthogonal coordinate system. Reinath 8 derived expressions for the uncertainty in the computed orthogonal velocity, Nobes et al 15 suggest the use of the condition number of the transformation matrix as a measure of the suitability of a viewing configuration and Elliot et al 16 suggest special case geometries where laser frequency fluctuations are cancelled out in the transformation to the orthogonal velocity components.…”