Publication de 6 numéros par an
ISSN Imprimer: 2150-766X
ISSN En ligne: 2150-7678
Indexed in
DEVELOPMENT OF LASER DIAGNOSTIC TECHNIQUES FOR FULL-FIELD VELOCITY MEASUREMENTS
RÉSUMÉ
The significance of velocity fields becomes evident in the discussion of heat-transfer measurement techniques in internal combustion engines. In the analysis of convective heat-transfer, local velocity values are of general interest. To obtain a maximum number of valuable data sets of the flow field, the illuminating laser sheet is positioned into the plane of main flow direction. Injected particles following the streamline of the flow become visible when flooded with a laser light during a certain exposure time. The resulting trace pattern is recorded on photographic film for following image analysis procedures. Two methods are presented in order to cover the dynamic range of velocity measurements.
In the case of speckle velocimetry, a Young's fringe processor for speckle photographs is described, which allows measurement of fringe separation and orientation with an estimated accuracy of 1% and 1°, respectively.
We also address the problem of image processing associated with data reduction, data filtering and data evaluation to characterize the flow more in an automatic mode than with manual support. First, the image is enhanced, and a high contrast value assignment by thresholding is performed.
This is followed by image data-analysis procedures which allow determination of the total displacement distance over the whole particle trace image as well as calculation of the flow direction. The acquired data ratio of the particle trace lengths, in combination with the exposure time, determines a two-dimensional vector field plot and gives access to the effective velocity values.