Optimization of the Shape of Receiving Aperture in a Phase Doppler System
The phase centroid of an aperture used in a phase/Doppler velocimeter (PDV) is introduced. It is defined as the point detector whose phase response is identical to the finite-area aperture of PDV. The phase centroid is fixed only for certain aperture shapes and certain particle size ranges. Guidelines are provided to obtain a spatially invariant phase centroid.
It is also shown that displacement of the phase centroid with the particle size can be used to advantage, so as to extend the size range of a system without sacrificing its sensitivity to sizing small particles. Using special aperture shapes, the phase-diameter relationship may be made non-linear (even if the corresponding point detectors have a linear response), so as to have a high sensitivity for small particles and reduce it gradually to cover a large size range within 360° range of phase shift. This arrangement leads to a rather uniform percent-of-the- reading sensitivity of the system. Furthermore, the ambiguity associated with the particle trajectory can be suppressed using shaped apertures.
KeywordsPhase Doppler Particulate Two-Phase Flow Optical Diagnostics
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