Optimizations for optical velocity measurements in narrow gaps

Raimund Schlüßler; Christian Blechschmidt; Jürgen W. Czarske; Andreas Fischer

doi:10.1117/1.OE.52.9.094101

Abstract

Measuring the flow velocity in small gaps or near a surface with a nonintrusive optical measurement technique is a challenging measurement task, as disturbing light reflections from the surface appear. However, these measurements are important, e.g., in order to understand and to design the leakage flow in the tip gap between the rotor blade end face and the housing of a turbomachine. Hence, methods to reduce the interfering light power and to correct measurement errors caused by it need to be developed and verified. Different alternatives of minimizing the interfering light power for optical flow measurements in small gaps are presented. By optimizing the beam shape of the applied illumination beam using a numerical diffraction simulation, the interfering light power is reduced by up to a factor of 100. In combination with a decrease of the reflection coefficient of the rotor blade surface, an additional reduction of the interfering light power below the used scattered light power is possible. Furthermore, a correction algorithm to decrease the measurement uncertainty of disturbed measurements is derived. These improvements enable optical three-dimensional three-component flow velocity measurements in submillimeter gaps or near a surface.

Citation Download Citation

Raimund Schlüßler, Christian Blechschmidt, Jürgen W. Czarske, Andreas Fischer, "Optimizations for optical velocity measurements in narrow gaps," Optical Engineering 52(9), 094101 (3 September 2013). https://doi.org/10.1117/1.OE.52.9.094101

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