COMPARISON OF OPTICAL MEASUREMENT TECHNIQUES FOR TURBOMACHINERY FLOWFIELDS

A preliminary set of measurements were made of the flowfield in the Pu rdue Research Centrifugal Compressor using a laser two-focus (L2F) vel ocimeter and a laser Doppler velocimeter (LDV). After a review of the preliminary results, the LDV system was chosen to continue this resear ch due to the advantages it demonstrated over the L2F system in making measurements in this flowfield. The L2F data are compared and contras ted to the LDV data. While this comparison is not to insinuate the loc al features of the LDV data are universally correct, an evaluation of the global features of the compressor flowfieid based upon the LDV mea surements demonstrate consistency, i.e., measurements at various plane s in the flowfield demonstrate conservation of mass and a reasonable d istribution of work in the compressor. In addition, methodologies to d etermine the effect of the measurement volume geometry for the two sys tems are presented. Finally, the advantages and disadvantages of using the L2F system for turbomachinery flowfields is discussed in terms of measurement accuracy, applicability to general turbomachinery flowfie lds, and the capability to make measurements in regions of high noise due to stray reflections. Specific examples based upon this experiment al work are presented.