An experimental investigation was undertaken to study the effect of various fences and vortex generator configurations in reducing the exit flow distortion and improving total pressure recovery in two-dimensional S-duct diffusers of different radius ratios. Detailed measurements including total pressure and velocity distribution, surface static pressure, skin friction, and boundary layer measurements were taken in a uniform inlet flow at a Reynolds number of 7.8×105. These measurements are presented here along with static pressure rise, distortion coefficient, and the transverse velocity vectors at the duct exit determined from the measured data. The results indicate that substantial improvement in static pressure rise and flow quality is possible with judicious deployment of fences and vortex generators.

Experimental studies have been carried out to compare the performance of two dimensional straight and curved diffusers of same area ratio and effective divergence angle in the Reynolds number range of7.8 X 105 to 1.29 X 105. Free stream turbulence effects have.also been studied at the increased turbulence level to 3.4per cent. The results indicate that straight diffuser pressure recovery is slightly higher as compared to the curved diffusers. However, stream turbulence, which improves the pressure recovery in both cases, has been observed to have greater effect in case of curved diffuser. Boundary layer velocity profiles on the diffuser surfaces have also been presented at various streamwise stations. It is observed that the growth of inner surface boundary layer has a major effects on losses in case of a curved diffuser. Nomenclature

In this paper, results are presented of an experimental investigation into the effectiveness of vortex generator jets in controlling secondary flows in two-dimensional S-duct diffusers. The experiments were performed in uniform and distorted inflow conditions and the performance evaluation of the diffuser was carried out in terms of static pressure recovery and quality of the exit flow. In the case with inflow distortion, tapered fin vortex generators were employed in addition to vortex generator jets to control flow separation that was detected on the wall with inflow distortion. Detailed measurements including total pressure, velocity distribution, surface static pressure, skin friction, and boundary layer measurements were taken at a Reynolds number of 7.8×105. These results are presented in terms of static pressure rise, distortion coefficient, and total pressure loss coefficient at the duct exit. For uniform inflow, the use of vortex generator jets resulted in more than a 30 percent decrease in total pressure loss and flow distortion coefficients. In combination with passive device (tapered fin vortex generators), the vortex generator jets reduce total pressure losses by about 25 percent for distorted inflow conditions. A potential application of this method may include control of secondary flows in turbo machinery.

This paper describes a study of the suitability of various loss models for axial turbines as assessed with a streamline curvature computing scheme for the meridional flow involved. The important loss models in this study include the Balje/Binsley loss correlation and its modification, and a recently modified form of the Ainley/Mathieson/Dunham/Came loss correlation. Test cases for the application of the computing scheme include single-, three-, and four-stage turbines for which extensive design and measured data are available. The computed results have been compared with test results for design and off-design mass flow rates and design pressure ratio. The results indicate that the Balje/Binsley profile loss correlation with the modified Dunham/Came secondary loss correlation give results that compare best with measured data. A modified form of the Ainley/Mathieson/Dunham/Came loss model is nearly as accurate.

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