Performance Improvement of S-shaped Diffuser Using Momentum Imparting Technique

Abstract

This paper presents the improvement in performance of S-shaped diffuser with rectangular inlet having aspect ratio 2 & rectangular outlet having area ratio 2 having downstream settling length of 0.5B at Reynolds number 1.37 × 10 5 with a uniform velocity of 30 m/s due to momentum imparting technique. In this technique a cylinder of 0.3B diameter is placed at the inflexion plane across the width of the diffuser. Cylinder is rotated at different speed varying from 1500 rad/s to 4000 rad/s to impart momentum to the retarded fluid. A computer program based on finite volume technique, using standard k-e turbulence model, has been adopted and modified to predict the flow. The results obtained from this study indicate increased pressure recovery accompanied with decrease in non-uniformity in flow at the exit till 3000 rad/s. Beyond this rotational speed, the recovery drops with simultaneous increase in non-uniformity. The pressure recovery of 53.56% without cylinder improves to 85.53% with 3000 rad/s rotational speed of the cylinder. The corresponding decrease in Non-uniformity in flow at the exit is around 2%. This paper also shows the qualitative representation of secondary flow velocity in the form of contours at the diffuser exit. These variations also support the outcome of this study.