A theoretical and experimental investigation of flow through short axisymmetric contractions

Investigations have been made into the effect of curtailing the length of contracting ducts upon their performance. These ducts had wall velocity distributions approximating to a step change in velocity/pressure. Each duct had an overall contraction ratio of approximately 4:1, with outlet diameters of about 103 mm. Generally good agreement was obtained between the theoretical and experimental results. The presence of the boundary layer, however, reduces the effective area ratio of the contraction. It was inferred that a contraction boundary with a monotonic wall velocity distribution can be terminated at inlet and outlet wall slopes of 2 and 3.5 deg, respectively without impairing its performance. Also, adverse pressure gradients up to -0.38 can be permitted on the final portion of the contraction boundary without risking flow separation.