Performance Chart and Optimum Geometries of Conical Diffusers with Uniform Inlet Flow and Tailpipe Discharge

Abstract

To obtain the best performance and the optimum geometries for a wide range of conical diffusers, experiments using air flow have been carried out on many conical diffusers having a uniform inlet flow except for the thin inlet boundary layer and tailpipe discharge. When the cone angle, 2α, is between 4 and 30 degrees, the performance may be expressed with a fair degree of accuracy by the functions of cone angles and area ratios with and without appreciable stall, respectively. Pressure recovery coefficients and effectiveness are shown on one chart, together with the optimum geometry lines of diffusers, when the tailpipe length is longer than its pressure recovery length. The pressure recovery length of the tailpipe is examined experimentally. If the tailpipe length is longer than three times the diameter of the tailpipe, the decrease in performance is less than two percent, as compared with the case having a sufficiently long tailpipe. This is true even in the diffuser with a cone angle as large as 30 degrees.