One-Dimensional Performance Prediction of Subsonic Vaned Diffusers

A simple one-dimensional theory to predict the performance of a diffuser using as few empirical factors as possible is presented. The prediction method uses two empirical functions to assess both the pressure recovery and the losses. The functions have been calibrated from experimental data from the company’s standard diffusers. The method is, however, adaptable for any type of subsonic vaned diffusers, provided that the empirical functions can be calibrated from measurements. The pressure rise in the diffuser is calculated from the continuity equation, taking into account the blockage, while the losses are determined by means of displacement and momentum thickness. These values are calculated at design point from an integral boundary layer calculation. To take into account the influence of flow separation at off-design, the calculated displacement and momentum thickness are increased according to empirical functions. When designing a new impeller, the method provides a simple way to evaluate the diffuser, resulting in the best combination in terms of efficiency and range. It further provides a simple means of estimating the change to be expected in a known stage performance characteristic due to a modification of the diffuser geometry.[S0889-504X(00)01703-7]