To date, experimental studies of the flow in logarithmic spiral curved diffusers have been carried out under various conditions in order to clarify their characteristics and to improve their performances. In this study, effects of the existence of a guide vane and the variation in logarithmic spiral angle on the pressure distributions along both diffuser walls, the velocity and vector distributions in a curved diffuser, and the diffuser efficiency are clarified. As a result of this study, the following became clear. The diffuser efficiency was improved for all logarithmic spiral angles when a guide vane was interposed in the curved diffuser, and the improvement in the diffuser efficiency was enhanced as the logarithmic spiral angle β was made large. In the range increased of values for which this experiment was performed, consequently, a desirable diffuser efficiency could be obtained over a wide range of the logarithmic spiral angle β as compared with the result for the case in which a guide vane was not interposed.
