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In operating a turbomachine at off-design conditions various instabilities caused by anomalous flow phenomena occur and sometimes lead to the damage of a turbomachine. In order to avoid these phenomena various devices characteristic to each phenomenon have been developed, however they make turbomachines large-sized and cause efficiency drop. The present author has developed a very simple and innovative device, termed “J-groove,” of suppressing various anomalous flow phenomena commonly by controlling the angular momentum of the main flow. It has been revealed that J-groove makes an operation of a turbomachine stable in all flow range, causes little efficiency drop, and can be easily applied to an existing machine. Here is reviewed totally the results of suppressing various anomalous flow phenomena in turbomachines. Keywords : J-Groove, Anomalous Flow Phenomenon, Surge, Cavitation, Performance-curve Instability 1. Introduction In operating a turbomachine at off-design conditions there occur various instabilities caused by anomalous flow phenomena such as surge, rotating stall, cavitation, abnormal axial thrust, impeller whirl and so on. These anomalous phenomena often cause vibration and noise and sometimes lead to the damage of turbomachines. To avoid these phenomena various devices characteristic to each phenomenon have been developed so far[1]. However they make turbomachines large-sized and cause efficiency drop. The present author has found a very simple and innovative device to control and suppress a flow rotation considerably[2]. This device is only to install many shallow grooves on the inner casing wall of a turbomachine in the direction of pressure rise. As a turbomachine is principally an energy converter utilizing flow rotation, this device has a possibility of controlling the internal flow drastically. Thus the present device has been applied to various anomalous flow phenomena in many types of turbomachine and has succeeded in commonly suppressing various instabilities by controlling an angular momentum of the main flow. The present device, termed “J-groove,” shows variously different effects depending on the place of installation. When installed near the entrance of an impeller, J-groove has succeeded in suppressing the whirl of inlet flow, which made the performance-curve instability characterized by a rising head-capacity curve very stable. Thus J-groove can suppress surge without dropping the maximum efficiency in mixed flow and axial flow pumps[3][4]. When installed at the entrance of diffuser of a centrifugal flow type, rotating stall in a vaned and a vaneless diffusers has been perfectly suppressed in the entire flow range and the pressure fluctuation has disappeared[5][6]. Moreover it has improved cavitation performance[7] and reduced axial thrust largely[8]

J-Groove Technique for Suppressing Various Anomalous Flow Phenomena in Turbomachines