Passive Control of Abnormal flow phenomena in Turbomachinery

The objective of this study is to suppress and control The abnormal phenomena in turbomachinery dueswirl flow such as a rotating stall in the vaned and vanless diffuser性能-curve instability caused by the reverse flow at the impeller inlet in the centrifugal，mixed and axial pumpsa rotating cavitation in the pumps and the draft surge of water turbine by use of the angularmomentum defect of flow in the shallow grooves mounted parallel to the pressure gradient on thecasing wall.In this study，following results and remarks been obtained. the performance curve instabilitycharacterized by a local dent in head-capacity curve or an uprising head-capacity curve in mixedflow pump has been suppressed and controlled by use of the shallow grooves located with properdimension. suppression of rotating stall in The vaneless diffuser has been obtained and made . suppression of rotating stall in The vaneless diffuserclear the mechanism of reducing a swirl by the grooves theoretically and experimentally. by theoptimization of groove dimension，the rotating stall of the vaned diffuser has been suppressed completely. To reveal the possibilityand the effect of the shallow grooves on controlling and reducing the swirl intensity of a runneroutlet flow,a steady rotational flow in a conical diffuser of divergent angle of 30 degree was studiedexperimentally. The results showed that The shallow grooves with adequate dimensions can reduce Theswirl rate of the main flow 85% of the inlet swirl without additional hydraulic loss.This studyshowed that the abnormal flow phenomena in turbomachinery can control without decreasing theefficiency by use of the shallow grooves mounted parallel to the pressure gradient on the casingwall。

The objective of this study is to suppress and control the abnormal phenomena in turbomachinery due to the swirl flow such as a rotating stall in the vaned and vanless diffuser, a performance-curve instability caused by the reverse flow at the impeller inlet in the centrifugal, mixed and axial pumps, a rotating cavitation in the pumps and the draft surge of water turbine by use of the angular momentum defect of flow in the shallow grooves mounted parallel to the pressure gradient on the casing wall.In this study, the following results and remarks have been obtained.・ The performance curve instability characterized by a local dent in head-capacity curve or an uprising head-capacity curve in mixed flow pump has been suppressed and controlled by use of the shallow grooves located with proper dimension.・ The suppression of rotating stall in the vaneless diffuser has been obtained and made clear the mechanism of reducing a swirl by the grooves theoretically and experimentally.・ By the optimization of groove dimension, the rotating stall of the vaned diffuser has been suppressed completely.・ To reveal the possibility and the effect of the shallow grooves on controlling and reducing the swirl intensity of a runner outlet flow, a steady rotational flow in a conical diffuser of divergent angle of 30 degree was studied experimentally. The results showed that the shallow grooves with adequate dimensions can reduce the swirl rate of the main flow 85% of the inlet swirl without additional hydraulic loss.This study showed that the abnormal flow phenomena in turbomachinery can control without decreasing the efficiency by use of the shallow grooves mounted parallel to the pressure gradient on the casing wall.