Visualisation of rotating stall in an axial flow fan

• The visualisation of a flow field was performed within the rotor blades passage.
• Phase-locked averaging on the blade passing and rotating stall event was performed.
• 1020 PIV images were sorted and phase-locked averaged to replicate rotating stall.
• A sequence of images was composed presenting a flow field changing over 10° angular steps.
• The initiation and development of flow distortion and flow normalisation were clearly shown.

Visualisation of a flow field was performed within the rotor blade passage of an axial flow fan operating under rotating stall conditions. A PIV system was used to capture the velocity field at an 80% span of the rotor blade. PIV triggering was synchronized with the observed blades’ passing, and over 1000 PIV images were obtained. These were then phase-locked averaged, and a sequence of 36 images was composed. The successive images represented the evolution of a flow field within the blade passage with 10° angular steps and made it possible for the structure and behaviour of the flow within the rotor blade passage to be analysed under rotating stall conditions. The initiation and development of flow distortion were clearly shown to be influenced by the advance of the rotating stall cell and the restoration of normal flow with the rotating stall cell moving away.

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