Flow Instabilities in Cavitating and Non-Cavitating Pumps
Abstract
It is well known that flow instabilities called rotating stall and surge may occur in non-cavitating turbomachines at flow rates smaller than design. Rotating stall is a local instability at the turbomachinery which is basically not dependent on the hydraulic system in which the turbomachine is installed. The stalled region rotates faster than impeller. Surge is a system instability in a hydraulic system which includes a turbomachinery and a capacitance (tank) which stores the working fluid depending on the pressure at the capacitance. For pumps, if a certain quantity of air is trapped in the pipeline it serves as a capacitance and a surge may occur even if the pipeline does not include external capacitance. Both rotating stall and surge occur at smaller flow rates where the performance curve has a positive slope. On the other hand, cavitation instabilities called rotating cavitation and cavitation surge may occur even at the design flow rate. Rotating cavitation is a local instability in which the cavitated region rotates, for the most cases, faster than impeller. Cavitation surge is a system instability caused by cavitation. For cavitation surge, the cavitation at the inlet of turbomachinery serves as a capacitance and it can occur in a system without any external capacitance. The present lecture is intended to explain the mechanisms of the instabilities, rotating stall, surge, rotating cavitation, and cavitation surge, as well as the characteristics of those instabilities, based on dimensional stability analyses.
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 01, 2006
- Accession Number
- ADA476506
Entities
People
- Yoshinobu Tsujimoto
Organizations
- Osaka University