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Clarification of Performance Curve Instability Mechanism Using Large Eddy Simulation of Internal Flow of a Mixed-Flow Pump

[+] Author Affiliations
Isao Hagiya, Masashi Fukaya

Hitachi, Ltd., Hitachinaka, Japan

Chisachi Kato

University of Tokyo, Meguro, Japan

Yoshinobu Yamade

Mizuho Information & Research Institute, Inc., Chiyoda, Japan

Takahide Nagahara

Hitachi, Ltd., Tsuchiura, Japan

Paper No. AJKFluids2015-33438, pp. V01AT33A008; 7 pages
doi:10.1115/AJKFluids2015-33438
From:
  • ASME/JSME/KSME 2015 Joint Fluids Engineering Conference
  • Volume 1A: Symposia, Part 2
  • Seoul, South Korea, July 26–31, 2015
  • Conference Sponsors: Fluids Engineering Division
  • ISBN: 978-0-7918-5721-3
  • Copyright © 2015 by JSME

abstract

We analyzed the internal flows of a test mixed-flow pump exhibiting performance curve instability at low flow rates by using LES to clarify the performance curve instability mechanism. The LES was conducted using the open source software FrontFlow/blue [1]. In particular, we investigated in detail the flows at the flow rates, where the head curve had a positive slope under low flow rate condition.

We clarified that Euler’s head drop caused by a stall near the tip of the rotor-blades is a dominant factor at the instability of the test pump. At the bottom point of the positive slope of the head curve, stall regions covered all the rotor-blade passages on the tip side. The drop of the angular momentum in the impeller caused by the stall on the leading edge side exceeds the increment caused by the decrease in the flow rate on the trailing edge at the bottom point of the positive slope.

At the middle point of the positive slope of the head curve we also found regions with low-velocities in some blade passages. Such regions, namely stall cells, rotated around the impeller for one revolution while the impeller rotated almost about 20 revolutions in the direction opposite to the impeller’s rotation. The region with low-velocity first appears at the trailing edge and expands toward the leading edge. The angle of attack of the neighbouring blade in the direction opposite to the rotation of the blade increases and that blade pitch begins to stall. When that blade pitch is fully stalled, it is no longer loaded and the positive pressure gradient in that blade pitch decreases. The blade pitch is most likely to accept the excess flow. It recovers from the stalled state.

Copyright © 2015 by JSME

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