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research-article

An experimental study of stall suppression and associated changes to the flow structures in the tip region of an axial low speed fan rotor by axial casing grooves

[+] Author and Article Information
Huang Chen

Department of Mechanical Engineering, Johns Hopkins University, 223 Latrobe Hall, 3400 N. Charles Street, Baltimore, MD 21218
hchen98@jhu.edu

Yuanchao Li

Department of Mechanical Engineering, Johns Hopkins University, 223 Latrobe Hall, 3400 N. Charles Street, Baltimore, MD 21218
yli131@jhu.edu

Subhra Shankha Koley

Department of Mechanical Engineering, Johns Hopkins University, 223 Latrobe Hall, 3400 N. Charles Street, Baltimore, MD 21218
skoley1@jhu.edu

Nick Doeller

Department of Mechanical Engineering, Johns Hopkins University, 223 Latrobe Hall, 3400 N. Charles Street, Baltimore, MD 21218
nwdoeller@gmail.com

Joseph Katz

Department of Mechanical Engineering, Johns Hopkins University, 122 Latrobe Hall, 3400 N. Charles Street, Baltimore, MD 21218
katz@jhu.edu

1Corresponding author.

ASME doi:10.1115/1.4037910 History: Received August 23, 2017; Revised September 05, 2017

Abstract

The effects of axial casing grooves on the performance and flow structures in the tip region of an axial low speed fan rotor are studied experimentally in the JHU refractive index-matched liquid facility. The four-per-passage semicircular grooves are skewed by 45°, overlapping partially with the blade leading edge and extending upstream. They reduce the stall flow rate by 40% compared to the same machine with a smooth endwall. Stereo-PIV measurements show that the inflow into the downstream side of the grooves and the outflow from their upstream side varies periodically, peaking when the inlet is aligned with the blade pressure side. This periodic suction has three effects: First, substantial fractions of the leakage flow and the tip leakage vortex (TLV) are entrained into the groove, causing a reduction in TLV strength starting from mid-chord. Second, the grooves prevent the formation of large scale backflow vortices (BFVs), which are associated with the TLV, propagate from one blade passage to the next, and play a key role in the onset of rotating stall in the untreated fan. Third, the flow exiting from the grooves causes periodic variations of the relative flow angle around the blade leading edge, presumably affecting the blade loading. The distributions of turbulent kinetic energy provide statistical evidence that in contrast to the untreated casing, very little turbulence originating from the TLV and BFV of one blade propagates across the tip gap to the next passage.

Copyright (c) 2017 by ASME
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