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Research Papers

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 North Charles Street,
Baltimore, MD 21218
e-mail: hchen98@jhu.edu

Yuanchao Li

Department of Mechanical Engineering,
Johns Hopkins University,
223 Latrobe Hall,
3400 North Charles Street,
Baltimore, MD 21218
e-mail: yli131@jhu.edu

Subhra Shankha Koley

Department of Mechanical Engineering,
Johns Hopkins University,
223 Latrobe Hall,
3400 North Charles Street,
Baltimore, MD 21218
e-mail: skoley1@jhu.edu

Nick Doeller

Department of Mechanical Engineering,
Johns Hopkins University,
223 Latrobe Hall,
3400 North Charles Street,
Baltimore, MD 21218
e-mail: nwdoeller@gmail.com

Joseph Katz

Department of Mechanical Engineering,
Johns Hopkins University,
122 Latrobe Hall,
3400 North Charles Street,
Baltimore, MD 21218
e-mail: katz@jhu.edu

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received August 23, 2017; final manuscript received September 5, 2017; published online October 3, 2017. Editor: Kenneth Hall.

J. Turbomach 139(12), 121010 (Oct 03, 2017) (14 pages) Paper No: TURBO-17-1135; doi: 10.1115/1.4037910 History: Received August 23, 2017; Revised September 05, 2017

The effects of axial casing grooves (ACGs) 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 deg, overlapping partially with the blade leading edge (LE) and extending upstream. They reduce the stall flow rate by 40% compared to the same machine with a smooth endwall. Stereo-particle image velocimetry (SPIV) measurements show that the inflow into the downstream side of the grooves and the outflow from their upstream side vary periodically, peaking when the inlet is aligned with the blade pressure side (PS). 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 midchord. 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 LE, presumably affecting the blade loading. The distributions of turbulent kinetic energy (TKE) 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 © 2017 by ASME
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Figures

Grahic Jump Location
Fig. 1

(a) Configuration of the one and a half stages axial low speed fan and (b) a perspective view of the IGV with ACGs

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Fig. 2

The ACG configuration: (a) radial view and (b) streamwise view (looking upstream). All dimensions are in mm.

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Fig. 3

Experimental setups for: (a) cavitation flow visualization, (b) SPIV in three meridional planes, (c) SPIV in a (z, θ) plane intersecting the blade tip at r* = 0.96, and (d) 2D time-resolved PIV inside a groove

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Fig. 4

Performance curves for h/c = 1.8%, with and without the ACGs

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Fig. 5

Sample cavitation images showing vortical structures in the rotor passage without (left column) and with ACG (right column). Top row (a) and (b): φ = 0.35, and bottom row (c) and (d): φ = 0.25. Entrances to the grooves are indicated by solid gray lines, and their outlines are marked by dashed lines. Insert in (d) is a magnified view of the groove corner.

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Fig. 6

Ensemble-averaged in-plane velocity vectors (nearly Uz, Uθ) superimposed on contours of the radial velocity component (r* = 0.96). Vectors are diluted by 4:1 in both directions for clarity. The values of s/c indicate the intersection of the θ2 plane with the blade chord: (a) s/c = 0, (b) s/c = 0.22, (c) s/c = 0.33, (d) s/c = 0.55, (e) s/c = 0.66, and (f) s/c = 0.98.

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Fig. 7

Cavitation images at: (a) s/c = 0.22 and (b) s/c = 0.33

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Fig. 8

Samples of instantaneous vectors of in-plane velocity components and contours of plane-normal vorticity in the center plane of the groove. (a) s/c = 0.22, when the blade PS is exposed to the groove, and (b) s/c = 0.44, when the SS is located downstream of the groove.

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Fig. 9

Ensemble-averaged vorticity and velocity distributions in meridional planes θ1 (left column), θ2 (middle column), and θ3 (right column) when θ2 intersects the blade at s/c = 0.22. Top row: <ωθ>/Ω; second row: Ur/UT; third row: Uz/UT and bottom row: Uθ/UT. Vectors are diluted by 5:1 in both directions for clarity in the top row. Dash lines indicate the zero values.

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Fig. 10

Ensemble-averaged vorticity and velocity distributions in meridional planes θ1 (left column), θ2, (middle column), and θ3 (right column) when θ2 intersects the blade at s/c = 0.33. Top row: <ωθ>/Ω; second row: Ur/UT; third row: Uz/UT and bottom row: Uθ/UT.

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Fig. 11

Ensemble-averaged vorticity and velocity distributions in meridional planes θ1 (left column), θ2, (middle column), andθ3 (right column) when θ2 intersects the blade at s/c = 0.55. Top row: <ωθ>/Ω; second row: Ur/UT; third row: Uz/UT and bottom row: Uθ/UT.

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Fig. 12

Positive circulation: (a) over the entire blade SS and (b) in the TLV

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Fig. 13

(a) Contours of the distribution of Uθ at s/c = 0.44 and φ = 0.25 in the untreated rotor. The black lines are contours of circumferential vorticity. (b) A sample image shown an early phase of BFV formation at s/c = 0.44. The arrow shows the measured direction of ensemble-averaged vorticity at the point indicated in (a).

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Fig. 14

Contours comparing the distribution of Uθ at φ = 0.25 and s/c = −0.11, i.e., upstream of the blade LE, in the: (a) rotor with ACGs and (b) untreated rotor. Dashed lines indicate the location of the blade LE at s/c = 0.0.

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Fig. 15

Comparison of TKE distributions with casing grooves (left column) and smooth casing (right column): (a) and (b) s/c = 0.22, (c) and (d) s/c = 0.33, and (e) and (f) s/c = 0.66. Note the scale for the insert in (a) has a significant smaller range.

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Fig. 16

Distribution of relative flow angles in the rotor reference frame. (a) (z, θ) plane at r* = 0.96, (b) and (c) θ1, θ2 planes when the θ2 plane is at s/c = 0. Insert in (b) shows the relative flow angle in θ1 for the untreated case.

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