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Research Papers

On the Interactions of a Rotor Blade Tip Flow With Axial Casing Grooves in an Axial Compressor Near the Best Efficiency Point

[+] Author and Article Information
Huang Chen

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

Yuanchao Li

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

Joseph Katz

Department of Mechanical Engineering,
Johns Hopkins University,
122 Latrobe Hall,
3400 N. 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 14, 2018; final manuscript received August 21, 2018; published online October 22, 2018. Editor: Kenneth Hall.

J. Turbomach 141(1), 011007 (Oct 22, 2018) (14 pages) Paper No: TURBO-18-1201; doi: 10.1115/1.4041293 History: Received August 14, 2018; Revised August 21, 2018

Experiments in a refractive index-matched axial turbomachine facility show that semicircular skewed axial casing grooves (ACGs) reduce the stall flowrate by 40% but cause a 2.4% decrease in the maximum efficiency. Aiming to elucidate mechanism that might cause the reduced efficiency, stereo-PIV measurements examine the impact of the ACGs on the flow structure and turbulence in the tip region near the best efficiency point (BEP), and compare them to those occurring without grooves and at low flowrates. Results show that the periodic inflow into the groove peaks when the rotor blade pressure side (PS) overlaps with the downstream end of the groove, but diminishes when this end faces the suction side (SS). Entrainment of the PS boundary layer and its vorticity generates a vortical loop at the entrance to the groove, and a “discontinuity” in the tip leakage vortex (TLV) trajectory. During exposure to the SS, the backward tip leakage flow separates at the entrance to the groove, generating a counter-rotating circumferential “corner vortex,” which the TLV entrains into the passage at high flowrates. Interactions among these structures enlarge the TLV and create a broad area with secondary flows and elevated turbulence near the groove's downstream corner. A growing shear layer with weaker turbulence also originates from the upstream corner. The groove also increases the flow angle upstream of the blade tip and varies it periodically. Accordingly, the circulation shed from the blade tip and strength of leakage flow increase near the blade leading edge (LE).

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References

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Figures

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Fig. 1

(a) Configuration of the one and a half stages compressor. (b) and (c) The ACG configurations. All dimensions are in mm.

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Fig. 2

Experimental setups for (a) SPIV in meridional planes, and (b) SPIV in (z, θ) planes

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Fig. 3

Performance curves with and without the ACGs: (a) static head rise and (b) efficiency

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Fig. 4

Sample cavitation images showing vortical structures in the rotor passage with ACG (a) and (b) at φ = 0.35 for two different blade phases, and (c) at φ = 0.38. Entrances to the grooves are indicated by solid white lines, and their outlines are marked by dashed lines.

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Fig. 5

Ensemble-averaged vorticity (<ωθ>/Ω) distributions superimposed on vectors of (Uz, Ur) in meridional planes with casing grooves (left column) and a smooth end wall (right column) at φ = 0.35. A reference vector showing UT is indicated in the figure. Arrows in (d) highlight the counter-rotating vortex pair. Vectors are diluted by 3:1 in both directions for clarity: (a) and (e) s/c = 0.22, (b) and (f) s/c = 0.33, (c) and (g) s/c = 0.55, (d) and (h) s/c = 0.66.

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Fig. 6

A sample instantaneous vorticity (ωθ/Ω) and (Uz, Ur) distributions in the downstream meridional plane for s/c = 0.55 and φ = 0.35. Vectors are diluted by 2:1 in both directions.

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Fig. 7

Effect of flowrate on the distributions of <ωθ> (contour) superimposed on vectors of (Uz, Ur) at s/c = 0.44. Vectors are diluted by 4:1 in both directions: (a) s/c = 0.44, φ = 0.25, (b) s/c = 0.44, φ = 0.35, and (c) s/c = 0.44, φ = 0.38.

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Fig. 8

The distributions of <ωθ>/Ω around the blade tip for s/c = 0.66 and φ = 0.38. Vectors are diluted by 3:1 in both directions.

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Fig. 9

(a)–(d) Ensemble-averaged in-plane velocity vectors (nearly Uz, Uθ) superimposed on contours of the radial velocity (top row) and radial vorticity (second row) components at s/c = 0.33 and φ = 0.35. Left column: r* = 0.96. Right column: r* = 0.98. Vectors are diluted by 4:1 in both directions. (a) R1 plane, Ur, (b) R2 plane, Ur, (c) R1 plane, 〈ωr〉, (d) R2 plane, 〈ωr〉, and (e) a sketch illustrating the vortex-groove interactions.

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Fig. 10

Flow features at s/c = 0.33 and φ = 0.25 illustrating the vortex-groove interactions. (a) Ur contours in a radial plane at r* = 0.96. (b) and (c) θ>/Ω distributions at two meridional planes.

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Fig. 11

(a)–(d) Ensemble-averaged in-plane velocity vectors (nearly Uz, Uθ) superimposed on contours of the radial velocity (top row) and radial vorticity (second row) components at s/c = 0.55 and φ = 0.35. Left column: r* = 0.96; right column: r* = 0.98. (a) R1 plane, Ur, (b) R2 plane, Ur, (c) R1 plane, 〈ωr〉, (d) R2 plane, 〈ωr〉, and (e) a sketch illustrating the vortex-groove interactions.

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Fig. 12

Ensemble-averaged in-plane velocity vectors (nearly Uz, Uθ) at (a) r* = 0.96, and (b) r* = 0.98 superimposed on contours of the radial velocity at s/c = 0.55 and φ = 0.38: (a) R1 plane, Ur, (b) R2 plane, Ur

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Fig. 13

Distributions of relative flow angles in the rotor reference frame at s/c = −0.11 and φ = 0.35 in meridional planes (a) without and (b) with casing grooves, and (c) in (z, θ) plane at blade tip with casing grooves. Results from φ = 0.25 are shown in (d) for comparison. Dashed lines in (a) and (b) indicate the location of the blade LE at s/c = 0: (a) φ = 0.35, smooth end wall, meridional plane, (b) φ = 0.35, axial casing groove, meridional plane, (c) φ = 0.35, axial casing groove, R1 plane, and (d) φ = 0.25, axial casing groove, R1 plane.

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Fig. 14

Comparisons of (a) total positive circulation at blade SS and (b) tip leakage flow strength normal to the blade chord with and without casing grooves

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Fig. 15

Distribution of TKE (a) with and (b) without ACGs at s/c = 0.55 and φ = 0.35. Note the scale for the insert in (a) has a significantly smaller range. Contour lines show the circumferential vorticity.

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