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Research Papers

Numerical Assessment of the Noise Signature Sidewall Contamination of a Linear Cascade With Moving Bars

[+] Author and Article Information
Manuel A. Burgos

Department of Fluid Dynamics, Universidad Politécnica de Cartagena, 30203 Cartagene, Spainmanuel.burgos@upct.es

Roque Corral

Department of Technology and Methods, Industria de Turbo Propulsores S.A., 28830 Madrid, Spainroque.corral@itp.es

J. Turbomach 133(1), 011006 (Sep 09, 2010) (10 pages) doi:10.1115/1.4000487 History: Received July 29, 2008; Revised February 13, 2009; Published September 09, 2010; Online September 09, 2010

The effect of the finite extent of a linear cascade on the acoustic and vortical modes generated at the cascade exit by a set of moving bars located at the inlet is assessed by means of a numerical study. The sidewall interference is studied for an airfoil, which is representative of the midsection of a low pressure turbine airfoil. The deviations from the purely periodic steady state have been also investigated. It is concluded that both the unsteady pressure distributions on the airfoil and the mode-decomposition at the cascade exit show a reasonable matching with the purely periodic case, provided that the nominal interblade phase angle is taken into account to postprocess the numerical data. This conclusion is a key element to the investigation of the scattering and propagation of pure tones in turbomachinery in high speed linear cascades.

Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Sketch of nonperiodic unsteady phenomena

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Figure 2

Typical hybrid-cell grid and associated dual mesh

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Figure 3

Sketch of the field interactions that take place in a rotor/stator configuration at two different time instants

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Figure 4

Nondimensional unsteady pressure amplitude on the midairfoil of a seven-airfoil cascade produced by a vortical periodic disturbance for different IBPAs (Mis=0.5 and St=4.9). Solid line: periodic solution. Dashed line: cascade solution.

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Figure 5

Comparison of the unsteady pressure distribution on the different airfoils of the CLT2 cascade (Mis=0.5, σ=−120 deg, and St=4.9)

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Figure 6

Modulus of unsteady pressure perturbation due to a vortical sinusoidal perturbation on a cascade made up of seven CLT2 airfoils. Mis=0.5, σ=−120 deg, and St=4.9.

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Figure 7

Phase error in the midpoints of the pressure side (circles) and suction side (squares) of the CLT2 seven-airfoil cascade as a function of the IBPA (Mis=0.5 and St=4.9)

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Figure 8

Comparison of the normalized vertical velocity (a) and static pressure (b) mode-decomposition at the exit of the CLT2 seven-airfoil cascade (△) with the periodic case (●) (σ=30 deg, Mexit=0.5, St=4.9, Re=∞, and N=7)

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Figure 9

Comparison of the normalized vertical velocity (a) and static pressure (b) mode-decomposition at the exit of the CLT2 seven-airfoil cascade (△) with the periodic case (●) (σ=180 deg, Mexit=0.5, St=4.9, Re=∞, and N=7)

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Figure 10

Comparison of the normalized vorticity mode at the exit of the CLT2 seven-airfoil cascade (triangles) with the periodic case (circles) for different IBPAs

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Figure 11

Grid sensitivity study on Mach number (top left), unsteady pressure (top right), vortical modes (bottom left), and acoustic modes (bottom right) for the CLT2 linear cascade. IBPA=30 deg, Mexit=0.5, St=4.9, Re=∞, and N=7. o: fine mesh and △: coarse mesh.

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Figure 12

Influence of the cascade airfoil number of in the vortical modes for the IBPA=30 deg, Mexit=0.5, St=4.9, and Re=∞. Left: N=5. Right: N=9 for the CLT2 linear cascade.

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Figure 13

Sketch of the nominal (solid line) and perturbed (dashed line) five-airfoil cascades for geometry sensitivity studies

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Figure 14

Cascade geometry sensitivity on Mach number (top left), unsteady pressure (top right), vortical modes (bottom left), and acoustic modes (bottom right) for the CLT2 linear cascade. IBPA=30 deg, Mexit=0.5, St=4.9, and Re=∞.

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Figure 15

Comparison of the normalized unsteady pressure (bottom) mode-decomposition at the exit of the CLT2 seven-airfoil cascade (◻) for an exit isentropic Mach number (top) of 0.8 and St=4.9 with the periodic case (△) for σ=30 deg (left) and σ=180 deg (right)

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Figure 16

Comparison of the normalized vertical velocity (a) and unsteady pressure (b) mode-decomposition at the exit of the CLT2 seven-airfoil cascade with the periodic case (△) for σ=30 deg, M=0.5, St=2.2, and Re=∞

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Figure 17

Isentropic Mach number distribution for the CLT2 airfoil. Mexit=0.5 and Re=1.5×105.

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Figure 18

Mode-decomposition of the normalized vertical velocity (top) and unsteady pressure (bottom) at the exit of the CLT2 seven-airfoil cascade (◻) for σ=30 deg (left) and σ=180 deg (right). St=4.9, Mexit=0.5, and Re=1.5×105.

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