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Research Papers

Numerical Investigation on the Self-Induced Unsteadiness in Tip Leakage Flow for a Transonic Fan Rotor

[+] Author and Article Information
Juan Du

 Graduate School of Chinese Academy of Sciences, Beijing 100190, China; Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing 100190, China; Key Laboratory of Advanced Energy and Power, IET, CAS, Beijing 100190, China

Feng Lin

 Tri-State University, Angola, IN 46703

Hongwu Zhang, Jingyi Chen

Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing 100080, China; Key Laboratory of Advanced Energy and Power, CAS, Beijing 100080, China

J. Turbomach 132(2), 021017 (Jan 20, 2010) (9 pages) doi:10.1115/1.3145103 History: Received August 14, 2008; Revised February 23, 2009; Published January 20, 2010; Online January 20, 2010

A numerical investigation on the self-induced unsteadiness in tip leakage flow is presented for a transonic fan rotor. NASA Rotor 67 is chosen as the computational model. It is found that under certain conditions the self-induced unsteadiness can be originated from the interaction of two important driving “forces:” the incoming main flow and the tip leakage flow. Among all the simulated cases, the self-induced unsteadiness exists when the size of the tip clearance is equal to or larger than the design tip clearance. The originating mechanism of the unsteadiness is clarified through time-dependent internal flow patterns in the rotor tip region. It is demonstrated that when strong enough, the tip leakage flow impinges the pressure side of neighboring blade and alters the blade loading significantly. The blade loading in turn changes the strength of the tip leakage flow and results in a flow oscillation with a typical signature frequency. This periodic process is further illustrated by the time-space relation between the driving forces. A correlation based on the momentum ratio of tip leakage flow over the incoming main flow at the tip region is used as an indicator for the onset of the self-induced unsteadiness in tip leakage flow. It is discussed that the interaction between shock wave and tip leakage vortex does not initiate the self-induced unsteadiness, but might be the cause of other types of unsteadiness, such as broad-banded turbulence unsteadiness.

Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 3

Computed and measured adiabatic efficiency characteristic for design tip clearance. (a) Operating condition near peak efficiency (Point I). (b) Operating condition near stall (Point II).

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Figure 4

Comparison of computed and measured relative Mach number at 90% span from hub for design tip clearance

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Figure 5

Computed total pressure ratio characteristic for three tip clearance sizes

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Figure 6

Static pressure rms distribution for Rotor 67 at T2

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Figure 7

Frequency and amplitude characteristics in the rotor tip region at 99% span

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Figure 1

Measurement location and computation region

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Figure 2

Computational geometry and grid distribution for Rotor 67

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Figure 9

Schematic of the unsteady process of self-induced tip leakage flow

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Figure 10

Contour plot of velocity perturbation of tip leakage flow

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Figure 11

Schematic of formation of B2 at 20/30 T with an addition of instantaneous velocity of tip leakage flow

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Figure 12

Relative total pressure coefficient distribution for operating conditions S1, S2, and U3. (a) 3D, steady (S1); (b) 3D, steady (S2); and (c) 3D, unsteady (U3).

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Figure 13

Relative total pressure coefficient distribution at 98.4% span for tip clearance of 2.2% tip chord. (a) Steady (S3) and (b) unsteady (U3).

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Figure 8

Instant plots taken from 99% span at T2 operating condition. (a) Static pressure coefficient. (b) Relative total pressure coefficient. (c) Pressure coefficient distribution on blade pressure surface.

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Figure 14

Correlation for unsteadiness of tip leakage flow

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Figure 15

Pressure coefficient distribution on blade suction surface at six time instants

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Figure 16

Static pressure rms distribution for 99% span at T2 operating condition for 1.1% tip blade chord

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Figure 17

3D normalized absolute vorticity magnitude distribution at T2 operating condition

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Figure 18

Instant static pressure coefficient contours taken from 99% span at T2 operating condition in multiblade passages

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