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Research Papers

Effects of Upstream Wake Phasing on Transonic Axial Compressor Performance

[+] Author and Article Information
S. P. R. Nolan

Department of Aeronautics and Astronautics, Gas Turbine Laboratory, MIT, Cambridge, MA 02139sprn@alum.mit.edu

B. B. Botros, C. S. Tan, J. J. Adamczyk, E. M. Greitzer

Department of Aeronautics and Astronautics, Gas Turbine Laboratory, MIT, Cambridge, MA 02139

S. E. Gorrell

Department of Mechanical Engineering, Brigham Young University, Provo, UT 84602sgorrell@byu.edu

The code used for the unsteady simulations, which are both three-dimensional and two-dimensional, was MSU TURBO .

In the actual numerical experiment the spacing between IGVs is larger than that of the rotor, but additional rows of vortices are drawn in the figure to help make the arguments more transparent.

This can also be argued using the Euler turbine equation referred to the vortices that move through the blade passage (7). For a row of vortices of circulation Γ per unit length of the row, moving with speed uv, the stagnation enthalpy difference across the row is Γuv.

In order to specify a nonuniform stagnation pressure at the inlet, a modified version MISES was used. Professor Mark Drela provided instruction for these modifications.

The specific cutoff depends on the eventual use of the measurement, but values of DPT that caused work input changes that were below a tenth of a percent, say, would be below such a threshold.

J. Turbomach 133(2), 021010 (Oct 21, 2010) (12 pages) doi:10.1115/1.4000572 History: Received July 20, 2009; Revised August 20, 2009; Published October 21, 2010; Online October 21, 2010

The effect on rotor work of the phase of an upstream wake relative to the rotor is examined computationally and analytically for a transonic blade row. There can be an important impact on the time-mean performance when the time-dependent circulation of the shed vortices in the wake is phase-locked to the rotor position, as it occurs when there is strong interaction between the rotor static pressure field and the upstream vanes. The rotor work is found to depend on the path of the wake vortices as they travel through the blade passage; for the configurations examined, the calculated change in time-mean rotor work was approximately 3%. It is shown that the effect on work input can be analyzed in terms of the influence of the time-mean relative stagnation pressure nonuniformity associated with the unsteady (but phase-locked) wake vortex flow field, in that the changes in vortex path alter the location of the nonuniformity relative to the rotor. Lower pressure rise and work input occurs when the rotor blade is embedded in a region of low time-mean relative stagnation pressure than when immersed in a region of high relative stagnation pressure. In addition to the work changes, which are essentially two-dimensional effects, it is demonstrated that the location of the wake may affect the tip clearance flow, implying a potential impact on the pressure rise capability and rotor stability limits. Model calculations are presented to give estimates of the magnitude and nature of this phenomenon.

Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Vorticity contours at midspan in SMI IGV-rotor configuration at two different interbladerow spacings. The pink line shows the path of the counterclockwise rotating vortices in the rotor frame.

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Figure 2

Relative position of vane and rotor at time t=0

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Figure 3

Vorticity contours in two-dimensional SMI IGV-rotor configuration at two different interbladerow spacings. The pink line shows the path of the counterrotating vortices in the rotor frame. The Far geometry has an axial gap of 122% of the rotor pitch, while the Mid geometry has an axial gap equal to 109% of the rotor pitch.

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Figure 4

Efficiency and stagnation temperature rise versus mass flow for Far and Mid geometries

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Figure 5

Unsteady vortex flow field and time-mean representation. The dotted line shows the path of the counterclockwise rotating vortices in the rotor frame. In 5b, label “1” denotes fluid with high relative stagnation pressure, while label “2” denotes fluid with low relative stagnation pressure.

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Figure 6

Time-mean relative stagnation pressure contours for Far and Mid geometries extracted from unsteady computations. The Far geometry has a vane-rotor axial gap equal to 122% of the rotor pitch, while the Mid geometry has an axial gap equal to 109% of the rotor pitch.

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Figure 7

Stagnation temperature rise versus mass flow from steady computations. The relative stagnation pressure contours corresponding to the circled data points are shown in Fig. 8.

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Figure 8

Relative stagnation pressure contours for wake position 1 (high relative stagnation pressure fluid over blade) and wake position 3 (low relative stagnation fluid over blade). These contours correspond to the circled data points from Fig. 7.

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Figure 9

Time-mean relative stagnation pressure contours for Mid and Close geometries. The Mid geometry has a vane-rotor axial gap equal to 109% of the rotor pitch, while the Close geometry has an axial gap equal to 95% of the rotor pitch.

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Figure 10

Diffuser pressure rise coefficient Cp versus the diffuser area ratio for two different inlet velocity profiles. The inlet profiles are shown in the inlay figure.

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Figure 11

Rotor inlet nominal stagnation pressure nonuniformity (based on the time-mean of the unsteady computations)

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Figure 12

Circumferential force variation (DFC) versus the pitchwise position of inlet stagnation pressure profile for different amplitudes of inlet nonuniformity

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Figure 13

Circumferential force variation (DFC) versus the pitchwise position of inlet stagnation pressure profile for different rotor inlet Mach numbers

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Figure 14

Vorticity contours for SMI deswirler-rotor geometry

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Figure 15

Amplitude of relative stagnation pressure profile versus vane trailing edge thickness/vane pitch. The same interbladerow spacing (L/W=1.22) was used for all data points in this plot.

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Figure 16

Relative stagnation pressure at domain inlet for test case (stratified inlet position 1)

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Figure 17

Stagnation-to-static pressure rise coefficient versus mass flow. The inlay figure shows the contours of relative stagnation pressure for position 3, at the bladetip span, near stall.

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Figure 18

Control volume used in analysis of rotor circumferential force

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Figure 19

Decrease in the exit area in a blade passage. The dotted line coming off the suction surface represents the edge of the suction side boundary layer. In case 1, deviation at the rotor exit causes the rotor exit velocity to change from the solid arrow (no deviation) to the arrow with the dotted line. In case 2, the boundary layer blockage causes the change from an ideal situation with no blockage.

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