0
Research Papers

The Effect of Aspect Ratio on Compressor Performance

[+] Author and Article Information
Ho-On To

Whittle Laboratory,
University of Cambridge,
Cambridge, UK
e-mail: hot20@cam.ac.uk

Robert J. Miller

Whittle Laboratory,
University of Cambridge,
Cambridge, UK,
e-mail: rjm76@cam.ac.uk

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the Journal of Turbomachinery. Manuscript received February 4, 2019; final manuscript received March 13, 2019; published online April 15, 2019. Assoc. Editor: Kenneth Hall.

J. Turbomach 141(8), 081011 (Apr 15, 2019) (12 pages) Paper No: TURBO-19-1026; doi: 10.1115/1.4043219 History: Received February 04, 2019; Accepted March 15, 2019

The optimum aspect ratio at which maximum efficiency occurs is relatively low, typically between 1 and 1.5. At these aspect ratios, inaccuracies inherently exist in the decomposition of the flow field into freestream and endwall components due to the absence of a discernible freestream. In this paper, a unique approach is taken: a “linear repeating stage” concept is used in conjunction with a novel way of defining the freestream flow. Through this approach, physically accurate decomposition of the flow field for aspect ratios as low as ∼0.5 can be achieved. This ability to accurately decompose the flow leads to several key findings. First, the endwall flow is found to be dependent on static pressure rise coefficient and endwall geometry, but independent of the aspect ratio. Second, the commonly accepted relationship that endwall loss coefficient varies inversely with the aspect ratio is shown to be physically inaccurate. Instead, a new term, which the authors refer to as the “effective aspect ratio,” should replace the term “aspect ratio.” Moreover, not doing so can result in efficiency errors of ∼0.6% at low aspect ratios. Finally, there exists a low aspect ratio limit below which the two endwall flows interact causing a large separation to occur along the span. From these findings, a low-order model is developed to model the effect of varying aspect ratio on compressor performance. The last section of the paper uses this low-order model and a simple analytical model to show that to a first order, the optimum aspect ratio is just a function of the loss generated by the endwalls at zero clearance and the rate of change in profile loss due to blade thickness. This means that once the endwall configuration has been selected, i.e., cantilever or shroud, the blade thickness sets the optimum aspect ratio.

Copyright © 2019 by ASME
Your Session has timed out. Please sign back in to continue.

References

Smith, L. H., 1970, “Casing Boundary Layers in Multistage Axial-Flow Compressors,” Flow Res. Blading, 106, pp. 635–647.
Wennerstrom, A. J., 1989, “Low Aspect Ratio Axial Flow Compressors: Why and What It Means,” ASME J. Turbomach., 111(4), pp. 357–365. [CrossRef]
McKenzie, A. B., 1997, Axial Flow Fans and Compressors, Ashgate Publishing Limited, Farnham, United Kingdom.
Koch, C. C., 1981, “Stalling Pressure Rise Capability of Axial Flow Compressor Stages,” ASME J. Eng. Gas Turb. Power, 103(4), pp. 645–656. [CrossRef]
Spalart, P. R., and Allmaras, S. R., 1992, “A One-Equation Turbulence Model for Aerodynamic Flows,” 30th Aerospace Sciences Meeting and Exhibit, Reno, NV, AIAA Paper No. 92-0439.
Wellborn, S. R., and Okiishi, T. H., 1999, “The Influence of Shrouded Cavity Flows on Multistage Compressor Performance,” ASME J. Turbomach., 121(3), pp. 486–497. [CrossRef]
Freeman, C., 1985, “Effect of Tip Clearance Flow on Compressor Stability and Engine Performance,” VKI for Fluid Dynamics Lecture Series 5.
Youngren, H., and Drela, M., 1991, “Viscous/Inviscid Method for Preliminary Design of Transonic Cascades,” 27th Joint Propulsion Conference.
Wright, P. I., and Miller, D. C., 1991, “An Improved Compressor Performance Prediction Model,” European Conference of Turbomachinery: Latest Developments in a Changing Scene, IMechE C423/028.
Goodhand, M. N., and Miller, R. J., 2012, “The Impact of Real Geometries on Three-Dimensional Separations in Compressors,” ASME J. Turbomach., 134(2), p. 021007. [CrossRef]

Figures

Grahic Jump Location
Fig. 1

Variation in lost efficiency with AR (fixed thickness and clearance)

Grahic Jump Location
Fig. 2

Lost efficiency versus number of repeating stage iterations (AR = 1.7, ɛ/c = 1.0%, t/c = 4.1%, and Rec = 6.3 × 105)

Grahic Jump Location
Fig. 3

Spanwise distribution of stage exit whirl angle after different number of repeats (AR, ɛ/c, and t/c, Rec as mentioned in Fig. 2)

Grahic Jump Location
Fig. 4

Entropy contours (note use of mixing planes)

Grahic Jump Location
Fig. 5

(a)–(c) Flow decomposition; discernible freestream (AR = 1.7)

Grahic Jump Location
Fig. 6

(a)–(c) Flow decomposition; no discernible freestream (AR = 0.7)

Grahic Jump Location
Fig. 7

Entropy generation due to endwalls versus AR (ɛ/c = 2.0%, t/c = 4.1%, and Rec = 6.3 × 105)

Grahic Jump Location
Fig. 8

Dependence of endwall flow on pressure rise coefficient (and independence of AR)

Grahic Jump Location
Fig. 9

Blockage-to-chord dependence on pressure rise coefficient (and independence of AR)

Grahic Jump Location
Fig. 10

Endwall loss varies inversely with effective AR and not AR (ɛ/c = 1.0%)

Grahic Jump Location
Fig. 11

Endwall loss and blockage versus AR (ɛ/c = 2.0%, t/c = 4.1%, Rec = 6.3 × 105)

Grahic Jump Location
Fig. 12

Low-order model structure

Grahic Jump Location
Fig. 13

Endwall configuration used to decouple effects: (a) cantilevered and (b) shrouded

Grahic Jump Location
Fig. 14

Variation in endwall loss coefficient with blade-row pressure rise coefficient over characteristic (cantilevered)

Grahic Jump Location
Fig. 15

Comparison of endwall loss coefficient for cantilevered and shrouded endwalls

Grahic Jump Location
Fig. 16

Comparison of blockage-to-chord for cantilevered and shrouded endwalls

Grahic Jump Location
Fig. 17

Profile loss variation with thickness-to-chord (MISES)

Grahic Jump Location
Fig. 18

Profile loss variation with Reynolds number (MISES)

Grahic Jump Location
Fig. 19

Comparison of profile and endwall loss variation with Reynolds number (ɛ/c = 2.0%)

Grahic Jump Location
Fig. 20

Validation of a low-order model against CFD

Grahic Jump Location
Fig. 21

Breakdown of lost efficiency using the low-order model (t/h = 4.7%, ɛ/h = 1.2%, and Reh = 5.5 × 105)

Grahic Jump Location
Fig. 22

Contours of optimum AR, ɛ/c, and η (low-order model, cantilevered, Reh = 5.5 × 105)

Grahic Jump Location
Fig. 23

Contours of optimum AR, ɛ/c, and η (low-order model, cantilevered, ɛ/h = 1.2%)

Grahic Jump Location
Fig. 24

Comparison of optimum AR for the endwall configurations of Fig. 13 (low-order model, ɛ/h = 0%)

Grahic Jump Location
Fig. 25

The variation of maximum pressure rise coefficient with AR (t/h = 4.7%, ɛ/h = 1.2%, and Reh = 5.5 × 105)

Grahic Jump Location
Fig. 26

Breakdown of lost efficiency using simple analytical model of Eq. (12) (t/h = 4.7%, ɛ/h = 1.2%, and Reh = 5.5 × 105)

Grahic Jump Location
Fig. 27

AR range with efficiencies within 0.1% of optimum (low-order model, cantilever, ɛ/h = 1.2%, Reh = 5.5 × 105)

Tables

Errata

Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In