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Research Papers

# Design and Test of an Aspirated Counter-Rotating Fan

[+] Author and Article Information
Jack L. Kerrebrock, Alan H. Epstein, Ali A. Merchant, Gerald R. Guenette, David Parker, Jean-Francois Onnee, Fritz Neumayer

Gas Turbine Laboratory,  Massachusetts Institute of Technology, Cambridge, MA 02139

NASA-Glenn Research Center, Cleveland, OH 44135

Aamir Shabbir

University of Toledo, Toledo, OH 43606

J. Turbomach 130(2), 021004 (Feb 12, 2008) (8 pages) doi:10.1115/1.2776951 History: Received September 05, 2006; Revised September 06, 2006; Published February 12, 2008

## Abstract

The design and test of a two-stage, vaneless, aspirated counter-rotating fan is presented in this paper. The fan nominal design objectives were a pressure ratio of 3:1 and adiabatic efficiency of 87%. A pressure ratio of 2.9 at 89% efficiency was measured at the design speed. The configuration consists of a counter-swirl-producing inlet guide vane, followed by a high tip speed $(1450ft∕s)$ nonaspirated rotor and a counter-rotating low speed $(1150ft∕s)$ aspirated rotor. The lower tip speed and lower solidity of the second rotor result in a blade loading above conventional limits, but enable a balance between the shock loss and viscous boundary layer loss; the latter of which can be controlled by aspiration. The aspiration slot on the second rotor suction surface extends from the hub up to 80% span. The bleed flow is discharged inward through the blade hub. This fan was tested in a short duration blowdown facility. Particular attention was given to the design of the instrumentation to measure efficiency to 0.5% accuracy. High response static pressure measurements were taken between the rotors and downstream of the fan to determine the stall behavior. Pressure ratio, mass flow, and efficiency on speed lines from 90% to 102% of the design speed are presented and discussed along with comparison to computational fluid dynamics predictions and design intent. The results presented here complement those presented earlier for two aspirated fan stages with tip shrouds, extending the validated design space for aspirated compressors to include designs with conventional unshrouded rotors and with inward removal of the aspirated flow.

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## Figures

Figure 1

Design calculations of the effect of rotor speeds and IGV counterswirl on fan efficiency: (a) efficiency variation with Rotor 1 and 2 tip speeds; (b) efficiency variation with IGV counterswirl and Rotor 2 tip speed

Figure 2

Contours of Mach number in Rotor 2 at midspan: (a) peak efficiency; (b) peak pressure ratio

Figure 3

Predicted fan design speed pressure ratio and efficiency at different levels of aspiration

Figure 4

Blowdown facility

Figure 5

Counter-rotating fan test section

Figure 6

Aspiration passage geometry in Rotor 2

Figure 7

Typical variation of flow conditions during a blowdown test

Figure 8

Measured corrected rotor speed variations

Figure 9

Compressor pressure ratio as predicted by APNASA (solid lines) and as measured (points)

Figure 10

Adiabatic efficiency as predicted using APNASA (solid lines) and as measured (points)

Figure 11

Spanwise pressure and temperature distributions

Figure 12

Measured stall margin versus pressure ratio

Figure 13

Velocity triangles in the frame of reference of the first rotor

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