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Research Papers

Inner Workings of Shrouded and Unshrouded Transonic Fan Blades

[+] Author and Article Information
A. R. Wadia, P. N. Szucs

 GE Aircraft Engines, Cincinnati, OH 45215

J. Turbomach 130(3), 031010 (May 02, 2008) (11 pages) doi:10.1115/1.2776957 History: Received January 02, 2007; Revised January 13, 2007; Published May 02, 2008

This paper reports on the numerical assessment of the differences in aerodynamic performance between part span shrouded and unshrouded fan blades generally found in the first stage of multistage fans in low bypass ratio aircraft engines. Rotor flow fields for both blade designs were investigated at two operating conditions using a three-dimensional viscous flow analysis. Although designed to the same radius ratio, aspect ratio, and solidity, the unshrouded fan rotor had a slightly increased tip speed (+3%) and somewhat lower pressure ratio (3.2%) due to engine cycle requirements. Even when allowing for these small differences, the analysis reveals interesting differences in the level and in the radial distribution of efficiency between these two rotors. The reason for the improved performance of the shrouded rotor in part can be attributed to the shroud blocking off the radial migration of boundary layer fluid centrifuged from the hub on the suction side. As a result, the shock boundary layer interaction seems to be improved on the shrouded blade. At the cruise condition, the efficiency is the same for both rotors. The slightly better efficiency of the shrouded blade in the outer panel is nullified by the large efficiency penalty in the vicinity of the shroud. As there is no significant radial migration of fluid in the suction side boundary layer, as indicated by the analysis at this condition relative to the design speed case, the benefit due to the shroud is greatly reduced. At this speed and at lower speeds, the shroud becomes a net additional loss for the blade. Also of interest from the numerical results is the indication that significant blade ruggedization penalties to performance can be reduced in the case of the unshrouded blade through custom tailoring of its mean camber line.

Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Shrouded and unshrouded blades for low bypass ratio aircraft engine applications

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Figure 2

Comparison of spanwise distribution of maximum thickness-to-chord ratio for part span shrouded and unshrouded rotor configurations

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Figure 3

Grid for three-dimensional viscous analysis

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Figure 4

Comparison of measured and calculated radial profiles of total pressure and temperature for the shrouded blade at 95% speed

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Figure 5

Comparison of isentropic Mach number contours on suction surface at 100% speed

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Figure 6

Comparison of isentropic Mach number contours on pressure surface at 100% speed

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Figure 7

(a) Comparison of the calculated blade-to-blade Mach number contours at the blade tip for both rotors at 100% speed and (b) shrouded blade’s tip shock structure, measured using over-the-rotor-tip kulites, at 100% and 95% speeds

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Figure 8

Comparison of blade surface Mach number distribution near the blade tip at 100% speed

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Figure 9

Comparison of blade-to-blade Mach number contours at design speed at 59.2% immersion

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Figure 10

Comparison of blade surface Mach number distribution at 59.2% immersion at 100% speed

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Figure 11

Comparison of hub blade surface Mach number distribution at 100% speed

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Figure 12

Comparison of radial distribution of adiabatic efficiency calculated by the three-dimensional analysis at 100% speed

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Figure 13

Comparison of velocity vectors deep in the suction side boundary layer (y+∼20) at 100% speed

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Figure 14

Comparison of velocity vectors deep within the boundary layer on the pressure side (y+∼20) at 100% speed

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Figure 15

Comparison of circumferential distribution of loss coefficient near the blade tip at design speed

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Figure 16

Comparison of suction side Mach number contours at 95% speed

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Figure 17

Comparison of pressure side Mach number contours at 95% speed

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Figure 18

Comparison of the calculated blade-to-blade Mach number contours near the blade tip at 95% speed

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Figure 19

Comparison of blade surface Mach number distribution near the tip at 95% speed

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Figure 20

Comparison of spanwise distribution of adiabatic efficiency calculated by the three-dimensional analysis at 95% speed

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Figure 21

Comparison of velocity vectors deep within the boundary layer on the suction side at 95% speed

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Figure 22

Comparison of radial variation of loss in efficiency attributed to the part span shroud at design speed for the shrouded rotor

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Figure 23

Comparison of the design and off-design integrated average total pressure loss coefficient due to the part span shroud

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Figure 24

Isentropic Mach number distribution along the upper and lower surfaces of the part span shroud near the pressure side of the shrouded rotor

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Figure 25

Isentropic Mach number distribution along the upper and lower surfaces of the part span shroud at midpassage (blade to blade) between two adjacent rotor blades at 95% and 100% speeds

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Figure 26

Isentropic Mach number distribution along the upper and lower surfaces of the part span shroud near the suction surface of the shrouded rotor at 95% and 100% speeds

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