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Research Papers

The Effect of an Eroded Leading Edge on the Aerodynamic Performance of a Transonic Fan Blade Cascade

[+] Author and Article Information
Alexander Hergt

German Aerospace Center (DLR),
Institute of Propulsion Technology,
Cologne 51147, Germany
e-mail: alexander.hergt@dlr.de

J. Klinner, W. Steinert, S. Grund, M. Beversdorff, A. Giebmanns, R. Schnell

German Aerospace Center (DLR),
Institute of Propulsion Technology,
Cologne 51147, Germany

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received July 4, 2014; final manuscript received July 10, 2014; published online September 16, 2014. Editor: Ronald Bunker.

J. Turbomach 137(2), 021006 (Sep 16, 2014) (11 pages) Paper No: TURBO-14-1112; doi: 10.1115/1.4028215 History: Received July 04, 2014; Revised July 10, 2014

Especially at transonic flow conditions the leading edge shape influences the performance of a fan profile. At the same time the leading edge of a fan profile is highly affected by erosion during operation. This erosion leads to a deformation of the leading edge shape and a reduction of the chord length. In the present experimental and numerical study, the aerodynamic performance of an original fan profile geometry is compared to an eroded fan profile with a blunt leading edge (BLE) and a chord length reduced by about 1%. The experiments are performed at a linear fan blade cascade in the Transonic Cascade Wind Tunnel of DLR in Cologne. The inflow Mach number during the tests is 1.25 and the Reynolds number 1.5 × 106. All tests are carried out at a low inflow turbulence level of 0.8%. The results of the investigation show that losses are increased over the whole operating range of the cascade. At the aerodynamic design point (ADP) the losses raise by 25%. This significant loss increase can be traced back to the increase of the shock losses at the leading edge. The change in shock structure is investigated and described in detail by means of particle image velocimetry (PIV) measurements and Schlieren imaging. Additionally, the unsteady fluctuation of the shock position is measured by a high-speed shadowgraphy. Then the frequency range of the fluctuation is obtained by a Fourier analysis of the time resolved shock position. Furthermore, liquid crystal measurements are performed in order to analyze the influence of the leading edge shape on the development of the suction side boundary layer. The results show that for the original fan blade the transition occurs at the shock position on the blade suction side by a separation bubble whereas the transition onset is shifted upstream for the fan blade with the BLE.

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References

Figures

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Fig. 1

Transonic fan blade cascade with planar endwall (five of six blades)

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Fig. 2

Fan blade with OLE and BLE

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Fig. 3

Cross section of the DLR transonic cascade wind tunnel

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Fig. 4

Cascade parameters, definition of MPs and boundary layer suction design

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Fig. 5

Multiblock grid topology

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Fig. 6

Experimental loss—inflow angle characteristics of the datum and the BLE cascade (M1 = 1.25)

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Fig. 7

Experimental shock loss—inflow angle characteristics of the datum and the BLE cascade (M1 = 1.25)

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Fig. 8

Isentropic Mach number distribution of the datum cascade at OP 1 and OP 2 (M1 = 1.25, AVDR ≈ 1.12)

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Fig. 9

Inflow angle distribution of the datum and the BLE cascade at OP 1 and OP 2 (M1 = 1.25, AVDR ≈ 1.12), (L2F-MP at midspan)

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Fig. 13

Numerical Mach number distribution at the leading edge of the datum cascade at OP 1

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Fig. 14

Numerical Mach number distribution at the leading edge of the BLE cascade at OP 1

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Fig. 15

Schlieren pattern (top), schematic diagram of the shock position (middle), PIV-measurement at the leading edge (bottom) at OP 2 of the datum cascade

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Fig. 16

Schlieren pattern (top), schematic diagram of the shock position (middle), PIV-measurement at the leading edge (bottom) at OP 2 of the BLE cascade

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Fig. 17

Power density spectra of the shock motion at OP 1 and OP 2

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Fig. 18

Shock fluctuation around the averaged shock position along xn at OP 2

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Fig. 19

Adiabatic wall temperature estimated for the laminar and turbulent boundary layer at OP 1 and OP 2 (liquid crystal color spectrum on the left hand side)

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Fig. 20

Liquid crystal measurement on the blade suction side of the datum (left) and the BLE cascade (right) at OP 1

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Fig. 21

Liquid crystal measurement on the blade suction side of the datum (left) and the BLE cascade (right) at OP 2

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Fig. 12

Schlieren pattern (top), schematic diagram of the shock position (middle), PIV-measurement at the leading edge (bottom) at OP 1 of the BLE cascade

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Fig. 11

Schlieren pattern (top), schematic diagram of the shock position (middle), PIV-measurement at the leading edge (bottom) at OP 1 of the datum cascade

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Fig. 10

Loss distribution in the wake behind the datum and the BLE cascade at OP 1 and OP 2 (M1 = 1.25, AVDR ≈ 1.12) (midspan)

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Fig. 22

Performance map of the original fan compared to the fan with BLE (left) and reshaped leading edge (right) [6]

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