Research Papers: Gas Turbines: Turbomachinery

Investigation on the Effect of Surface Wettability on a Two-Phase Flow in a Compressor Cascade

[+] Author and Article Information
Niklas Neupert

Laboratory for Turbomachinery,
Helmut Schmidt University,
Hamburg D-22043, Germany
e-mail: Niklas.Neupert@gmx.de

Janneck Christoph Harbeck

Laboratory for Turbomachinery,
Helmut Schmidt University,
Hamburg D-22043, Germany
e-mail: Harbeck@hsu-hh.de

Franz Joos

Laboratory for Turbomachinery,
Helmut Schmidt University,
Hamburg D-22043, Germany
e-mail: Joos@hsu-hh.de

Contributed by the Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received September 14, 2017; final manuscript received October 22, 2017; published online June 25, 2018. Editor: David Wisler.

J. Eng. Gas Turbines Power 140(10), 102603 (Jun 25, 2018) (9 pages) Paper No: GTP-17-1513; doi: 10.1115/1.4040180 History: Received September 14, 2017; Revised October 22, 2017

In recent years overspray fogging has become a powerful means for power augmentation of industrial gas turbines. Despite the positive thermodynamic effect on the cycle droplets entering the compressor increase the risk of water droplet erosion. Further deposited water leads to a higher sensitivity toward fouling due to an increased stickiness of the blades. Therefore, erosion resistant hydrophobic coatings are applied to the first stages of compressors. Although some patents claim the use of such coatings the aerodynamic impact of a different wettability is not regarded so far. This issue was addressed in the field of aerodynamic efficiency of wings in heavy rain showing higher penalty for hydrophobic coatings. In this study, the issue of a different blade surface wettability in a linear transonic compressor cascade is addressed. Different coatings are applied resulting in contact angles of 51–95 deg. The inflow Mach number was fixed at design inflow Mach number, and the inflow angle was varied over a broad range. The effect on the water film pattern is analyzed in terms of position of film breakup, rivulet width, and totally wetted surface. The performance of the cascade under two-phase flow was analyzed using laser Doppler anemometry/phase Doppler anemometry measurement technique in terms of loss coefficient based on wake momentum thickness and flow turning. It is shown that the wettability of the surface has significant effects on the film structure leading to a lower fraction of wetted surface with increasing contact angle. The influence on performance is limited to effects in the proximity of the surface and is dependent on operation point. While in design conditions hydrophilic coating show lower losses, the trend is vice-versa for off-design conditions. The data represent first experimental work on the influence of surface wettability in a droplet-laden flow supporting positive features for hydrophobic coatings in gas turbine compressors.

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Fig. 1

Definition of impact region

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Fig. 2

Image of the water film pattern

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Fig. 3

Assumed shape of rivulets and equilibrium of forces at the contact line

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Fig. 4

Illustration of the wind tunnel

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Fig. 5

Inlet droplet spectrum

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Fig. 6

Measurement setup nonintrusive method

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Fig. 7

Results of the image processing: (a) resulting image from [11] and (b) final Image including the rivulets

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Fig. 8

Results of the contact angle measurement: (a) gray scale image of the droplet and (b) final image including the drop shape and the tangent in the triple point

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Fig. 9

Validation of the contact angle measurement

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Fig. 10

Experimentally derived 3D water patterns for all contact angles and α = 2 deg

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Fig. 11

Comparison of the film breakup position

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Fig. 12

Comparison of the rivulet width

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Fig. 13

Comparison of the wetted surfaces

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Fig. 14

Deflection Δβ over the incidence angle α for all coatings in comparison to dry airflow (black)

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Fig. 15

Loss coefficient ω over the incidence angle α for all coatings in comparison to dry airflow (black)

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Fig. 16

Noramalized velocity ratio (w2/w1)/(w2/w1)¯ for all coatings for α = 0 deg and α = 4 deg: (a) α = 0 deg and (b) α = 4 deg




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