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Importance of surface curvature in modelling droplet impingement on fan blades

Importance of surface curvature in modelling droplet impingement on fan blades
Importance of surface curvature in modelling droplet impingement on fan blades
The surface roughening of fan blade leading-edges on large civil aeroengines, due to Water Droplet Erosion (WDE), can lead to a decrease in engine performance and increase the risk of flutter. To model the impingement of a high-speed water droplet on a surface, researchers have frequently assumed the droplet is (a) perfectly spherical, (b) impinging perpendicularly, on a (c) smooth, flat, homogeneous surface. However, the situation presented by the leading-edge of a fan blade calls into question one of these previously used assumptions. It is reasonable to assume a surface is flat, if in reality it is curved, when the radius of curvature of the surface is significantly larger than the droplet radius. In other contexts where WDE occurs, the typical droplet size has either been sufficiently small (e.g. droplet diameter in steam turbines) or the radius of curvature of the surface sufficiently large (e.g. wind turbine blades) that it has been sensible to assume the surface is flat; this does not appear to be the case for the WDE of fan blades.

The equations describing the kinematics of an impinging water droplet on a flat surface were reformulated for a curved surface. These novel equations were used, along with established conditions for the onset of lateral outflow jetting, to model the impingement of a droplet on a curved surface. European Aviation Safety Agency publications provided the input values typical for a large, high-bypass, civil turbofan, operating at 100% rpm. The results suggest the relatively similar radius of curvature of the leading-edge of a fan blade and radius of the impinging water droplet will significantly affect the onset of lateral outflow jetting. Jetting is predicted to commence substantially sooner; with the initial high-pressure stage expected to last less than half the time predicted for a flat surface. This substantially shorter initial stage is likely to have significant implications for the WDE that occurs as a result of multiple droplet impingements. Over the years, various attempts have been made to extend the frequently-used set of assumptions, described at the start of this abstract. However, we can find no studies where the effect of the curvature of the surface has been explored. Thus, currently, there are no appropriate theoretical treatments describing the liquid kinematics of a typical water droplet impingement on the leading-edge of a fan blade; this research seeks to rectify this.
surface curvature, droplet impingement, fan blades
American Society Of Mechanical Engineers (ASME)
Burson-Thomas, Charles B.
a02c68a7-4447-4b03-abd5-41ca055cab24
Wellman, Richard
933354f5-e4ff-448e-b6b5-4caef14187a4
Wood, Robert
d9523d31-41a8-459a-8831-70e29ffe8a73
Harvey, Terence
3b94322b-18da-4de8-b1af-56d202677e04
Burson-Thomas, Charles B.
a02c68a7-4447-4b03-abd5-41ca055cab24
Wellman, Richard
933354f5-e4ff-448e-b6b5-4caef14187a4
Wood, Robert
d9523d31-41a8-459a-8831-70e29ffe8a73
Harvey, Terence
3b94322b-18da-4de8-b1af-56d202677e04

Burson-Thomas, Charles B., Wellman, Richard, Wood, Robert and Harvey, Terence (2018) Importance of surface curvature in modelling droplet impingement on fan blades. In Proceedings of ASME Turbo Expo 2018: Turbomachinery Technical Conference & Exposition. American Society Of Mechanical Engineers (ASME). 14 pp . (In Press)

Record type: Conference or Workshop Item (Paper)

Abstract

The surface roughening of fan blade leading-edges on large civil aeroengines, due to Water Droplet Erosion (WDE), can lead to a decrease in engine performance and increase the risk of flutter. To model the impingement of a high-speed water droplet on a surface, researchers have frequently assumed the droplet is (a) perfectly spherical, (b) impinging perpendicularly, on a (c) smooth, flat, homogeneous surface. However, the situation presented by the leading-edge of a fan blade calls into question one of these previously used assumptions. It is reasonable to assume a surface is flat, if in reality it is curved, when the radius of curvature of the surface is significantly larger than the droplet radius. In other contexts where WDE occurs, the typical droplet size has either been sufficiently small (e.g. droplet diameter in steam turbines) or the radius of curvature of the surface sufficiently large (e.g. wind turbine blades) that it has been sensible to assume the surface is flat; this does not appear to be the case for the WDE of fan blades.

The equations describing the kinematics of an impinging water droplet on a flat surface were reformulated for a curved surface. These novel equations were used, along with established conditions for the onset of lateral outflow jetting, to model the impingement of a droplet on a curved surface. European Aviation Safety Agency publications provided the input values typical for a large, high-bypass, civil turbofan, operating at 100% rpm. The results suggest the relatively similar radius of curvature of the leading-edge of a fan blade and radius of the impinging water droplet will significantly affect the onset of lateral outflow jetting. Jetting is predicted to commence substantially sooner; with the initial high-pressure stage expected to last less than half the time predicted for a flat surface. This substantially shorter initial stage is likely to have significant implications for the WDE that occurs as a result of multiple droplet impingements. Over the years, various attempts have been made to extend the frequently-used set of assumptions, described at the start of this abstract. However, we can find no studies where the effect of the curvature of the surface has been explored. Thus, currently, there are no appropriate theoretical treatments describing the liquid kinematics of a typical water droplet impingement on the leading-edge of a fan blade; this research seeks to rectify this.

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GT2018-75032 - Other
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More information

Accepted/In Press date: 13 March 2018
Venue - Dates: ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition (GT2018), Oslo, Norway, 2018-06-11 - 2018-06-15
Keywords: surface curvature, droplet impingement, fan blades

Identifiers

Local EPrints ID: 418793
URI: https://eprints.soton.ac.uk/id/eprint/418793
PURE UUID: 8ed1ae6c-3c29-4ce0-9767-81c906eb7865
ORCID for Robert Wood: ORCID iD orcid.org/0000-0003-0681-9239

Catalogue record

Date deposited: 22 Mar 2018 17:30
Last modified: 14 Mar 2019 01:52

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