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Effect of imperfection geometry on the stability of 3d boundary layers

Placidi, Marco and Atkin, Chris J. (2018) Effect of imperfection geometry on the stability of 3d boundary layers In: The 6th European Conference on Computational Mechanics (Solids, Structures and Coupled Problems) (ECCM 6) and the 7th European Conference on Computational Fluid Dynamics (ECFD 7), 11-15 Jun 2018, Glasgow, UK.

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Abstract

Interest in laminar flow flight due to both economic and environmental factors has recently seen a resurgence (Tufts et al., 2017). Within this topic, the study of the detailed effect of surface excrescences on laminar/turbulent transition has received significant attention (Fage, 1943; Schlichting, 1979). However, most of the previous work has focused on the effect of steps in 2D environments (i.e. in the absence of a pressure gradient), while the effect of steps on a 3D wings has received less attention (Bender et al., 2005). Therefore, experiments on the stability of 3D boundary layers were performed in a very low turbulence wind tunnel by examining the effect of different excrescences, of a height of approximately one-third of the local displacement thickness, δ*, located at 20% chord. Three different stepped geometries (see figure 1) are considered in order to mimic the leading edge to wing box joint characterising new concepts of laminar flow wings. Results show, as expected, that all surface imperfections reduce the extent of the laminar flow region when compared to the case in the absence of a step. However, despite the severity of the excrescences, this reduction is very moderate, which suggests scope to relax current laminar flow wing tolerances. The pyramidal geometry (in figure 1c), with more gradual forward- and aft-facing steps is it found to be optimum, as the performance degradation is the lowest. Results also suggest that the different step geometries have an influence on both the excitation of the primary modes (and its harmonics) and the onset of the nonlinear phase of the instability. Further analysis will follow in the full paper.

Item Type: Conference or Workshop Item (Conference Paper)
Divisions : Faculty of Engineering and Physical Sciences > Mechanical Engineering Sciences
Authors :
NameEmailORCID
Placidi, Marcom.placidi@surrey.ac.uk
Atkin, Chris J.
Date : 11 June 2018
Uncontrolled Keywords : Surface imperfection; Laminar/turbulent transition; Crossflow instability
Related URLs :
Depositing User : Clive Harris
Date Deposited : 17 Oct 2018 12:30
Last Modified : 17 Oct 2018 12:30
URI: http://epubs.surrey.ac.uk/id/eprint/849713

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