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Fluid-structure interactions of membrane wings in free-flight and in ground-effect

Fluid-structure interactions of membrane wings in free-flight and in ground-effect
Fluid-structure interactions of membrane wings in free-flight and in ground-effect
Currently, there is a growing demand to improve the aerodynamic performance of Micro-Air-Vehicles for extended mission time, higher payload capacity and improved agility. Their wings have to operate within a challenging Reynolds number regime of Re =10(4)-10(5) which is known for its low energy content in the boundary layer, causing early flow separation and loss in lift production. Flexible wings, inspired from bats, could potentially exploit given flow separations by forming lift carrying shedding structures close to the upper wing surface. The aspect-ratio is one key parameter which modifies these vortex formations and their ability to couple with the membrane. However, vortex related lift production comes at a price of increased drag and limitation in aerodynamic efficiency. Membrane wings in ground-effect could combine ground-effect related efficiency enhancement with flexibility related stall improvements. Therefore, two separate wind tunnel experiments are conducted to understand the impact of aspect-ratio and ground-effect on the fluid-structure interaction of membrane wings. Multiple high-speed recordings involve lift, drag and pitch moment measurements with a load-cell, membrane deformation measurements with photogrammetry and digital image correlation (DIC)and flow measurements with planar/stereo particle image velocimetry (PIV). Next to time-averaged quantities, reduced order models are used to group predominant flow and membrane dynamics. Synchronised fluid-membrane coupling of flexible membrane wings allows to exploit separated flow conditions to provide further lift enhancement from vortical flow formations. An exemplary membrane wing at [alpha] = 25(o) shows similar vortex-shedding to a rigid at-plate at [alpha] = 15(o), but comes with 50 % more lift production. Higher aspect-ratios are found to exploit the benefits of wing flexibility to a larger extend, showing a gain in peak-lift of up to 60% for an aspect-ratio of 2 and 31% for an aspect-ratio of 1 (in reference to rigid at-plates). Membrane wings extend their performance window in ground-effect conditions by delaying ground-effect induced premature flow separation by [DELTA alpha] = 5(o). In addition, membrane wings in ground-effect are found to be up to 30% more efficiency than rigid at-plates.
Bleischwitz, Robert
461358e1-6d90-4a9d-bc11-4a68595d4b7a
Bleischwitz, Robert
461358e1-6d90-4a9d-bc11-4a68595d4b7a
Ganapathisubramani, Bharathram
5e69099f-2f39-4fdd-8a85-3ac906827052

Bleischwitz, Robert (2016) Fluid-structure interactions of membrane wings in free-flight and in ground-effect. University of Southampton, Faculty of Engineering and the Environment, Doctoral Thesis, 169pp.

Record type: Thesis (Doctoral)

Abstract

Currently, there is a growing demand to improve the aerodynamic performance of Micro-Air-Vehicles for extended mission time, higher payload capacity and improved agility. Their wings have to operate within a challenging Reynolds number regime of Re =10(4)-10(5) which is known for its low energy content in the boundary layer, causing early flow separation and loss in lift production. Flexible wings, inspired from bats, could potentially exploit given flow separations by forming lift carrying shedding structures close to the upper wing surface. The aspect-ratio is one key parameter which modifies these vortex formations and their ability to couple with the membrane. However, vortex related lift production comes at a price of increased drag and limitation in aerodynamic efficiency. Membrane wings in ground-effect could combine ground-effect related efficiency enhancement with flexibility related stall improvements. Therefore, two separate wind tunnel experiments are conducted to understand the impact of aspect-ratio and ground-effect on the fluid-structure interaction of membrane wings. Multiple high-speed recordings involve lift, drag and pitch moment measurements with a load-cell, membrane deformation measurements with photogrammetry and digital image correlation (DIC)and flow measurements with planar/stereo particle image velocimetry (PIV). Next to time-averaged quantities, reduced order models are used to group predominant flow and membrane dynamics. Synchronised fluid-membrane coupling of flexible membrane wings allows to exploit separated flow conditions to provide further lift enhancement from vortical flow formations. An exemplary membrane wing at [alpha] = 25(o) shows similar vortex-shedding to a rigid at-plate at [alpha] = 15(o), but comes with 50 % more lift production. Higher aspect-ratios are found to exploit the benefits of wing flexibility to a larger extend, showing a gain in peak-lift of up to 60% for an aspect-ratio of 2 and 31% for an aspect-ratio of 1 (in reference to rigid at-plates). Membrane wings extend their performance window in ground-effect conditions by delaying ground-effect induced premature flow separation by [DELTA alpha] = 5(o). In addition, membrane wings in ground-effect are found to be up to 30% more efficiency than rigid at-plates.

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Published date: June 2016
Organisations: University of Southampton, Aerodynamics & Flight Mechanics Group

Identifiers

Local EPrints ID: 397261
URI: https://eprints.soton.ac.uk/id/eprint/397261
PURE UUID: d5cfe159-43fd-4fe3-919f-a3d4933e4216
ORCID for Bharathram Ganapathisubramani: ORCID iD orcid.org/0000-0001-9817-0486

Catalogue record

Date deposited: 13 Jul 2016 13:51
Last modified: 06 Jun 2018 12:33

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