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Simultaneous surface pressure and high-speed PIV measurements in stalled airfoil

Simultaneous surface pressure and high-speed PIV measurements in stalled airfoil
Simultaneous surface pressure and high-speed PIV measurements in stalled airfoil
The time-resolved velocity field (2D2C high-speed PIV) and surface pressure (pressure taps) of a stalled NACA0012 airfoil have been simultaneously measured. These measurements enable cross-evaluation of the velocity field and pressure time series. The present paper evaluates the flow field and surface pressure using POD, cross-correlation and conditional averaging. First, the flow and surface pressure are analysed independently. Both the time-average and the dynamic structures of the flow are presented. Distinct frequency bands are observed in the energy spectra of the surface-pressure signal. It is shown that a high-pressure event at the foremost pressure port (at x/c = 0.34) is followed by high-pressure events at the other pressure ports (x/c = 0.51-0.93), indicating a decaying pressure wave that travels over the surface with roughly half the free-stream velocity. Next, the link between the flow field and the surface pressure is explored. Using cross-correlation, it is shown that the pressure signal correlates with specific regions in the flow. Conditional averages of the flow fields, conditioned to high-pressure events at the surface, indicate that these pressure events are caused by coherent structures in the flow. These structures consist of a train of alternating vortices that induce velocity components toward and away from the surface, causing high-and low-pressure events at this surface. By filtering the pressure signal with different frequency bands, the flow structures responsible for different peaks in the energy spectra are recovered. A POD analysis indicates that the energy of the coherent flow structures leading to surface-pressure fluctuations only contain a fraction of the total energy of the flow. While POD and cross-correlation are applied to a full time-series, the conditional averages show that coherent structures in the flow can be identified in real-time using the surface pressure. Identification of coherent structures in the flow using only the surface pressure signal enables real-time control of such structures.
Instituto Superior Tecnico
Berk, Tim
6d080fa4-abf6-4a81-9e35-178e8454e755
Lacagnina, Giovanni
b6c548d0-38b3-4f0f-9f0a-9849cb910113
Paruchuri, Chaitanya
5c1def64-6347-4be3-ac2d-b9f6a314b81d
Joseph, Phillip
9c30491e-8464-4c9a-8723-2abc62bdf75d
Ganapathisubramani, Bharathram
5e69099f-2f39-4fdd-8a85-3ac906827052
Berk, Tim
6d080fa4-abf6-4a81-9e35-178e8454e755
Lacagnina, Giovanni
b6c548d0-38b3-4f0f-9f0a-9849cb910113
Paruchuri, Chaitanya
5c1def64-6347-4be3-ac2d-b9f6a314b81d
Joseph, Phillip
9c30491e-8464-4c9a-8723-2abc62bdf75d
Ganapathisubramani, Bharathram
5e69099f-2f39-4fdd-8a85-3ac906827052

Berk, Tim, Lacagnina, Giovanni, Paruchuri, Chaitanya, Joseph, Phillip and Ganapathisubramani, Bharathram (2018) Simultaneous surface pressure and high-speed PIV measurements in stalled airfoil. In 19th International Symposium on Applications of Laser and Imaging Techniques to Fluid Mechanics. Instituto Superior Tecnico..

Record type: Conference or Workshop Item (Paper)

Abstract

The time-resolved velocity field (2D2C high-speed PIV) and surface pressure (pressure taps) of a stalled NACA0012 airfoil have been simultaneously measured. These measurements enable cross-evaluation of the velocity field and pressure time series. The present paper evaluates the flow field and surface pressure using POD, cross-correlation and conditional averaging. First, the flow and surface pressure are analysed independently. Both the time-average and the dynamic structures of the flow are presented. Distinct frequency bands are observed in the energy spectra of the surface-pressure signal. It is shown that a high-pressure event at the foremost pressure port (at x/c = 0.34) is followed by high-pressure events at the other pressure ports (x/c = 0.51-0.93), indicating a decaying pressure wave that travels over the surface with roughly half the free-stream velocity. Next, the link between the flow field and the surface pressure is explored. Using cross-correlation, it is shown that the pressure signal correlates with specific regions in the flow. Conditional averages of the flow fields, conditioned to high-pressure events at the surface, indicate that these pressure events are caused by coherent structures in the flow. These structures consist of a train of alternating vortices that induce velocity components toward and away from the surface, causing high-and low-pressure events at this surface. By filtering the pressure signal with different frequency bands, the flow structures responsible for different peaks in the energy spectra are recovered. A POD analysis indicates that the energy of the coherent flow structures leading to surface-pressure fluctuations only contain a fraction of the total energy of the flow. While POD and cross-correlation are applied to a full time-series, the conditional averages show that coherent structures in the flow can be identified in real-time using the surface pressure. Identification of coherent structures in the flow using only the surface pressure signal enables real-time control of such structures.

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195_paper_LXLASER2018_FINAL - Accepted Manuscript
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More information

Published date: 2018
Venue - Dates: 19th International Symposium on Applications of Laser and Imaging Techniques to Fluid Mechanics, Lisbon, Portugal, 2018-07-16 - 2018-07-19

Identifiers

Local EPrints ID: 424652
URI: https://eprints.soton.ac.uk/id/eprint/424652
PURE UUID: 5120684a-fa24-4391-8f56-f6525f81be8c
ORCID for Giovanni Lacagnina: ORCID iD orcid.org/0000-0002-8038-1127
ORCID for Bharathram Ganapathisubramani: ORCID iD orcid.org/0000-0001-9817-0486

Catalogue record

Date deposited: 05 Oct 2018 11:39
Last modified: 14 Mar 2019 01:37

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