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Simultaneous surface pressure and high-speed PIV measurements in stalled airfoil
University of Southampton.
University of Southampton.ORCID iD: 0000-0002-8038-1127
University of Southampton.
University of Southampton.
Show others and affiliations
2018 (English)Conference paper, Published paper (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
2018.
Keywords [en]
PIV, Surface Pressure, NACA0012, Stall
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-252831OAI: oai:DiVA.org:kth-252831DiVA, id: diva2:1322526
Conference
19th International Symposium on Applications of Laser and Imaging Techniques to Fluid Mechanics
Note

QC 20190624

Available from: 2019-06-10 Created: 2019-06-10 Last updated: 2019-06-24Bibliographically approved

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Lacagnina, Giovanni
Fluid Mechanics and Acoustics

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CiteExportLink to record
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Citation style
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