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Incipient stall characterization from skin-friction maps

Massimo Miozzi (Institute of Marine Engineering, CNR-INM, Rome, Italy)
Alessandro Capone (Institute of Marine Engineering, CNR-INM, Rome, Italy)
Christian Klein (Institute of Aerodynamics and Flow Technology, Deutsches Zentrum für Luft-und Raumfahrt e.V. (DLR), Göttingen, Germany)
Marco Costantini (Institute of Aerodynamics and Flow Technology, Deutsches Zentrum für Luft-und Raumfahrt e.V. (DLR), Göttingen, Germany)

International Journal of Numerical Methods for Heat & Fluid Flow

ISSN: 0961-5539

Article publication date: 7 August 2020

Issue publication date: 10 March 2021

105

Abstract

Purpose

The purpose of this study is the characterization of the dramatic variation in the flow scenario occurring at incipient stall conditions on a NACA0015 hydrofoil at moderate Reynolds numbers via the experimental analysis of time- and space-resolved skin-friction maps. The examined flow conditions are relevant for a variety of applications, including renewable energy production and unmanned and micro-aerial vehicles.

Design/methodology/approach

Grounding on the global temperature data acquired via temperature-sensitive paint, the proposed methodology adopts two approaches: one to obtain time-resolved, relative skin-friction vector fields by means of an optical-flow-based algorithm and the other one to extract quantitative, time-averaged skin-friction maps after minimization of the dissimilarity between the observed passive transport of temperature fluctuations and that suggested by the Taylor hypothesis.

Findings

Through the synergistic application of the proposed methods, the time-dependent evolution of the incipient stall over the hydrofoil suction side is globally described by firstly identifying the trailing edge separation at an angle of attack (AoA) AoA = 11.5°, and then by capturing the onset of upstream oriented, mushroom-like structures at AoA = 13°. The concomitant occurrence of both scenarios is found at the intermediate incidence AoA = 12.2°.

Originality/value

The qualitative, time-resolved skin-friction topology, combined with the quantitative, time-averaged distribution of the streamwise friction velocity, enables to establish a portrait of the complex, three-dimensional, unsteady scenario occurring at the examined flow conditions, thus providing new, fundamental information for a deeper understanding of the incipient stall development and for its control.

Keywords

Acknowledgements

This work has been supported by the Flagship Project RITMARE, The Italian Research for the Sea, coordinated by the Italian National Research Council and funded by the Italian Ministry of Education, University and Research. Fabio Di Felice (CNR-INM) is acknowledged for the organizational and logistic support. Lorenzo Fratto is acknowledged for the support in TSP data analysis.

Citation

Miozzi, M., Capone, A., Klein, C. and Costantini, M. (2021), "Incipient stall characterization from skin-friction maps", International Journal of Numerical Methods for Heat & Fluid Flow, Vol. 31 No. 2, pp. 674-693. https://doi.org/10.1108/HFF-10-2019-0733

Publisher

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Emerald Publishing Limited

Copyright © 2020, Emerald Publishing Limited

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