Incipient stall characterization from skin-friction maps. Issue 2 (27th July 2020)

• Record Type: Journal Article
• Authors: Miozzi, Massimo; Capone, Alessandro; Klein, Christian; Costantini, Marco
• Is Part Of: International journal of numerical methods for heat & fluid flow. Volume 31:Issue 2(2021)
• Page Start: 674
• Page End: 693
• Publication Date: 2020-07-27
• Subjects: Skin friction -- Laminar separation bubble -- NACA 0015 -- Stall -- Taylor hypothesis -- Temperature-sensitive paint; Heat -- Transmission -- Mathematics -- Periodicals; Fluid dynamics -- Mathematics -- Periodicals; 536.2
• DOI: 10.1108/HFF-10-2019-0733
• Languages: English
• ISSNs: 0961-5539

Abstract

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.