Skin friction and coherent structures within a laminar separation bubble

Miozzi, Massimo; Capone, Alessandro; Costantini, Marco; Fratto, L.; Klein, Christian; Felice, Fabio Di

doi:10.1007/s00348-018-2651-8

Cited by 51 publications

(84 citation statements)

References 74 publications

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“…12 Estimated oil-film thickness distribution on the GLOFSFE-evaluation region for all examined data points. The gray areas indicate masked areas due to missing image data to the surface and the formation of a laminar separation bubble (see Miozzi et al (2019), among others). The critical lines (i.e., the separation and reattachment lines), as well as the areas in their vicinity, are regions where the wall shear stress is zero or nearly zero.…”

Section: Repeatability Of the Results And Evaluation Of The Glofsfe Ementioning

confidence: 99%

“…In the case of two-dimensional bumps, the critical roughness height has been mainly related to the ratio between the bump height and the bump length (Holmes et al 1985), but factors such as the pressure gradient and the Mach number may also have an effect on the bump influence on boundary-layer stability and transition (Costantini et al 2019). For threedimensional roughness elements, Braslow (1966) reported Re k,cr = 100 − 900 (depending on the ratio between wallnormal and span-wise size of the roughness element).…”

Section: Critical Limit Of Roughnessmentioning

confidence: 99%

“…In recent years, an advanced approach using heat-flux data to extract the skin-friction field, in which surface temperature data measured by temperature-sensitive paint (TSP) are analyzed, has been proposed Liu 2019). Using this approach, skin-friction fields were obtained from TSP data in underwater applications (Miozzi et al 2019(Miozzi et al , 2020. The application of the TSP-based approach for transonic air flows is still on-going and requires validation.…”

Section: Introductionmentioning

confidence: 99%

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Feasibility of skin-friction field measurements in a transonic wind tunnel using a global luminescent oil film

et al. 2021

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The feasibility of skin-friction field measurements using the global luminescent oil-film skin-friction field estimation method was evaluated for a challenging case of a supercritical airfoil model under transonic wind-tunnel conditions (freestream Mach number of 0.72) at a high Reynolds number (10 million, based on the model chord length). The oil-film thickness and skin-friction coefficient distributions were estimated over the airfoil model upper surface for a range of angles of attack (from $$-0.4^{\circ }$$ - 0 . 4 ∘ to $$2.0^{\circ }$$ 2 . 0 ∘ ), thus enabling the study of different boundary-layer stability situations with laminar–turbulent transition, including cases with shock-wave/boundary-layer interaction. Conventional pressure measurements on the surface and in the wake of the model as well as Schlieren flow visualizations were conducted to support the oil-film based investigations. In the laminar-flow regions, the oil-film thickness could be generally kept below the critical limit of roughness that would induce premature boundary-layer transition. The skin friction in this region could be estimated with a moderate confidence level, as confirmed for portions of the chord by the reasonable agreement with numerical data obtained via laminar boundary-layer computations. Moreover, the location of transition onset was evaluated from the skin-friction estimations with relatively low uncertainty, thus enabling the examination of the transition location evolution with varying angle of attack. The estimated locations of transition onset were shown to be in general agreement with reference transition locations measured via temperature-sensitive paint. On the other hand, the oil-film thickness in the turbulent-flow regions was larger than the height of the viscous sublayer, which led to an hydraulically rough surface with increased skin friction, as compared to the clean configuration. For this reason, quantitative skin-friction estimations were not feasible in the turbulent-flow regions. The global effects of the oil-film setup on the flow around the airfoil were evaluated from the estimations of the aerodynamic coefficients. In particular, it was shown that the presence of the specific base coat used for the application of the oil film already induced a significant increase in airfoil drag, as compared to the clean configuration, whereas a thin oil film led to negligible or small additional increases in drag. Based on the present observations, considerations for the further improvement of the global luminescent oil-film skin-friction field estimation method in transonic flow experiments at high Reynolds numbers are elucidated. Graphic abstract

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Section: Repeatability Of the Results And Evaluation Of The Glofsfe Ementioning

confidence: 99%

Section: Critical Limit Of Roughnessmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Feasibility of skin-friction field measurements in a transonic wind tunnel using a global luminescent oil film

et al. 2021

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“…Due to relatively large temperature magnitudes and gradients, TSPs were initially implemented in hypersonic flows [66,[76][77][78], allowing for the formation of qualitative [77] and quantitative [76] relationships between surface temperature and heat transfer. By increasing thermal contrast with an external heating source, TSPs have also been implemented to study near-wall behaviour in the subsonic regime [68,79].…”

Section: Temperature Measurementsmentioning

confidence: 99%

“…Following an approach outlined by Liu & Woodiga [80], Miozzi et al [81] used TSPs to analyze the topology and coherent structures within an LSB formed on a NACA 0015 hydrofoil. This analysis was further developed by Miozzi et al [79] who tracked the thermal signatures of near-wall disturbances in high-speed image sequences. A cross-correlation technique was used to determine the time, ∆t, elapsed for the thermal signature of a disturbance to travel a distance of ∆x.…”

Section: Temperature Measurementsmentioning

confidence: 99%

Characterization of Laminar Separation Bubbles Using Infrared Thermography

Wynnychuk

Yarusevych

2019

AIAA Aviation 2019 Forum

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Boutilier & Yarusevych [7] for estimation of the characteristic points in a laminar separation bubble using static pressure distributions shown with an example pressure distribution (Re L = 27, 000) 4.2 Comparison of inviscid and measured pressure distributions at Re L = 27, 000 4.3 Distribution of static pressure coefficient for highlighted flow conditions. . ix 4.4 Contours of mean streamwise velocity at highlighted Reynolds numbers. .

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