Simulation and characterization of the laminar separation bubble over a NACA-0012 airfoil as a function of angle of attack

ElJack, Eltayeb; Soria, Julio; ElAwad, Yasir A; Ohtake, Tomohisa

doi:10.1103/physrevfluids.6.034701

Cited by 20 publications

(8 citation statements)

References 31 publications

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“…As discussed in Section IV.B, although the instantaneous data for the SLE-10 case shows separation, the flow transition at this configuration is highly unsteady (see included animation as supplementary material), such that the transition location periodically oscillates in the streamwise direction. This unsteadiness is consistent with the observations of various studies [39,47] that report the presence of oscillations of the laminar separated shear layer near the stall angle.…”

Section: Time Averaged Flowsupporting

confidence: 92%

Flow Separation in Airfoils with Rough Leading Edges

et al. 2023

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In this study we consider the flow over airfoils with leading-edge roughness, designed to mimic the ice depositions that may occur on an aircraft in flight. The focus of this investigation is the effect of the angle of attack on the mean-flow three-dimensionality. In our previous work (Kumar et al., Journal of Turbulence, Vol. 22, No. 11, 2021, pp. 735–760), we found stationary spanwise inhomogeneities in the form of alternating regions of fast- and slow-moving fluid, which were termed “flow channels.” In the present study we investigate further this phenomenon. We observe the formation of hairpin vortices downstream of the roughness elements, which eventually merge; this causes the formation of wider channels that remain coherent and affect the trailing-edge separation. With increasing angle of attack, the intensity of flow channeling can increase or decrease depending on the topology of the leading-edge roughness. Its effect on the trailing-edge separation remains, however, significant. The mean-separation line is highly distorted, and the separation length can vary by up to 30% of the chord length along the span.

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Section: Time Averaged Flowsupporting

confidence: 92%

Flow Separation in Airfoils with Rough Leading Edges

et al. 2023

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“…Recently, Eljack et al. (2021) observed SV and LSB together in flow past a NACA 0012 airfoil at and . Although not pointed out by them, a kink can be seen in their plots as well for the surface distribution.…”

Section: Resultsmentioning

confidence: 89%

Secondary vortex, laminar separation bubble and vortex shedding in flow past a low aspect ratio circular cylinder

Chopra¹,

Mittal²

2021

J. Fluid Mech.

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Large eddy simulation of flow past a circular cylinder of low aspect ratio ( $AR=1$ and $3$ ), spanning subcritical, critical and supercritical regimes, is carried out for $2\times 10^3 \le Re \le 4\times 10^5$ . The end walls restrict three-dimensionality of the flow. The critical $Re$ for the onset of the critical regime is significantly lower for small aspect ratio cylinders. The evolution of secondary vortex (SV), laminar separation bubble (LSB) and the related transition of boundary layer with $Re$ is investigated. The plateau in the surface pressure due to LSB is modified by the presence of SV. Proper orthogonal decomposition of surface pressure reveals that although the vortex shedding mode is most dominant throughout the $Re$ regime studied, significant energy of the flow lies in a symmetric mode that corresponds to expansion–contraction of the vortex formation region and is responsible for bursts of weak vortex shedding. A triple decomposition of the time signals comprising of contributions from shear layer vortices, von Kármán vortex shedding and low frequency modulation due to the symmetric mode of flow is proposed. A moving average, with appropriate size of window, is utilized to estimate the component due to vortex shedding. It is used to assess the variation, with $Re$ , of strength of vortex shedding as well as its coherence along the span. Weakening of vortex shedding in the high subcritical and critical regime is followed by its rejuvenation in the supercritical regime. Its spanwise correlation is high in the subcritical regime, decreases in the critical regime and improves again in the supercritical regime.

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“…The response of a laminar separation bubble (LSB) to the change of the external flow characteristics has been investigated in a number of previous studies, e.g. Marxen & Henningson (2011), Hosseinverdi & Fasel (2019), Rodríguez, Gennaro & Souza (2021), Eljack et al (2021), Toppings & Yarusevych (2022), Jaroslawski et al (2023). At low Reynolds numbers and/or high angles of attack, the bursting process of an LSB may occur, causing an abrupt change of the bubble length due to a small variation in flow parameters.…”

Section: Introductionmentioning

confidence: 99%

“…Marxen & Henningson (2011), Hosseinverdi & Fasel (2019), Rodríguez, Gennaro & Souza (2021), Eljack et al. (2021), Toppings & Yarusevych (2022), Jaroslawski et al. (2023).…”

Section: Introductionmentioning

confidence: 99%

A data-driven analysis of short and long laminar separation bubbles

Dellacasagrande,

Lengani,

Simoni

et al. 2023

J. Fluid Mech.

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This work investigates the statistical response of short and long laminar separation bubbles to external flow parameters, such as Reynolds number, free-stream turbulence intensity and streamwise pressure gradient, known to govern bubble formation and characteristics. A parametric experimental campaign has been performed using particle image velocimetry on a flat plate to provide a comprehensive database for the characterization of separation-induced transition in both short and long separation bubbles. The proper orthogonal decomposition (POD) was applied to the data set of all dividing streamlines commonly used to identify a laminar separation bubble. This provides an optimal state-space basis for the data-driven classification of the state of a laminar separation bubble, with the leading modes capturing the change in length and height of the laminar separation bubble in response to changes in the flow parameters. When projected onto the POD subspace constituted by the first three leading modes, the normalized data from the present study and the results from prior investigations not used in the modal analysis collapse on the same trajectory in the low-dimensional space. The present POD basis can be therefore adopted for the description of the general response of the time-mean shape of a laminar separation bubble to changes in the main influencing parameters. A well-defined pattern was observed in the case of short laminar separation bubbles in the reduced-order space defined by the first three POD coefficients, whereas a higher dispersion in the long-bubble regime indicates an increased sensitivity of long bubbles to the external flow characteristics.

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Simulation and characterization of the laminar separation bubble over a NACA-0012 airfoil as a function of angle of attack

Cited by 20 publications

References 31 publications

Flow Separation in Airfoils with Rough Leading Edges

Flow Separation in Airfoils with Rough Leading Edges

Secondary vortex, laminar separation bubble and vortex shedding in flow past a low aspect ratio circular cylinder

A data-driven analysis of short and long laminar separation bubbles

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