Laminar Separation, Transition, and Turbulent Reattachment near the Leading Edge of Airfoils

Arena, Andrea; Mueller, Thomas

doi:10.2514/3.50815

Cited by 102 publications

(46 citation statements)

References 4 publications

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“…In agreement with the typical characteristics of a separation bubble described by Arena and Mueller (1980), as the angle of attack increases the whole bubble moves toward the stagnation point and becomes shorter in length. Moreover, the extension of the laminar portion of the separated shear shortens, the St plateau practically disappearing at the highest e values.…”

Section: Quantitative Datasupporting

confidence: 69%

Boundary layer diagnostics by means of an infrared scanning radiometer

Luca¹,

Carlomagno²,

Buresti

1990

Experiments in Fluids

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A computerized infrared (IR) scanning radiometer is employed to characterize the boundary layer development over a model wing, having a G6ttingen 797 cross-section, by measuring the temperature distribution over its heated surface. The Reynolds analogy is used to relate heat transfer measurements to skin friction. The results show that IR thermography is capable of rapidly detecting location and extent of transition and separation regions of the boundary layer over the whole surface of the tested model wing. Thus, the IR technique appears to be a suitable and effective diagnostic tool for aerodynamic research in wind tunnels. List of symbolsc airfoil chord cj local skin friction coefficient = 2r/(~o V 2) Cp specific heat coefficient at constant pressure h local convective heat transfer coefficient Nu Nusselt number = h x/.;. Nu, Nusselt number based on airfoil chord = hc/2 Pr Prandtl number %tl/St Qj wall heat flux due to Joule heating Ql heat flux loss Re Reynolds number ~o Vx/# Re c Reynolds number based on airfoil chord = ~ Vc/la St Stanton number = h/~ % V T,.wall temperature T,, w adiabatic wall temperature

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Section: Quantitative Datasupporting

confidence: 69%

Boundary layer diagnostics by means of an infrared scanning radiometer

Luca¹,

Carlomagno²,

Buresti

1990

Experiments in Fluids

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“…Prediction of two-and three-dimensional separated flows has also been carried out by Cutrone et al 23 Many authors have non-dimensionalised the dominant instability frequency using momentum thickness and edge velocity at separation as characteristic length and velocity scale. Ripley and Pauley 10 Extensive studies have been presented in the past to understand the transition of a separation bubble formed over a flat plate, whereas relatively few attempts except the experiments of Mueller et al [29][30][31][32][33] and LES of Yang and Voke 17 have been made to elucidate the separated flow characteristics from the leading edge of an aerofoil. Further, the study on leading edge separation bubble is important as it dictates the downstream boundary layer and stalling characteristics.…”

Section: Introductionmentioning

confidence: 98%

An experimental investigation of a laminar separation bubble on the leading-edge of a modelled aerofoil for different Reynolds numbers

Samson

Sarkar

2015

Proceedings of the Institution of Mechanical Engineers, Part C:

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This paper describes the dynamics of a laminar separation bubble formed on the semi-circular leading edge of constant thickness aerofoil model. Detailed experimental studies are carried out in a low-speed wind tunnel, where surface pressure and time-averaged velocity in the separated region and as well as in the downstream are presented along with flow field visualisations through PIV for various Reynolds numbers ranging from 25,000 to 75,000 (based on the leading edge diameter). The results illustrate that the separated shear layer is laminar up to 20% of separation length and then the perturbations are amplified in the second half attributing to breakdown and reattachment. The bubble length is highly susceptible to change in Reynolds number and plays an important role in outer layer activities. Further, the transition of a separated shear layer is studied through variation of intermittency factor and comparing with existing correlations available in the literature for attached flow and as well as separated flow. Transition of the separated shear layer occurs through formation of K-H rolls, where the intermittency following spot propagation theory appears valid. The predominant shedding frequency when normalised with respect to the momentum thickness at separation remains almost constant with change in Reynolds number. The relaxation is slow after reattachment and the flow takes about five bubble lengths to approach a canonical layer.

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“…As a result, the separated shear layer reattaches to the surface as a turbulent state, which results in the rapid recovery of the surface pressure distribution. 19,21,22 In particular, the plateau pressure distribution has often been thought as a general feature of the LSB, 1-4 and thus in many prior studies, 18,19,[21][22][23][24][25][26][27][28][29] the formation of the LSB has been judged by the appearance of the plateau pressure distribution. With respect to the relation between the pressure distribution and the LSB characteristics, Anyoji et al 30 have experimentally measured surface pressure distributions of a 5% thickness blunt flat plate using pressure-sensitive paint (PSP) technique at the plate length based Reynolds numbers of Re c = 4.9 × 10 3 , 6.1 × 10 3 , 1.1 × 10 4 , 2.0 × 10 4 , and 4.1 × 10 4 .…”

Section: Introductionmentioning

confidence: 98%

“…The physical reasoning of the plateau pressure distribution within the LSB has been explained by prior studies. 3,18,20,26 Within the laminar part of the LSB (plateau pressure distribution region), the velocity of the flow under the separated shear layer is circulated slowly and thus practically stationary. As a result, the streamwise pressure gradient is nearly zero, which results in the plateau pressure distribution.…”

Section: Introductionmentioning

confidence: 99%

Mechanisms of surface pressure distribution within a laminar separation bubble at different Reynolds numbers

et al. 2015

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Mechanisms behind the pressure distribution and skin friction within a laminar separation bubble (LSB) are investigated by large-eddy simulations around a 5% thickness blunt flat plate at the chord length based Reynolds number 5.0 × 103, 6.1 × 103, 1.1 × 104, and 2.0 × 104. The characteristics inside the LSB change with the Reynolds number; a steady laminar separation bubble (LSB_S) at the Reynolds number 5.0 × 103 and 6.1 × 103, and a steady-fluctuating laminar separation bubble (LSB_SF) at the Reynolds number 1.1 × 104, and 2.0 × 104. Different characteristics of pressure and skin friction distributions are observed by increasing the Reynolds number, such that a gradual monotonous pressure recovery in the LSB_S and a plateau pressure distribution followed by a rapid pressure recovery region in the LSB_SF. The reasons behind the different characteristics of pressure distributions at different Reynolds numbers are discussed by deriving the Reynolds averaged pressure gradient equation. It is confirmed that the viscous stress distributions near the surface play an important role in determining the formation of different pressure distributions. Depending on the Reynolds numbers, the viscous stress distributions near the surface are affected by the development of a separated laminar shear layer or the Reynolds shear stress. In addition, we show that the same analyses can be applied to the flows around a NACA0012 airfoil.

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Laminar Separation, Transition, and Turbulent Reattachment near the Leading Edge of Airfoils

Cited by 102 publications

References 4 publications

Boundary layer diagnostics by means of an infrared scanning radiometer

Boundary layer diagnostics by means of an infrared scanning radiometer

An experimental investigation of a laminar separation bubble on the leading-edge of a modelled aerofoil for different Reynolds numbers

Mechanisms of surface pressure distribution within a laminar separation bubble at different Reynolds numbers

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