Boundary layer receptivity

Kerschen, E. J.

doi:10.2514/6.1989-1109

Cited by 71 publications

(29 citation statements)

References 12 publications

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“…This was consistent with the findings of Kerschen 54 and Parekh et al 55  Different wavelengths were evident in the boundary-layer response. Signals at the T-S wavelength were dominant near the wall, while toward the edge of the boundary layer, disturbances of the freestream convective wavelength were observed.…”

Section: Dns Validationsupporting

confidence: 93%

Receptivity: The Inspiration of Mark Morkovin (Invited)

Reed

Saric

2015

45th AIAA Fluid Dynamics Conference

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This paper provides a review of the current findings in receptivity for subsonic/transonic flows, including a discussion of the origin of the concept via Mark Morkovin, a remarkable aeronautical engineer, educator, and colleague. Disturbances external to the boundary layer -whether freestream sound or vorticity -can interact with surface roughness, the leading edge, or other inhomogeneities and enter the boundary layer as steady and/or unsteady fluctuations of the basic state. This process establishes the initial conditions of disturbance amplitude, frequency, phase, and scales for the breakdown of laminar flow. The past decades have seen considerable progress in the understanding of receptivity mechanisms guided by the roadmap (Morkovin et al. 1 ).

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Section: Dns Validationsupporting

confidence: 93%

Receptivity: The Inspiration of Mark Morkovin (Invited)

Reed

Saric

2015

45th AIAA Fluid Dynamics Conference

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“…Receptivity establishes the initial conditions of disturbance amplitude, frequency, and phase for the breakdown of laminar (Morkovin 1969;Saric et al 2002). Reviews of different receptivity mechanisms are given by Goldstein & Hultgren (1989); Kerschen (1989); Heinrich et al (1988);Choudhari & Streett (1994);Crouch (1994); Nishioka & Morkovin (1986); Kozlov & Ryzhov (1990);Wlezien (1994); Saric et al (2002); Kachanov (2000). The early theoretical work of Goldstein ( , 1985; Zavol'skii et al (1983);Ruban (1985) solidified the mechanisms by which long-wavelength freestream disturbances at a particular frequency are converted to a wavelength commensurate with the boundary-instability wave.…”

Section: Introductionmentioning

confidence: 99%

“…The early theoretical work of Goldstein ( , 1985; Zavol'skii et al (1983);Ruban (1985) solidified the mechanisms by which long-wavelength freestream disturbances at a particular frequency are converted to a wavelength commensurate with the boundary-instability wave. From a theoretical, numerical and experimental points of view the receptivity mechanism of isolated small height roughness is well understood (Gaster 1965;Murdock 1980;Kerschen 1989Kerschen , 1990Dietz 1999;Wu 2001;Saric et al 2002). The receptivity mechanism shows that the deviation on the length scale of eigen modes from a smooth surface can excite T-S waves by interacting with free-stream disturbances or acoustic noise.…”

Section: Introductionmentioning

confidence: 99%

The behaviour of Tollmien–Schlichting waves undergoing small-scale localised distortions

Sherwin

Hall

et al. 2016

J. Fluid Mech.

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This paper is concerned with the behaviour of Tollmien-Schlichting (T-S) waves experiencing small localised distortions within an incompressible boundary layer developing over a flat-plate. In particular, the distortion is produced by an isolated roughness element located at Re xc = 440 000. We considered the amplification of an incoming T-S wave governed by the two-dimensional linearised Navier-Stokes equations, where the base flow is obtained from the two-dimensional non-linear Navier-Stokes equations. We compare these solutions with asymptotic analyses which assume a linearised triple-deck theory for the base flow and determine the validity of this theory in terms of the height of the smallscale humps/indentations taken into account. The height of the humps/indentations is denoted by h which is considered to be less than or equal to x c Re −5/8 xc (corresponding to h/δ 99 < 6% for our choice of Re xc ). The rescaled widthd(≡ d/(x c Re −3/8 xc )) of the distortion is of the order O(1) and the width d is shorter than the T-S wavelength (λ T S = 11.3 δ 99 ).We observe that for distortions which are smaller than 0.1 of the inner deck height (h/δ 99 < 0.4%) the numerical simulations confirm the asymptotic theory in the vicinity of the distortion. For larger distortions which are still within the inner deck (0.4% < h/δ 99 < 5.5%) and where the flow is still attached the numerical solutions show that both humps and indentations are destabilising and deviate from the linear theory even in the vicinity of the distortion.We numerically determine the transmission coefficient which provides the relative amplification of the T-S wave over the distortion as compared to the flat-plate. We observe that for small distortions, h/δ 99 < 5.5%, where the width of the distortion is of order of the boundary layer a maximum amplification of only 2% is achieved. This amplification can however be increased as the width of the distortion is increased or if multiple distortions are present. Increasing the height of the distortion so that the flow separates (7.2% < h/δ 99 < 12.8%) leads to a substantial increase in the transmission coefficient of the hump up to 350 %.

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“…on various 2D and 3D streamwise-localised surface roughness elements resulting in excitation of various 2D and 3D non-stationary instability modes (such as TS modes, crossflow modes, Görtler modes, etc.) (Gaster 1965;Murdock 1980;Goldstein 1983;Ruban 1984;Goldstein 1985;Goldstein & Hultgren 1987;Kerschen 1989Kerschen , 1990Hall 1990;Denier, Hall & Seddougui 1991;Bassom & Hall 1994;Choudhari 1994;Saric 1994;Bassom & Seddougui 1995;Duck, Ruban & Zhikharev 1996;Dietz 1999;Wu 2001b;Saric et al 2002;Templelmann 2011). The receptivity mechanism shows that the deviation on the length scale of eigenmodes from a smooth surface can excite TS waves by interacting with free-stream disturbances or acoustic noise.…”

Section: Motivation Behind the Study Of Steps In Boundary Layersmentioning

confidence: 99%

Influence of localised smooth steps on the instability of a boundary layer

Lombard

Sherwin

2017

J. Fluid Mech.

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We consider a smooth, spanwise-uniform forward-facing step defined by a Gauss error function of height 4 %-30 % and four times the width of the local boundary layer thickness δ 99 . The boundary layer flow over a smooth forward-facing stepped plate is studied with particular emphasis on stabilisation and destabilisation of the twodimensional Tollmien-Schlichting (TS) waves and subsequently on three-dimensional disturbances at transition. The interaction between TS waves at a range of frequencies and a base flow over a single or two forward-facing smooth steps is conducted by linear analysis. The results indicate that for a TS wave with a frequency F ∈ [140, 160] (F = ων/U 2 ∞ × 10 6 , where ω and U ∞ denote the perturbation angle frequency and free-stream velocity magnitude, respectively, and ν denotes kinematic viscosity), the amplitude of the TS wave is attenuated in the unstable regime of the neutral stability curve corresponding to a flat plate boundary layer. Furthermore, it is observed that two smooth forward-facing steps lead to a more acute reduction of the amplitude of the TS wave. When the height of a step is increased to more than 20 % of the local boundary layer thickness for a fixed width parameter, the TS wave is amplified, and thereby a destabilisation effect is introduced. Therefore, the stabilisation or destabilisation effect of a smooth step is typically dependent on its shape parameters. To validate the results of the linear stability analysis, where a TS wave is damped by the forward-facing smooth steps direct numerical simulation (DNS) is performed. The results of the DNS correlate favourably with the linear analysis and show that for the investigated frequency of the TS wave, the K-type transition process is altered whereas the onset of the H-type transition is delayed. The results of the DNS suggest that for the perturbation with the non-dimensional frequency parameter F = 150 and in the absence of other external perturbations, two forward-facing smooth steps of height 5 % and 12 % of the boundary layer thickness delayed the H-type transition scenario and completely suppressed for the K-type transition. By considering Gaussian white noise with both fixed and random phase shifts, it is demonstrated by DNS that transition is postponed in time and space by two forward-facing smooth steps.

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Boundary layer receptivity

Cited by 71 publications

References 12 publications

Receptivity: The Inspiration of Mark Morkovin (Invited)

Receptivity: The Inspiration of Mark Morkovin (Invited)

The behaviour of Tollmien–Schlichting waves undergoing small-scale localised distortions

Influence of localised smooth steps on the instability of a boundary layer

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