scholarly journals Features of the interaction of localized free-stream disturbances with the straight and swept wing boundary layer

2019 ◽  
Vol 1404 ◽  
pp. 012092
Author(s):  
M M Katasonov ◽  
V V Kozlov ◽  
A M Pavlenko ◽  
I A Sadovskii
Keyword(s):  
Boundary Layer ◽  
Free Stream ◽  
Swept Wing

scholarly journals Algebraically decaying modes and wave packet pseudo-modes in swept Hiemenz flow

2009 ◽  
Vol 643 ◽  
pp. 309-332 ◽  
Author(s):  
DOMINIK OBRIST ◽  
PETER J. SCHMID
Keyword(s):  
Boundary Layer ◽  
Wave Packet ◽  
Free Stream ◽  
Travelling Wave ◽  
Swept Wing ◽  
Algebraic Decay ◽  
Infinite Domains ◽  
The Family ◽  
Hiemenz Flow ◽  
Attachment Line

The modal structure of the swept Hiemenz flow, a model for the flow near the attachment line of a swept wing, consists of eigenfunctions which exhibit (super-)exponential or algebraic decay as the wall-normal coordinate tends to infinity. The subset of algebraically decaying modes corresponds to parts of the spectrum which are characterized by a significant sensitivity to numerical discretization. Numerical evidence further suggests that a continuous spectrum covering a two-dimensional range of the complex plane exists. We investigate the family of uniform swept Hiemenz modes using eigenvalue computations, numerical simulations and the concept of wave packet pseudo-modes. Three distinct branches of the family of algebraically decaying eigenmodes are identified. They can be superimposed to produce wavefronts propagating towards or away from the boundary layer and standing or travelling wave packets in the free stream. Their role in the exchange of information between the free stream and the attachment-line boundary layer for the swept Hiemenz flow is discussed. The concept of wave packet pseudo-modes has been critical in the analysis of this problem and is expected to lead to further insights into other shear flows in semi- or bi-infinite domains.

scholarly journals Transition in an infinite swept-wing boundary layer subject to surface roughness and free-stream turbulence

2021 ◽  
Vol 931 ◽  
Author(s):  
Luca De Vincentiis ◽  
Dan S. Henningson ◽  
Ardeshir Hanifi
Keyword(s):  
Boundary Layer ◽  
Free Stream ◽  
Flow Instability ◽  
Transition To Turbulence ◽  
Computational Domain ◽  
Swept Wing ◽  
Free Stream Turbulence ◽  
Roughness Elements ◽  
Layer Flow ◽  
Institute Of Technology

The instability of an incompressible boundary-layer flow over an infinite swept wing in the presence of disc-type roughness elements and free-stream turbulence (FST) has been investigated by means of direct numerical simulations. Our study corresponds to the experiments by Örlü et al. (Tech. Rep., KTH Royal Institute of Technology, 2021, http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-291874). Here, different dimensions of the roughness elements and levels of FST have been considered. The aim of the present work is to investigate the experimentally observed sensitivity of the transition to the FST intensity. In the absence of FST, flow behind the roughness elements with a height above a certain value immediately undergoes transition to turbulence. Impulse–response analyses of the steady flow have been performed to identify the mechanism behind the observed flow instability. For subcritical roughness, the generated wave packet experiences a weak transient growth behind the roughness and then its amplitude decays as it is advected out of the computational domain. In the supercritical case, in which the flow transitions to turbulence, flow as expected exhibits an absolute instability. The presence of FST is found to have a significant impact on the transition behind the roughness, in particular in the case of a subcritical roughness height. For a height corresponding to a roughness Reynolds number $Re_{hh}=461$ , in the absence of FST the flow reaches a steady laminar state, while a very low FST intensity of $Tu =0.03\,\%$ causes the appearance of turbulence spots in the wake of the roughness. These randomly generated spots are advected out of the computational domain. For a higher FST level of $Tu=0.3\,\%$ , a turbulent wake is clearly visible behind the element, similar to that for the globally unstable case. The presented results confirm the experimental observations and explain the mechanisms behind the observed laminar–turbulent transition and its sensitivity to FST.

Transition in the Infinite Swept Attachment Line Boundary Layer

1979 ◽  
Vol 30 (4) ◽  
pp. 607-629 ◽  
Author(s):  
D.I.A. Poll
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Flat Plate ◽  
Boundary Layers ◽  
Free Stream ◽  
Plate Boundary ◽  
Swept Wing ◽  
Civil Aircraft ◽  
Transition Behaviour ◽  
Attachment Line

SummaryThe transition behaviour of the boundary layer which is formed along an infinite swept attachment line has been studied experimentally. Circular trip wires and turbulent flat plate boundary layers have been used as sources of disturbance and the range of parameters covered has been such that the results are directly applicable to full scale flight conditions. Simple criteria have been deduced which allow the state of the boundary layer to be determined for given geometric and free stream properties. Sample calculations for typical swept wing configurations suggest that the majority of civil aircraft will have turbulent attachment lines in the cruise and that subsequent relaminarisation in regions of favourable pressure gradient is unlikely.

Swept-wing boundary-layer receptivity

2012 ◽  
Vol 700 ◽  
pp. 490-501 ◽  
Author(s):  
David Tempelmann ◽  
Ardeshir Hanifi ◽  
Dan S. Henningson
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Free Stream ◽  
Stokes Equations ◽  
Cross Flow ◽  
Leading Edge ◽  
Navier Stokes ◽  
Flow Mode ◽  
Swept Wing ◽  
Worst Case

AbstractAdjoint solutions of the linearized incompressible Navier–Stokes equations are presented for a cross-flow-dominated swept-wing boundary layer. For the first time these have been computed in the region upstream of the swept leading edge and may therefore be used to predict receptivity to any disturbances of the incoming free stream as well as to surface roughness. In this paper we present worst-case scenarios, i.e. those external disturbances yielding maximum receptivity amplitudes of a steady cross-flow disturbance. In the free stream, such an ‘optimal’ disturbance takes the form of a streak which, while being convected downstream, penetrates the boundary layer and smoothly turns into a growing cross-flow mode. The ‘worst-case’ surface roughness has a wavy shape and is distributed in the chordwise direction. It is shown that, under such optimal conditions, the boundary layer is more receptive to surface roughness than to incoming free stream disturbances.

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