Passive control of transition in three-dimensional boundary layers, with emphasis on discrete roughness elements

2011 ◽  
Vol 369 (1940) ◽  
pp. 1352-1364 ◽  
Author(s):  
William S. Saric ◽  
Andrew L. Carpenter ◽  
Helen L. Reed
Keyword(s):  
Laminar Flow ◽  
Passive Control ◽  
Three Dimensional ◽  
Flight Test ◽  
Test Results ◽  
Swept Wing ◽  
Control Techniques ◽  
Roughness Elements ◽  
Dimensional Boundary ◽  
Laminar Flow Control

A brief review of laminar flow control techniques is given and a strategy for achieving laminarization for transonic transport aircraft is discussed. A review of some flight-test results on swept-wing transition is presented. It is also shown that polished leading edges can create large regions of laminar flow because the flight environment is relatively turbulence free and the surface finish reduces the initial amplitude of the stationary crossflow vortex.

Mechanisms of flow tripping by discrete roughness elements in a swept-wing boundary layer

2016 ◽  
Vol 796 ◽  
pp. 158-194 ◽  
Author(s):  
Holger B. E. Kurz ◽  
Markus J. Kloker
Keyword(s):  
Boundary Layer ◽  
Roughness Element ◽  
Three Dimensional ◽  
Finite Size ◽  
Roughness Height ◽  
Swept Wing ◽  
Global Instability ◽  
Critical Height ◽  
Roughness Elements ◽  
Dimensional Boundary

The effects of a spanwise row of finite-size cylindrical roughness elements in a laminar, compressible, three-dimensional boundary layer on a wing profile are investigated by direct numerical simulations (DNS). Large elements are capable of immediately tripping turbulent flow by either a strong, purely convective or an absolute/global instability in the near wake. First we focus on an understanding of the steady near-field past a finite-size roughness element in the swept-wing flow, comparing it to a respective case in unswept flow. Then, the mechanisms leading to immediate turbulence tripping are elaborated by gradually increasing the roughness height and varying the disturbance background level. The quasi-critical roughness Reynolds number above which turbulence sets in rapidly is found to be $Re_{kk,qcrit}\approx 560$ and global instability is found only for values well above 600 using nonlinear DNS; therefore the values do not differ significantly from two-dimensional boundary layers if the full velocity vector at the roughness height is taken to build $Re_{kk}$. A detailed simulation study of elements in the critical range indicates a changeover from a purely convective to a global instability near the critical height. Finally, we perform a three-dimensional global stability analysis of the flow field to gain insight into the early stages of the temporal disturbance growth in the quasi-critical and over-critical cases, starting from a steady state enforced by damping of unsteady disturbances.

Investigation of suction for laminar flow control of three-dimensional boundary layers

2010 ◽  
Vol 658 ◽  
pp. 117-147 ◽  
Author(s):  
RALF MESSING ◽  
MARKUS J. KLOKER
Keyword(s):  
Boundary Layer ◽  
Three Dimensional ◽  
Direct Numerical Simulations ◽  
Boundary Layer Flows ◽  
Roughness Elements ◽  
Stabilizing Effect ◽  
Dimensional Boundary ◽  
Flow Deformation ◽  
Laminar Flow Control ◽  
Upstream Flow

Direct numerical simulations are employed to investigate the effects of discrete suction orifices at the wall on the disturbance evolution in laminar three-dimensional boundary-layer flows with favourable pressure gradient. Suction panels with many suction orifices can excite unstable crossflow (CF) modes even if the orifice spacing is smaller than the chordwise/spanwise wavelengths of unstable modes, caused by imperfections in the orifice order or suction strength. It has been found that the most unstable steady vortex mode leads to strong CF vortices that invoke turbulence by secondary instability even on the active suction panel. The deliberate excitation and support of stabilizing vortices that have less than two-thirds of the spanwise wavelength of the most amplified ones – known from the upstream flow deformation or micrometre-sized roughness elements technique – by the orifice order on the panel can secure the desired stabilizing effect of suction and lower the necessary suction amount significantly.

Silk-Screen Print Technique in Laminar Flow Control

2011 ◽  
Vol 317-319 ◽  
pp. 1433-1437
Author(s):  
Jue Wang ◽  
Dong Li
Keyword(s):  
Fluid Dynamics ◽  
Laminar Flow ◽  
Flow Control ◽  
Leading Edge ◽  
Swept Wing ◽  
Roughness Elements ◽  
Silk Screen ◽  
Laminar Flow Control ◽  
Screen Print

Silk-Screen Print Technique was used to print roughness elements at the leading edge of a swept wing for crossflow (CF) dominated Laminar Flow control (LFC) in fluid dynamics. Crossflow was studied to be sensitive to the spacing and height of the roughness elements, as well as the density of the metal ink. Experiments in our research showed silk-screen print technique can precisely print the elements to dominate to delay transition.

Experimental and Theoretical Investigation of the Supersonic Boundary Layer Stability on the Swept Wing

2008 ◽  
Vol 3 (3) ◽  
pp. 34-38
Author(s):  
Sergey A. Gaponov ◽  
Yuri G. Yermolaev ◽  
Aleksandr D. Kosinov ◽  
Nikolay V. Semionov ◽  
Boris V. Smorodsky
Keyword(s):  
Boundary Layer ◽  
Three Dimensional ◽  
Leading Edge ◽  
Supersonic Boundary Layer ◽  
Mean Flow ◽  
Swept Wing ◽  
Wing Model ◽  
Dimensional Boundary ◽  
The Stability ◽  
Good Agreement

Theoretical and an experimental research results of the disturbances development in a swept wing boundary layer are presented at Mach number М = 2. In experiments development of natural and small amplitude controllable disturbances downstream was studied. Experiments were carried out on a swept wing model with a lenticular profile at a zero attack angle. The swept angle of a leading edge was 40°. Wave parameters of moving disturbances were determined. In frames of the linear theory and an approach of the local self-similar mean flow the stability of a compressible three-dimensional boundary layer is studied. Good agreement of the theory with experimental results for transversal scales of unstable vertices of the secondary flow was obtained. However the calculated amplification rates differ from measured values considerably. This disagreement is explained by the nonlinear processes observed in experiment

scholarly journals Influence of two-dimensional roughness element on boundary layer structure in the favourable pressure gradient region of the swept wing

2019 ◽  
Vol 234 (1) ◽  
pp. 20-27
Author(s):  
Stepan Tolkachev ◽  
Victor Kozlov ◽  
Valeriya Kaprilevskaya
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Layer Structure ◽  
Roughness Element ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Frequency Range ◽  
Swept Wing ◽  
Boundary Layer Structure ◽  
Roughness Elements

In this article, the results of research about stationary and secondary disturbances development behind the localized and two-dimensional roughness elements are presented. It is shown that the two-dimensional roughness element has a destabilizing effect on the disturbances induced by the three-dimensional roughness element lying upstream. In this case, the two-dimensional roughness element causes the appearance of stationary structures, and then secondary perturbations, whose frequency range lies lower than in the case of the stationary vortices excited by a three-dimensional roughness element.

Electrogasdynamic laminar flow control on a swept wing

2016 ◽  
Vol 59 ◽  
pp. 155-161 ◽  
Author(s):  
Sergey L. Chernyshev ◽  
Marat D. Gamirullin ◽  
Vladislav Yu. Khomich ◽  
Aleksandr P. Kuryachii ◽  
Vladimir M. Litvinov ◽  
...  
Keyword(s):  
Laminar Flow ◽  
Flow Control ◽  
Swept Wing ◽  
Laminar Flow Control

Mechanisms and passive control of crossflow-vortex-induced transition in a three-dimensional boundary layer

2002 ◽  
Vol 456 ◽  
pp. 49-84 ◽  
Author(s):  
PETER WASSERMANN ◽  
MARKUS KLOKER
Keyword(s):  
Boundary Layer ◽  
Passive Control ◽  
Three Dimensional ◽  
Plate Boundary ◽  
Secondary Instability ◽  
Base Flow ◽  
Transition Control ◽  
Dimensional Boundary ◽  
Layer Flow ◽  
Underlying Mechanisms

Crossflow-vortex-induced laminar breakdown in a three-dimensional flat-plate boundary-layer flow is investigated in detail by means of spatial direct numerical simulations. The base flow is generic for an infinite swept wing, with decreasing favourable chordwise pressure gradient. First, the downstream growth and nonlinear saturation states initiated by a crossflow-vortex-mode packet as well as by single crossflow-vortex modes with various spanwise wavenumbers are simulated. Second, the secondary instability of the flow induced by the saturated crossflow vortices is scrutinized, clearly indicating the convective nature of the secondary instability and strengthening knowledge of the conditions for its onset. Emphasis is on the effect of crossflow-vortex-mode packets and of the spanwise vortex spacing on the secondary stability properties of the saturation states. Saturated uniform crossflow vortices initiated by single crossflow-vortex modes turn out to be less unstable than vortices initiated by a packet of vortex modes, and closely spaced saturated vortices are even stable. Third, we investigate the transition control strategy of upstream flow deformation by appropriate steady nonlinear vortex modes as applied in wind tunnel experiments at the Arizona State University. A significant transition delay is shown in the base flow considered here, and the underlying mechanisms are specified.

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