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.

An Assessment of Three-Dimensional Turbulent Boundary Layer Prediction Methods

1973 ◽  
Vol 95 (3) ◽  
pp. 415-421 ◽  
Author(s):  
A. J. Wheeler ◽  
J. P. Johnston
Keyword(s):  
Boundary Layer ◽  
Eddy Viscosity ◽  
Three Dimensional ◽  
High Sensitivity ◽  
Boundary Layer Flows ◽  
Mean Velocity ◽  
Eddy Viscosity Model ◽  
Separating Flow ◽  
Dimensional Boundary ◽  
Stress Models

Predictions have been made for a variety of experimental three-dimensional boundary layer flows with a single finite difference method which was used with three different turbulent stress models: (i) an eddy viscosity model, (ii) the “Nash” model, and (iii) the “Bradshaw” model. For many purposes, even the simplest stress model (eddy viscosity) was adequate to predict the mean velocity field. On the other hand, the profile of shear stress direction was not correctly predicted in one case by any model tested. The high sensitivity of the predicted results to free stream pressure gradient in separating flow cases is demonstrated.

Boundary layer at a swept stagnation line of semi-infinite extent

1970 ◽  
Vol 41 (4) ◽  
pp. 737-750 ◽  
Author(s):  
Paul A. Libby ◽  
Karl K. Chen
Keyword(s):  
Boundary Layer ◽  
Numerical Solutions ◽  
Three Dimensional ◽  
Cross Flow ◽  
Differential Analysis ◽  
Eigenvalues And Eigenfunctions ◽  
Stagnation Line ◽  
Infinite Extent ◽  
Dimensional Boundary ◽  
Upstream Flow

A three-dimensional boundary layer developing along a semi-infinite swept stagnation line from a starting edge and evolving into that associated with such a line of infinite extent is calculated. A series solution useful for assessing the counteracting effects of cross-flow and mass transfer near the starting edge and for providing initial data for a subsequent streamwise, numerical solution is developed. The asymptotic behaviour far from the starting edge is examined and shown to involve only eigenfunction contributions associated with the far upstream flow. However, it is not presently possible to determine the relevant eigenvalues and eigenfunctions. Numerical solutions based on a difference-differential analysis yield the entire development of the boundary layer and indicate the streamwise length required for the case of the boundary layer at an infinite stagnation line to be obtained.

Instabilities of the von Kármán Boundary Layer

2015 ◽  
Vol 67 (3) ◽  
Author(s):  
R. J. Lingwood ◽  
P. Henrik Alfredsson
Keyword(s):  
Boundary Layer ◽  
Three Dimensional ◽  
Rotating Disk ◽  
Direct Numerical Simulations ◽  
Layer Model ◽  
Complex Flow ◽  
Von Karman ◽  
Dimensional Boundary ◽  
Flow Configurations ◽  
Von Kármán

Research on the von Kármán boundary layer extends back almost 100 years but remains a topic of active study, which continues to reveal new results; it is only now that fully nonlinear direct numerical simulations (DNS) have been conducted of the flow to compare with theoretical and experimental results. The von Kármán boundary layer, or rotating-disk boundary layer, provides, in some senses, a simple three-dimensional boundary-layer model with which to compare other more complex flow configurations but we will show that in fact the rotating-disk boundary layer itself exhibits a wealth of complex instability behaviors that are not yet fully understood.

scholarly journals Optimal Perturbations in Boundary-Layer Flows Over Rough Surfaces

2013 ◽  
Vol 135 (12) ◽  
Author(s):  
S. Cherubini ◽  
M. D. de Tullio ◽  
P. De Palma ◽  
G. Pascazio
Keyword(s):  
Boundary Layer ◽  
Three Dimensional ◽  
Base Flow ◽  
Immersed Boundary ◽  
Boundary Layer Flows ◽  
Instability Theory ◽  
Roughness Elements ◽  
Tollmien Schlichting ◽  
Layer Flow ◽  
Lagrangian Optimization

This work provides a three-dimensional energy optimization analysis, looking for perturbations inducing the largest energy growth at a finite time in a boundary-layer flow in the presence of roughness elements. The immersed boundary technique has been coupled with a Lagrangian optimization in a three-dimensional framework. Four roughness elements with different heights have been studied, inducing amplification mechanisms that bypass the asymptotical growth of Tollmien–Schlichting waves. The results show that even very small roughness elements, inducing only a weak deformation of the base flow, can strongly localize the optimal disturbance. Moreover, the highest value of the energy gain is obtained for a varicose perturbation. This result demonstrates the relevance of varicose instabilities for such a flow and shows a different behavior with respect to the secondary instability theory of boundary layer streaks.

scholarly journals Optimal Perturbations in Boundary Layer Flows Over Rough Surfaces

2012 ◽  
Author(s):  
S. Cherubini ◽  
M. D. de Tullio ◽  
P. De Palma ◽  
G. Pascazio
Keyword(s):  
Boundary Layer ◽  
Three Dimensional ◽  
Base Flow ◽  
Immersed Boundary ◽  
Boundary Layer Flows ◽  
Instability Theory ◽  
Roughness Elements ◽  
Tollmien Schlichting ◽  
Layer Flow ◽  
Lagrangian Optimization

This work provides a three-dimensional energy optimization analysis, looking for perturbations inducing the largest energy growth at a finite time in a boundary-layer flow in the presence of roughness elements. Amplification mechanisms are described which by-pass the asymptotical growth of Tollmien–Schlichting waves. The immersed boundary technique has been coupled with a Lagrangian optimization in a three-dimensional framework. Two types of roughness elements have been studied, characterized by a different height. The results show that even very small roughness elements, inducing only a weak deformation of the base flow, can strongly localize the optimal disturbance. Moreover, the highest value of the energy gain is obtained for a varicose perturbation, pointing out the importance of varicose instabilities for such a flow and a different behavior with respect to the secondary instability theory of boundary layer streaks.

Receptivity mechanisms in three-dimensional boundary-layer flows

2009 ◽  
Vol 618 ◽  
pp. 209-241 ◽  
Author(s):  
LARS-UVE SCHRADER ◽  
LUCA BRANDT ◽  
DAN S. HENNINGSON
Keyword(s):  
Boundary Layer ◽  
Free Stream ◽  
Three Dimensional ◽  
Leading Edge ◽  
Nonlinear Process ◽  
Transition To Turbulence ◽  
Boundary Layer Flows ◽  
Free Stream Turbulence ◽  
Dimensional Boundary ◽  
Layer Flow

Receptivity in three-dimensional boundary-layer flow to localized surface roughness and free-stream vorticity is studied. A boundary layer of Falkner–Skan–Cooke type with favourable pressure gradient is considered to model the flow slightly downstream of a swept-wing leading edge. In this region, stationary and travelling crossflow instability dominates over other instability types. Three scenarios are investigated: the presence of low-amplitude chordwise localized, spanwise periodic roughness elements on the plate, the impingement of a weak vortical free-stream mode on the boundary layer and the combination of both disturbance sources. Three receptivity mechanisms are identified: steady receptivity to roughness, unsteady receptivity to free-stream vorticity and unsteady receptivity to vortical modes scattered at the roughness. Both roughness and vortical modes provide efficient direct receptivity mechanisms for stationary and travelling crossflow instabilities. We find that stationary crossflow modes dominate for free-stream turbulence below a level of about 0.5%, whereas higher turbulence levels will promote the unsteady receptivity mechanism. Under the assumption of small amplitudes of the roughness and the free-stream disturbance, the unsteady receptivity process due to scattering of free-stream vorticity at the roughness has been found to give small initial disturbance amplitudes in comparison to the direct mechanism for free-stream modes. However, in many environments free-stream vorticity and roughness may excite interacting unstable stationary and travelling crossflow waves. This nonlinear process may rapidly lead to large disturbance amplitudes and promote transition to turbulence.

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