scholarly journals Tollmien-Schlichting/vortex interactions in compressible boundary-layer flows

1994 ◽  
Vol 53 (2) ◽  
pp. 191-214 ◽  
Author(s):  
NICHOLAS D. BLACKABY
Keyword(s):  
Boundary Layer ◽  
Compressible Boundary Layer ◽  
Boundary Layer Flows ◽  
Vortex Interactions ◽  
Tollmien Schlichting

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.

scholarly journals Cancellation of Tollmien–Schlichting waves with surface heating

2021 ◽  
Vol 128 (1) ◽  
Author(s):  
Georgia S. Brennan ◽  
Jitesh S. B. Gajjar ◽  
Richard E. Hewitt
Keyword(s):  
Boundary Layer ◽  
Asymptotic Methods ◽  
Three Dimensional ◽  
Exact Formula ◽  
Surface Heating ◽  
Two Dimensional ◽  
Boundary Layer Flows ◽  
Dimensional Boundary ◽  
Tollmien Schlichting ◽  
Layer Flow

AbstractTwo-dimensional boundary layer flows in quiet disturbance environments are known to become unstable to Tollmien–Schlichting waves. The experimental work of Liepmann et al. (J Fluid Mech 118:187–200, 1982), Liepmann and Nosenchuck (J Fluid Mech 118:201–204, 1982) showed how it is possible to control and reduce unstable Tollmien–Schlichting wave amplitudes using unsteady surface heating. We consider the problem of an oncoming planar compressible subsonic boundary layer flow with a three-dimensional vibrator mounted on a flat plate, and with surface heating present. It is shown using asymptotic methods based on triple-deck theory that it is possible to choose an unsteady surface heating distribution to cancel out the response due to the vibrator. An approximation based on the exact formula is used successfully in numerical computations to confirm the findings. The results presented here are a generalisation of the analogous results for the two-dimensional problem in Brennan et al. (J Fluid Mech 909:A16-1, 2020).

Three-dimensional laminar compressible boundary layers with large injection

1975 ◽  
Vol 71 (4) ◽  
pp. 711-727 ◽  
Author(s):  
C. S. Vimala ◽  
G. Nath
Keyword(s):  
Boundary Layer ◽  
Swirling Flow ◽  
Three Dimensional ◽  
Large Mass ◽  
Variable Cross Section ◽  
Variable Cross ◽  
Compressible Boundary Layer ◽  
Boundary Layer Flows ◽  
Compressible Boundary Layers ◽  
Layer Flow

The effect of large mass injection on the following three-dimensional laminar compressible boundary-layer flows is investigated by employing the method of matched asymptotic expansions: (i) swirling flow in a laminar compressible boundary layer over an axisymmetric surface with variable cross-section and (ii) laminar compressible boundary-layer flow over a yawed infinite wing in a hypersonic flow. The resulting equations are solved numerically by combining the finite-difference technique with quasi-linearization. An increase in the swirl parameter, the yaw angle or the wall temperature is found to be capable of bringing the viscous layer nearer the surface and reducing the effects of massive blowing.

scholarly journals On the Asymptotic Approach to Thermosolutal Convection in Heated Slow Reactive Boundary Layer Flows

2008 ◽  
Vol 2008 ◽  
pp. 1-15
Author(s):  
Stanford Shateyi ◽  
Precious Sibanda ◽  
Sandile S. Motsa
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Flow ◽  
Chemical Species ◽  
Reynolds Numbers ◽  
Thermosolutal Convection ◽  
Boundary Layer Flows ◽  
Instability Waves ◽  
Tollmien Schlichting ◽  
Layer Flow ◽  
Negative Buoyancy

The study sought to investigate thermosolutal convection and stability of two dimensional disturbances imposed on a heated boundary layer flow over a semi-infinite horizontal plate composed of a chemical species using a self-consistent asymptotic method. The chemical species reacts as it diffuses into the nearby fluid causing density stratification and inducing a buoyancy force. The existence of significant temperature gradients near the plate surface results in additional buoyancy and decrease in viscosity. We derive the linear neutral results by analyzing asymptotically the multideck structure of the perturbed flow in the limit of large Reynolds numbers. The study shows that for small Damkohler numbers, increasing buoyancy has a destabilizing effect on the upper branch Tollmien-Schlichting (TS) instability waves. Similarly, increasing the Damkohler numbers (which corresponds to increasing the reaction rate) has a destabilizing effect on the TS wave modes. However, for small Damkohler numbers, negative buoyancy stabilizes the boundary layer flow.

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