scholarly journals Generation of disturbances in the boundary layer of a flat plate by periodic low-frequency motion of the surface section

2019 ◽  
Vol 234 (1) ◽  
pp. 109-114
Author(s):  
Mikhail M Katasonov ◽  
Victor V Kozlov ◽  
Alexandr M Pavlenko
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Wave Packets ◽  
Three Dimensional ◽  
Plate Boundary ◽  
Low Frequency ◽  
Localized Structures ◽  
Surface Section ◽  
Periodic Impulse ◽  
Low Frequency Motion

The development of localized disturbances, generated by periodic impulse lifting of three-dimensional surface in the flat plate boundary layer at Reδ1 > 400 is experimentally investigated. It is shown that a large amplitude surface lifting leads simultaneously to the formation of two types of perturbations in the boundary layer: longitudinal localized structures and two wave packets. Spatial development of oscillations at the central frequency of the wave packets is consistent with the linear theory of hydrodynamic stability.

scholarly journals Investigation of the Development of Localized Disturbances in the Boundary Layer of a Flat Plate under Conditions of Moderate Degree of the Incoming Flow Turbulence behind the Surface Step

2021 ◽  
Vol 16 (1) ◽  
pp. 65-80
Author(s):  
Ivan A. Sadovsky ◽  
Mikhail M Katasonov ◽  
Alexander M. Pavlenko
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Wave Packets ◽  
Low Frequency ◽  
Separated Flow ◽  
Moderate Degree ◽  
Incoming Flow ◽  
Free Stream Turbulence ◽  
Surface Section ◽  
Flow Turbulence

In a wind tunnel on a flat plate in a separated flow behind a rectangular step, the emergence and development of localized disturbances generated by low-frequency impulse deviations of the local surface section under conditions of low and moderate degrees of the incoming flow turbulence is studied. The results were obtained by hot-wire anemometry at low subsonic flow velocity. It was found that impulse deviations of the wall generate disturbances, which are socalled Streaky structures and wave packets of oscillations. The separation of the laminar boundary layer accelerates the growth of wave packets with subsequent turbulization of the near-wall flow. The specific features of the behavior of localized disturbances under conditions of moderate degree of free-stream turbulence are revealed.

On the Criterion for the Determination Transition Onset and Breakdown to Turbulence in Wall-Bounded Flows1

2004 ◽  
Vol 126 (4) ◽  
pp. 626-633 ◽  
Author(s):  
J. Jovanovic´ ◽  
M. Pashtrapanska
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Local Equilibrium ◽  
Three Dimensional ◽  
Plate Boundary ◽  
Correlation Technique ◽  
Equilibrium Solutions ◽  
Onset Of Turbulence ◽  
Transition Criterion ◽  
Flat Plate Boundary Layer

Starting from the basic conservation laws of fluid flow, we investigated transition and breakdown to turbulence of a laminar flat plate boundary layer exposed to small, statistically stationary, two-component, three-dimensional disturbances. The derived equations for the statistical properties of the disturbances are closed using the two-point correlation technique and invariant theory. By considering the equilibrium solutions of the modeled equations, the transition criterion is formulated in terms of a Reynolds number based on the intensity and the length scale of the disturbances. The deduced transition criterion determines conditions that guarantee maintenance of the local equilibrium between the production and the viscous dissipation of the disturbances and therefore the laminar flow regime in the flat plate boundary layer. The experimental and numerical databases for fully developed turbulent channel and pipe flows at different Reynolds numbers were utilized to demonstrate the validity of the derived transition criterion for the estimation of the onset of turbulence in wall-bounded flows.

Evolution of wave packets in supersonic flat-plate boundary layer

2015 ◽  
Vol 22 (1) ◽  
pp. 17-27 ◽  
Author(s):  
A. A. Yatskikh ◽  
Yu. G. Ermolaev ◽  
A. D. Kosinov ◽  
N. V. Semionov
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Wave Packets ◽  
Plate Boundary ◽  
Flat Plate Boundary Layer

Receptivity to free-stream vorticity of flow past a flat plate with elliptic leading edge

2010 ◽  
Vol 653 ◽  
pp. 245-271 ◽  
Author(s):  
L.-U. SCHRADER ◽  
L. BRANDT ◽  
C. MAVRIPLIS ◽  
D. S. HENNINGSON
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Free Stream ◽  
Three Dimensional ◽  
Low Frequency ◽  
Leading Edge ◽  
Sound Waves ◽  
Streamwise Vorticity ◽  
Low Frequencies ◽  
Free Stream Turbulence

Receptivity of the two-dimensional boundary layer on a flat plate with elliptic leading edge is studied by numerical simulation. Vortical perturbations in the oncoming free stream are considered, impinging on two leading edges with different aspect ratio to identify the effect of bluntness. The relevance of the three vorticity components of natural free-stream turbulence is illuminated by considering axial, vertical and spanwise vorticity separately at different angular frequencies. The boundary layer is most receptive to zero-frequency axial vorticity, triggering a streaky pattern of alternating positive and negative streamwise disturbance velocity. This is in line with earlier numerical studies on non-modal growth of elongated structures in the Blasius boundary layer. We find that the effect of leading-edge bluntness is insignificant for axial free-stream vortices alone. On the other hand, vertical free-stream vorticity is also able to excite non-modal instability in particular at zero and low frequencies. This mechanism relies on the generation of streamwise vorticity through stretching and tilting of the vertical vortex columns at the leading edge and is significantly stronger when the leading edge is blunt. It can thus be concluded that the non-modal boundary-layer response to a free-stream turbulence field with three-dimensional vorticity is enhanced in the presence of a blunt leading edge. At high frequencies of the disturbances the boundary layer becomes receptive to spanwise free-stream vorticity, triggering Tollmien–Schlichting (T-S) modes and receptivity increases with leading-edge bluntness. The receptivity coefficients to free-stream vortices are found to be about 15% of those to sound waves reported in the literature. For the boundary layers and free-stream perturbations considered, the amplitude of the T-S waves remains small compared with the low-frequency streak amplitudes.

Dynamics of three-dimensional coherent structures in a flat-plate boundary layer

1994 ◽  
Vol 275 ◽  
pp. 257-283 ◽  
Author(s):  
Dietmar Rempfer ◽  
Hermann F. Fasel
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Coherent Structures ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Plate Boundary ◽  
Galerkin Projection ◽  
Power Budget ◽  
Energy Flows ◽  
Flat Plate Boundary Layer

An investigation is presented that analyses the energy flows that are connected to the dynamical behaviour of coherent structures in a transitional flat-plate boundary layer. Based on a mathematical description of the three-dimensional coherent structures of this flow as provided by the Karhunen–Loève procedure, energy equations for the coherent structures are derived by Galerkin projection of the Navier–Stokes equations in vorticity transport formulation onto the corresponding basis of eigenfunctions. In a first step, the time-averaged energy balance – showing the energy flows that support the different coherent structures and thus maintain the fluctuations of the velocity field – is considered. In a second step, the instantaneous power budget is investigated for the particularly interesting case of a coherent structure providing a prime contribution to the characteristic spike events of the transitional boundary layer. As this structure shows a strong variation in energy, the question about which mechanisms cause these variations is addressed. Our results show that the occurrence of a spike must be attributed to an autonomous event and cannot be interpreted as just an epiphenomenon of the passage of a Λ-vortex.

scholarly journals On the evolution of laminar to turbulent transition and breakdown to turbulence

2003 ◽  
Vol 7 (2) ◽  
pp. 59-76
Author(s):  
Jovan Jovanovic ◽  
Mira Pashtrapanska
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Local Equilibrium ◽  
Three Dimensional ◽  
Plate Boundary ◽  
Correlation Technique ◽  
Equilibrium Solutions ◽  
Laminar To Turbulent Transition ◽  
Transition Criterion ◽  
Flat Plate Boundary Layer

Starting from the basic conservation laws of fluid flow, we investigated transition and breakdown to turbulence of a laminar flat plate boundary layer exposed to small, statistically stationary, two-component, three-dimensional disturbances. The derived equations for the statistical properties of the disturbances are closed using the two-point correlation technique and invariant theory. By considering the equilibrium solutions of the modeled equations, the transition criterion is formulated in terms of a Reynolds number based on the intensity and the length scale of the disturbances. The deduced transition criterion determines conditions that guarantee maintenance of the local equilibrium between the production and the viscous dissipation of the disturbances and therefore the laminar flow regime in the flat plate boundary layer. The experimental and numerical databases for fully developed turbulent channel and pipe flows at different Reynolds numbers were utilized to demonstrate the validity of the derived transition criterion for the estimation of the onset of turbulence in wall-bounded flows.

scholarly journals Transition Prediction in Incompressible Boundary Layer with Finite-Amplitude Streaks

Energies ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 2147
Author(s):  
Juan Ángel Martín ◽  
Pedro Paredes
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Three Dimensional ◽  
Plate Boundary ◽  
High Amplitude ◽  
Finite Amplitude ◽  
Critical Conditions ◽  
Bypass Transition ◽  
Transition Delay ◽  
Flat Plate Boundary Layer

Modulating the boundary layer velocity profile is a very promising strategy for achieving transition delay and reducing the friction of the plate. By perturbing the flow with counter-rotating vortices that undergo transient, non-modal growth, streamwise-aligned streaks are formed inside the boundary layer, which have been proved (theoretical and experimentally) to be very robust flow structures. In this paper, we employ efficient numerical methods to perform a parametric stability investigation of the three-dimensional incompressible flat-plate boundary layer with finite-amplitude streaks. For this purpose, the Boundary Region Equations (BREs) are applied to solve the nonlinear downstream evolution of finite amplitude streaks. Regarding the stability analysis, the linear three-dimensional plane-marching Parabolized Stability Equations (PSEs) concept constitutes the best candidate for this task. Therefore, a thorough parametric study is presented, analyzing the instability characteristics with respect to critical conditions of the modified incompressible zero-pressure-gradient flat-plate boundary layer, by means of finite-amplitude linearly optimal and suboptimal disturbances or streaks. The parameter space is extended from low- to high- amplitude streaks, accurately documenting the transition delay for low-amplitude streaks and the amplitude threshold for streak shear layer instability or bypass transition, which drastically displaces the transition front upstream.

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