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.

On the generation of steady streamwise streaks in flat-plate boundary layers

2012 ◽  
Vol 698 ◽  
pp. 211-234 ◽  
Author(s):  
Jens H. M. Fransson ◽  
Alessandro Talamelli
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
High Speed ◽  
Control Method ◽  
Plate Boundary ◽  
High Amplitude ◽  
Base Flow ◽  
Stream Velocity ◽  
Bypass Transition ◽  
Streamwise Streaks

AbstractA study on the generation and development of high-amplitude steady streamwise streaks in a flat-plate boundary layer is presented. High-amplitude streamwise streaks are naturally present in many bypass transition scenarios, where they play a fundamental role in the breakdown to turbulence process. On the other hand, recent experiments and numerical simulations have shown that stable laminar streamwise streaks of alternating low and high speed are also capable of stabilizing the growth of Tollmien–Schlichting waves as well as localized disturbances and to delay transition. The larger the streak amplitude is, for a prescribed spanwise periodicity of the streaks, the stronger is the stabilizing mechanism. Previous experiments have shown that streaks of amplitudes up to 12 % of the free stream velocity can be generated by means of cylindrical roughness elements. Here we explore the possibility of generating streaks of much larger amplitude by using a row of miniature vortex generators (MVGs) similar to those used in the past to delay or even prevent boundary layer separation. In particular, we present a boundary layer experiment where streak amplitudes exceeding 30 % have been produced without having any secondary instability acting on them. Furthermore, the associated drag with the streaky base flow is quantified, and it is demonstrated that the streaks can be reinforced by placing a second array of MVGs downstream of the first one. In this way it is possible to make the control more persistent in the downstream direction. It must be pointed out that the use of MVGs opens also the possibility to set up a control method that acts twofold in the sense that both transition and separation are delayed or even prevented.

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.

Studies of Wake-Induced Bypass Transition of a Flat-Plate Boundary Layer: Comparisons Between Two Transition Modes Induced by Small Sphere Wake and Thin Wire Wake

2005 ◽  
Author(s):  
Ken-ichi Funazaki ◽  
Takahiro Otsuki
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Plate Boundary ◽  
Transition Process ◽  
Bypass Transition ◽  
Velocity Data ◽  
Turbulent Spot ◽  
Transition Modes ◽  
The Wire ◽  
Flat Plate Boundary Layer

This study aims at deepening the understanding of wake-induced bypass transition process of a flat-plate boundary layer using two types of wake generating objects, which are small spheres and thin wires. Main focus is on emergence of isolated turbulent spots from the influence of the wake passage over the boundary layer. Precursors of the wake-induced turbulent spot, which have not been observed in an explicit manner in any other previous studies, are also of concern in this study. It is expected that wakes from the wires are so weak that an isolated turbulent spot may be induced by the wire wake, while the position of the spot emergence varies randomly along the wire. A multi-channel sensor with 7 hot-wire probes acquires the velocity data of the flow over the flat plate subjected to the wake passage. These velocity data reveal the spot shape and spot generation rate. In addition, the existence of Klebanoff mode in this wake-affected boundary layer is examined.

scholarly journals J0530204 Studies on Wake-Induced Bypass Transition over Flat Plate Boundary Layer

2014 ◽  
Vol 2014 (0) ◽  
pp. _J0530204--_J0530204-
Author(s):  
Eitaro KOYABU ◽  
Takashi HONMA ◽  
Mitsuki FUJIWARA ◽  
Ayumi MITOH ◽  
Eiji SOBU
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Plate Boundary ◽  
Bypass Transition ◽  
Flat Plate Boundary Layer

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.

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

1994 ◽  
Vol 260 ◽  
pp. 351-375 ◽  
Author(s):  
Dietmar Rempfer ◽  
Hermann F. Fasel
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Coherent Structures ◽  
Three Dimensional ◽  
Plate Boundary ◽  
Complete Information ◽  
Dynamical Behaviour ◽  
Higher Order ◽  
Temporal Behaviour ◽  
Flat Plate Boundary Layer

Using a data base generated by a numerical simulation, the three-dimensional coherent structures of a transitional, spatially evolving boundary layer are determined and their spatio-temporal behaviour is investigated in detail. The coherent structures are calculated by the proper orthogonal decomposition method (POD), which leads to an expansion of the flow field variables into Karhunen-Loéve eigenfunctions. It is shown that the dynamical coherent structures of the flat-plate boundary layer can be described by pairs of eigenfunctions that contain complete information on the spatial evolution of the structures. It is further demonstrated that first-order coherent structures determined by POD correspond to structures that are observed in experiments. In the region of the boundary layer where the spike signals of transition occur, higher-order coherent structures also play an essential role. By considering these higher-order structures as well as their dynamical behaviour in time, a compact description of the flow phenomena in the boundary layer can be obtained. The description of the events occurring at the spike stages of the transitional boundary layer shows, from a coherent structures point of view, striking similarities to the bursting event of fully turbulent boundary layers.

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