Unsteady Boundary Layers on a Flat Plate Disturbed by Periodic Wakes: Part II — Measurements of Unsteady Boundary Layers and Discussion

1994 ◽  
Author(s):  
K. Funazaki
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Boundary Layers ◽  
Time Domain ◽  
Indirect Effect ◽  
Transition Model ◽  
Hot Wire ◽  
Turbulent Spot ◽  
Boundary Layer Interaction ◽  
Unsteady Boundary Layers

As the second part of the study, detailed hot-wire anemometry measurements of wake-affected boundary layers on the flat plate are made. These measurements are organized in order, first, to check the standpoint of the modeling of the wake-induced transition proposed in Part I, and second, to observe wake-boundary layer interaction in detail from a viewpoint of direct and indirect effect of the wake passage upon turbulent spot generation within the boundary layer, as described by Walker (1993). The validity of the presumed state of the wake-affected boundary layer in the distance-time domain, which constitutes the basis of the transition model, is confirmed to great extent. However, it is also found that the criterion for the onset of the wake-induced transition adopted in Part I should be reconsidered. Some successful attempts are therefore made to specify the transition onset.

Unsteady Boundary Layers on a Flat Plate Disturbed by Periodic Wakes: Part II—Measurements of Unsteady Boundary Layers and Discussion

1996 ◽  
Vol 118 (2) ◽  
pp. 337-344 ◽  
Author(s):  
K. Funazaki
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Boundary Layers ◽  
Time Domain ◽  
Indirect Effect ◽  
Transition Model ◽  
Hot Wire ◽  
Turbulent Spot ◽  
Boundary Layer Interaction ◽  
Unsteady Boundary Layers

As the second part of the study, detailed hot-wire anemometry measurements of wake-affected boundary layers on the flat plate are made. These measurements are organized in order, first, to check the standpoint of the modeling of the wake-induced transition proposed in Part I, and second, to observe wake–boundary layer interaction in detail from a viewpoint of direct and indirect effect of the wake passage upon turbulent spot generation within the boundary layer, as described by Walker (1993). The validity of the presumed state of the wake-affected boundary layer in the distance–time domain, which constitutes the basis of the transition model, is confirmed to great extent. However, it is also found that the criterion for the onset of the wake-induced transition adopted in Part I should be reconsidered. Some successful attempts are therefore made to specify the transition onset.

Studies on Bypass Transition of a Boundary Layer Subjected to Localized Periodic External Disturbances

2004 ◽  
Author(s):  
K. Funazaki ◽  
Y. Wakita ◽  
T. Otsuki
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
External Disturbance ◽  
Transition Process ◽  
Bypass Transition ◽  
Hot Wire ◽  
Turbulent Spot ◽  
External Disturbances ◽  
Small Sphere ◽  
Probe Sensor

This study aims at clarification of wake-induced bypass transition process of a boundary layer on a flat plate with no pressure gradient. Special attention is paid to inception as well as growth of a turbulent spot created by the incoming wake as an external disturbance. To meet this goal a unique wake generator is invented to create an isolated turbulent spot. A multi-probe sensor with seven single-hot-wire probes is used to measure wake-affected boundary layer. The wake generator consists of a disk, pillars and a very thin wire with a small sphere on it. The sphere on the wire generates periodic wakes behind it when it passes across the main flow in front of the test flat plate. These sphere wakes impinge the flat plate in a spatially and timewisely localized manner so that the wakes periodically leave narrow affected zones inside the boundary layer. The observations confirm that an isolated turbulence spot emerges from each of those wake-affected zones. It is also found that the turbulent spot observed in this study bears a close resemblance to the conventional turbulent spot that takes a shape of arrowhead pointing downstream.

Experimental Studies on Wake-Induced Transition of Turbulent Boundary Layers

2012 ◽  
Author(s):  
Keiji Takeuchi ◽  
Susumu Fujimoto ◽  
Eitaro Koyabu ◽  
Tetsuhiro Tsukiji
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Boundary Layers ◽  
Turbulence Intensity ◽  
Intensity Distribution ◽  
Experimental Studies ◽  
Turbulent Boundary Layers ◽  
Bypass Transition ◽  
Pressure Gradients ◽  
Hot Wire

Wake-induced bypass transition of boundary layers on a flat plate subjected to favorable and adverse pressure gradients was investigated. Detailed boundary layer measurements were conducted using two hot-wire probes. A spoked-wheel-type wake generator was used to create periodic wakes in front of the flat plate. The main focus of this study was to reveal the effect of the Strouhal number, which changed by using different numbers of wake-generating bars, on the turbulence intensity distribution and the transition onset position of the boundary layer on the flat plate using two hot-wire probes.

Predicting Transition on Concave Surfaces

2006 ◽  
Author(s):  
Mark W. Johnson
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Boundary Layers ◽  
Laminar Boundary Layer ◽  
Rapid Development ◽  
Current Work ◽  
Concave Surface ◽  
Transition Model ◽  
Surface Boundary ◽  
Flat Plates

Boundary layers on concave surfaces differ from those on flat plates due to the presence of Taylor Goertler (T-G) vortices. These vortices cause momentum transfer normal to the blade’s surface and hence result in a more rapid development of the laminar boundary layer and a fuller profile than is typical of a flat plate. Transition of boundary layers on concave surfaces also occurs at a lower Rex than on a flat plate. Concave surface transition correlations have been formulated previously from experimental data, but they are not comprehensive and are based on relatively sparse data. The purpose of the current work was to attempt to model the physics of both the laminar boundary layer development and transition process in order to produce a transition model suitable for concave surface boundary layers. The development of the laminar boundary layer on a concave surface was modeled by considering the profiles at the upwash and downwash locations separately. The profiles of the boundary layers at these two locations were then combined to successfully approximate the spanwise averaged profile. The ratio of the boundary layer thicknesses at the two locations was found to be as great as 50 and this leads to laminar boundary layer shape factors as low as 1.3 and skin friction coefficients up to 12 times the value for a flat plate laminar boundary layer. Boundary layers therefore grow much more rapidly on concave surfaces than on flat plates. The transition model assumed that transition commenced in the upwash location boundary layer at the same transition inception Reθ observed on a flat plate. Transition at the downwash location then results from the growth of turbulent spots from the upwash location rather than through the initiation of spots. The model showed that initially curvature promotes transition because of the thickened upwash boundary layer, but for strong curvature the T-G vortices effectively stabilise the boundary layer and transition then occurs at a higher Reθ than on a flat plate. Results from the transition model were in broad agreement with experimental observations. The current work therefore provides a basis for the modeling of transition on concave surfaces.

Predicting Transition on Concave Surfaces

2006 ◽  
Vol 129 (4) ◽  
pp. 750-755 ◽  
Author(s):  
Mark W. Johnson
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Boundary Layers ◽  
Laminar Boundary Layer ◽  
Rapid Development ◽  
Current Work ◽  
Concave Surface ◽  
Transition Model ◽  
Surface Boundary ◽  
Flat Plates

Boundary layers on concave surfaces differ from those on flat plates due to the presence of Taylor-Goertler (T-G) vortices. These vortices cause momentum transfer normal to the blade’s surface and hence result in a more rapid development of the laminar boundary layer and a fuller profile than is typical of a flat plate. Transition of boundary layers on concave surfaces also occurs at a lower Rex than on a flat plate. Concave surface transition correlations have been formulated previously from experimental data, but they are not comprehensive and are based on relatively sparse data. The purpose of the current work was to attempt to model the physics of both the laminar boundary layer development and transition process in order to produce a transition model suitable for concave surface boundary layers. The development of the laminar boundary layer on a concave surface was modeled by considering the profiles at the upwash and downwash locations separately. The profiles of the boundary layers at these two locations were then combined to successfully approximate the spanwise averaged profile. The ratio of the boundary layer thicknesses at the two locations was found to be as great as 50 and this leads to laminar boundary layer shape factors as low as 1.3 and skin friction coefficients up to 12 times the value for a flat plate laminar boundary layer. Boundary layers therefore grow much more rapidly on concave surfaces than on flat plates. The transition model assumed that transition commenced in the upwash location boundary layer at the same transition inception Reθ observed on a flat plate. Transition at the downwash location then results from the growth of turbulent spots from the upwash location rather than through the initiation of spots. The model showed that initially curvature promotes transition because of the thickened upwash boundary layer, but for strong curvature the T-G vortices effectively stabilize the boundary layer and transition then occurs at a higher Reθ than on a flat plate. Results from the transition model were in broad agreement with experimental observations. The current work therefore provides a basis for the modeling of transition on concave surfaces.

scholarly journals Evolution of localized artificial disturbance in 2D and 3D supersonic boundary layers

2018 ◽  
Vol 234 (1) ◽  
pp. 115-123 ◽  
Author(s):  
Aleksey Yatskikh ◽  
Yury Yermolaev ◽  
Alexander Kosinov ◽  
Nikolai Semionov ◽  
Alexander Semenov
Keyword(s):  
Boundary Layer ◽  
Wave Packet ◽  
Flat Plate ◽  
Boundary Layers ◽  
Plate Boundary ◽  
Hot Wire ◽  
Swept Wing ◽  
Artificial Disturbance ◽  
2D And 3D ◽  
Symmetric Shape

The evolution of a controlled broadband wave packet in flat-plate and swept-wing supersonic boundary layers was experimentally investigated at Mach number M = 2. The wave packet was introduced into the boundary layer by a localized pulse electrical discharge. The structure and evolution downstream of the wave packet were studied by hot-wire measurements. It was found that the wave packet has a symmetric shape in a flat-plate boundary layer, whereas there is asymmetry in case of a swept-wing one. The spectral analysis of the development of different modes of the wave packet was provided.

Eigen-Functions of Linearized Unsteady Boundary Layer Equations

1993 ◽  
Vol 115 (4) ◽  
pp. 597-602 ◽  
Author(s):  
S. H. Lam ◽  
N. Rott
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Boundary Layers ◽  
Pressure Gradients ◽  
Unsteady Boundary Layer ◽  
Boundary Layer Equations ◽  
Eigen Solutions ◽  
Unsteady Boundary Layers ◽  
Special Case ◽  
Dependent Factor

The Lam and Rott theory of linearized unsteady boundary layers is revisited, and some new results are obtained. The exact outer eigen-solution for a flat plate found in the original paper is shown to be a special case of the Prandtl-Glauert transposition theorem. The streamwise coordinate-dependent factor of the inner eigen-solutions, first found by M. E. Goldstein for the flat plate, is generalized for arbitrary pressure gradients.

scholarly journals A Theory for Wake-Induced Transition

1989 ◽  
Author(s):  
R. E. Mayle ◽  
K. Dullenkopf
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Flow ◽  
Flat Plate ◽  
Free Stream ◽  
Plate Boundary ◽  
Transition Model ◽  
Model Comparisons ◽  
Turbulent Wakes ◽  
Flat Plate Boundary Layer

A theory for transition from laminar to turbulent flow as the result of unsteady, periodic passing of turbulent wakes in the free stream is developed using Emmons’ transition model. Comparisons made to flat plate boundary layer measurements and airfoil heat transfer measurements confirm the theory.

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