scholarly journals Separated rows structure of vortex streets behind triangular objects

2019 ◽  
Vol 862 ◽  
pp. 216-226
Author(s):  
Ildoo Kim
Keyword(s):  
Boundary Layer ◽  
Thin Layer ◽  
Boundary Layers ◽  
Experimental Studies ◽  
Soap Film ◽  
Separation Distance ◽  
Two Dimensional ◽  
Spatial Structures ◽  
Physical Mechanisms ◽  
Vortex Streets

We discuss two distinct spatial structures of vortex streets. The ‘conventional mushroom’ structure is commonly discussed in many experimental studies, and the exotic ‘separated rows’ structure is characterized by a thin layer of irrotational fluid between two rows of vortices. In a two-dimensional soap film channel, we generate the exotic vortex arrangement by using triangular objects. This setting allows us to vary the thickness of boundary layers and their separation distance independently. We find that the separated rows structure appears only when the boundary layer is thinner than 40 % of the separation distance. We also discuss two physical mechanisms of the breakdown of vortex structures. The conventional mushroom structure decays due to the mixing, and the separated rows structure decays because its arrangement is hydrodynamically unstable.

The Departure from Equilibrium of Turbulent Boundary Layers

1968 ◽  
Vol 19 (1) ◽  
pp. 1-19 ◽  
Author(s):  
H. McDonald
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Kinetic Energy ◽  
Stress Distribution ◽  
Boundary Layers ◽  
Turbulent Boundary Layers ◽  
Two Dimensional ◽  
Pressure Distributions ◽  
Momentum Integral ◽  
State Examination

SummaryRecently two authors, Nash and Goldberg, have suggested, intuitively, that the rate at which the shear stress distribution in an incompressible, two-dimensional, turbulent boundary layer would return to its equilibrium value is directly proportional to the extent of the departure from the equilibrium state. Examination of the behaviour of the integral properties of the boundary layer supports this hypothesis. In the present paper a relationship similar to the suggestion of Nash and Goldberg is derived from the local balance of the kinetic energy of the turbulence. Coupling this simple derived relationship to the boundary layer momentum and moment-of-momentum integral equations results in quite accurate predictions of the behaviour of non-equilibrium turbulent boundary layers in arbitrary adverse (given) pressure distributions.

Effects of Curvature on Laminar Boundary Layers in Sink-Type Flows

1969 ◽  
Vol 91 (3) ◽  
pp. 353-358 ◽  
Author(s):  
W. A. Gustafson ◽  
I. Pelech
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Momentum Equation ◽  
Similarity Solutions ◽  
Momentum Thickness ◽  
Two Dimensional ◽  
Thickness Increase ◽  
Laminar Boundary Layers ◽  
Converging Channel ◽  
Special Case

The two-dimensional, incompressible laminar boundary layer on a strongly curved wall in a converging channel is investigated for the special case of potential velocity inversely proportional to the distance along the wall. Similarity solutions of the momentum equation are obtained by two different methods and the differences between the methods are discussed. The numerical results show that displacement and momentum thickness increase linearly with curvature while skin friction decreases linearly.

A Reference Temperature Method for Compressible Laminar Boundary Layers

1973 ◽  
Vol 2 (4) ◽  
pp. 201-204
Author(s):  
R. Camarero
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Wall Temperature ◽  
Reference Temperature ◽  
Integral Approach ◽  
Pressure Gradients ◽  
Two Dimensional ◽  
Laminar Boundary Layers ◽  
Temperature Method ◽  
Compressibility Effects

A calculation procedure for the solution of two-dimensional and axi-symmetric laminar boundary layers in compressible flow has been developed. The method is an extension of the integral approach of Tani to include compressibility effects by means of a reference temperature. Arbitrary pressure gradients and wall temperature can be specified. Comparisons with experiments obtained for supersonic flows over a flat plate indicate that the method yields adequate results. The method is then applied to the solution of the boundary layer on a Basemann inlet.

Criteria for Boundary Layer Transition

2011 ◽  
Author(s):  
Stefan Becker ◽  
Donald M. McEligot ◽  
Edmond Walsh ◽  
Eckart Laurien
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Boundary Layer Flow ◽  
Leading Edge ◽  
Boundary Layer Transition ◽  
Turbulence Level ◽  
Two Dimensional ◽  
Freestream Turbulence ◽  
Layer Transition ◽  
Layer Flow

New results are deduced to assess the validity of proposed transition indicators when applied to situations other than boundary layers on smooth surfaces. The geometry employed utilizes a two-dimensional square rib to disrupt the boundary layer flow. The objective is to determine whether some available criteria are consistent with the present measurements of laminar recovery and transition for the flow downstream of this rib. For the present data — the proposed values of thresholds for transition in existing literature that are based on the freestream turbulence level at the leading edge are not reached in the recovering laminar run but they are not exceeded in the transitioning run either. Of the pointwise proposals examined, values of the suggested quantity were consistent for three of the criteria; that is, they were less than the threshold in laminar recovery and greater than it in the transitioning case.

Velocity profiles and fence drag for a turbulent boundary layer along smooth and rough flat plates

1976 ◽  
Vol 76 (2) ◽  
pp. 383-399 ◽  
Author(s):  
K. G. Ranga Raju ◽  
J. Loeser ◽  
E. J. Plate
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Boundary Layers ◽  
Roughness Parameter ◽  
Velocity Profiles ◽  
Published Data ◽  
Two Dimensional ◽  
Flat Plates ◽  
Form Drag ◽  
Displacement Thickness

The properties of a turbulent boundary layer were investigated as they relate to the form drag on a two-dimensional fence. Detailed measurements were performed at zero pressure gradient of velocity profiles along smooth, rough and transitional flat plates. Upon comparison with other published data, these measurements resulted in simple formulae for the displacement thickness and the local shear coefficient and in a modification to the universal velocity defect law for equilibrium boundary layers.With these boundary layers, experiments were performed to determine the drag on a two-dimensional fence. These data were analysed along with data from previous investigations. It was found that after suitable blockage corrections all form-drag coefficients for two-dimensional fences collapsed on a single curve if they were calculated with the shear velocity as the reference velocity and plotted against the ratio of the fence height to the characteristic roughness parameter of the approaching flow.

The production of subharmonic waves in the nonlinear evolution of wavepackets in boundary layers

1999 ◽  
Vol 399 ◽  
pp. 301-318 ◽  
Author(s):  
MARCELLO A. F. MEDEIROS ◽  
MICHAEL GASTER
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Nonlinear Interaction ◽  
Strong Influence ◽  
Nonlinear Evolution ◽  
Nonlinear Behaviour ◽  
Two Dimensional ◽  
Tollmien Schlichting ◽  
Acoustic Excitations ◽  
Dimensional Wave

The nonlinear evolution of wavepackets in a laminar boundary layer has been studied experimentally. The packets were generated by acoustic excitations injected into the boundary layer through a small hole in the plate. Various packets with different phases relative to the envelope were studied. It was found that for all the packets the nonlinearity involved the appearance of oblique modes of frequency close to the subharmonic of the dominant two-dimensional wave. Moreover, the results confirmed that the phase had a strong influence on the strength of the nonlinear interaction. The experimental observations also indicated that although a subharmonic resonance appeared to be present in the process, it alone could not explain the nonlinear behaviour. The experiment demonstrated that the process must also involve a mechanism that generates oblique waves of frequency lower than the Tollmien–Schlichting band.

The radial spread of a liquid jet over a horizontal plane

1964 ◽  
Vol 20 (3) ◽  
pp. 481-499 ◽  
Author(s):  
E. J. Watson
Keyword(s):  
Boundary Layer ◽  
Turbulent Flow ◽  
Thin Layer ◽  
Hydraulic Jump ◽  
Horizontal Plane ◽  
Boundary Layer Theory ◽  
Liquid Jet ◽  
Two Dimensional ◽  
Two Dimensional Flow ◽  
Radial Spread

When a smooth jet of water falls vertically on to a horizontal plane, it spreads out radially in a thin layer bounded by a circular hydraulic jump, outside which the depth is much greater. The motion in the layer is studied here by means of boundary-layer theory, both for laminar and for turbulent flow, and relations are obtained for the radius of the hydraulic jump. These relations are compared with experimental results. The analogous problems of two-dimensional flow are also treated.

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.

The Interaction of Thermal Radiation in Optically Thick Boundary Layers

1967 ◽  
Vol 89 (4) ◽  
pp. 309-312 ◽  
Author(s):  
J. L. Novotny ◽  
Kwang-Tzu Yang
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Boundary Layers ◽  
Optical Thickness ◽  
Asymptotic Expansions ◽  
Energy Equation ◽  
Two Dimensional ◽  
Small Temperature ◽  
Dimensional Boundary

An analysis is presented to examine the role of the Rosseland or optically thick approximation in convection-radiation interaction situations. The analysis is formulated for the flow of a gray gas in a laminar two-dimensional boundary layer under the restriction of small temperature differences within the flow field. The boundary-layer energy equation is treated using the method of matched asymptotic expansions based on a parameter which characterizes the optical thickness of the gas. Two illustrative examples of the resulting equations are presented.

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