scholarly journals On the different contributions of coherent structures to the spectra of a turbulent round jet and a turbulent boundary layer

2001 ◽  
Vol 448 ◽  
pp. 367-385 ◽  
Author(s):  
T. B. NICKELS ◽  
IVAN MARUSIC
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Turbulent Flows ◽  
Coherent Structures ◽  
Isotropic Turbulence ◽  
Structural Models ◽  
Spectral Measurements ◽  
Round Jet ◽  
Good Account ◽  
Single Size

This paper examines and compares spectral measurements from a turbulent round jet and a turbulent boundary layer. The conjecture that is examined is that both flows consist of coherent structures immersed in a background of isotropic turbulence. In the case of the jet, a single size of coherent structure is considered, whereas in the boundary layer there are a range of sizes of geometrically similar structures. The conjecture is examined by comparing experimental measurements of spectra for the two flows with the spectra calculated using models based on simple vortex structures. The universality of the small scales is considered by comparing high-wavenumber experimental spectra. It is shown that these simple structural models give a good account of the turbulent flows.

scholarly journals Numerical Simulation of Coherent Structures in the Turbulent Boundary Layer under Different Stability Conditions

Energies ◽  
2020 ◽  
Vol 13 (5) ◽  
pp. 1068
Author(s):  
Shujin Laima ◽  
Hehe Ren ◽  
Hui Li ◽  
Jinping Ou
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Correlation Coefficient ◽  
Wind Velocity ◽  
Coherent Structures ◽  
Stability Conditions ◽  
Velocity Spectrum ◽  
Turbulent Eddy ◽  
Stable Conditions ◽  
The Stability

Coherent structures in the turbulent boundary layer were investigated under different stability conditions. Qualitative analyses of the flow field, spatial correlation coefficient field and pre-multiplied wind velocity spectrum showed that the dominant turbulent eddy structure changed from small-scale motions to large- and very-large-scale motions and then to thermal plumes as the stability changed from strong stable to neutral and then to strong unstable. A quantitative analysis of the size characteristics of the three-dimensional turbulent eddy structure based on the spatial correlation coefficient field showed that under near-neutral stability, the streamwise, wall-normal and spanwise extents remained constant at approximately 0.3 δ , 0.1 δ and 0.2 δ ( δ , boundary layer height), respectively, while for other conditions, the extent in each direction varied in a log-linear manner with stability; only the spanwise extent under stable conditions was also independent of stability. The peak wavenumber of the pre-multiplied wind velocity spectrum moves towards small values from stable conditions to neutral condition and then to unstable conditions; thus, for the wind velocity spectrum, another form is needed that takes account the effects of the stability condition.

Effect of plate manipulators on coherent structures in a turbulent boundary layer

AIAA Journal ◽  
1990 ◽  
Vol 28 (11) ◽  
pp. 1877-1884 ◽  
Author(s):  
Candace E. Wark ◽  
Ahmed M. Naguib ◽  
Hassan M. Nagib
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Coherent Structures

Wall Heat Flux Under Persistent Vortices

2002 ◽  
Author(s):  
R. E. Breidenthal
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Turbulent Boundary Layer ◽  
Turbulent Flows ◽  
Laminar Flows ◽  
Wall Heat Flux ◽  
Recent Theory ◽  
Turbulent Wall

It is commonly perceived that turbulent flows yield turbulent wall fluxes, while laminar flows yield correspondingly laminar wall fluxes. Experiments support a recent theory that turbulent flows can yield laminar wall fluxes if the flow is “persistent.” Adding strong, stationary vortices to a turbulent boundary layer lowers the wall heat flux to a laminar value.

Evolution of Lagrangian coherent structures in a cylinder-wake disturbed flat plate boundary layer

2016 ◽  
Vol 792 ◽  
pp. 274-306 ◽  
Author(s):  
Guo-Sheng He ◽  
Chong Pan ◽  
Li-Hao Feng ◽  
Qi Gao ◽  
Jin-Jun Wang
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Coherent Structures ◽  
Plate Boundary ◽  
Boundary Layer Transition ◽  
Lagrangian Coherent Structures ◽  
Hydrogen Bubble ◽  
Layer Transition ◽  
Low Speed Streaks ◽  
Flat Plate Boundary Layer

Evolution of Lagrangian coherent structures (LCS) in a flat plate boundary layer transition induced by the wake of a circular cylinder is investigated. Both hydrogen bubble visualization and particle image velocimetry (PIV) techniques are used. It is found that downstream of the cylinder, the disturbance in the boundary layer experiences a fast growth followed by a slow decay in the transition. Lagrangian coherent structures are revealed by qualitative hydrogen bubble visualizations and quantitative finite-time Lyapunov exponents (FTLE) fields derived from the PIV data. The evolution of the LCS is considered from the very beginning of the transition up to when the boundary layer becomes fully developed turbulent flow. The mean convection velocity and average inclination angle of the LCS are first extracted from the FTLE fields. The streamwise length of the low-speed streaks seems to increase, while their spanwise distance decreases in the boundary layer transition. Proper orthogonal decomposition (POD) of the PIV data shows that low-speed streaks associated with the hairpin vortices and hairpin packets are the dominant coherent structures close to the wall in the transitional and turbulent boundary layer. The POD modes also reveal a variety of scales in the turbulent boundary layer. Moreover, it is found that large-scale coherent structures can modulate the amplitude of the small-scale ones.

Axisymmetric Turbulent Boundary Layers in Zero Pressure-Gradient Flows

1972 ◽  
Vol 39 (1) ◽  
pp. 25-32 ◽  
Author(s):  
G. N. V. Rao ◽  
N. R. Keshavan
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Turbulent Flows ◽  
Outer Part ◽  
Stability Limit ◽  
Circular Cylinders ◽  
Law Of The Wall ◽  
Probable Effect ◽  
Stress Layer ◽  
The Stability

An experimental and theoretical study of the axisymmetric turbulent boundary layer on circular cylinders over a range of radius Reynolds numbers Ra from 425 to 2 × 105, suggests the existence of a law of the wall in the form u* = A log Y* + B, where Y* = (uτa/ν) log (r/a). The constant A depends only on Ra while B has been found to depend on Ra as well as auτ/ν. It was observed that from the beginning of transition to turbulent flow in the boundary layer, there was a “negative wake” region in the outer part of the boundary layer which progressively disappeared as the flow was swept downstream, giving, at some station, a velocity profile (called here the “marginal profile”), which had no wake component. Further downstream, there was progressively increasing positive wake component. In these regions, it is surmized that the penetration of the viscous effect from the wall to larger distances across the boundary layer (as indicated by the absence of a constant stress layer), as well as the probable effect of viscosity in the wake portion (as in a purely axisymmetric wake), yielded similarlity of the defect (U − u)/uτ, only in terms of the quantity (ruτ/ν) for a given Ra. From a study of the rate of decrease of Cf with Rx in laminar and turbulent flows, there is reason to believe that an initially turbulent boundary layer will undergo relaminarization if Ra is less than about 15,000 which may be compared with the stability limit of 11,000 found by Rao [6].

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