Experimental 3D Analysis of the Large Scale Behaviour of a Plane Turbulent Mixing Layer

2005 ◽  
Vol 74 (2) ◽  
pp. 207-233 ◽  
Author(s):  
Philippe Druault ◽  
Joël Delville ◽  
Jean-paul Bonnet
Keyword(s):  
Turbulent Mixing ◽  
Large Scale ◽  
Mixing Layer ◽  
3D Analysis ◽  
Turbulent Mixing Layer

Large-scale structures in a forced turbulent mixing layer

1985 ◽  
Vol 150 ◽  
pp. 23-39 ◽  
Author(s):  
M. Gaster ◽  
E. Kit ◽  
I. Wygnanski
Keyword(s):  
Turbulent Mixing ◽  
Large Scale ◽  
Phase Distribution ◽  
Mixing Layer ◽  
Global Scale ◽  
Travelling Wave ◽  
Mean Flow ◽  
Turbulent Mixing Layer ◽  
Large Scale Structures ◽  
Scale Structures

The large-scale structures that occur in a forced turbulent mixing layer at moderately high Reynolds numbers have been modelled by linear inviscid stability theory incorporating first-order corrections for slow spatial variations of the mean flow. The perturbation stream function for a spatially growing time-periodic travelling wave has been numerically evaluated for the measured linearly diverging mean flow. In an accompanying experiment periodic oscillations were imposed on the turbulent mixing layer by the motion of a small flap at the trailing edge of the splitter plate that separated the two uniform streams of different velocity. The results of the numerical computations are compared with experimental measurements.When the comparison between experimental data and the computational model was made on a purely local basis, agreement in both the amplitude and phase distribution across the mixing layer was excellent. Comparisons on a global scale revealed, not unexpectedly, less good accuracy in predicting the overall amplification.

Large-scale clustering of coherent fine-scale eddies in a turbulent mixing layer

2018 ◽  
Vol 72 ◽  
pp. 100-108
Author(s):  
Toshitaka Itoh ◽  
Yoshitsugu Naka ◽  
Yuki Minamoto ◽  
Masayasu Shimura ◽  
Mamoru Tanahashi
Keyword(s):  
Turbulent Mixing ◽  
Large Scale ◽  
Mixing Layer ◽  
Fine Scale ◽  
Turbulent Mixing Layer

A ‘turbulent spot’ in an axisymmetric free shear layer. Part 2

1980 ◽  
Vol 98 (1) ◽  
pp. 97-135 ◽  
Author(s):  
A. K. M. F. Hussain ◽  
S. J. Kleis ◽  
M. Sokolov
Keyword(s):  
Time Series ◽  
Reynolds Stress ◽  
Coherent Structure ◽  
Turbulent Mixing ◽  
Large Scale ◽  
Mixing Layer ◽  
Turbulent Mixing Layer ◽  
Phase Average ◽  
Background Turbulence ◽  
Stream Functions

The mechanics of a spark-induced coherent structure (called a ‘spot’) in the turbulent mixing layer of a 12.7 cm diameter incompressible air jet has been investigated through phase-locked measurements at three streamwise stations. Phase averages have been obtained from 200 realizations of X-wire (time-series) data after these are optimally time-aligned with respect to one another through an iterative process of maximization of cross-correlation of individual realizations with the ensemble average. Realizations that are grossly out of alignment owing to turbulence-induced distortions have been rejected; the rejection ratio increases with increasing radial position. Data include phase-average time series of background turbulence intensities, coherent and background Reynolds stresses, vorticity and intermittency at different transverse positions. Spatial distributions of these properties over the extent of the spot have been presented as contour maps. The computed pseudo-stream-functions have been compared with the phase-average streamlines inferred from the measured distributions of the velocity vector. Comparison with the phase-average intermittency contours show that the pseudo-stream-functions are reliable and, even though the integration involved produces smoothed-out stream functions, are most useful in deducing the structure dynamics and its convection velocity.The spark-induced spot is an elongated large-scale coherent vortical structure spanning the entire thickness of the mixing layer, which moves downstream at a convection velocity of about 0.68Ue. The dynamics of the turbulent mixing layer spot, whose signature is buried in the large-amplitude background fluctuations, is much more complicated than that of the boundary-layer spot. The spot transports jet-core fluid outwards at its front and entrains ambient fluid primarily at its back; the outward-momentum transport dominates the inward transport. The Reynolds stress contribution by the spot structure is noticeably larger than that due to the background turbulence. The coherent structure vorticity is significantly modified by the structure-induced organization of the background Reynolds stress at the locations of ‘saddle points’ of the latter's distribution. The vorticity, intermittency and other turbulence measures, zone averaged over the extent of the spot, compare well with the time-average values, thus suggesting that the spark-induced ‘spot’ is probably not different from a naturally occurring large-scale coherent structure.

A Model of Coherent Disturbances in Compressible Mixing Layers

2002 ◽  
Author(s):  
Hong Yang ◽  
Anatoli Tumin
Keyword(s):  
Turbulent Mixing ◽  
Large Scale ◽  
Eddy Viscosity ◽  
Mixing Layer ◽  
Governing Equations ◽  
Turbulent Mixing Layer ◽  
Eddy Viscosity Model ◽  
Temperature And Pressure ◽  
Mean Time ◽  
Theoretical Results

A theoretical model of harmonic perturbations in a compressible turbulent mixing layer is proposed. The model is based on the triple decomposition method. It is assumed that the instantaneous velocities, temperature, and pressure consist of three distinctive components: mean (time-averaged), coherent (phase-averaged), and random (turbulent) motion. The interaction between incoherent turbulent fluctuations and large-scale coherent disturbances is incorporated by the Newtonian eddy viscosity model. The governing equations for the coherent disturbances have the same form as in laminar flow with substitution of the Reynolds number and the Prandtl number by their turbulent counterparts. A slight divergence of the flow is also taken into account. Theoretical results and comparison with experimental data reveal the significance of interaction between the coherent and random constituents of the flow.

scholarly journals Modulation of the velocity gradient tensor by concurrent large-scale velocity fluctuations in a turbulent mixing layer

2015 ◽  
Vol 777 ◽  
Author(s):  
O. R. H. Buxton
Keyword(s):  
Velocity Gradient ◽  
Turbulent Mixing ◽  
Large Scale ◽  
Mixing Layer ◽  
Small Scale ◽  
Velocity Fluctuations ◽  
Turbulent Mixing Layer ◽  
Local Maxima ◽  
Leibler Divergence ◽  
Small Scales

The modulation of small-scale velocity and velocity gradient quantities by concurrent large-scale velocity fluctuations is observed by consideration of the Kullback–Leibler divergence. This is a measure that quantifies the loss of information in modelling a statistical distribution of small-scale quantities conditioned on concurrent positive large-scale fluctuations by that conditioned on negative large-scale fluctuations. It is observed that the small-scale turbulence is appreciably ‘rougher’ when the concurrent large-scale fluctuation is positive in the low-speed side of a fully developed turbulent mixing layer, which gives further evidence to the convective scale modulation argument of Buxton & Ganapathisubramani (Phys. Fluids, vol. 26, 2014, 125106, 1–19). The definition of the small scales is varied, and regardless of whether the small-scale fluctuations are dominated by dissipation or have the characteristic features of inertial range turbulence they are shown to be modulated by the concurrent large-scale fluctuations. The modulation is observed to persist even when there is a large gap in wavenumber space between the small and large scales, although local maxima are observed at intermediate length scales that are significantly larger than the predefined small scales. Finally, it is observed that the modulation of small-scale dissipation is greater than that for enstrophy with the modulation of the vortex stretching term, indicative of the interaction between strain rate and rotation, being intermediate between the two.

Effects of heat release on the large-scale structure in turbulent mixing layers

1989 ◽  
Vol 199 ◽  
pp. 297-332 ◽  
Author(s):  
P. A. Mcmurtry ◽  
J. J. Riley ◽  
R. W. Metcalfe
Keyword(s):  
Heat Release ◽  
Turbulent Mixing ◽  
Large Scale ◽  
Mixing Layer ◽  
Large Scale Structure ◽  
Scale Structure ◽  
Mixing Layers ◽  
Turbulent Mixing Layer ◽  
Large Scale Structures ◽  
Scale Structures

The effects of chemical heat release on the large-scale structure in a chemically reacting, turbulent mixing layer are investigated using direct numerical simulations. Three-dimensional, time-dependent simulations are performed for a binary, single-step chemical reaction occurring across a temporally developing turbulent mixing layer. It is found that moderate heat release slows the development of the large-scale structures and shifts their wavelengths to larger scales. The resulting entrainment of reactants is reduced, decreasing the overall chemical product formation rate. The simulation results are interpreted in terms of turbulence energetics, vorticity dynamics, and stability theory. The baroclinic torque and thermal expansion in the mixing layer produce changes in the flame vortex structure that result in more diffuse vortices than in the constant-density case, resulting in lower rotation rates of the large-scale structures. Previously unexplained anomalies observed in the mean velocity profiles of reacting jets and mixing layers are shown to result from vorticity generation by baroclinic torques.

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