scholarly journals NUMERICAL SIMULATION OF SECONDARY CIRCULATION IN THE LEE OF HEADLANDS

1984 ◽  
Vol 1 (19) ◽  
pp. 162 ◽  
Author(s):  
Roger A. Falconer ◽  
Eric Wolanski ◽  
Lida Mardapitta-Hadjipandeli
Keyword(s):  
Numerical Simulation ◽  
Numerical Model ◽  
Shear Layer ◽  
Eddy Viscosity ◽  
Mixing Layer ◽  
Secondary Circulation ◽  
Shear Stresses ◽  
Free Shear Layer ◽  
Lateral Velocity ◽  
Lateral Mixing

The paper gives details of a study to refine and further develop a two-diirensional depth average numerical model to predict more accurately the eddy shedding features often observed in the lees of headlands. Details are given of the application of the model to Rattray Island, just east of Bowen, North Queensland, Australia, where the strong tidal currents flowing past the island give rise to separation and hydrodynamic circulation in the lee of the island. In the governing differential equations used to predict the secondary circulation, particular emphasis has been placed on the representation of the shear stresses associated with the free shear lateral mixing layer in the downstream wake of the headland. Use of an experimentally determined lateral velocity distribution in the shear layer, together with an eddy viscosity approach, have led to the use of a relatively simple turbulence model, including both free shear layer and bed generated turbulence. A comparison of the numerically predicted velocities with corresponding field measured results around Rattray Island has shown an encouraging agreement, although there were some differences. The main difference between both sets of results was that the vorticity strength of the secondary circulation predicted in the numerical model was noticeably less than that measured in the field.

Assessment of turbulence models using DNS data of compressible plane free shear layer flow

2021 ◽  
Vol 931 ◽  
Author(s):  
D. Li ◽  
J. Komperda ◽  
A. Peyvan ◽  
Z. Ghiasi ◽  
F. Mashayek
Keyword(s):  
Shear Layer ◽  
Compressible Flows ◽  
Eddy Viscosity ◽  
Turbulence Models ◽  
Correlation Coefficients ◽  
Free Shear Layer ◽  
Smagorinsky Model ◽  
Reynolds Analogy ◽  
Velocity Fluctuations ◽  
Scale Similarity

The present paper uses the detailed flow data produced by direct numerical simulation (DNS) of a three-dimensional, spatially developing plane free shear layer to assess several commonly used turbulence models in compressible flows. The free shear layer is generated by two parallel streams separated by a splitter plate, with a naturally developing inflow condition. The DNS is conducted using a high-order discontinuous spectral element method (DSEM) for various convective Mach numbers. The DNS results are employed to provide insights into turbulence modelling. The analyses show that with the knowledge of the Reynolds velocity fluctuations and averages, the considered strong Reynolds analogy models can accurately predict temperature fluctuations and Favre velocity averages, while the extended strong Reynolds analogy models can correctly estimate the Favre velocity fluctuations and the Favre shear stress. The pressure–dilatation correlation and dilatational dissipation models overestimate the corresponding DNS results, especially with high compressibility. The pressure–strain correlation models perform excellently for most pressure–strain correlation components, while the compressibility modification model gives poor predictions. The results of an a priori test for subgrid-scale (SGS) models are also reported. The scale similarity and gradient models, which are non-eddy viscosity models, can accurately reproduce SGS stresses in terms of structure and magnitude. The dynamic Smagorinsky model, an eddy viscosity model but based on the scale similarity concept, shows acceptable correlation coefficients between the DNS and modelled SGS stresses. Finally, the Smagorinsky model, a purely dissipative model, yields low correlation coefficients and unacceptable accumulated errors.

scholarly journals Numerical Simulation on 2D/3D Reacting Free Shear Layer.

1994 ◽  
Vol 60 (580) ◽  
pp. 4171-4176
Author(s):  
Xiao Wang ◽  
Shigeharu Ohyagi ◽  
Toshitaka Fujiwara
Keyword(s):  
Numerical Simulation ◽  
Shear Layer ◽  
Free Shear Layer

Phase decorrelation of coherent structures in a free shear layer

1991 ◽  
Vol 230 ◽  
pp. 319-337 ◽  
Author(s):  
Chih-Ming Ho ◽  
Yitshak Zohar ◽  
Judith K. Foss ◽  
Jeffrey C. Buell
Keyword(s):  
Shear Layer ◽  
Coherent Structures ◽  
Physical Mechanism ◽  
Mixing Layer ◽  
Single Frequency ◽  
Free Shear Layer ◽  
Phase Jitter ◽  
Laminar Mixing

The vortices near the origin of an initially laminar mixing layer have a single frequency with a well-defined phase; i.e. there is little phase jitter. Further downstream, however, the phase jitter increases suddenly. Even when the flow is forced, this same transition is observed. The forcing partially loses its influence because of the decorrelation of the phase between the forcing signal and the passing coherent structures. In the present investigation, this phenomenon is documented and the physical mechanism responsible for the phase decorrelation is identified.

Direct numerical simulation of a separated turbulent boundary layer

1998 ◽  
Vol 374 ◽  
pp. 379-405 ◽  
Author(s):  
Y. NA ◽  
P. MOIN
Keyword(s):  
Numerical Simulation ◽  
Boundary Layer ◽  
Shear Stress ◽  
Turbulent Boundary Layer ◽  
Direct Numerical Simulation ◽  
Shear Layer ◽  
Stokes Equations ◽  
Pressure Fluctuations ◽  
Shear Stresses ◽  
Computational Domain

A separated turbulent boundary layer over a flat plate was investigated by direct numerical simulation of the incompressible Navier–Stokes equations. A suction-blowing velocity distribution was prescribed along the upper boundary of the computational domain to create an adverse-to-favourable pressure gradient that produces a closed separation bubble. The Reynolds number based on inlet free-stream velocity and momentum thickness is 300. Neither instantaneous detachment nor reattachment points are fixed in space but fluctuate significantly. The mean detachment and reattachment locations determined by three different definitions, i.e. (i) location of 50% forward flow fraction, (ii) mean dividing streamline (ψ=0), (iii) location of zero wall-shear stress (τw=0), are in good agreement. Instantaneous vorticity contours show that the turbulent structures emanating upstream of separation move upwards into the shear layer in the detachment region and then turn around the bubble. The locations of the maximum turbulence intensities as well as Reynolds shear stress occur in the middle of the shear layer. In the detached flow region, Reynolds shear stresses and their gradients are large away from the wall and thus the largest pressure fluctuations are in the middle of the shear layer. Iso-surfaces of negative pressure fluctuations which correspond to the core region of the vortices show that large-scale structures grow in the shear layer and agglomerate. They then impinge on the wall and subsequently convect downstream. The characteristic Strouhal number St=fδ*in/U0 associated with this motion ranges from 0.0025 to 0.01. The kinetic energy budget in the detachment region is very similar to that of a plane mixing layer.

Numerical Simulation on a Planar Supersonic Free Shear Layer Secondary Instability

2006 ◽  
Author(s):  
Qing Shen ◽  
Fenggan Zhuang ◽  
Faming Guan ◽  
Qiang Wang ◽  
Xiangjiang Yuan
Keyword(s):  
Numerical Simulation ◽  
Shear Layer ◽  
Secondary Instability ◽  
Free Shear Layer

Numerical simulation of the compressible mixing layer past an axisymmetric trailing edge

2007 ◽  
Vol 591 ◽  
pp. 215-253 ◽  
Author(s):  
FRANCK SIMON ◽  
SEBASTIEN DECK ◽  
PHILIPPE GUILLEN ◽  
PIERRE SAGAUT ◽  
ALAIN MERLEN
Keyword(s):  
Numerical Simulation ◽  
Shear Layer ◽  
Large Scale ◽  
Free Stream ◽  
Mixing Layer ◽  
Adverse Pressure Gradient ◽  
Layer Growth ◽  
Trailing Edge ◽  
Azimuthal Mode ◽  
Compressible Mixing Layer

Numerical simulation of a compressible mixing layer past an axisymmetric trailing edge is carried out for a Reynolds number based on the diameter of the trailing edge approximately equal to 2.9 × 106. The free-stream Mach number at separation is equal to 2.46, which corresponds to experiments and leads to high levels of compressibility. The present work focuses on the evolution of the turbulence field through extra strain rates and on the unsteady features of the annular shear layer. Both time-averaged and instantaneous data are used to obtain further insight into the dynamics of the flow. An investigation of the time-averaged flow field reveals an important shear-layer growth rate in its initial stage and a strong anisotropy of the turbulent field. The convection velocity of the vortices is found to be somewhat higher than the estimated isentropic value. This corroborates findings on the domination of the supersonic mode in planar supersonic/subsonic mixing layers. The development of the shear layer leads to a rapid decrease of the anisotropy until the onset of streamline realignment with the axis. Due to the increase of the axisymmetric constraints, an adverse pressure gradient originates from the change in streamline curvature. This recompression is found to slow down the eddy convection. The foot shock pattern features several convected shocks emanating from the upper side of the vortices, which merge into a recompression shock in the free stream. Then, the flow accelerates and the compressibility levels quickly drop in the turbulent developing wake. Some evidence of the existence of large-scale structures in the near wake is found through the domination of the azimuthal mode m = 1 for a Strouhal number based on trailing-edge diameter equal to 0.26.

A turbulent mixing layer constrained by a solid surface. Part 2. Measurements in the wall-bounded flow

1984 ◽  
Vol 139 ◽  
pp. 347-361 ◽  
Author(s):  
D. H. Wood ◽  
P. Bradshaw
Keyword(s):  
Shear Stress ◽  
Shear Layer ◽  
Normal Stress ◽  
Mixing Layer ◽  
Turbulent Energy ◽  
Free Shear Layer ◽  
Calculation Methods ◽  
Turbulent Mixing Layer ◽  
High Reynolds ◽  
The Individual

The single- and two-point measurements made in a high-Reynolds-number single-stream mixing layer growing to encounter a wind-tunnel floor on its high-velocity side that were described by Wood & Bradshaw (1982) have been extended to the wall-bounded flow. It is shown that the expected large amplification of the normal-stress components in the plane of the wall does not occur until after the mixing layer reaches the surface. There is some evidence that the double-roller component of the large-eddy structure of the original free shear layer is being re-established in the wall-bounded flow after having been stretched and weakened by the initial effect of the wall. The triple-product terms appearing in the turbulent-energy and shear-stress equations are altered in a way that cannot be reproduced by models used in current calculation methods. It appears that all the pressure-fluctuation terms in the individual normal-stress and shear-stress transport equations respond in a non-monotonic manner to the imposition of the wall. The implications for calculation methods suitable for predicting the change from an initially unaffected free shear layer to a wall-bounded flow are discussed.

Large-scale motions in a plane wall jet

2019 ◽  
Vol 877 ◽  
pp. 239-281 ◽  
Author(s):  
Ebenezer P. Gnanamanickam ◽  
Shibani Bhatt ◽  
Sravan Artham ◽  
Zheng Zhang
Keyword(s):  
Reynolds Number ◽  
Shear Layer ◽  
Large Scale ◽  
Plane Wall ◽  
Shear Stresses ◽  
Wall Jet ◽  
Wall Region ◽  
Free Shear Layer ◽  
Large Scale Structures ◽  
Scale Structures

The plane wall jet (PWJ) is a wall-bounded flow in which a wall shear layer develops in the presence of extremely energetic flow structures of the outer free-shear layer. The structure of a PWJ, developing in still air, was studied with the focus on the large scales in the flow. Wall-normal hot-wire anemometry (HWA) measurements along with double-frame particle image velocimetry (PIV) measurements (wall-normal–streamwise plane) were carried out at streamwise distances up to $162b$, where $b$ is the slot width of the PWJ exit. The nominal PWJ Reynolds number based on exit parameters was $Re_{j}\approx 5940$. Comparisons with a zero-pressure-gradient boundary layer (ZPGBL) at nominally matched friction Reynolds number $Re_{\unicode[STIX]{x1D70F}}$ were also carried out as appropriate, to highlight key features of the PWJ structure. Consistent with previous work, the PWJ showed a dependence of the peak turbulent stresses on the jet exit Reynolds number. The turbulent production showed a peak corresponding to the near-wall cycle similar to the peak seen in the ZPGBL. However, another turbulent production peak was observed in the outer free-shear layer that was an order of magnitude larger than the inner one. Along with the change in sign of the viscous and Reynolds shear stresses, the PWJ was shown to have a region of very low turbulent production between these two peaks. The dissipation rate increased over the PWJ layer with a peak also in the outer region. Visualizations of the flow and two-point correlations reveal that the most energetic large-scale structures within a PWJ are vortical motions in the wall-normal–streamwise plane similar to those structures seen in free-shear layers. These structures are referred to as J (for jet) type structures. In addition two-point correlations reveal the existence of large-scale structures in the wall region which have a signature similar to those structures seen in canonical boundary layers. These structures are referred to as W (for wall) type structures. Instantaneous PIV realizations and flow visualizations reveal that these W type large-scale features are consistent with the paradigm of hairpin vortex packets in the wall region. The J type structures were seen to intrude well into the wall region while the W type structures were also seen to extend into the outer shear layer. Further, these large-scale structures were shown to modulate the amplitude of the finer scales of the flow.

On the Free Shear Layer Downstream of a Backstep in Supersonic Flow

1973 ◽  
Vol 95 (3) ◽  
pp. 361-366 ◽  
Author(s):  
P. M. Gerhart ◽  
H. H. Korst
Keyword(s):  
Experimental Data ◽  
Shear Layer ◽  
Reasonable Agreement ◽  
Mixing Layer ◽  
Outer Region ◽  
Initial Boundary ◽  
Supersonic Stream ◽  
Free Shear Layer ◽  
Rate Of Spread ◽  
Technique Comparison

The free shear layer downstream of a backstep immersed in a supersonic stream is analyzed. The effects of the initial boundary layer and the expansion at the step corner are taken into account. The shear layer is divided into two distinct regions, an outer rotational nondissipative region and an inner dissipative locally similar mixing region which spreads both into the rotational outer region and the wake. The dynamic characteristics of the shear layer including the rate of spread of the inner mixing layer and the location of the jet boundary streamline are determined by an integral technique. Comparison of predicted velocity profiles with experimental data shows reasonable agreement.

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