Interactions of a stationary finite-sized particle with wall turbulence

2007 ◽  
Vol 594 ◽  
pp. 271-305 ◽  
Author(s):  
LANYING ZENG ◽  
S. BALACHANDAR ◽  
PAUL FISCHER ◽  
FADY NAJJAR
Keyword(s):  
Numerical Simulations ◽  
Finite Size ◽  
Turbulent Channel Flow ◽  
Direct Numerical Simulations ◽  
Wall Turbulence ◽  
Streamwise Vortices ◽  
Turbulent Structures ◽  
Lift Forces ◽  
Drag And Lift ◽  
Particle Force

Reliable information on forces on a finite-sized particle in a turbulent boundary layer is lacking, so workers continue to use standard drag and lift correlations developed for a laminar flow to predict drag and lift forces. Here we consider direct numerical simulations of a turbulent channel flow over an isolated particle of finite size. The size of the particle and its location within the turbulent channel are systematically varied. All relevant length and time scales of turbulence, attached boundary layers on the particle, and particle wake are faithfully resolved, and thus we consider fully resolved direct numerical simulations. The results from the direct numerical simulation are compared with corresponding predictions based on the standard drag relation with and without the inclusion of added-mass and shear-induced lift forces. The influence of turbulent structures, such as streaks, quasi-streamwise vortices and hairpin packets, on particle force is explored. The effect of vortex shedding is also observed to be important for larger particles, whoseReexceeds a threshold.

Wall turbulence manipulation by large-scale streamwise vortices

2002 ◽  
Vol 473 ◽  
pp. 23-58 ◽  
Author(s):  
GAETANO IUSO ◽  
MICHELE ONORATO ◽  
PIER GIORGIO SPAZZINI ◽  
GAETANO MARIA DI CICCA
Keyword(s):  
Large Scale ◽  
Time Derivative ◽  
Vortex Generator ◽  
Turbulent Channel Flow ◽  
Wall Turbulence ◽  
Spanwise Direction ◽  
Streamwise Vortices ◽  
Turbulent Structures ◽  
Reduced Frequency ◽  
Flow Manipulation

This paper describes an experimental study of the manipulation of a fully developed turbulent channel flow through large-scale streamwise vortices originated by vortex generator jets distributed along the wall in the spanwise direction. Apart from the interest in flow management itself, an important aim of the research is to observe the response of the flow to external perturbations as a technique for investigating the structure of turbulence. Considerable mean and fluctuating skin friction reductions, locally as high as 30% and 50% respectively, were measured for an optimal forcing flow intensity. Mean and fluctuating velocity profiles are also greatly modified by the manipulating large-scale vortices; in particular, attenuation of the turbulence intensity was measured. Moreover the flow manipulation caused an increase in longitudinal coherence of the wall organized motions, accompanied by a reduced frequency of burst events, demonstrated by a reduction of the velocity time derivative PDFs and by an higher intermittency. A strong transversal periodic organization of the flow field was observed, including some typical behaviours in each of the periodic boxes originated by the interaction of the vortex pairs. Results are interpreted and discussed in terms of management of the near-wall turbulent structures and with reference to the wall turbulence regeneration mechanisms suggested in the literature.

scholarly journals Unravelling turbulence near walls

2009 ◽  
Vol 630 ◽  
pp. 1-4 ◽  
Author(s):  
IVAN MARUSIC
Keyword(s):  
Laminar Flow ◽  
Turbulent Flow ◽  
Numerical Simulations ◽  
Turbulent Flows ◽  
Direct Numerical Simulations ◽  
Aircraft Wing ◽  
Physical Mechanisms ◽  
Drag And Lift

Turbulent flows near walls have been the focus of intense study since their first description by Ludwig Prandtl over 100 years ago. They are critical in determining the drag and lift of an aircraft wing for example. Key challenges are to understand the physical mechanisms causing the transition from smooth, laminar flow to turbulent flow and how the turbulence is then maintained. Recent direct numerical simulations have contributed significantly towards this understanding.

Direct numerical simulations of rotating turbulent channel flow

2008 ◽  
Vol 598 ◽  
pp. 177-199 ◽  
Author(s):  
OLOF GRUNDESTAM ◽  
STEFAN WALLIN ◽  
ARNE V. JOHANSSON
Keyword(s):  
Numerical Simulations ◽  
Channel Flow ◽  
Rotation Number ◽  
Turbulent Channel Flow ◽  
Shear Velocity ◽  
Direct Numerical Simulations ◽  
A Value ◽  
Rotation Numbers ◽  
Wall Shear ◽  
Two Sides

Fully developed rotating turbulent channel flow has been studied, through direct numerical simulations, for the complete range of rotation numbers for which the flow is turbulent. The present investigation suggests that complete flow laminarization occurs at a rotation number Ro = 2Ωδ/Ub ≤ 3.0, where Ω denotes the system rotation, Ub is the mean bulk velocity and δ is the half-width of the channel. Simulations were performed for ten different rotation numbers in the range 0.98 to 2.49 and complemented with earlier simulations (done in our group) for lower values of Ro. The friction Reynolds number Reτ = uτδ/ν (where uτ is the wall-shear velocity and ν is the kinematic viscosity) was chosen as 180 for these simulations. A striking feature of rotating channel flow is the division into a turbulent (unstable) and an almost laminarized (stable) side. The relatively distinct interface between these two regions was found to be maintained by a balance where negative turbulence production plays an important role. The maximum difference in wall-shear stress between the two sides was found to occur for a rotation number of about 0.5. The bulk flow was found to monotonically increase with increasing rotation number and reach a value (for Reτ = 180) at the laminar limit (Ro = 3.0) four times that of the non-rotating case.

scholarly journals Effects of radiation in turbulent channel flow: analysis of coupled direct numerical simulations

2014 ◽  
Vol 753 ◽  
pp. 360-401 ◽  
Author(s):  
R. Vicquelin ◽  
Y. F. Zhang ◽  
O. Gicquel ◽  
J. Taine
Keyword(s):  
Heat Flux ◽  
Numerical Simulations ◽  
Boundary Layers ◽  
Temperature Fluctuations ◽  
Turbulent Channel Flow ◽  
Turbulent Heat Flux ◽  
Direct Numerical Simulations ◽  
Turbulent Heat Transfer ◽  
Radiative Energy ◽  
Turbulent Heat

AbstractThe role of radiative energy transfer in turbulent boundary layers is carefully analysed, focusing on the effect on temperature fluctuations and turbulent heat flux. The study is based on direct numerical simulations (DNS) of channel flows with hot and cold walls coupled to a Monte-Carlo method to compute the field of radiative power. In the conditions studied, the structure of the boundary layers is strongly modified by radiation. Temperature fluctuations and turbulent heat flux are reduced, and new radiative terms appear in their respective balance equations. It is shown that they counteract turbulence production terms. These effects are analysed under different conditions of Reynolds number and wall temperature. It is shown that collapsing of wall-scaled profiles is not efficient when radiation is considered. This drawback is corrected by the introduction of a radiation-based scaling. Finally, the significant impact of radiation on turbulent heat transfer is studied in terms of the turbulent Prandtl number. A model for this quantity, based on the new proposed scaling, is developed and validated.

Direct numerical simulations of roughness-induced transition in supersonic boundary layers

2012 ◽  
Vol 693 ◽  
pp. 28-56 ◽  
Author(s):  
Suman Muppidi ◽  
Krishnan Mahesh
Keyword(s):  
Numerical Simulations ◽  
Shear Layer ◽  
Boundary Layers ◽  
Plate Boundary ◽  
Direct Numerical Simulations ◽  
Transition To Turbulence ◽  
Streamwise Vortices ◽  
Mean Flow ◽  
The Mean ◽  
Near Wall

AbstractDirect numerical simulations are used to study the laminar to turbulent transition of a Mach 2.9 supersonic flat plate boundary layer flow due to distributed surface roughness. Roughness causes the near-wall fluid to slow down and generates a strong shear layer over the roughness elements. Examination of the mean wall pressure indicates that the roughness surface exerts an upward impulse on the fluid, generating counter-rotating pairs of streamwise vortices underneath the shear layer. These vortices transport near-wall low-momentum fluid away from the wall. Along the roughness region, the vortices grow stronger, longer and closer to each other, and result in periodic shedding. The vortices rise towards the shear layer as they advect downstream, and the resulting interaction causes the shear layer to break up, followed quickly by a transition to turbulence. The mean flow in the turbulent region shows a good agreement with available data for fully developed turbulent boundary layers. Simulations under varying conditions show that, where the shear is not as strong and the streamwise vortices are not as coherent, the flow remains laminar.

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