A near-wall predictive model for passive scalars using minimal flow unit

2021 ◽  
Vol 33 (4) ◽  
pp. 045119
Author(s):  
Bo-Yuan Zhang ◽  
Wei-Xi Huang ◽  
Chun-Xiao Xu
Keyword(s):  
Predictive Model ◽  
Flow Unit ◽  
Minimal Flow ◽  
Passive Scalars ◽  
Near Wall

A minimal flow unit for the study of turbulence with passive scalars

2014 ◽  
Vol 15 (11) ◽  
pp. 731-751 ◽  
Author(s):  
Paolo Orlandi ◽  
Sergio Pirozzoli ◽  
Matteo Bernardini ◽  
George F. Carnevale
Keyword(s):  
Flow Unit ◽  
Minimal Flow ◽  
Passive Scalars

Prediction of near-wall turbulence using minimal flow unit

2018 ◽  
Vol 841 ◽  
pp. 654-673 ◽  
Author(s):  
Guang Yin ◽  
Wei-Xi Huang ◽  
Chun-Xiao Xu
Keyword(s):  
Joint Probability ◽  
Flow Unit ◽  
Wall Turbulence ◽  
Minimal Flow ◽  
Velocity Fluctuations ◽  
Wall Velocity ◽  
Near Wall Turbulence ◽  
Joint Probability Density ◽  
Good Agreement ◽  
Near Wall

In the present study, direct numerical simulation (DNS) is carried out in a minimal channel at $Re_{\unicode[STIX]{x1D70F}}=2000$ to sustain healthy turbulence below $y^{+}=100$. Turbulence intensities are compared with those of the motions at the same scales as the minimal channel in the full-sized channel at $Re_{\unicode[STIX]{x1D70F}}=2003$ (Hoyas & Jiménez, Phys. Fluids, vol. 20 (10), 2008, article 101511). They show good agreement in $y^{+}<100$. The universal signals for the three velocity components similar to that in the predictive model of Marusic et al. (Science, vol. 329 (5988), 2010, pp. 193–196) are extracted from the DNS data of the full-sized channel. They correspond well to the near-wall velocity fluctuations in the minimal flow unit (MFU). The predictive models for the three components of near-wall velocity fluctuations are proposed based on the MFU data. The predicted turbulence intensities as well as the joint probability density functions of velocity fluctuations agree well with the DNS results of the full-sized channel turbulence.

The minimal flow unit in near-wall turbulence

1991 ◽  
Vol 225 ◽  
pp. 213-240 ◽  
Author(s):  
Javier Jiménez ◽  
Parviz Moin
Keyword(s):  
Wall Stress ◽  
Wall Layer ◽  
Flow Unit ◽  
Wall Turbulence ◽  
Longitudinal Vortex ◽  
Spanwise Direction ◽  
Wall Region ◽  
Low Velocity ◽  
Good Agreement ◽  
Near Wall

Direct numerical simulations of unsteady channel flow were performed at low to moderate Reynolds numbers on computational boxes chosen small enough so that the flow consists of a doubly periodic (in x and z) array of identical structures. The goal is to isolate the basic flow unit, to study its morphology and dynamics, and to evaluate its contribution to turbulence in fully developed channels. For boxes wider than approximately 100 wall units in the spanwise direction, the flow is turbulent and the low-order turbulence statistics are in good agreement with experiments in the near-wall region. For a narrow range of widths below that threshold, the flow near only one wall remains turbulent, but its statistics are still in fairly good agreement with experimental data when scaled with the local wall stress. For narrower boxes only laminar solutions are found. In all cases, the elementary box contains a single low-velocity streak, consisting of a longitudinal strip on which a thin layer of spanwise vorticity is lifted away from the wall. A fundamental period of intermittency for the regeneration of turbulence is identified, and that process is observed to consist of the wrapping of the wall-layer vorticity around a single inclined longitudinal vortex.

Active control in the turbulent wall layer of a minimal flow unit

1996 ◽  
Vol 329 ◽  
pp. 341-371 ◽  
Author(s):  
Henry A. Carlson ◽  
John L. Lumley
Keyword(s):  
High Speed ◽  
Wall Layer ◽  
Flow Unit ◽  
Wall Region ◽  
Minimal Flow ◽  
Test Bed ◽  
Low Speed ◽  
Turbulent Wall ◽  
Friction Drag Reduction ◽  
Smart Skin

Direct simulations of flow in a channel with complex, time-dependent wall geometries facilitate an investigation of smart skin control in a turbulent wall layer (with skin friction drag reduction as the goal). The test bed is a minimal flow unit, containing one pair of coherent structures in the near-wall region: a high- and a low-speed streak. The controlling device consists of an actuator, Gaussian in shape and approximately twelve wall units in height, that emerges from one of the channel walls. Raising the actuator underneath a low-speed streak effects an increase in drag, raising it underneath a high-speed streak effects a reduction – indicating a mechanism for control. In the high-speed region, fast-moving fluid is lifted by the actuator away from the wall, allowing the adjacent low-speed region to expand and thereby lowering the average wall shear stress. Conversely, raising an actuator underneath a low-speed streak allows the adjacent high-speed region to expand, which increases skin drag.

A low-dimensional approach for the minimal flow unit

1998 ◽  
Vol 362 ◽  
pp. 121-155 ◽  
Author(s):  
BÉRENGÈRE PODVIN ◽  
JOHN LUMLEY
Keyword(s):  
Turbulent Channel Flow ◽  
Dynamical Behaviour ◽  
Flow Unit ◽  
Minimal Flow ◽  
Dimensional Parameters ◽  
Dimensional Models ◽  
Modelling Assumptions ◽  
Low Dimensional ◽  
Proper Orthogonal ◽  
The Relationship

The proper orthogonal decomposition (POD) is applied to the minimal flow unit (MFU) of a turbulent channel flow. Our purpose is to establish a numerical validation of low-dimensional models based on the POD. The simplest (two-mode) model possible is built for the simplified flow in the minimal unit. The dynamical behaviour predicted by the model is compared with that actually occurring in the direct numerical simulation of the flow. The various modelling assumptions which underlie the construction of low-dimensional models are examined and confronted with numerical evidence. The relationship between intermittency in the MFU and intermittent low-dimensional parameters is investigated closely. The agreement observed is quite satisfactory, especially given the crudeness of the truncation considered. To further demonstrate the adequacy of the model, we develop a dynamical filtering procedure to recover information from realistic (partial) measurements. The success obtained illustrates the versatility of the low-dimensional paradigm.

On near-wall turbulence in minimal flow units

2017 ◽  
Vol 65 ◽  
pp. 192-199 ◽  
Author(s):  
Guang Yin ◽  
Wei-Xi Huang ◽  
Chun-Xiao Xu
Keyword(s):  
Wall Turbulence ◽  
Minimal Flow ◽  
Flow Units ◽  
Near Wall Turbulence ◽  
Near Wall
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