Grid generated turbulence under the rigid boundary influence

Raushan, Pankaj Kumar; Singh, Santosh Kumar; Debnath, Koustuv

doi:10.1016/j.jweia.2018.10.003

Cited by 26 publications

(25 citation statements)

References 41 publications

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“…None of the aforementioned works investigated how a turbulent boundary layer evolves when subjected to FST which itself is also evolving. Raushan, Singh & Debnath (2018) examined a flow of this type, posing the inverse question: how does the spatial development of a boundary layer influence grid generated freestream turbulence. They used three different passive grids in an open water channel to create different levels of freestream turbulence.…”

Section: Introductionmentioning

confidence: 99%

Spatial development of a turbulent boundary layer subjected to freestream turbulence

Jooss

Bracchi

et al. 2021

J. Fluid Mech.

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Section: Introductionmentioning

confidence: 99%

Spatial development of a turbulent boundary layer subjected to freestream turbulence

Jooss

Bracchi

et al. 2021

J. Fluid Mech.

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“…In order to unveil how "the larger, energetic motions which occur relatively seldom are the principal source of Reynolds stress" (Wallace and Brodkey, 1977), and to single out the contribution of intense Reynolds shear stress events within each quadrant, the socalled "hole analysis" is often applied in different contexts, from turbulent boundary layers (Willmarth and Lu 1972;Lu and Willmarth 1973), flow over wall roughness (Raupach, 1981) and vegetated canopies (Poggi et al, 2004;Yue et al, 2007), to grid turbulence (Raushan et al, 2018). A hyperbolic threshold is used to define the "hole" and contributions outside that region, i.e.…”

Section: Resultsmentioning

confidence: 99%

How gable roofs change the mechanisms of turbulent vertical momentum transfer: A LES study on two-dimensional urban canyons

Badas

Garau

Querzoli

2021

Journal of Wind Engineering and Industrial Aerodynamics

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A Large Eddy Simulation (LES) study on the presence of gable roofs in urban canyons is presented: two canyon aspect ratios, ARC = 1, 2, ( = / corresponding to the ratio of the canyon width, W, to the eaves' height, H) and variable roof slope, ( = 0°, 10°, 20°, 30°, 45°) in a periodic configuration are considered. The vertical turbulent momentum flux is analysed by means of the quadrant analysis both in terms of spatial maps and mean vertical profiles in order to assess how the presence of a gable roof and its slope affects the mechanisms of mixing in the roughness sublayer. A gradual modification with increasing roof slope is apparent for the mean flow patterns as well as for the shear layer thickness. On the contrary, the contribution of ejections and sweeps at the rooftop goes through an abrupt change when passing from flat-to gable-roof buildings. This behaviour arises for both the investigated flow regimes. We observed that with gable roofs the imbalance between sweeps and ejections is monotonically increasing with . However, the case of flat roof is not in continuity with the small pitch ones, as itgives much higher values of imbalance, comparable to what was observed for the largest analysed pitches (45°). Keywords Street canyon  Urban boundary layer  Gable roof  Large Eddy Simulation  Quadrant analysis Manuscript File Click here to view linked References

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“…In the present experiments, three different mesh sizes (M 1 , M 2 and M 3 ) of the grids were used. The detailed description of the experimental set-up for study is given in Raushan et al 15 The velocity measurements were taken at the decay region of the grids for multiple mesh sizes. Regular bi-planar grids having three different mesh sizes (M 1 ¼ 1.05 cm, M 2 ¼ 1.5 cm and M 3 ¼ 2.0 cm) with constant diameter of rod was used.…”

Section: Experimentation and Measurement Descriptionmentioning

confidence: 99%

“…Here, M 1, M 2 and M 3 correspond to smaller, medium and the largest mesh sizes, respectively. The detailed information of the grid materials, solidity ratio ðÞ of the grids and the mounting arrangement of instruments used for the present investigation is provided in the Raushan et al 13,15 The measurement locations were constant at different downstream distance from the grids (Figure 1). The turbulence generated by different mesh size at the downstream of the grids changed from non-homogeneous velocity field close to the grid to homogeneous and isotropic (within a close approximation) turbulence in the FF region.…”

Section: Experimentation and Measurement Descriptionmentioning

confidence: 99%

“…The rigid boundaries also initiate dissipation mechanism and its interaction with grid turbulence affects the decay of turbulence in the close and extreme zone of the grid. [14][15][16] Thus, the centre of attention for the present work is towards the understanding of the spatial growth of inhomogeneous turbulence in the close and extreme region of the grid under rigid boundary interaction. In this work, the decay of the energy spectrum using the approach of the Fourier and the Hilbert transform, test of isotropy, joint probability density function, local intermittency measure (LIM) and Shannon entropy are under taken and discussed to provide improved understanding of the decay of grid-generated turbulence.…”

Section: Introductionmentioning

confidence: 99%

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Role of rigid boundary on the decay of turbulence generated by passive-grid for free surface flow

Raushan

Singh

Debnath

2020

Proceedings of the Institution of Mechanical Engineers, Part C:

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The present study aims to investigate the flow characteristics of grid-generated turbulence under the consideration of solid boundary in free surface flow. To understand the nature of isotropy and anisotropy in the flow, the turbulent intensity is evaluated at the downstream of the grid for different mesh sizes. The energy spectrums based on the Fast Fourier and marginal Hilbert–Huang transform are presented to understand the decay of energy in the associated spectral frequency domain. It is observed that the peak of energy associated with the Fourier spectrum decreases in the near-field region of the grid with the increase in mesh size of the grid. Further, to characterise the concentrated velocity fluctuations, the paper strives to analyse the joint probability distribution function and the local intermittency measure in the close and far stream of the grid. The autocorrelation functions and the magnitude of integral length scale of the stream-wise fluctuating velocity components are also presented at two different vertical levels from the solid boundary. The normalised Shannon entropy is also evaluated to characterise the degree of the orderness or disorderness in the flow due to the interaction of grid and rigid boundary.

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Grid generated turbulence under the rigid boundary influence

Cited by 26 publications

References 41 publications

Spatial development of a turbulent boundary layer subjected to freestream turbulence

Spatial development of a turbulent boundary layer subjected to freestream turbulence

How gable roofs change the mechanisms of turbulent vertical momentum transfer: A LES study on two-dimensional urban canyons

Role of rigid boundary on the decay of turbulence generated by passive-grid for free surface flow

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