Three-dimensional numerical simulations and proper orthogonal decomposition analysis of flow over different bottom-mounted ribs

Fraga, Vinicius Serta; Yin, Guang; Ong, Muk Chen

doi:10.1080/17445302.2021.1877939

Cited by 5 publications

(2 citation statements)

References 40 publications

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“…One plane normal to the spanwise direction and a set of 2D planes normal to the flow direction and are used to formulate the POD basis. Similar POD analysis is also reported in Serta Fraga et al [26]. The location of sampling planes is shown in Fig.…”

Section: Proper Orthogonal Decomposition Analysissupporting

confidence: 88%

“…The basic assumption is that with increasing number of snapshots or with the sampling interval refinement, the most energetic modes spatial structures will converge towards the same solution. This method is based on the orthogonality between modes as proposed by Muld et al [27] and also used in Serta Fraga et al [26]. The orthogonality is a property of POD and for identical modes it is equal to 1.…”

Section: Proper Orthogonal Decomposition Analysismentioning

confidence: 99%

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Three-Dimensional Large Eddy Simulations and Proper Orthogonal Decomposition Analysis of Flow Around a Flexibly Supported Circular Cylinder

Janocha

Fabricius

Yin

et al. 2022

Volume 7: CFD and FSI

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Three-dimensional (3D) numerical simulations of the flow around a cylinder undergoing vortex-induced vibration (VIV) at Re = 3900 (defined as Re = U∞D/ v, where U∞ is the inlet flow velocity, D is the diameter of the cylinder and v is the fluid kinematic viscosity) are performed using Large Eddy Simulations (LES). Detailed mesh and time-step convergence studies are carried out for the flow past a stationary cylinder to obtain the optimal mesh and time step. The validation studies are performed by comparing the present results with the previous published experimental data and numerical results to confirm feasibility of the present numerical model for predicting the wake characteristics. The numerical model is then applied to investigate the flow around a self-excited cylinder vibrating in the cross-flow direction at three different reduced velocity. The effects of the reduced velocity are analyzed based on the cross-flow vibration amplitudes, the power spectral densities of lift and drag coefficients and the wake flow coherent structures. Different vortex shedding modes are identified and categorized using the iso-surfaces of the pressure coefficient and the Q-criterion. The dominant 3D wake flow features are extracted and discussed by carrying out the Proper Orthogonal Decomposition (POD) for flow velocities on multiple two-dimensional (2D) sampling planes in the wake region. The modes on the XY planes display a traveling-wave behavior and the modes on the XZ planes shows cells of streamwise vortices, which displays the three-dimensionality of the wake flow.

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Section: Proper Orthogonal Decomposition Analysissupporting

confidence: 88%

Section: Proper Orthogonal Decomposition Analysismentioning

confidence: 99%

Three-Dimensional Large Eddy Simulations and Proper Orthogonal Decomposition Analysis of Flow Around a Flexibly Supported Circular Cylinder

Janocha

Fabricius

Yin

et al. 2022

Volume 7: CFD and FSI

View full text Add to dashboard Cite

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Entrainment of the shear layer separated from a wall-mounted fence

Li,

Wang

2024

J. Fluid Mech.

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Turbulent entrainment at the turbulent/non-turbulent interface (TNTI) plays an important role in understanding the turbulent diffusion. While entrainment in fully developed canonical turbulent flows has been extensively studied, the evolution of entrainment in spatially developing flows remains poorly understood. In this work, characteristics of entrainment and the effect of vortices on entrainment of the shear layer separated from a wall-mounted fence are studied by the experiment in a water channel. The shedding vortex experiences a series of stages, including generation, growth, deformation and breakdown into smaller vortices. With the development of the flow, entrainment varies correspondingly. The prograde vortex near the TNTI is found to suppress entrainment but have little effect on the detrainment process, while the retrograde vortex promotes entrainment and suppresses detrainment as well. Consequently, the local entrainment velocity is decreased by the prograde vortex and increased more significantly by the retrograde vortex. Along the streamwise direction, the time-mean entrainment velocity is smallest where the prograde vortex is strongest in the vortex deformation stage. However, the largest time-mean entrainment velocity is located where the enstrophy gradient near the TNTI is greatest after reattachment, rather than where the retrograde vortex is strongest shortly after the breakdown of the shedding vortex, because the scarcity of retrograde vortices in the vicinity of the TNTI makes their long-time cumulative contribution not as significant as their local enhancement. The present study reveals how entrainment evolves in the separated and reattaching flow, and improves our understanding of the effect of vortices on entrainment.

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Turbulent boundary layer structures downstream of a square cylinder

Wang,

Zhou,

Chen

et al. 2024

Physics of Fluids

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Particle image velocimetry is used to investigate the coherent structures within a turbulent boundary layer (TBL) perturbed by a slender square cylinder. A moderate Reynolds number of Reτ=3691 is considered. The cylinder is immersed in different vertical regions of the TBL, from the viscous sublayer to the logarithmic layer, depending on the value of the cylinder–wall gap ratio within the range of G/D=0.0−2.0. Here, G is the distance between the wall and the lower surface of the cylinder, and D is the cross-section size of the square cylinder. The results reveal a substantial influence of the TBL statistics and structures. Utilizing velocity correlation and proper orthogonal decomposition (POD), we highlight the intriguing influence of large-/very large-scale turbulent structures induced by the cylinder. When the cylinder is positioned on or in close proximity to the wall, periodic shedding of vortices is not apparent. In the presence of a cylinder, the large-/very large-scale turbulent structures are reduced in size compared with those in the undisturbed TBL, owing to the interaction between the flow around the cylinder and the boundary layer turbulence. The lower modes of the POD in the disturbed TBL are similar to those of the undisturbed flow field. However, the large-/very large-scale turbulent structures are increasingly affected by the strengthening of the shedding vortices with increasing G/D when the cylinder is located in the logarithmic region. As a result, the Kármán vortex street becomes the dominant structure associated with the higher POD modes at sufficiently high cylinder–wall gap ratios.

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Three-dimensional numerical simulations and proper orthogonal decomposition analysis of flow over different bottom-mounted ribs

Cited by 5 publications

References 40 publications

Three-Dimensional Large Eddy Simulations and Proper Orthogonal Decomposition Analysis of Flow Around a Flexibly Supported Circular Cylinder

Three-Dimensional Large Eddy Simulations and Proper Orthogonal Decomposition Analysis of Flow Around a Flexibly Supported Circular Cylinder

Entrainment of the shear layer separated from a wall-mounted fence

Turbulent boundary layer structures downstream of a square cylinder

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