Topology-free immersed boundary method for incompressible turbulence flows: An aerodynamic simulation for “dirty” CAD geometry

Onishi, K.; Tsubokura, Makoto

doi:10.1016/j.cma.2021.113734

Cited by 20 publications

(9 citation statements)

References 51 publications

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“…This study uses the code ‘CUBE’ developed by the Riken Centre for Computational Science (Jansson et al. 2019; Onishi & Tsubokura 2021). It combines the building cube method (BCM) with the topology-independent immersed boundary method (IBM).…”

Section: Methodsmentioning

confidence: 99%

Topological description of near-wall flows around a surface-mounted square cylinder at high Reynolds numbers

et al. 2021

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This study topologically describes near-wall flows around a surface-mounted cylinder at a high Reynolds number ( $Re$ ) of $5\times 10^4$ and in a very thick boundary layer, which were partially measured or technically approximated from the literature. For complete and rational flow construction, we use high-resolution simulations and critical-point theory. The large-scale near-wake vortex is composed of two connected segments rolled up from the sides of the cylinder and from the free end. Another large-scale side vortex clearly roots on two notable foci on the lower side wall. In the junction region, the side vortex moves upwards with a curved trajectory, which induces the formation of nodes on the ground surface. In the free-end region, the side vortex is compressed, which results in a smaller trailing-edge vortex and its downstream movement. Only tip vortices are observed in the far wake. The origin of the tip vortices and their distinction from the near-wake vortex are discussed. Further analyses suggest that $Re$ independence should be treated with high caution when $Re$ increases from 500 to ${O}(10^4)$ . The occurrence of upwash flow behind the cylinder strongly depends on the increase in $Re$ , the mechanism of which is also provided. The separation–reattachment process in the junction region and the trailing-edge vortices are discovered only at a high $Re$ . The former should significantly affect the strength of the side vortex in the junction region and the latter should cause a sharp drop in pressure near the trailing edge.

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Section: Methodsmentioning

confidence: 99%

Topological description of near-wall flows around a surface-mounted square cylinder at high Reynolds numbers

et al. 2021

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“…One of the core innovations we have realized to achieve significant reduction in turnaround time in developing largescale parallel computing method is to combine the hierarchical Cartesian grid and the immersed boundary method (IBM), which does not require preprocessing work [14].…”

Section: Rapid Mesh Generation Based On the Immersed Boundary Methodsmentioning

confidence: 99%

Digital transformation of droplet/aerosol infection risk assessment realized on "Fugaku" for the fight against COVID-19

Ando¹,

Bale²,

Li³

et al. 2021

Preprint

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The fastest supercomputer in 2020, Fugaku, has not only achieved digital transformation of epidemiology in allowing end-to-end, detailed quantitative modeling of COVID-19 transmissions for the first time, but also transformed the behavior of the entire Japanese public through its detailed analysis of transmission risks in multitudes of societal situations entailing heavy risks. A novel aerosol simulation methodology was synthesized out of a combination of a new CFD methods meeting industrial demands, CUBE [8], which not only allowed the simulations to scale massively with high resolution required for micrometer virus-containing aerosol particles, but also extremely rapid time-to-solution due to its ability to generate the digital twins representing multitudes of societal situations in minutes not week, attaining true overall application high performance; such simulations have been running for the past 1.5 years on Fugaku, cumulatively consuming top supercomputer-class resources and the result communicated by the media as well as becoming official public policies. Keywords COVID-19 • Computational fluid dynamics • Building cube method • Immersed boundary method • Dirty CAD • Droplet/Aerosol transmission • societal behavioral change * All authors are listed in alphabetical order by surnames.

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“…It is expressed using the delta function and applied as a correction term of the momentum equation for each calculation grid point. In topology-free IBM 17 , the existence of an object is implemented by dividing it into a fluid region Ω f , solid region Ω s , and boundary region Ω IB . The distribution function D is expressed in Eq.…”

Section: B Topology-free Immersed Boundary Methodsmentioning

confidence: 99%

“…By this transformation, the solution becomes robust and does not cause calculation errors regardless of the shape complexity. However, the calculation accuracy near the wall drops to the first-order accuracy as the grid resolution increases because it cannot be completely replaced in theory, as presented by Onishi et al 17 .…”

Section: B Topology-free Immersed Boundary Methodsmentioning

confidence: 99%

Numerical analysis of the efficiency of face masks for preventing droplet airborne infections

Onishi,

Iida,

Yamakawa

et al. 2021

Preprint

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In this study, the flow field around face masks was visualized and evaluated using computational fluid dynamics. The protective efficiency of face masks suppressing droplet infection owing to differences in the shape, medium, and doubling usage is predicted. Under the ongoing COVID-19 pandemic condition, many studies have been conducted to highlight that airborne transmission is the main transmission route. However, the virus infection prevention effect of face masks has not been sufficiently discussed, and thus remains as a controversial issue. Therefore, we aimed to provide a beneficial index for the society. The topology-free immersed boundary method, which is advantageous for complex shapes, was used to model the flow in the constriction area, including the contact surface between the face and mask. The jet formed from the oral cavity is guided to the outside through the surface of the mask and leaks from the gap between the face and mask.A Darcy-type model of porous media was used to model the flow resistance of masks. A random variable stochastic model was used to measure particle transmittance. We evaluated the differences in the amount of leakage and deposition of the droplets during exhalation and inhalation, depending on the differences in the conditions between the surgical and cloth masks owing to coughing and breathing. The obtained result could be attributed to the epidemiological measures adopted against both the reduction of the risk of infecting others by suppressing the exhalation, and the inhalation amounts. I. INTRODUCTIONUnder the ongoing COVID-19 pandemic conditions, it is becoming clear that the infection route by droplet dispersion plays a dominant role. Hydrodynamic considerations are significant in exploring the spread mechanism of COVID-19, and computational fluid dynamics (CFD) is expected to be utilized in all physical aspects of droplet transmission, from the formation of droplets to transportation by airflow 1 . However, the number of studies on the efficiency of face masks for droplet infection is insufficient. In addition, some numerical indicators for clarifying the effectiveness of wearing masks would be beneficial for the society, which is still a controversial issue.Many visualized study results on the personal protective equipment (PPE), particularly face masks, have been reported over the last year. Verma et al. 2 demonstrated the effect of face masks

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Topology-free immersed boundary method for incompressible turbulence flows: An aerodynamic simulation for “dirty” CAD geometry

Cited by 20 publications

References 51 publications

Topological description of near-wall flows around a surface-mounted square cylinder at high Reynolds numbers

Topological description of near-wall flows around a surface-mounted square cylinder at high Reynolds numbers

Digital transformation of droplet/aerosol infection risk assessment realized on "Fugaku" for the fight against COVID-19

Numerical analysis of the efficiency of face masks for preventing droplet airborne infections

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