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Rotating thermal convection, commonly encountered in natural and industrial environments, is typically influenced by both buoyancy forces and boundary rotation. In this study, we conduct direct numerical simulations to explore the effect of rotating bottom on the flow structure and heat transport of Rayleigh–Bénard convection (RBC) in a cylindrical cavity. This cavity has a radius-to-height ratio of 1 and is filled with an incompressible fluid with a Prandtl number of 0.7. Our results show that the axisymmetric convection pattern, observed in RBC for R a ∈ [ 4000 , 8000 ] without rotation, transitions into a double roll structure at low rotating speeds (ω), while for R a ≤ 4000 , the pattern remains axisymmetric, independent of ω. We then focus on the impact of bottom rotation on heat transport in the axisymmetric regime. Based on the variation in the Nusselt number (Nu) with ω , two distinct regimes are identified: a convection-dominated regime at low ω , where Nu closely resembles that of standard RBC, and a rotation-dominated regime at high ω , where strong shear induced by the rotating bottom intensifies the meridional circulation, significantly boosting global heat flux. The critical rotating speed, ω * , marking the transition between these regimes, follows different power-law relations below and above the buoyant convection onset (R a c ): ω * ∼ R a − 0.64 for R a < R a c and ω * ∼ R a 0.33 for R a > R a c . As ω increases, the exponents for N u ∼ R a λ and R e ∼ R a γ evolve before converging to λ ≈ 0.3 and γ = 0.5 , respectively. Scaling laws for Nu and Re as functions of ω and Ra in the rotation-dominated regime are finally derived: N u ∼ R a 0.3 ω 0.64 and R e ∼ R a 0.5 ω. [ABSTRACT FROM AUTHOR]

We employ the direct numerical simulation to study the heat transfer behavior and flow structures in a vertical convection system with rough sidewalls. The parameters are chosen with Rayleigh number spanning the range of 1 × 10 8 ≤ R a ≤ 3 × 10 10 and Prandtl number fixed at 1.0. The results reveal that the impact of rough walls on the Nusselt number Nu and the Reynolds number Re is influenced by the height of the rough element h. When h is not sufficiently high, the roughness impedes the flows within the boundary layer and traps massive heat between rough elements, and both Nu and Re are lower than those in the smooth-wall case. However, the extent of the Nu and Re reduction regimes decreases as Ra increases. For sufficiently large Ra, the reduction regime for both Nu and Re may vanish, and roughness breaks up the limitation of the thermal boundary layer and facilitates the eruption of thermal plumes from roughness tips, resulting in the enhancement of both Nu and Re. Based on these results, the critical heights h c for Nu and h c r for Re are identified. Both exhibit similar scaling behavior with Ra, with h c consistently being larger than h c r for the same value of Ra. [ABSTRACT FROM AUTHOR]

Transport of exhaled droplets and aerosol suspension is a main route for the transmission of highly infectious respiratory diseases. A poorly ventilated room, where human body heat drives the flow and the pathogen motion, is one such paradigmatic situation with an elevated risk of viral transmission. Here, we report a numerical study on human body heat-driven buoyancy convection in a slender rectangular geometry with the geometric size of 12 × 1 × 3 m3. Using large-scale three-dimensional simulations, we reveal how different spacings between human body heat sources can potentially spread pathogenic species between occupants in a room. Morphological transition in airflow takes place as the distance between human heat sources is varied, which shapes distinct patterns of disease transmission: For sufficiently large distance, individual buoyant plume creates a natural barrier, forming buoyant jets that block suspension spread between occupants. Thermal plumes exhibit significant individual effects. However, for small distances, a collective effect emerges and thermal plumes condense into superstructure, facilitating long-distance suspension transport via crossing between convection rolls. In addition, we quantify the impact of morphological transition on the transport of viral particles by introducing tracer particles. The quantitative analysis shows that under certain critical distances, the infection risk becomes significantly elevated due to this transition and collective behavior. Our findings highlight the importance of reasonable social distancing to reduce indoor cross-transmission of viral particles between people and provide new insights into the hidden transitional behavior of pathogen transmission in indoor environments. [ABSTRACT FROM AUTHOR]

Practical extreme ultraviolet (EUV) sources yield the desired 13.5 nm radiation but also generate debris, significantly limiting the lifespan of the collector mirror in lithography. In this study, we explore the role of buffer gas in transporting debris particles within an EUV source vessel using direct numerical simulations. Our study involves a 2 × 1 × 1m3 rectangular cavity with an injecting jet flow subjected to sideward outlet. Debris particles are introduced into the cavity with specified initial velocities, simulating a spherical radiating pattern with particle diameters ranging from 0.1 to 1 μm. Varying the inflow velocity (from 1 to 50 m/s) of the buffer gas reveals a morphological transition in the flow field. At low inflow velocities, the flow remains steady, whereas higher inflow velocities induce the formation of clustered corner rolls. Upon reaching sufficiently high inflow velocities, the jet flow can penetrate the entire cavity, impacting the end wall. Interestingly, the resulting recirculation flow leads to the spontaneous formation of spiraling outflow. The distinct flow structures at various inflow velocities lead to distinct patterns of particle transport. For low-speed gas, it is efficient in expelling all particles smaller than 0.4 μm, while for high-speed gas, those fine particles accumulate near the end wall and are challenging to be extracted. Our findings highlight the significance of controlling flow conditions for effective debris particle transport and clearance in diverse applications especially in EUV source vessels. [ABSTRACT FROM AUTHOR]

This study investigates the effect of vibration on the flow structure transitions in thermal vibrational convection (TVC) systems, which occur when a fluid layer with a temperature gradient is excited by vibration. Direct numerical simulation (DNS) of TVC in a two-dimensional enclosed square box is performed over a range of dimensionless vibration amplitudes $0.001 \le a \le 0.3$ and angular frequencies $10^{2} \le \omega \le 10^{7}$ , with a fixed Prandtl number of 4.38. The flow visualisation shows the transition behaviour of flow structure upon the varying frequency, characterising three distinct regimes, which are the periodic-circulation regime, columnar regime and columnar-broken regime. Different statistical properties are distinguished from the temperature and velocity fluctuations at the boundary layer and mid-height. Upon transition into the columnar regime, columnar thermal coherent structures are formed, in contrast to the periodic oscillating circulation. These columns are contributed by the merging of thermal plumes near the boundary layer, and the resultant thermal updrafts remain at almost fixed lateral position, leading to a decrease in fluctuations. We further find that the critical point of this transition can be described nicely by the vibrational Rayleigh number ${{Ra}}_{vib}$. As the frequency continues to increase, entering the so-called columnar-broken regime, the columnar structures are broken, and eventually the flow state becomes a large-scale circulation (LSC), characterised by a sudden increase in fluctuations. Finally, a phase diagram is constructed to summarise the flow structure transition over a wide range of vibration amplitude and frequency parameters. [ABSTRACT FROM AUTHOR]

The interscale transfer of kinetic energy and Reynolds stress in homogeneous shear turbulence (HST) is numerically investigated using three-dimensional bandpass filtering technique. The flow fields of a statistically steady HST are obtained using direct numerical simulation at three Reynolds numbers 2000, 5000, and 12 500 based on box depth. Visualizations of typical flow structures of bandpass filtered fields show that the small-scale structures are nearly isotropic, whereas the large-scale ones show the preferential alignment with the direction of mean shear. Quantitative results of both kinetic energy and Reynolds stress fluxes between two specific scales show the existence of scale locality. In specific, the eddies of a length scale L mostly transfer their energy or Reynolds stress to eddies of size 0.3L to 0.4L, which seems to be independent in the limit of the high Reynolds number. Furthermore, through the analysis on the vortex stretching, it is shown that the small-scale structures of scale L ω are stretched mostly by straining structures of size about 2 L ω , while large-scale structures are stretched mostly by mean shear. Finally, the evaluation of alignment between vortical structures and strain rate shows that small-scale structures are more likely to align with the strain structures of five times their size, and large-scale ones are mainly align with the mean shear strain. These findings can help enhance our comprehension of the interscale transfer and scale interaction of vortical structures in turbulence. [ABSTRACT FROM AUTHOR]

We experimentally study the heat transfer and flow characteristics of thermal convection in a rectangular cell with built-in lattice channels. The working fluid used is water with a Prandtl number of 5.5, and the Rayleigh number ranges from 2.5 × 10 8 to 6.9 × 10 9 . Three proposed models with different channel sizes and positions and the classical Rayleigh–Bénard convection (RBC) are studied, and the heat transfer and flow structure characteristics are analyzed using measured temperature signals. The first model included two short channels placed near the top and bottom plates, which disrupt the mixing zone and enhance heat transport. The second model involves relatively long channels positioned at the center of the cell, but far from the thermal boundary layer, resulting in a more coherent bulk flow that also enhances heat transport. For these two configurations, the heat transfer enhancement rate is approximately 20% compared to standard RBC. The third model uses long lattice channels that almost touches the top and bottom plates. This configuration results in a maximum heat transfer enhancement of about 138% due to the organized boundary layer and bulk flow induced by lattice channels. The presence of channels also results in a two-order smaller standard deviation of temperature, indicating a significant reduction in fluctuations. However, the average temperatures in the center of some channels were significantly different from the mean system temperature, suggesting the existence of cold or hot fluid flow through the channel. Our experimental results show that the inclusion of channels with appropriate lengths and positions can effectively regulate the flow near the boundary layer and in the bulk, leading to significant enhancements in heat transfer. [ABSTRACT FROM AUTHOR]

Thermal convection in nature and industrial applications usually encounters time-varying internal heating (IH); however, the effect of temporal modulation on temperature responses and heat fluxes of the system has been rarely explored. Here, we numerically studied the IH convection with a temporally periodic heating source. We conducted direct numerical simulations over Rayleigh number (Ra) range 10 5 ≤ R a ≤ 10 9 at fixed Prandtl number Pr = 1 with dimensionless modulation frequency 4 × 10 − 5 ≤ f ≤ 10 − 1 and amplitude fixed at Ω = 1. We first find that the introduction of periodic modulation has a slight effect on the heat transport over the individual plates and flow strength except for the lowest Ra. We then focus on the characteristics of the amplitude A and phase lag Δ ϕ of the globally averaged temperature response to the periodic modulation. Three regimes of the phase response are identified: (i) in-phase regime, where synchronous response is found at small frequencies with the vanished phase lag Δ ϕ and A keeping at constant value; (ii) transition regime, where both Δ ϕ and A decrease with increasing f for moderate frequencies; and (iii) half anti-phase regime, where Δ ϕ attains the minimal value − π / 2. We also find that the transition behavior between three regimes can be well described using the normalization of the Ra-dependent critical frequency with the scaling R a − 0.30 . To explain the regime transition, we further theoretically deduce an analytical solution for A and Δ ϕ , which agrees well with the numerical results. This solution can explain why f R a 0.30 gives a good description of the transition behavior. Our present findings provide a fundamental understanding of the underlying mechanism of temporal modulation on IH systems and have substantial implications for the investigation of convective system with periodic heating source. [ABSTRACT FROM AUTHOR]

The flow past a cylinder near a plane wall for small gap ratios (G / D = 0.1 , 0.3 , and 0.9) and fixed ReD = 1000 is numerically studied. The fundamental flow features are characterized by the instantaneous and mean fields. Then, the dynamics of cylinder-wake/boundary-layer interaction are revealed by the turbulent momentum transport and kinetic energy production. The turbulent fluctuations caused by the secondary vortex (SV) (at G / D = 0.3 , 0.9) and the novel tertiary vortex (TV) (at G / D = 0.9) can be observed in the distributions of Reynolds stresses. For G / D = 0.1 and G / D = 0.3 , the wake/boundary-layer interaction is dominated by ejection and sweep events, which are related to the generation of the hairpin vortex. These two bursting events lead to the momentum transport between the high- and low-speed sides. For G / D = 0.9 , the ejection event is not found in the interaction region because the head of the hairpin vortex is entrained into the wake. The upper roller (RU) helps to transport high-momentum fluid toward the wall in this case, although it does not take part in the interaction directly. The shedding of RU, the lower roller (RL), SV (at G / D = 0.3 and 0.9), and KH (Kelvin–Helmholtz) vortex (at G / D = 0.1) and the generation of the hairpin vortex are crucial to turbulent kinetic energy (TKE) production. The RU, KH vortex, and SV transfer ⟨ u ′ u ′ ⟩ out to ⟨ v ′ v ′ ⟩ and ⟨ w ′ w ′ ⟩ resulting redistribution of the TKE. While RL, surviving for a shorter time, transfers ⟨ v ′ v ′ ⟩ out to ⟨ u ′ u ′ ⟩ and ⟨ w ′ w ′ ⟩ , helping explain why it disappears quickly, TV only transfers out ⟨ v ′ v ′ ⟩ out to ⟨ u ′ u ′ ⟩ , and its TKE comes from other terms rather than the production term. The redistribution of TKE due to the generation of the hairpin vortex can result in the slower growth rate of the secondary disturbance growth stage, promoting the wall boundary layer transition. [ABSTRACT FROM AUTHOR]

In this paper, we report that reversals of the large-scale circulation in two-dimensional Rayleigh–Bénard (RB) convection can be suppressed by imposing sinusoidally distributed heating to the bottom plate. We examine how the frequency of flow reversals depends on the dimensionless wavenumber $k$ of the spatial temperature modulation with various modulation amplitude $A$. For sufficiently large $k$ , the flow reversal frequency is close to that in the standard RB convection under uniform heating. However, when $k$ decreases, the frequency of flow reversal gradually becomes lower and can even be largely reduced. Furthermore, we examine the growth of the corner roll and the global flow structure based on Fourier mode decomposition, and reveal that the size of the corner roll diminishes as the wavenumber decreases. The reason is that the regions occupied by the cold phase can absorb heat from the hot plumes and thus lower their temperature, which reduces the corner roll's kinetic energy input provided by the buoyancy force, and weakens the feeding process of the corner rolls. This results in the locking of the corner roll into a smaller region near the corner, making it harder for a reversal to occur. Using the concept of horizontal convection caused by non-uniform heating, we find a relevant parameter $k/A$ to describe briefly how the reversal frequency depends on wavenumber and modulation amplitude. The present work provides a new way to control the flow reversals in RB convection through modifying temperature boundary conditions. [ABSTRACT FROM AUTHOR]

Vertical convection (VC) under the action of vertical vibration in a square cavity has been investigated using direct numerical simulation. The simulations are conducted with Prandtl number Pr fixed at 4.38 and Rayleigh number Ra ranging from 10 8 to 10 10 . To examine the influence of vertical vibration, the dimensionless vibration frequency is varied in the range of 0 ≤ ω ≤ 1000 and a small dimensionless amplitude is fixed at a = 1.52 × 10 − 3 . First, for low vibration frequency, trivial results are obtained where flow structures and the scalings of Nu and Re resemble that of the standard VC cases. In contrast, when the vibration frequency ω increases beyond a critical value ω * , a strong shearing effect from vibration leads to abundant eruptions of thermal plumes from sidewalls, and thus a laminar-turbulent transition of the bulk flow. As a result, heat-transport is greatly enhanced and the scaling exponent β of N u ∼ R a β substantially increases in such the vibration-dominated regime. In specific, the scaling relations obtained transit from N u ∼ R a 0.25 and R e ∼ R a 0.37 at ω = 0 in the laminar regime to N u ∼ R a 0.42 and R e ∼ R a 0.52 at ω ≳ 300 in the turbulent regime. Analysis of the mean flow field shows that the vibration thins the thermal boundary layer and enhances the thermal dissipation rate in the bulk region. Furthermore, we found that the trend of Nu and Re can be well described by the vibrational Rayleigh number R a vib . In particular, Nu is insensitive to R a vib for R a vib ≤ R a vib * , whereas N u (ω) / N u (0) ∼ (R a vib / R a vib *) 0.42 for R a vib > R a vib * , where the critical vibrational Rayleigh number exhibits a scaling relation R a vib * ∼ R a 0.68 obtained from numerical results. [ABSTRACT FROM AUTHOR]

The heat transfer enhancement achieved by the additional electric field in Rayleigh–Bénard convection (RBC) of a dielectric fluid is numerically studied beyond the Rayleigh number Ra = 105. We carried out direct numerical simulations of RBC in a rectangular enclosure under the strong injection condition with a fixed non-dimensional injection parameter C = 10, a fixed mobility number M = 10, two Rayleigh numbers Ra = 105 and Ra = 106, and two Prandtl numbers Pr = 1 and Pr = 10 to investigate the characteristics of flow structure and heat transfer and evaluate the dependence on these parameters. It is observed that the flow structure exhibits multiple states with various steady or unsteady flow patterns such as four cells, three cells, and two cells (up/down). It is found that the introduction of an electric field is an effective way to achieve heat transfer enhancement. The heat flux is augmented more efficiently for a large Prandtl number and a low Rayleigh number, where the electric field has a strong effect relative to buoyancy. It is also found that heat transfer is most efficient when the flow pattern is in a three cells flow state. [ABSTRACT FROM AUTHOR]

Thermal convection in a tilted three-dimensional rectangular box has been systematically investigated by direct numerical simulation. The Rayleigh number Ra varies from 107 to 109, the Prandtl number Pr is set to 0.7, and the tilted angle β ranges from 0° to 90°. The effects of tilting on large-scale circulation (LSC), Nusselt number (Nu), Reynolds number (Re), and boundary layers (BLs) and the Ra-dependency are investigated. For large β exceeding certain values, say 45°, the stable temperature stratification forms in the bulk, resulting in low Re and Nu. It is found that the tilting leads to a distinct trend for Nu and Re: Nu first increases to some extent for small β, then nearly stays unchanged for moderate β, and finally decreases for large β, while Re initially increases for small β and then directly declines with increasing β. Based on the analysis of flow structures, with increasing β, it is found that the volume of the high-velocity tube (HVT) initially increases for 107 ≤ Ra ≤ 108 but decreases for Ra = 109, which is responsible for the variation in Nu at small β. The probability density functions of instantaneous convective heat transport within the HVT show higher probabilities for large values when β increases, implying that LSC tends to be more coherent and causing different tilting behaviors between Nu and Re. Finally, we find that, except for β = 90°, the normalized profiles of viscous and thermal BLs tend to have universal profiles, deviating from the BL of the Prandtl–Blasius–Pohlhausen (PBP) type to some extent regardless of β. Only the thermal BL for β = 90° is found to be in good agreement with the classic PBP laminar BL profile. [ABSTRACT FROM AUTHOR]

Spontaneous and stochastic reversal of large scale flow structure is an intriguing and crucial phenomenon in turbulent Rayleigh-Bénard type natural convection. This paper proposes a new control approach to eliminate the reversals through stabilising the corner flows using two small sidewall controllers. Based on a series of direct numerical simulations, it is shown that the control can successfully stop the growth of corner vortices and suppress the reversal of large-scale circulation, if the width of sidewall controllers installed within or near the top of corner vortices is large enough. When the controllers are located around the centre, they can easily break up the large-scale structures or even divide the single roll mode into a double-roll mode for very large widths. Moreover, the influence of sidewall controllers on the heat transport is studied. It is shown that the heat transport efficiency can be slightly enhanced or suppressed when the proper location and width are chosen. The present findings provide a new idea to control the large-scale flow structure and reversals in thermally driven convection through sidewall controlling. [ABSTRACT FROM AUTHOR]

We carry out numerical simulations of oscillatory Rayleigh–Bénard convection under lateral periodic conditions over the Rayleigh number range of 10 6 ≤ Ra ≤ 10 8 and the vibration frequency range of 0 ≤ ω ≤ 1000. It is demonstrated that high-frequency vibration achieves a significant enhancement of the intensity of convective flows and the heat-transport efficiency. The phase decomposition method is adopted to distinguish between the vibration-generated oscillatory flows and the fluctuating fields. It is shown that although the contribution of oscillatory flows on heat transport vanishes, the oscillating properties in near-wall regions introduce a strong shear effect to increase the intensity of fluctuating velocities both in the bulk regime and within boundary layers, destabilize thermal boundary layers, and trigger massive eruptions of thermal plumes, which achieves an enhancement of heat transfer. Our results further reveal a universal scaling law between the vibrational Reynolds and Rayleigh numbers, i.e., Re vib ∼ Ra vib 1 / 2 , which can be well described by our proposed analytical model. Moreover, it is shown that vibrational influences are different for the fluctuating velocity and temperature fields. [ABSTRACT FROM AUTHOR]

Oxidative stress is widely involved in pathophysiological processes of cardiac remodeling. Molecules associated with antioxidant functions may be ideal targets for reversing cardiac remodeling. Sestrin2 is the important component of endogenous antioxidant defense, while there is little information on the pathophysiological roles of it in cardiac remodeling. The aim of this study was to investigate whether Sestrin2 is closely involved in cardiac remodeling, and whether the protective effect of pentamethylquercetin (PMQ) on cardiac remodeling is related to upregulation of the Sestrin2 endogenous antioxidant system. We generated a transverse aorta constriction (TAC)-induced pressure-overload cardiac-remodeling model in mice, and also established an isoproterenol (ISO)-induced neonatal rat cardiomyocyte (NRCM) hypertrophy model. The data showed Sestrin2 expression was downregulated significantly, and Nrf2 and HO-1 expression was also reduced in myocardial tissue or NRCM of model group, whereas keap1 expression was upregulated. PMQ significantly ameliorated cardiac remodeling and rectified the abnormal expression of Sestrin2/Nrf2/keap1. Sestrin2 small interfering RNA (SiRNA) reduced the protective effect of PMQ on NRCMs, as well as abolished its regulating effect on the Nrf2/keap1 pathway. In conclusion, Sestrin2 may be an important target in the anti-myocardial remodeling of PMQ. • Sestrin2 is an important endogenous defense factor against cardiac remodeling. • Sestrin2 can regulate Nrf2/keap1 endogenous antioxidant system in cardiac remodeling. • The protective effect of PMQ on cardiac remodeling is Sestrin2 dependent. [ABSTRACT FROM AUTHOR]

Diabetic patients have a signifiantly higher risk of developing all forms of dementia. Pentamethylquercetin (PMQ) has been proven to have potential as an anti-diabetic agent. Nevertheless, whether PMQ can improve diabetes-induced cognitive dysfunction has not been investigated. To address this, we evaluated the effectiveness and underlying mechanisms of PMQ for ameliorating diabetes-related cognitive dysfunction in vivo and in vitro. Our results showed that Goto-Kakizaki (GK) rats displayed impairment in their learning abilities and memory capabilities. Furthermore, GK rats reflected cognitive dysfunction in proportion to the intensity of insulin resistance index. In addition, dendritic spine density and the % cell viability significantly decreased in hippocampus neurons. High glucose conditions induced hippocampal neurons damage, inflicted dendritic spine dysontogenesis, and reduced Akt/cAMP response element-binding protein activation. Treatment with PMQ in GK rats significantly ameliorated cognitive deficits and neuronal damage and increased dendritic spine density, at least in part, by improving insulin resistance and metabolic disorders. Furthermore, PMQ significantly activated the Akt/cAMP response element-binding protein pathway and increased the expression of memory-related proteins in the downstream part of the Akt/cAMP response element-binding protein pathway, such as synaptophysin and glutamate receptor 1. In addition, PMQ inhibited high glucose-induced cellular toxicity. LY294002 appeared to partly inhibit PMQ-mediated protective effects in hippocampal neurons. The results suggest that insulin resistance could predominantly reduce Akt/cAMP response element-binding protein activation in the brain, which is associated with a higher risk of cognitive dysfunction. PMQ could provide a new potential option for the prevention of cognitive dysfunction in diabetes. [ABSTRACT FROM AUTHOR]