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.

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Our study uncovered two thermal plume regimes-individual and collective-and a critical distancing threshold that triggers a transition between them, revealing novel disease spread patterns through the resulting morphological phase transition of airflow.Exhaled droplet and aerosol-mediated transmission of respiratory diseases, including SARS-CoV-2, is exacerbated in poorly ventilated environments where body heat-driven airflow prevails. Employing large-scale simulations, we reveal how the human body heat can potentially spread pathogenic species between occupants in a room. Morphological phase transition in airflow takes place as the distance between human heat sources is varied which shapes novel patterns of disease transmission: For sufficiently large distance, individual buoyant plume creates a natural barrier, forming a "thermal armour" that blocks suspension spread between occupants. However, for small distances,

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Thermal convection usually encounters time-varying internal heating(IH), however, the effect of temporal modulation on the IH system has been rarely explored. Here, we numerically studied the IH convection with a temporally-periodic heating source. We conducted DNSs over Rayleigh number range 105{less than or equal to} Ra{less than or equal to}109 at fixed Prandtl number Pr=1 with modulation frequencies 4x10-5{less than or equal to} f{less than or equal to}10-1 and fixed amplitude Ω=1. We 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 ΔΦ 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 ΔΦ and A keeping at constant value; (ii) transition regime, where both ΔΦ and A decrease with increasing f for moderate frequencies; (iii) anti-phase regime, where ΔΦ 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 Ra-0.30. To explain the regime transition, we further theoretically deduce an analytical solution for A and ΔΦ, which agrees well with the numerical results. This solution can explain why fRa0.30 gives a good description of the transition behavior. Our findings reveal the underlying mechanism of temporal modulation on IH systems and have substantial implications for the investigation of convective systems with periodic heating.