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The vortex dynamics of a supersonic flow past an impulsively started circular cylinder are studied numerically. A well-developed high-order finite difference method is adopted to solve the two-dimensional Navier–Stokes equations. In particular, Ma = 1.1 and Re = 2.2 × 104 are selected to report the vortex evolution process. The results confirm that the α-, β-, sub-α-, and sub-β-phenomena observed in incompressible flow in the separated region do exist in the supersonic regime. In addition, the influence of Mach number and Reynolds number on the vortex is also studied, and the vortex changes are compared at Ma = 1.1, 1.7 and Re = 1 × 104, 2 × 104, 2.5 × 104, 3 × 104, 5 × 104, and 1 × 105. [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]

The flow around a rectangular cylinder exhibits intricate features, encompassing phenomena such as separation, reattachment, boundary layer transition, and relaminarization. This study explores the intense transport of turbulent fluctuations in these complex flow phenomena, including momentum and turbulent kinetic energy (TKE) transport, for three aspect ratios (L / D = 5 , 10 and 15) at a medium Reynolds number (R e = 1000). The connection between these transports and crucial vortical structures is elucidated for the first time. On the lateral side of the cylinder, strong momentum transport occurs, dominated by ejection and sweep events associated with the hairpin vortex. The generation of the LE vortex also leads to active TKE production. The existence of the LE separation bubble, as well as the relaminarization of the downstream boundary layer at L / D = 10 and 15, affects the distribution of production terms. This perspective offers an effective yet novel approach that has not been previously addressed in prior researches. The redistribution of TKE results in a disturbance growth, linked to boundary layer transition. The source term reveals that streamwise TKE carried into the recirculating region is closely related to the frequency prior amplified by the LE shear layer. In the wake behind TE, turbulent transports are influenced by vortex shedding patterns. • Turbulent transports are studied, shedding light on the impact of geometry on flow dynamics. • Turbulent transports are analyzed, helping enhance RANS closure models. • The connection between transport phenomena and crucial vortical structures is elucidated. • The transition and relaminarization of the boundary layer impact turbulent transports. [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]

Turbulent Rayleigh-Bénard convection in a square cavity with rough horizontal walls is investigated at a fixed Prandtl number Pr = 0.7 over the Rayleigh number range of 106 ≤ Ra ≤ 109. We have proposed five models with rough elements of the same height but different spatial distributions to evaluate their influences on the heat transport and flow structures of the system. It is found that the flow reversal can be promoted at a Rayleigh number around 107. In all the rough models, the heat transfer is impeded at a low Ra and enhanced at a Rayleigh number beyond a critical value. Interestingly, the heat transfer and flow structure can be clustered by the sparsity of the rough element distribution. Different scaling exponents for heat transfer are identified for sparsely distributed rough models and compactly distributed models. On the other hand, the spatial distribution of rough elements has little effect on the scaling of the Reynolds number. [ABSTRACT FROM AUTHOR]

We report an experimental study of turbulent Rayleigh-Bénard convection in a cylindrical cell of aspect ratio unity, focusing on the effects of the Prandtl number (Pr). Purified water was used as the convecting fluid. Five different Pr between 3.58 and 9.40 were achieved by changing the mean temperature of water, and the measurements were carried out over the Rayleigh number range 2.63 × 108 ≤ Ra ≤ 3.89 × 1010. Over the present parameter range, the measured Nusselt number Nu is found to scale as Nu ∼ Raβ with β = 0.30 and to be independent of Pr. Based on the oscillation period of the measured temperature, the Reynolds number Re scales as Re ∼ Ra0.47Pr−0.72. The local temperature fluctuations at the cell center and near the cell's sidewall were measured, and their relations with Ra and Pr were studied. Our results further reveal that the non-Oberbeck-Boussinesq effects of water have a relatively small influence on the measured scaling relation Nu ∼ Raβ. [ABSTRACT FROM AUTHOR]