Yuehong Qian’s research while affiliated with Zhejiang Normal University and other places

This study investigates the propagation of sound waves within deep-sea low-sound-speed channels using the lattice Boltzmann method, with a key focus on the influence of depth-dependent sound speed on wave propagation. The depth-variable sound speed condition is realized through the incorporation of an external force proportional to the density gradient. After the model verification, investigations into the two-dimensional spreading of sound sources reveal that the depth-dependent sound speed curves the wave propagation. When source depths differing from the low-sound-speed channel, wave paths deviate due to contrasting speeds above and below. When the sound source is situated within the low-sound-speed channel, waves exhibit converging patterns. The simulations also detail the total reflection behavior of sound waves. When the incident angle falls exceeds the critical angle, the waves remain intact within the low-sound-speed channel, thereby enabling the preservation of high amplitude acoustic signals even at remote locations. The subsequent simulations of sound wave propagation around obstacles demonstrate that the low-sound-speed channel also exhibits better signal transmission capabilities in the presence of obstacles. In a uniform sound speed environment, acoustic wave propagation around a submarine exhibits a symmetric pattern. By contrast, under depth-evolving speed conditions, submarines operating at various depths manifest distinct propagation characteristics, such as asymmetric wave propagation during shallow diving, as well as wave attenuation or even silencing when cruising within low-sound-speed channels. These findings underscore the profound implications of depth-evolving sound speed on underwater acoustic signal detection and transmission.

The effect of gap width and partition thickness on the flow mechanism and heat transfer of partitioned thermal convection is investigated using a thermal lattice Boltzmann method from Ra ¼ 8 � 10 6 to Ra ¼ 1 � 10 8. Partitioning effects on the heat transfer and the physical mechanism of flow are analyzed using the velocity field and temperature field of the convection. Numerical simulation results show that the optimal gap width decreases and that the optimal partition thickness increases with increasing Rayleigh number (Ra). Gap width and partition thickness have a joint effect on the heat transfer. We have counted the comprehensive influence of dimensionless gap width (D �) and dimensionless partition thickness (S �) on diaphragm heat on Nu under Ra ¼ 10 8. The results show that the global maximum of Nu appears in the regions of 0.004<D � <0.006 and 0.02<S � <0.035. Two important factors affecting the partitioned thermal convection have been found. In addition, an interesting relationship between the average Nusselt number and the presence of leakage vortices is also discussed in this study. ARTICLE HISTORY

In this paper, the wake characteristics of Zell 2000 wind turbine under different tip velocity ratios are studied by using the lattice Boltzmann method and large eddy simulation. The adaptive mesh refinement method is performed to capture the fine flow structure and wake characteristics development. In this paper, we mainly focus on the effect of the tip speed ratio on the flow structure and unsteady characteristics of wind turbine wake. The three‐dimensional flow vorticity structures, the section vorticity diagram, the pressure fluctuation of wake and the lift coefficient of wind turbine wake are utilized to explore the effect of the tip speed ratio on the unsteady physics mechanism of wind turbine wake. With the increase of the tip speed ratio, the distance between two adjacent vortex rings along the axial direction gradually decreases, as the position of the broken vortex circles gradually approaches the center of the blade, separated vortexes are rapidly generated, and the coherent structure appears closer to the wind turbine. A relationship is established between the tip speed ratios and the positions of the broken vortex circles. It is further found that the dominant frequency amplitude gradually increases with the increase of tip speed ratio and the pressure amplitude spectra of vortex increases with the decrease of the distance between the wake and the center of the blade axis. The above series of studies can provide significant physical insight into deep understanding the influence of the tip speed ratio on the wake characteristics of wind turbines.

In this paper, the spatiotemporal evolution of wind turbine (WT) wake characteristics is studied based on lattice Boltzmann method-large eddy simulations (LBM-LES) and grid adaptive encryption at different incoming flow velocities. It is clearly captured that secondary flow occurs in the vortex ring under shear force in the incoming flow direction, the S-wave and the Kelvin–Helmholtz instability occur in the major vortex ring mainly due to the unstable vortex ring interface with small disturbance of shear velocity along the direction of flow velocity. The S-wave and Kelvin–Helmholtz instability are increasingly enhanced in the main vortex ring, and three-dimensional disturbances are inevitable along the mainstream direction when it evolves along the flow direction. With increasing incoming flow, the S-wave and Kelvin–Helmholtz instability are gradually enhanced due to the increasing shear force in the flow direction. This is related to the nonlinear growth mechanism of the disturbance. The analysis of the velocity signal, as well as the pressure signal with a fast Fourier transform, indicates that the interaction between the vortices effectively accelerates the turbulence generation. In the near-field region of the wake, the dissipation mainly occurs at the vortex at the blade tip, and the velocity distribution appears asymmetric around the turbine centerline under shear and the mixing of fluids with different velocities in the wake zone also leads to asymmetric distributions.

Two-dimensional direct numerical simulations of partitioned thermal convection are performed using the thermal lattice Boltzmann method for the Rayleigh number (Ra) of 109 and the Prandtl number (Pr) of 7.02 (water). The influence of the partition walls on the thermal boundary layer is mainly focused on. Moreover, to better describe the spatially nonuniform thermal boundary layer, the definition of the thermal boundary layer is extended. The numerical simulation results show that the gap length significantly affects the thermal boundary layer and Nusselt number (Nu). The gap length and partition wall thickness have a coupled effect on the thermal boundary layer and the heat flux. Based on the shape of the thermal boundary layer distribution, two different heat transfer models are identified at different gap lengths. This study provides a basis for improving the understanding of the effect of partitions on the thermal boundary layer in thermal convection.

Turbulent Rayleigh–Bénard convection with a mixed isothermal–adiabatic bottom boundary is simulated to investigate the effect of a nonideal thermal boundary on vortex structure and small-scale characteristics in turbulent convection. Simulations of convection with element aspect ratios of the mixed isothermal–adiabatic boundary cell ranging from [Formula: see text] to [Formula: see text] are performed at fixed Rayleigh and Prandtl numbers. Within the parameters adopted in this paper, the large-scale circulation under the mixed boundary condition is found to be consistent with that under the classical isothermal condition. However, the shape characteristics and distribution of plumes are strongly affected by the presence of a mixed isothermal–adiabatic boundary. Compared with the isothermal system, the mixed boundary breaks up the corner vortex structures and reduces the vortex intensity at the corners. Some complex vortex structures, such as a horseshoe vortex, appear in the case of a mixed isothermal–adiabatic thermal boundary. The vortices in side and face regions are governed by an enhancement rule that is related to the ratio of the element width to the typical plume size. The structure functions of scales above the element scale are greatly affected by the presence of a mixed boundary. The temperature structure function exhibits discrete characteristics, especially in the near-bottom region. However, the velocity structure function of the velocity retains continuous characteristics in all regions. The small-scale characteristics observed here help provide better understanding of the effect of a discrete boundary on buoyancy-driven turbulent convection.