Article
Mechanics
Running Hu, Xinliang Li, Changping Yu
Summary: This paper studies the energy and helicity transfers of helical rotating turbulence and discusses their antisymmetry and conservation. Three expressions for helicity transfers are presented and their relationships are discussed. Direct numerical simulations show that helicity can reduce inverse energy cascades, mainly due to transhelical energy fluxes and the interactions of two-dimensional modes.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Running Hu, Xinliang Li, Changping Yu
Summary: The multiscale dynamics of streamwise-rotating channel turbulence is studied using direct numerical simulations. It is found that stronger rotation weakens the turbulence in the buffer layer, while other layers experience enhanced turbulence. Additionally, small- and large-scale inclined structures exhibit different angles with the streamwise direction, with the difference becoming more pronounced at higher rotation rates. The Coriolis force and pressure-velocity correlation are identified as important factors in sustaining the inclined structures.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
X. Q. He, A. D. Bragg, Y. L. Xiong, P. Fischer
Summary: This study used direct numerical simulations to investigate the behavior of a rotating two-dimensional flow that is heated at its equator, where buoyancy and Coriolis forces lead to rich flow behavior. The research found a non-monotonic dependence of flow properties on the Rossby number for a given Rayleigh number, and large-scale mean circulations strongly influenced by rotation.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Sunao Oka, Susumu Goto
Summary: We conduct direct numerical simulations to investigate the effect of spherical solid particles on the attenuation of turbulence in a periodic cube. Our results show that the additional energy dissipation rate in the wake of particles determines the degree of turbulence attenuation. Based on this observation, we propose formulae to describe the condition and degree of turbulence intensity attenuation.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Ke Yu, Tim Colonius, D. I. Pullin, Gregoire Winckelmans
Summary: This study investigates the evolution of an initially spherical region of turbulence in free space using direct numerical simulation and large-eddy simulation. The results show that regardless of different low-wavenumber behaviors, the turbulent sphere exhibits similar timewise growth exponents, with little effect on the inertial scales. Intermittency and ejections of vortex rings are observed at the boundary of the spherical region, occurring at the integral scale of the initial turbulence field.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Takeshi Matsumoto, Michio Otsuki, Takeshi Ooshida, Susumu Goto
Summary: We studied the correlation function and mean linear response function of velocity Fourier mode of statistically steady-state, homogeneous and isotropic turbulence in Eulerian and Lagrangian coordinates through direct numerical simulation. The relation between the two functions was found to be disproportional, contrary to the fluctuation-dissipation theorem. Characteristic times associated with the functions were identified and compared between Eulerian and Lagrangian coordinates, showing different scalings in the inertial range.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Francisco Alcantara-Avila, Sergio Hoyas, Maria Jezabel Perez-Quiles
Summary: A direct numerical simulation of turbulent heat transfer in a channel flow was conducted at a Reynolds number of and a Prandtl number of air, . The study obtained mean values and intensities of temperature, calculated parameters such as the von Karman constant and the Nusselt number, and proposed correlations. It was observed that an asymptotic behavior of the von Karman constant was present as the Reynolds number increased.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
John Panickacheril John, Diego A. Donzis, Katepalli R. Sreenivasan
Summary: A systematic study on dissipative anomaly in compressible turbulence was conducted using direct numerical simulations. It was found that the classical incompressible scaling does not apply to total dissipation in compressible turbulence. The solenoidal dissipation follows the same scaling as incompressible turbulence, while the dilatational part exhibits dissipative anomaly. Based on these findings, new criteria for energy cascade were proposed.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Kartik P. Iyer, Katepalli R. Sreenivasan, P. K. Yeung
Summary: Through direct numerical simulations, it is found that the nonlinear advection term in the Navier-Stokes equations amplifies with increasing Reynolds number, making the vortex stretching mechanism more intermittent. Previous findings of global suppression of nonlinearity are restricted to low Reynolds numbers.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Bernardo P. Brener, Matheus A. Cruz, Roney L. Thompson, Rodrigo P. Anjos
Summary: This study explores the ill conditioning of the Reynolds average Navier-Stokes (RANS) equations when employing an explicit data-driven Reynolds stress tensor closure, showing that ill conditioning occurs across various cases even when the linear term of the Reynolds stress tensor is treated implicitly. The study proposes a new strategy for solving the RANS equations that outperforms previous procedures in mitigating error propagation to the mean velocity field, emphasizing the importance of incorporating information from the DNS mean velocity field.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
M. Wasy Akhtar, Rodolfo Ostilla-Monico
Summary: Direct numerical simulations were conducted to study the effect of modulated forcing on turbulent shear flows in non-rotating and rotating plane Couette flow. The results showed that the shear at the plates was independent of the forcing frequency, and anti-cyclonic rotation significantly changed the system's response to periodic forcing.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Fujihiro Hamba
Summary: This study introduces a new expression for scale-space energy density to explain the non-uniformity of turbulence, evaluating both homogeneous and non-homogeneous parts. The distribution of turbulent energy in non-homogeneous turbulence changes with scales.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Jiahan Wang, Joern Sesterhenn, Wolf-Christian Mueller
Summary: This study compares different structure detection schemes in two-dimensional turbulence and examines their effects on the inverse cascade. The results show that coherent structures contribute less to the cross-scale flux of energy, but play a significant role in deforming the energy spectrum at large scales.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Brendan Keith, Ustim Khristenko, Barbara Wohlmuth
Summary: This paper introduces a class of turbulence models based on fractional partial differential equations with stochastic loads, where solutions are incompressible velocity fields with Gaussian distributions. Interaction between turbulence and solid walls is achieved through various boundary conditions, allowing flexibility in simulating near-wall statistics. Two simple physical applications are emphasized, including the reproduction of fully developed shear-free and uniform shear boundary layer turbulence, with the former validated using experimental data. Additionally, the paper discusses the generation of inhomogeneous synthetic turbulence inlet boundary conditions, inspired by contemporary numerical wind tunnel simulations, as well as calibration of model parameters and efficient numerical methods.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Sergio Pirozzoli, Joshua Romero, Massimiliano Fatica, Roberto Verzicco, Paolo Orlandi
Summary: The study on turbulent flows in a smooth straight pipe of circular cross-section using DNS reveals systematic deviations from the Prandtl friction law with increasing friction Reynolds number, and supports the claim that the asymptotic state of pipe flow at extreme Reynolds numbers should be plug flow. The research also provides evidence for the applicability of the von Karman constant to the mean velocity profile in canonical wall-bounded flows.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Engineering, Mechanical
Muhammad Mohasan, Anas Bin Aqeel, Pengyu Lv, Yantao Yang, Huiling Duan
Summary: This study numerically investigates the impact of a water droplet onto a deep oil pool, focusing on cavity dynamics and the effects of pool liquid viscosity and impacting velocity. Different regimes with and without splashing are identified, and power-law scalings are proposed to describe the dependencies of cavity depth and time on impact velocity and pool liquid viscosity.
ACTA MECHANICA SINICA
(2021)
Article
Mechanics
Shufan Zou, Yantao Yang
Summary: This study proposes the possibility of spatial decoupling of the thermal boundary layer from the viscous boundary layer in turbulent convection through numerical experiments, demonstrating the corresponding scaling laws under ultimate regime conditions and supporting the physical conjecture of ultimate regime for turbulent convection.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Junyi Li, Yantao Yang
Summary: This study demonstrates that horizontal gradients of temperature and salinity can drive thermohaline intrusion. Different types of convection generate differential vertical fluxes from the top boundary, maintaining horizontal temperature and salinity gradients. This intrusion process provides an additional pathway for heat and salinity transfer horizontally.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Yuhang Du, Mengqi Zhang, Yantao Yang
Summary: This study investigates the convection flow driven by a heat-releasing concentration field through linear stability analysis and direct numerical simulations. The research reveals specific patterns in flow structures and concentration distribution under different parameters, with the global flux accurately described by the theoretical model.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Yantao Yang, Roberto Verzicco, Detlef Lohse, C. P. Caulfield
Summary: This study conducts numerical simulations for double-diffusive convection in the diffusive regime, and finds that staircase-like structures can spontaneously develop under certain conditions. Different initial perturbations lead to different layered states, which are significantly influenced by shear. The density flux ratio is found to be related to the square root of the ratio between salt diffusivity and thermal diffusivity.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Chemistry, Physical
Xuwen Qiu, Sheng Mao, Jun Yin, Yantao Yang
Summary: In this study, we investigate the precipitation process in a ternary polymer/solvent/non-solvent system by numerically solving the Cahn-Hilliard equation. The anisotropic mobility of the polymer is introduced and its effects on the porosity morphology of the polymer membrane are investigated. The results show that the anisotropy in polymer mobility leads to changes in the polymer pattern and influences the porosity structure of the membrane.
Article
Mathematics, Applied
M. Mohasan, A. B. Aqeel, Huiling Duan, Pengyu Lyu, Yantao Yang
Summary: This study numerically investigates the impact of droplets on a thin liquid film deposited on a structured surface. The results show that the surface structure has a significant effect on the crown height and radius of the droplets, and can prevent the droplets from breaking into satellite droplets.
APPLIED MATHEMATICS AND MECHANICS-ENGLISH EDITION
(2022)
Article
Physics, Fluids & Plasmas
Junyi Li, Yantao Yang
Summary: This study investigates the influence of background shear on fingering double diffusive convection. Numerical simulations reveal that a weak shear enhances the salinity flux, but this enhancement effect decreases with higher Rayleigh numbers. Stronger shear leads to a shift from salt fingers to salt sheets as dominant structures, with an increase in coherence length scale and decrease in salinity and heat fluxes.
PHYSICAL REVIEW FLUIDS
(2022)
Article
Computer Science, Interdisciplinary Applications
Wenyuan Chen, Shufan Zou, Qingdong Cai, Yantao Yang
Summary: In this study, a new technique is proposed to improve the calculation of the volume force representing the body boundary based on the moving-least-squares immersed boundary method. The error between the desired volume force and the actual force given by the original method is theoretically analyzed for boundaries with simple geometry. A spatially uniform coefficient is introduced to correct the force, and it can be determined by the least-square method over all boundary markers. The new method shows promising results in reducing boundary velocity residual and can be combined with the iterative method for further improvement.
JOURNAL OF COMPUTATIONAL PHYSICS
(2023)
Article
Mechanics
Yuhang Du, Yantao Yang
Summary: This study investigates the thermal convection driven by heat-releasing point particles through numerical simulations, revealing different flow regimes at different Stokes numbers and explaining the relation between different scaling laws. The preferential concentration of particles is also observed.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Yuanwei Bin, Xiang I. A. Yang, Yantao Yang, Rui Ni, Yipeng Shi
Summary: This study conducts direct numerical simulations to investigate the evolution of a pair of counter-rotating vortices in a stratified and turbulent environment. The authors observe a second vortex linking phenomenon and explore the effects of Froude number, background turbulence intensity, and Reynolds number on the vortices. The study also examines the secondary and tertiary vortices induced by the two main vortices, as well as the energy loss to gravitational waves in a strongly stratified environment.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Chenglong Hu, Ke Xu, Yantao Yang
Summary: Convective dissolution plays a significant role in long-term CO2 sequestration in deep saline aquifers, and the presence of an unstable geothermal gradient affects the dissolution process. In this study, direct numerical simulations were conducted in a three-dimensional porous medium under different concentration and thermal Rayleigh numbers. The results show that the flow structures change with increasing thermal Rayleigh number, leading to alterations in the distribution and motions of concentration fingers. A theoretical model is developed to describe the evolution of concentration flux and volume averaged concentration. The dissolved CO2 into the interior exhibits non-monotonic variations as the thermal Rayleigh number increases, with the maximum increment occurring when the density ratio is around unity.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Physics, Multidisciplinary
Leiqi Yuan, Shufan Zou, Yantao Yang, Shiyi Chen
Summary: In this study, a novel strategy is proposed to enhance heat transfer in convection turbulence. By introducing a standing-wave type boundary deformation, flow modulation can be achieved when the amplitude is comparable or larger than the boundary-layer thickness. The heat-flux enhancement primarily occurs in the near-wall regions affected by the boundary deformation at large wave numbers. The findings suggest that oscillating deformations of the boundary can effectively break the boundary layers and open new possibilities for modulating convection turbulence.
PHYSICAL REVIEW LETTERS
(2023)
Article
Mechanics
Yuhang Du, Yantao Yang
Summary: This work investigates convection turbulence driven by heat-releasing point particles that absorb energy from external sources. Both momentum and temperature fields are considered through two-way coupling, with particle dynamics including Stokes drag and gravity force. The main focus is on the gravity effect of particles on convection turbulence. Two regimes are identified at large and small Froude numbers, respectively. Within the large Froude number regime, transport properties show weak dependence on Froude number but strong dependence on Stokes number. In the regime with small Froude numbers, particles accumulate near the bottom plate in the boundary layer region. Scaling laws for the critical Froude number between the two regimes are derived and found to agree well with numerical results.
Article
Engineering, Mechanical
Yuhang Du, Mengqi Zhang, Yantao Yang
Summary: In this paper, the thermal convection flow driven by a heat-releasing concentration field is investigated. The linear stability analysis reveals that the most unstable mode is always the stationary one. Three-dimensional direct numerical simulations are used to study the fully developed flows.
ACTA MECHANICA SINICA
(2022)