Finite-thickness effect of the fluids on bubbles and spikes in Richtmyer–Meshkov instability for arbitrary Atwood numbers

This paper investigates the finite-thickness effect of two superimposed fluids on bubbles and spikes in Richtmyer–Meshkov instability(RMI) for arbitrary Atwood numbers by using the method of the small parameter expansion up to the second order. When the thickness of the two fluids tends to be infinity, our results can reproduce the classical results where RMI happens at the interface separating two semi-infinity-thickness fluids of different densities. It is found that the thickness has a large influence on the amplitude evolution of bubbles and spikes compared with those in classical RMI. Based on the thickness relationship of the two fluids, the thickness effect on bubbles and spikes for four cases is discussed. The thickness encourages(or reduces)the growth of bubbles or spikes, depending on not only Atwood number, but also the relationship of the thickness ratio of the heavy and light fluids, which is explicitly determined in this paper.

A new dynamic subgrid-scale model using artificial neural network for compressible flow

The subgrid-scale(SGS)kinetic energy has been used to predict the SGS stress in compressible flow and it was resolved through the SGS kinetic energy transport equation in past studies.In this paper,a new SGS eddy-viscosity model is proposed using artificial neural network to obtain the SGS kinetic energy precisely,instead of using the SGS kinetic energy equation.Using the infinite series expansion and reserving the first term of the expanded term,we obtain an approximated SGS kinetic energy,which has a high correlation with the real SGS kinetic energy.Then,the coefficient of the modelled SGS kinetic energy is resolved by the artificial neural network and the modelled SGS kinetic energy is more accurate through this method compared to the SGS kinetic energy obtained from the SGS kinetic energy equation.The coefficients of the SGS stress and SGS heat flux terms are determined by the dynamic procedure.The new model is tested in the compressible turbulent channel flow.From the a posterior tests,we know that the new model can precisely predict the mean velocity,the Reynolds stress,the mean temperature and turbulence intensities,etc.

Cyber-physical Integrated Planning of Distribution Networks Considering Spatial-temporal Flexible Resources

The rapid development of cyber technology and the increase of flexible resources have transformed the distribution network into a cyber-physical distribution system,while the accompanying multidimensional uncertainties have brought new planning challenges.In this paper,an innovative approach is proposed to effectively leverage distributed resources while considering the impact of cyber-physical coupling in distribution network planning.A cyber-physical integrated planning model of the distribution network is proposed,considering the effects of spatial-temporal flexible resources and multi-network coupling.Specifically,a three-layer optimization model is established and analyzed by the simulate anneal-particle swarm optimization algorithm.The upper layer achieves the optimization of the location and configuration of energy storage systems and smart terminal units.The middle layer optimizes the data load migration strategy using spatial-temporal flexible resources to solve the voltage exceeding problem caused by high penetration of distributed power access,while the lower layer optimizes the cyber side communication topology,improving the convergence speed and control performance of the distribution network.Then,the optimization model is analyzed iteratively with objective functions including total planning cost,operation excess loss and distributed control performance.Finally,the effectiveness and economy of the proposed planning scheme is verified and compared to traditional methods.

Horizontal and vertical gene transfer drive sediment antibiotic resistome in an urban lagoon system

Rapid urbanization has resulted in pervasive occurrence of antibiotic resistance genes(ARGs)in urban aquatic ecosystems.However,limited information is available concerning the ARG profiles and the forces responsible for their assembly in urban landscape lagoon systems.Here,we employed high-throughput quantitative PCR(HT-q PCR)to characterize the spatial variations of ARGs in surface and core sediments of Yundang Lagoon,China.The results indicated that the average richness and absolute abundance of ARGs were 11 and 53 times higher in the lagoon sediments as compared to pristine reference Tibetan lake sediments,highlighting the role of anthropogenic activities in ARG pollution.Co-occurrence network analysis indicated that various anaerobic prokaryotic genera belonging to Alpha-,Deltaproteobacteria,Bacteroidetes,Euryarchaeota,Firmicutes and Synergistetes were the potential hosts of ARGs.The partial least squares-path modeling(PLS-PM)analysis revealed positive and negative indirect effects of physicochemical factors and heavy metals on the lagoon ARG profiles,via biotic factors,respectively.The horizontal(mediated by mobile genetic elements)and vertical(mediated by prokaryotic communities)gene transfer may directly contribute the most to drive the abundance and composition of ARGs,respectively.Furthermore,the neutral community model demonstrated that the assembly of sediment ARG communities was jointly governed by deterministic and stochastic processes.Overall,this study provides novel insights into the diversity and distribution of ARGs in the benthic habitat of urban lagoon systems and underlying mechanisms for the spread and proliferation of ARGs.

Subgrid-scale model based on the vorticity gradient tensor for rotating turbulent flows

A new subgrid-scale(SGS)stress model is proposed for rotating turbulent flows,and the new model is based on the traceless symmetric part of the square of the velocity gradient tensor and the symmetric part of the vorticity gradient tensor(or the so-called vorticity strain rate tensor).The new subgrid-scale stress model is taken into account the effect of the vortex motions in turbulence,which is reflected on the anti-symmetric part of the velocity gradient tensor.In addition,the eddy viscosity of the new model reproduces the proper scaling as O(y^3)near the wall.Then,the new SGS model is applied in large-eddy simulation of the spanwise rotating turbulent channel flow.Different simulating cases are selected to test the new model.The results demonstrate that the present model can well predict the mean velocity profiles,the turbulence intensities,and the rotating turbulence structures.In addition,it needs no a second filter,and is convenient to be used in the engineering rotational flows.

Direct numerical simulation of hypersonic boundary layer transition over a liftingbody model HyTRV

Direct numerical simulation(DNS)of transition over a hypersonic lifting body model HyTRV developed by China Aerodynamics Research and Development Center is performed.The free-stream parameters are:the free-stream Mach number is 6,the unit Reynolds number is 10000/mm,the free-stream temperature is 79 K,the angle of attack is 0,and the wall temperature is 300 K.Weak random blowing-and-suction perturbations in the leading range are used to trigger the transition.A high order finite-difference code OpenCFD developed by the authors is used for the simulation,and grid convergence test shows that the transition locations are grid-convergence.DNS results show that transition occurs in central area of the lower surface and the concaved region of the upper surface,and the transition regions are also the streamline convergence regions.The transition mechanisms in different regions are investigated by using the spectrum and POD analysis.