典型城郊河流型湿地公园规划与设计:以广西荔浦荔江国家湿地公园为例

以广西荔浦荔江国家湿地公园为例,探索河流型湿地公园生态保护修复、科普宣教与科研监测等功能的实践模式。通过实地调研分析,对荔江国家湿地公园进行规划布局,规划分为湿地保育区、恢复重建区和合理利用区,形成“一廊连带、心聚多点”的总体空间结构,并从湿地恢复、地域特色、道路体系等多角度进行规划设计,结合场地风貌,打造具有湿地生态保护、科普宣教、科研监测、休闲健身等功能的城郊河流型湿地公园,为河流型湿地公园的规划设计提供借鉴意义。

The Effect of Mach Number on Turbulence Behaviors in Compressible Boundary Layers

The effects of Mach number on turbulence behaviors are investigated by means of direct numerical simulation of compressible turbulent boundary layers with the free-stream Mach numbers 2,4 and 6.Some typical turbulent quantities,including the velocity and vorticity fluctuations,intermittency,sweep and ejection events and turbulent kinetic energy budget,are analyzed.The turbulence intensities are significantly decreased with the increasing Mach number.The onset of intrinsic intermittency occurs nearer the wall for a higher Mach number.The ejection event is more frequent and the sweep event becomes less frequent.Moreover,the magnitudes of turbulent kinetic energy production,diffusion and transport terms are increased and the solenoidal dissipation is slightly decreased as the Mach number is increased.

Large-Eddy Simulation of Underexpanded Supersonic Swirling Jets

A large-eddy simulation of underexpanded supersonic swirling jets issuing into a quiescent environment was carried out for two typical swirl numbers.The corresponding nonswirling jet was also calculated for comparison and validation against the experimental data.The swirling effect on the various fundamental mechanisms that dictate the intricate flow phenomena,including flow features,shock cell structures.jet spreading characteristics and turbulence behaviors,was carefully analyzed,and it is found that the first shock cell length is reduced in the swirling jet in comparison with the nonswirling jet.A recirculation zone is formed in the high swirl number case,and the jet spreads quickly in the radial direction due to the swirling effect.Moreover,intensive turbulent fluctuations are generated along the jet shear layer and at the end of the jet potential core,which will be helpful in the mixing process.The obtained results provide a physical insight into understanding the mechanisms relevant to underexpanded supersonic swirling jets.

Statistical Analysis of Coherent Vortical Structures in a Supersonic Turbulent Boundary Layer

Characteristics of coherent vortical structures in a compressible turbulent boundary layer are statistically analyzed by means or airect numerical simulation of the compressible Navier-Stokes equations for Mach number M=2and Reynolds number Reθ≈1000 based on the inlet momentum thickness.It is found that a large variety of hairpin-like and cane-like vortical structures exist in the boundary layer and the most popular structure is the cane-like one.The injection and sweep events contribute a major proportion of the total Reynolds stress.This study indicates structural similarities with the incompressible case.Moreover,the length scales of coherent structures in the streamwise and spanwise directions increase with the distance from the wall.The inclination angle of vortical structures with respect to the streamwise direction increases from the suboayer to the buffer layer and then decreases from the buffer layer to the wake region.

FINITE ELEMENT ANALYSIS OF LAMINAR FLOW AND HEAT TRANSFER IN A BUNDLE OF CYLINDERS

Two-dimensional Navier-Stokes equations and energy equation governing incompressible laminar flow past a bundle of cylinders were numerically solved by using the finite element method. The velocity correction method was used for time advancement, and spatial discretization was carried out with the Galerkin weighted residual method. Viscous flows past the cylinder banks arranged in in-line cylinder bundles and staggered cylinder bundles, coupled with heat transfer, were investigated for pitch-diameter ratios of 1.5 and 2.0 and the Reynolds numbers from 50 to 500. Flow structures and heat transfer behavior were discussed. The results obtained agree well with available numerical data.

NUMERICAL STUDY ON THE VORTEX STRUCTURES IN THE WAKE OF AN OSCILLATING CIRCULAR CYLINDER IN A UNIFORM FLOW

Vortex shedding from a circular cylinder subjected to fortal oscillations at arbitrary angles(as shown in Fis. 1 for 0°<β<90°) with respect to the free stream is numerically investigated using the Navier-Stokes equations. The emphasis of this study is put on revealing the complicated vortex structures and their evolution in the near wake. In the present study, a number of possible vortex modes are also numerically simulated, and a variety of physical phenomena are duplicated and even renewed numerically. A parameter map indicating the classification of preferred vortex modes is firstly given in the frequency-amplitude plane.

DIRECT NUMERICAL SIMULATIONS OF TURBULENT CHANNEL FLOWS WITH CONSIDERATION OF THE BUOYANCY EFFECT OF THE BUBBLE PHASE

Turbulent channel flows with consideration of the buoyancy effect of the bubble phase is investigated by means of the Direct Numerical Simulation （DNS）. This two-phase system is solved by a two-way coupling Lagrangian-Eulerian approach. The Reynolds number based on the friction velocity and the half-width of the channel is 194, and the gravitational acceleration varies from -0.5 to 0.5, ranging from the upflow to the downflow cases. This study aims to reveal the influence of buoyancy on the turbulence behavior and the bubble motion. Some typical statistical quantities, including the averaged velocities and velocity fluctuations for the fluid and bubble phases, as well as the flow structures of the turbulence fluctuations, are analyzed.