一种基于TCP/IP网络通信的边界层风洞位移测试系统

边界层风洞是指可以模拟近地大气边界层风特性的风洞,其试验结果作为建筑设计的原始输入依据,其准确程度对最后的设计有着非常重要的影响.在现有的边界层风洞试验中,涉及到模型姿态和位移测量的项目越来越多,风洞试验中的位移测量技术为各国风洞普遍采用.以湖南大学HD-2风洞位移测试系统为例,介绍了一种基于TCP/IP网络通信的位移测试系统.     

Numerical computation of wind pressures on buildings

This paper discusses the computer simulation of wind pressures on buildings. The control volume technique is used to discretize the three-dimensional differential equations of the flow and the standard k-ε turbulence model is incorporated in the numerical modelling for closure. A modular-structure, computational tool named TWIST (Turbulent WInd Simulation Technique), has been developed and implemented in various computer systems including, for the first time, microcomputers. Computed mean values of wind-induced pressures on buildings agree well with experimental data obtained from boundary layer wind tunnels. The influence of various computational parameters such as the number of grid nodes on the time of computation and the computed results is also discussed.     

纵向脊状表面湍流猝发频率检测

在小型低速风洞中开展了一系列纵向脊状表面与光滑平板表面湍流边界层猝发频率检测研究,并获得了典型纵向脊状表面湍流猝发频率特性.试验在一小型低速风洞中开展,流场测试中使用恒温式IFA300智能型流动分析仪,测试模型采用有机玻璃材质的矩形平板结构;而在湍流边界层猝发频率检测中,则采用了一套基于Mu-level法的湍流猝发频率...     

LES of synthetic jets in boundary layer with laminar separation caused by adverse pressure gradient

In the development of synthetic jet actuators (SJAs) for active flow control, numerical simulation has played an important role. In controlling the boundary layer flow separation, an integrated numerical model which includes both the baseline flow and the SJA is still in its initial stage of development. This paper reports preliminary results of simulating the interaction between a synthetic jet and a laminar separation bubble caused by adverse pressure gradient in a boundary layer. The computational domain was three-dimensional and Large-eddy simulation (LES) was adopted. The initial and boundary conditions were defined using or referring to our wind tunnel experimental results. Prior to numerically simulating the interaction between the synthetic jets and the baseline flow, a numerical model for simulating the separation bubble was developed and verified. In the numerical model including the SJA, the synthetic jet velocity at the exit of the SJA was defined as an input. The numerical model was further verified by comparing the simulation with experimental results. Based on reasonable agreement between the numerical and experimental results, simulations were carried out to investigate the dependency of flow control using synthetic jets on the forcing frequency, focused on the lower frequency range of the Tollmien-Schlichting (T-S) instability, and on the forcing amplitude which was represented by the maximum jet velocity at the exit of the SJA. Supporting the hypothesis based on the experiment, LES results showed that the forcing frequency had stronger influence on SJA’s effective elimination of the separation bubble than the forcing amplitude did.     

The investigation of a compressible laminar boundary layer past an elliptical cone

The self-similar boundary layer on a sharp circular cone was calculated first by Vvedenskaya[1]. The boundary layer equations were solved in a plane containing an outflow line which lies in this case in the symmetry plane at the leeward side, and after that a solution was constructed by using a marching method along a circumferential coordinate. The calculation results for the boundary layer on an elliptic cone were presented in Bashkin's papers [2–4]. However, only the middle angles of attack (30–50°) were considered. where the outflow line of an external stream is located in the windward symmetry plane, and the flow pattern in the boundary layer is analogous to that of the circular cone. In the present the laminar boundary layer on an elliptic cone is studied for a wide range of angles of attack. The boundary layer has been calculated at small incidence when the outflow of an external flow were located out of the symmetry plane. In this case the equations are solved first in the plane containing the outflow line and then the solutions were constructed by a marching method along a circumferentialcoordinate to the windward and leeward symmetry planes. The distribution of the skin-friction coefficients and the Stanton's numbers on a cone surface was given. The similarity solution of a set of boundary layer equations was obtained for thin cones at large incidence when the stream on the windward side of the cone was directed to the cone nose. The calculations of the laminar boundary layer at hypersonic velocities were carried out to include the real equilibrium properties of the air.     

微致动器在流动控制中的应用研究

基于MEMS技术,研制了一种微气泡型致动器.对前缘布置有微致动器的三角翼进行了数值模拟和风洞实验,结果表明:微致动器可以改变三角翼前缘的旋涡流状态,扰动边界层,改变三角翼前缘分离涡位置,合理布置微致动器可以获得一定的滚转力矩,利用微致动器可以进行流动控制,进而改变飞行器的动力性能.     

A finite difference model for air pollution simulation

A 3-D model for atmospheric pollutant transport is proposed considering a set of coupled convection–diffusion–reaction equations. The convective phenomenon is mainly produced by a wind field obtained from a 3-D mass consistent model. In particular, the modelling of oxidation and hydrolysis of sulphur and nitrogen oxides released to the surface layer is carried out by using a linear module of chemical reactions. The dry deposition process, represented by the so-called deposition velocity, is introduced as a boundary condition. Moreover, the wet deposition is included in the source term of the governing equations using the washout coefficient. Before obtaining a numerical solution, the problem is transformed using a terrain conformal coordinate system. This allows to work with a simpler domain in order to build a mesh that provides finite difference schemes with high spatial accuracy. The convection–diffusion–reaction equations are solved with a high order accurate time-stepping discretization scheme which is constructed following the technique of Lax and Wendroff. Finally, the model is tested with a numerical experiment in La Palma Island (Canary Islands).     

Development of a MEMS-based control system for compressible flow separation

A MEMS-based sensor and actuator system has been designed and fabricated for separation control in the compressible flow regime. The MEMS sensors in the system are surface-micromachined shear stress sensors and the actuators are bulk-micromachined balloon vortex generators (VGs). A three-dimensional (3-D) wing model embedded with the shear stress sensors and balloon VGs was tested in a transonic wind tunnel to evaluate the performance of the control system in a range of Mach number between 0.2 and 0.6. At each Mach number tested, the shear stress sensors quantify the boundary layer on the surface of the wing model while the balloon VGs interact with the boundary layer in an attempt to provide flow control. The shear stress measurements indicate the presence of a separated flow on the trailing ramp section of the wing model at all Mach numbers tested when the balloon VGs are not activated. This result is confirmed by total pressure measurements downstream from the wing model where a wake profile is observed. When the balloon VGs are activated, the shear stress level on the trailing ramp increases with the Mach number. At the highest Mach number tested, this increase elevates the shear stress on the ramp to almost the same level as the unseparated flow, suggesting the possibility of a boundary layer reattachment. This result is supported by the downstream pressure measurements which show a large pressure recovery when the balloon VGs are activated. The wind tunnel experiment successfully demonstrated two aspects of the MEMS flow control system: the effectiveness of the microshear stress sensors in measuring the separation characteristics of a high-speed compressible flow and the ability of the microballoons in positively enhancing the aerodynamic performance of a high-speed wing through boundary layer modification.     

Numerical modeling of land and sea breeze circulation along a complex coastline

The wind distribution in the atmospheric boundary layer is affected by air motions on all scales. In low-latitude coastal areas, however, the wind flows generally are dominated by the diurnally varying land and sea breezes. These flow patterns have been known to exert great influence on local environments by spreading wind-driven brish fires, for example, or dispersing natural or man-made air pollutants. The purpose of this paper is to present a mathematical model that can simulate land and sea breezes in coastal areas.The model equations, based on the primitive equations for the planetary boundary layer with the hydrostatic approximation, are solved numerically with appropriate initial and boundary conditions obtained from interpolation of observational data. Turbulent diffusion of momentum and heat is parameterized through the use of similarity theory for the surface layer supplemented by empirical relationships. This model has been applied to the Tampa Bay area along the Gulf of Mexico. The computed wind field not only simulates the strong land-bound sea breeze at the surface during the day and a weak return flow during the night, but it also retrieves the essential features of land/sea breeze along a complex coastline.     

High-resolution satellite measurements of coastal wind field and sea state

Methods to derive wind speed and sea state by simple empirical models from synthetic aperture radar (SAR) data are presented and applied for use in high-resolution numerical modelling for coastal applications. The new radar satellite, TerraSAR-X (TS-X), images the surface of the sea with a high resolution up to 1 m. Therefore, not only wind information and integrated sea state parameters but also individual ocean waves with wavelengths down to 30 m are detectable. Two-dimensional information on the ocean surface retrieved using TS-X data is validated for different oceanographic applications: derivation of finely resolved wind fields (XMOD algorithm) and integrated sea state parameters (XWAVE algorithm). Both algorithms are capable of taking into account fine-scale effects in coastal areas. Wind and sea state information retrieved from SAR data are applied as the input for a wave numerical spectral model (wind forcing and boundary condition) running at a fine spatial horizontal resolution of 100 m. Results are compared to collocated buoy measurements. Studies are carried out for varying wind speeds and comparisons against wave height, simulated using original TS-X-derived wind data, showing the sensitivity of waves to local wind variation and thus the importance of local wind effects on wave behaviour in coastal areas. Examples for the German Bight (North Sea) are shown. The TS-X satellite scenes render well-developed ocean wave patterns of developed swell at the sea surface. Refraction of individual long swell waves at a water depth shallower than about 70 m, caused by the influence of underwater topography in coastal areas, is imaged on the radar scenes. A technique is developed for tracking wave rays depending on changes in swell wavelength and direction. We estimate the wave energy flux along wave tracks from deep water to the coastline based on SAR information: wave height and wavelength are derived from TS-X data.