On the influence of the characteristics of flow on pressure distribution around building models with a view to simulating the minimum height of the atmospheric boundary layer

Results of an investigation of the influence of the characteristics of flow on pressure distribution around building models are reported. The influence of the mean velocity profile, turbulence intensity, percentage boundary layer immersion ratio and the building model's aspect ratio on the pressure distribution was studied with the view of simulating the minimum height of the atmospheric boundary layer in a wind tunnel for building aerodynamics investigations. It is cautiously suggested that atmospheric boundary layer height of at least three times the building height should be simulated in the wind tunnel. Turbulence characteristics exercise primary influence on the flow around models and shear exercises secondary influence on the flow. Finally, it is imperative to simulate the correct turbulence intensity and scale in the simulated turbulent boundary layer. However, further tests should be carried out to study these problems in closer detail.     

大跨度三心柱面网壳风压分布试验研究

通过大气边界层风洞刚性模型同步测压试验,对大跨度三心柱面网壳表面风压分布特性进行了研究。根据试验结果分析了结构不同风向下的平均和脉动风压分布、典型测点脉动风压谱以及相关性等。结果表明:风向角对网壳表面风压分布有较大的影响,一般情况下,结构迎风面为正压区,顶部为负压区,尾流区受分离、涡脱和再附等特征紊流影响明显;结构的边沿处受柱涡、锥形涡影响明显,风压梯度变化剧烈。迎风面大部分区域脉动风压功率谱类似于典型的纵向风湍流谱,呈单峰形状,主要激励为来流湍流;边沿处风压谱受特征湍流影响明显。结构表面相关性随测点间距离的增加而不断减小;风向不同,相关性衰减差别较大。     

A parametric study on the influence of boundary conditions on the longitudinal pressure gradient in CFD simulations of an automotive wind tunnel

Computational fluid dynamics (CFD) is an important and extensively used tool for aerodynamic development in the vehicle industry today. Validation of virtual methods by comparison to wind tunnel experiments is a must because manufacturers aim to substitute physical tests on prototype vehicles with virtual simulations. An appropriate validation can be performed only if the wind tunnel geometry with representative boundary conditions is included in the numerical simulation, and if the flow of the empty wind tunnel is accurately predicted. One of the important flow parameters to predict is the longitudinal pressure distribution in the test section, which is dependent on both the wind tunnel geometry and the settings of the boundary layer control systems. This study investigates the effects of flow angularity at the inlet and different boundary layer control systems, namely, basic scoop suction, distributed suction, and moving belts, on the longitudinal pressure distribution in the full-scale aerodynamic wind tunnel of Volvo Cars using CFD and a systematic design of experiments approach. The study shows that the different suction systems used to reduce boundary layer thickness upstream of the vehicle have statistically significant effects on the longitudinal pressure distribution in the test section. However, the estimated drag difference induced on a typical vehicle by the difference in horizontal buoyancy between the tested settings is within the test-to-test uncertainty of the physical wind tunnel, thereby leading to the conclusion that force calculations in simulations are fairly insensitive to the tested parameters on the investigated intervals.

     

Modal parameter identification in atmospheric turbulence excitation flutter test based on Hilbert-Huang transform

In flutter tests, particularly in wind tunnel experiments, the aircraft model is generally excited by atmospheric turbulence, which increases the difficulty in precisely identifying the modal parameters. To estimate the modal parameters under turbulence excitation for flutter boundary prediction, a technique was developed and evaluated depending on the Hilbert-Huang transform in this paper. The results of simulated flutter cases show that the developed technique can identify modal frequencies more precisely than the modal damping ratio, while the estimation of the modal damping ratio is quite good. Finally, in a wind tunnel flutter test, good flutter boundaries were predicted in advance by using the modal parameters identified from the turbulence response at low airspeeds.

     

典型窄基输电塔风致响应气弹模型风洞试验

首先,采用离散刚度法,设计制作了典型窄基输电塔气动弹性模型;然后,通过大气边界层风洞试验,对窄基输电塔不同高度及风向下的位移、加速度响应特性进行了测试分析;最后,基于风洞试验结果计算了窄基输电塔风振系数并与规范结果进行了比较。结果表明,窄基输电塔位移均值响应主要为顺风向;顺、横风向脉动位移、加速度响应值都较大,随风向变化不明显,呈上下波动趋势;高度变化对脉动位移和加速度的响应影响略有不同。此外,根据中国荷载规范给出的输电塔横担处的风振系数值大于本次试验结果。     

风洞侧壁边界层控制算法优化及仿真分析研究

为提高风洞侧壁边界层控制系统性能,文中通过介绍NF-3大型低速翼型风洞多喷嘴级联吹气侧壁边界层控制系统的结构和原理,分析并优化侧壁边界层控制系统的控制算法,利用MATLAB软件实现了对优化前与优化后的控制算法的仿真,并对仿真结果进行了分析。仿真结果表明：神经网络自适应PSD控制算法可提高控制系统的稳定性、准确性和响应速度,在一定程度上能够减小阀门的时滞性和非线性对控制结果的影响。     

Wind pressure distribution on canopies attached to tall buildings

This paper presents the numerical simulations of wind pressure distributions on canopies attached to tall and medium-rise buildings. The most current wind pressure coefficients in wind load codes do not take into account the large scale canopies attached to tall and medium- rise L-shaped buildings. Wind pressure on canopies attached to buildings depends on the building geometry and its features, the location of canopies, surrounding buildings and terrain, as well as canopy sizes and wind directions. Numerical analysis results were compared and investigated using ANSYS CFX 11 codes. Numerical simulation of wind loading on a canopy attached near the base of a tall or medium-height L-shaped building has shown that the downward pressure on the canopy does not grow in proportion to the increase in the height of building-to-canopy ratio. As a result, the downward pressure acting on a canopy attached to a tall L-shaped building is considerably smaller than that of prismatic models used in other researches and we assume that this is due to the shape of the building itself. The results of numerical simulations of L-shaped models differ considerably from those of previous wind tunnel prismatic shape model tests.     

Short-term observation of wind energy potentiality in the Wol-Ryong wind site

Accurate analysis of the atmospheric wind profiles and climate characteristics in a certain area is a prerequisite for providing reliable information on a wind energy site. Two 2-D ultrasonic anemometers and one cup anemometer, arranged perpendicularly to the prevailing wind direction, were used to measure the atmospheric wind environment at a height of 4.5 m in the coastal region of Wol-Ryong, Jeju, South Korea. This study aims to estimate future wind resources with various estimation methods. The wind energy is theoretically estimated at 75 m, the hub height of 800 kW and 1500-kW-class wind turbines, at the Wol-Ryong site. Methods using three equations, a logarithmic profile, a modified logarithmic profile, and a power law, are applied for accurate prediction of the atmospheric wind profile. In addition, yearly wind power can be calculated by using the probability distribution from Weibull and Rayleigh profiles. It is found that the predicted wind speed is strongly affected by surface atmospheric conditions such as the friction velocity, atmospheric stability, and averaged roughness length. The Rayleigh profile gives more power generation than the Weibull distribution, especially under low-windspeed conditions. The logarithmic profile method seems to be the proper method for estimating the energy production at the Wol-Ryong site for neutral atmospheric conditions. On the other hand, the other two methods — the modified logarithmic profile method and the power law method — seem to be improper for neutral conditions.     

Pollutant dispersion over two-dimensional hilly terrain

Numerical prediction of the wind flow and pollutant dispersion over two-dimensional hilly terrain is presented. The wind tunnel experiments are conducted to validate the numerical results of the flow field. Measured mean velocity profiles, turbulence characteristics, and surface pressure distributions show good agreement with the numerical predictions. The hypothesis of Reynolds number independency for an atmospheric boundary layer flow over aerodynamically rough terrain is numerically confirmed. The linear theory provides generally good prediction of speed-up characteristics for gently sloped low hills. The effect of two-dimensional double hills on the dispersion of pollutants from continuously or temporally released line source of different emission heights and locations is also investigated. The ground-level concentrations are considerably reduced as emission heights are increased. The variances of ground-level concentration with respect to time from a temporally released source are strongly influenced by the flow separation.     

High-speed boundary-layer stability and transition

In this paper, peculiarities of laminar hypersonic (Mach numbers 4–16) boundary layer stability and its transition to a turbulent one are studied experimentally, both in different facilities and numerically. The influence of various factors (Mach number, temperature factor, stagnation temperature, pressure gradient, ratio of specific heats, entropy layer, dissociation, ionization and magnetic field) on the boundary-layer stability and the transition are considered.     

CLC-Ⅱ-D固定式边界层风廓线雷达系统及产品应用

风廓线雷达是一种先进探测垂直风速和温度廓线的设备,它能提供连续的高时空分辨率空中资料,是可推荐应用于业务的一种地基遥感设备。其风廓线雷达具有连续无人值守、可较好反映出边界层的大气湍流活动情况,能实时探测雷达顶空的三维风场信息。具有探测精度高、时空分辨率高特点,在灾害性天气监测和预报、军民用航空气象保障、公共安全应急气象保障等领域都有着广泛的应用前景。文章介绍了风廓线雷达的历史、CLC-Ⅱ-D型固定式边界层风廓线雷达的基本原理以及荆门市固定式边界层风廓线雷达软件产品的显示应用等内容。     

基于连续小波变换的二维边界层分离点判定

边界层分离点位置的检测是实现主动流动控制的基础和关键,采用可挠性的微型热膜传感器阵列对二维边界层分离点进行实时在线测量是一种新方法。针对小波变换在边界层分离流多尺度旋涡处理方面的优势,采用Morlet连续小波变换对传感器阵列信号进行时频域分析,根据边界层分离前后脉动旋涡频率段在时域上的百分比来确定分离点位置。结果显示采用该方法可以有效地判定出边界层分离点振荡区间。     

低速风洞试验中的热图技术

通过热像仪测量平板翼型在低速风洞中附面层转捩点的变化情况,把红外成像技术应用于航空领域。介绍了附面层的产生及特性、层流附面层和紊流附面层的区别和转捩点的概念;用热像仪采集了平板翼型附面层的热图;根据不同迎角和速度下平板翼型表面的温度分布分析转捩点的变化情况。该文对研究附面层表面的阻力、附面层气流的分离和飞机的气动特性具有一定的参考价值和指导意义。     

Heat transfer characteristics of gaseous slip flow in a micro-channel

Two-dimensional compressible momentum and energy equations with slip boundary conditions are solved to obtain the heat transfer characteristics of gaseous slip flow in a micro-channel with CWT (constant wall temperature) whose temperature is lower or higher than the inlet temperature (cooled case or heated case). The numerical methodology is based on the Arbitrary-Lagrangian-Eulerian (ALE) method. The stagnation temperature is fixed at 300 K and the computations were done for the wall temperature which ranges from 250 K to 350 K. The channel height ranges from 2 to 10 μm and the channel aspect ratio is 200. The stagnation pressure is chosen in such a way that the exit Mach number ranges from 0.1 to 0.7. The outlet pressure is fixed at atmospheric condition. The bulk temperature and the total temperature of the heated case are compared with those of the cooled case and also compared with temperatures of the incompressible flow in a conventional sized channel. Heat transfer characteristics of the gaseous flow are different from those of the liquid flow. And they are also different from each cooled and heated case. A correlation for the prediction of the heat transfer rate of the gaseous slip flow in a micro-channel is proposed.     

An experimental analysis of the effect of wind load on the stability of a container crane

This study was conducted to analyze the effects of wind loads on the stability of a 50-ton container crane using wind tunnel testing. The experiments were performed in order to furnish designers with data that can be used in the design of a container crane that is wind resistant, assuming an applied wind load of 75 m/s velocity. Data acquisition conditions for this experiment were established in accordance with similarity to a reduced-scale model. The scale of the container crane model, wind speed and time were selected as 1/200, 1/13.3, and 1/15, respectively, and the experiment was conducted using an Eiffel type atmospheric boundary-layer wind tunnel having a 11.52 m² cross-sectional area. All directional drag and overturning moment coefficients were investigated and uplift forces due to wind load at each supporting point were analyzed.     

Laser velocimetry of a plane mixing layer with a specific initial condition for study of turbulence characteristics of enhanced growth rate

Mixing layers are sensitive to the mixing angle and turbulence in the primary streams. Although there is extensive available research on this rather basic flow, there are still no suggestions for a clearly best configuration. For example, the combination of a laminar initial boundary layer and a large mixing angle has received little attention. In this work we test a new experimental configuration with large mixing angle and laminar/turbulent initial boundary layer that was not examined experimentally by LDA and PIV. This setup is expected to be a representation of the initial conditions that must result in better mixing. A plane mixing layer with a velocity ratio of 0.6 is produced by rebuilding an open circuit wind tunnel. Extensive calibration tests on velocity profiles and Reynolds stresses established the position of the self similar region. Velocity field measurements with laser Doppler anemometer (LDA) and particle image velocimeter (PIV) showed enhanced mixing layer growth. PIV plots showed the presence of stream-wise and cross stream vortices in the self-similar region without any considerable change in turbulence characteristics to that of reported in the literature. The article presents a combination of different experimental results that give a deeper understanding of this very configuration.     

The difference in the uplift force at each support point of a container crane between FSI analysis and a wind tunnel test

We analyzed the difference between FSI (fluid-structure interaction) analysis and a wind tunnel test regarding the uplift force at each support point of a container crane and also design stowing devices — a tie-down rod and a stowage pin — and an alarm system to prevent overturning of a container crane under wind loads. We know that FSI analysis agrees more with wind tunnel tests than with structural analysis, but the results of FSI analysis are different from those of the tests. To evaluate the effect of the wind load on the stability of the crane, two container cranes that are widely used in container terminals-50 ton-class and 61 ton-class container cranes-are adopted for the analytic model and 19 values are considered for the wind direction as the design parameter. First, a wind tunnel test for the reduced-scale container crane model is performed according to the wind direction using an Eiffel-type atmospheric boundary-layer wind tunnel. Next, FSI analysis for a full-scale container crane is conducted using ANSYS and CFX. Then, the uplift force obtained from FSI analysis is compared with that yielded by the wind tunnel test. Finally, a formula is suggested to compensate the difference between FSI analysis and the wind tunnel test.     

On the theory of ventilated wind tunnels

This paper gives a new and more accurate treatment of the theory of rectangular wind tunnels that are ventilated by means of longitudinal slots on one pair of opposite walls. An aerofoil is placed at zero incidence midway between the slotted walls. The cross-flow, which is induced by the slots on the basic two-dimensional flow, is calculated accurately. This permits an averaged boundary condition to be obtained which is more accurate than those previously published.

In the final section of the paper the wake and solid blockage caused by the slotted walls is calculated. Let the slots have a width 2σa and be spaced 2a apart and let the tunnel height be H. Then the theory yields the σ, 2a/H relation for zero blockage without any limit on the ratio 2a/H, which in earlier treatments is required to be small.     

Optimization of a subsonic wind tunnel nozzle with low contraction ratio via ball-spine inverse design method

The goal of wind tunnel design is to generate a uniform air flow with minimum turbulence intensity and low flow angle. The nozzle is the main component of wind tunnels to create a uniform flow with minimal turbulence. Pressure distribution along nozzle walls directly affects the boundary layer thickness, pressure losses and non-uniformity of flow velocity through the test section. Although reduction of flow turbulences and non-uniformity through the test section can be carried out by nozzles with high contraction ratio, it increases the construction cost of the wind tunnel. For decreasing the construction cost of nozzle with constant test section size and mass flow rate, the contraction ratio and length of nozzle should be decreased; that causes the non-uniformity of outlet velocity to increase. In this study, first, three types of nozzle are numerically investigated to compare their performance. Then, Sargison nozzle with contraction ratio of 12.25 and length of 7 m is scaled down to decrease its weight and construction cost. Having scaled and changed to a nozzle with contraction ratio of 9 and length of 5 m, its numerical solution reveals that the non-uniformity of outlet velocity increases by 21%. By using the Ballspine inverse design method, the pressure distribution of the original Sargison nozzle is first scaled and set as the target pressure of the scaled down nozzle and geometry correction is done. Having reached the target nozzle, numerical solution of flow inside the optimized nozzle shows that the non-uniformity just increases by 5% in comparison with the original Sargison nozzle.     

风洞测量中TCP/IP传输边界效应的研究

针对风洞实验中数据传递的失真问题,分析了边界效应问题产生的原因,阐述了利用TCP/IP协议传输引起的边界效应,提出利用UDP协议进行数据传输的思路,避免了边界效应的发生.