风机盘管送风角度对室内热环境的影响

本文根据天花板嵌入式风机盘管冬季运行时房间的热环境，建立空气流动的维紊流数学物理模型，利用CFD软件PHOENICS对不同送风角度下，室内的速度场及温度场进行了模拟计算，得到了空气流速及温度的分布，分析研究了不同送风角度对室内气流流动与温度分布的影响以及发生气流短路现象的可能性。结果表明不同送风角度下，人员活动区基本都能达到热舒适要求，但送风角度过大时将会产生气流短路现象。最后将模拟结果与现场测试结果进行了对比．结果表明两者没有太大的偏差，验证了计算模拟的准确性。     

传统四合院民居风环境的数值模拟研究

利用计算机数值模拟仿真,研究了不同合院形式的中国传统四合院民居在建筑设计上适宜冬季风环境的策略。通过分析比较,讨论了院落进深、面宽、楼层高度等建筑细节对四合院民居周围及院内风环境的影响。     

Consistent boundary conditions for flows within the atmospheric boundary layer

In computational wind engineering the neutrally stable atmospheric boundary layer (ABL) is often simulated using the standard k-ε model. The application of boundary conditions that are inconsistent with the profiles used at the inflow boundary causes streamwise gradients in the solution and prevents the simulation of a horizontally homogeneous boundary layer. In the present work these problems are overcome by applying a simple extension of the shear stress boundary condition at the top of the domain and by using one-dimensional models to generate inflow profiles in equilibrium with the ground boundary condition. This procedure allows the impact of the inconsistent boundary conditions to be quantitatively assessed. It is shown that inconsistent boundary conditions at the top of the domain result in erroneous streamwise gradients throughout the domain. These errors are reduced by enlarging the domain in the vertical direction but are not removed. The errors are also found in simulations with idealised and real topography included in the domain. A brief discussion of the impact of the errors on simulations of wind energy projects is given.     

处理溢流污水装置的沉淀池流态模拟及验证

合流制溢流污水处理装置是控制溢流污染的主要措施，而沉淀池的流态是决定其运行效果的关键因素。为此借助大型计算流体力学软件——Fluent，采用标准，k—ε双方程湍流模型，对沉淀单元的流态进行了数值模拟。结果表明，该装置处理合流制溢流污水的效果较好，对SS、COD和TP的去除率分别可达80％、75％和85％；出水SS浓度与出水流速有关，出水流速越大则SS浓度越高；设置斜板和挡板可改善沉淀池的流态，提高其除污效果。     

Study on two operating conditions of a full-scale oxidation ditch for optimization of energy consumption and effluent quality by using CFD model

The operating condition of an oxidation ditch (OD) has significant impact on energy consumption and effluent quality of wastewater treatment plants (WWTPs). An experimentally validated numerical tool, based on computational fluid dynamics (CFD) model, was proposed to optimize the operating condition by considering two important factors: flow field and dissolved oxygen (DO) concentration profiles. The model is capable of predicting flow pattern and oxygen mass transfer characteristics in ODs equipped with surface aerators and submerged impellers. Performance demonstration and comparison of two operating conditions (existing and improved) were carried out in two full-scale Carrousel ODs at the Ping Dingshan WWTP in Henan, China. A moving wall model and a fan model were designed to simulate surface aerators and submerged impellers, respectively. Oxygen mass transfer in the ditch was predicted by using a unit analysis method. In aeration zones, the mass inlets representing the surface aerators were set as one source of DO. In the whole straight channel, the oxygen consumption was modeled by using modified BOD-DO model. The following results were obtained: (1) the CFD model characterized flow pattern and DO concentration profiles in the full-scale OD. The predicted flow field values were within 1.98 ± 4.28% difference from the actual measured values while the predicted DO concentration values were within −4.71 ± 4.15% of the measured ones, (2) a surface aerator should be relocated to around 15 m from the curve bend entrance to reduce energy loss caused by fierce collisions at the wall of the curve bend, and (3) DO concentration gradients in the OD under the improved operating condition were more favorable for occurrence of simultaneous nitrification and denitrification (SND).     

On the validity of the cosine projection in wind-driven rain calculations on buildings

Wind-driven rain (WDR) is one of the most important boundary conditions governing the hygrothermal performance and the durability of building facades. Information concerning the quantity of WDR falling onto building facades is an essential requirement as a boundary condition for Heat–Air–Moisture transfer analyses and for building facade design. The quantity of WDR can be calculated with either semi-empirical methods (such as the WDR relationship) or numerical simulation methods that are based on Computational Fluid Dynamics (CFD). The WDR relationship is most often used. It applies the cosine projection to take into account the effect of varying wind direction on the WDR quantity or intensity. Up to now, the validity of the cosine projection for WDR calculations has not yet been investigated. Its use was suggested in the past and it has been adopted for all semi-empirical WDR calculations since then. Also, in the recently developed numerical simulation methods, it is tempting to apply the cosine projection to reduce the computational expense. In the present paper, the validity of the cosine projection is investigated based on 3D numerical simulations of WDR with CFD. It will be shown that the cosine projection, although generally accepted, is not valid and that it can give rise to significant errors.     

数值模拟在外延阶梯型中庭空调设计中的应用

本文采用CFD软件对外延阶梯型中庭室内热环境进行数值模拟,不仅预测和验证了热环境的舒适性,而且根据模拟结果得出该建筑的空调负荷。为该类中庭的建筑形式设计、室内舒适性和节能设计提供了参考依据。     

Study on transport characteristics of saliva droplets produced by coughing in a calm indoor environment

In this paper, the transport characteristics of saliva droplets produced by coughing are examined in a calm indoor environment. Three subjects are studied, with results indicating that more than 6.7 mg of saliva is expelled at speeds of up to 22 m/s during each individual cough, and that saliva droplets can travel further than 2 m. In addition, the dispersion processes of saliva droplets of different diameters expelled during coughing are analyzed using the Lagrangian equation. The results indicate that the transport characteristics of saliva droplets due to coughing change with size. The effects of gravity or inertia on droplets of 30 μm or less are negligible due to their small sizes, and therefore their transport is mostly influenced by the indoor flow field. Droplets of 50–200 μm, which are significantly affected by gravity, fall as the flow-field weakens. Droplets of 300 μm or more, which are affected more by inertia than gravity, fall difficultly. Moreover, the analytical results also indicate that the droplets’ transport is greatly influenced by the spatial relationship between the air-conditioner and the subjects. Finally, based on the experimental and analytical results, droplet infection by saliva droplets due to coughing is examined.     

大跨悬挑屋盖风压数值模拟及减风措施

运用计算流体动力学(CFD)方法进行了屋盖表面风荷载数值模拟,并与风洞试验结果进行了对比。在此基础上对加设女儿墙后的屋盖进行了CFD建模与计算,结果显示加设女儿墙可有效降低屋盖悬挑部分的最大风压和弯矩,并使屋盖上表面风压均匀化,可改善屋盖结构的受力状态。     

Optimization of indoor climate conditioning with passive and active methods using GA and CFD

This study aims at the development of an optimal design tool using a genetic algorithm (GA) and computational fluid dynamics (CFD). Random variables (fluctuating outdoor conditions), passive design elements (model variables) and active design elements (HVAC system) were set up to represent a realistic building environment. A combination of designs is determined based on the relationship between fluctuating outdoor conditions and the HVAC system in the optimal design search. Building environment designs should consider both active and passive design elements because the HVAC system keeps adjusting the supply air flow rate until the indoor climate reaches target conditions when outdoor conditions are changing.