Investigation of turbulent large-scale structures in indoor air flow in a wide parameter range using experiments in compressed sulphurhexafluoride

准确预测室内气流和客舱内气流的温度和速度的时空分布，对人体健康和供暖空调能源的经济利用具有重要意义。虽然实验流体力学和数值流体力学在预测室内空气流动方面已经取得了长足的进展，但在几米量级的空间尺度和几小时的时间尺度上准确地预测流场仍然是困难的，甚至是不可能的。造成这一困难的原因是室内空气流动表现为强迫对流和自然对流的混合。这种流动通常被称为混合对流，比纯强迫和纯自然对流更难预测。本项目的目标是克服对与室内空气流动有关的流动中的湍流结构形成机制缺乏了解的问题。根据2007年至2012年DFG联合项目“房间和客舱内湍流混合对流结构的形成”框架内建造和启用的独特实验设施SCALEX，本项目的申请人首次证明，在压力为5巴的压缩六氟化硫的小规模实验中再现室内空气流动是可能的。在这项初步工作的基础上，本项目的具体目标是全面分析各种参数的湍流结构，其范围比以往进行的任何实验室实验都要广泛。该目标应分三步实现，即1-对称制动机构的研究，2-磁滞的研究和3-暂态问题的研究。虽然目前的项目集中在基础研究问题上，但所考虑的几何形状代表了高度简化的飞机客舱模型。因此，该项目的预期结果不仅将有助于基本的流体力学，而且从长远来看，也将在航空工业以及火车和汽车的开发中发挥作用。

The accurate prediction of the spatial and temporal distribution of temperature and velocity in indoor air flows as well as in flows in passenger cabins is of great importance for human health as well as for the economic use of energy for heating and air conditioning. Although there has been considerable progress in both experimental and numerical fluid dynamics in predicting indoor air flows, it is still difficult or even impossible to accurately predict the flow field on spatial scales of the order of several meters and on temporal scales of several hours. The reason for this difficulty is in the fact that indoor air flows represent a blend of forced and natural convection. This type of flow is often referred to as mixed convection and is more difficult to predict than pure forced and pure natural convection. The goal of the present project is to overcome the lack of understanding of the mechanisms of turbulent structure formation in flows relevant to indoor air flows. Based on the unique experimental facility SCALEX which was constructed and commissioned in the framework of the joint DFG-project entitled Formation of structures in turbulent mixed convection in rooms and passenger cabins in the period from 2007 to 2012, the applicant of the present project has demonstrated for the first time that it is possible to reproduce indoor air flows in small scale experiments using compressed sulphurhexafluoride at pressures of 5 bar. Based on this preliminary work the specific goal of the present project consists in a comprehensive analysis of turbulent structures for a range of parameters which is wider than in any previously conducted laboratory experiment. The goal shall be achieved in three steps, namely 1 - investigation of symmetry braking mechanisms, 2 - investigation of hysteresis and 3 - investigation of transient problems. Although the present project is focussed on fundamental research issues, the considered geometry represents a highly simplified model of an aircraft passenger cabin. Therefore the expected results of the project will not only contribute to fundamental fluid dynamics but will - in the long term - also be useful in the aeronautic industry as well as in the development of trains and automobiles.