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

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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.