10.1002/bapi.200810049.abs

Die vorliegende Arbeit leistet einen Beitrag zur gekoppelten aero‐hygrothermischen Bauteilsimulation für Strukturen mit Hohlräumen. Den Schwerpunkt bildet dabei die Entwicklung eines CaFD‐Modells (Cavity Fluid Dynamics) und Computercodes, welche auf der Lösung der Navier‐Stokes‐Gleichungen für laminare Strömungen inkompressibler reibungsbehafteter Fluide basieren. Mit der Definition einer Softwareschnittstelle gelingt es, den zunächst eigenständig ausführbaren Strömungslöser CaFD‐Tool in Form einer dynamischen Bibliothek in den Quellcode der am Institut für Bauklimatik der Technischen Universität Dresden entwickelten Software DELPHIN 4 einzubinden. Mit der Formulierung eines vereinfachten Mehr‐Zonen‐Modells ist es möglich, die bei einem durchströmten Hohlraum oder Spalt auftretende Überlagerung von natürlicher und erzwungener Konvektion zu simulieren. Außerdem können die Feuchtefelder, verursacht durch Kondensationserscheinungen der eindringenden feucht‐warmen Raumluft im Hohlraum und im angrenzenden Baustoff quantifiziert werden. Neben der exakten energetischen Beurteilung der Bauteile lassen sich Möglichkeiten zur Vermeidung von Feuchteschäden aufzeigen.

Aero‐hygro‐thermal behaviour of building enslosure components with opened and enclosed air cavities.

Air cavities with different functions can be found in historical as well as in modern structural design. In the past, air cavities mainly have been made for practical reasons to improve the thermal insulation properties of wall and roof constructions. In modern architecture, hollow spaces frequently arise due to constructional or due to aesthetic reasons such as in glass curtain walls or in cladding of inside walls.

On environmental grounds the obligations towards the energy efficient construction and operating of buildings are tightened increasingly. This leads, under compliance with today's room climatic requirements, to the focusing of activities on appropriate use of building materials and the expenses and energy optimized design of building envelopes. On the rehabilitation of historical structures often questions regarding the hygro‐thermal evaluation of such air cavities and the therein occurring convection processes arise. So, a long term cross flow in open cavities with moisture‐loaded air can cause damages on the service ability and bearing capacity of components.

The consideration of cross flows in enclosed cavities of single components or in open constructions, such as wall or roof constructions, can be calculated at present only by use of special assumptions. For the solution of this complex problem the coupling of a CFD‐solver with a hygro‐thermal building simulation software has been carried out. Within the scope of a research project a CaFD (cavity fluid dynamics) simulation code has been developed which especially is adjusted to the requirements and boundary conditions of hygro‐thermal component simulations. Therefore, the functional range concentrates on building physical problems definitions of structural designs. With the implementation of the CaFD‐tool as an additional application for the software package DELPHIN 4.x, an independent operational CFD software module has been developed. By means of the SIMPLE‐Algorithm it solves the Navier‐Stokes‐Equations additionally under consideration of the heat and mass transport in the cavity. A data interface controls the interactive data interchange between DELPHIN and the CaFD‐tool.

The presentation of simulations of the aero‐hygro‐thermal behaviour of components with opened and enclosed air cavities completes the contribution. With selected test cases the coupled simulation is analysed and discussed more closely from the building physical point of view.