Abstract
M.Ing.
The characterisation of the flow field and thermal performance of supply air
windows (airflow windows operating in supply mode) have been a topic of interest for at least two
decades. Computational Fluid Dynamics (CFD) as well as other simulation methods have been used to
model and characterise the flow field, temperature distributions and thermal performance of the
supply air window in recent years. Where experimental validation of the velocity (only outlet
velocity) and temperature predictions has been provided the error between experiment and CFD (and
other forms of simulation) is in the order of 50 % and 3 ◦C (10-13 %), respectively. Furthermore, a
large part of the literature does not have experimental validation of the simulation results.
The significant error in many of the studies, that provide experimental val- idation of the
velocity field, is attributed to inappropriate turbulence mod- els, unrealistic boundary
conditions, neglecting significant three-dimensional effects, solar radiation effects not entirely
accounted for, mesh sensitivity studies neglected and material properties of glass and air assumed
constant.
The aim of this research was to characterise a supply air window in terms of its velocity field,
temperature distributions and thermal performance. This was done by mathematically modelling the
fluid dynamics and heat trans- fer processes in a supply air window and solving the model in a
commer- cial CFD code, namely ANSYS Fluent 12.1. Furthermore, an experimental rig was designed,
constructed and used to measure the flow field and tem- peratures with the aim of validating the
CFD models. The CFD models incorporated appropriate turbulence models, realistic boundary
conditions, three-dimensional effects, solar radiation, temperature dependent material properties
and a mesh sensitivity study. The CFD models and experiments were setup for forced and natural flow
conditions.
Laser Doppler Velocimetry has not been used for velocity field measure-
ments in an airflow window to date. The experimental setup made use of Laser Doppler Velocimetry to
measure the velocity field and turbulence in- tensities. The Laser Doppler Velocimeter (LDV) probe
was positioned using a three axis computer controlled traversing mechanism. Furthermore, flow
visualisation experiments were done to qualitatively capture the flow field.
The results from the CFD are partially in good agreement with the exper- imental work.
Qualitatively the flow field as predicted by CFD is in good agreement with the results from the
flow visualisation experiments. Quan- titatively the results from the CFD are in good agreement
with the tem- perature measurements, however, there is noticeable error between the LDV readings
and the velocities as well as turbulence intensity values predicted by CFD. The error, with
regards to velocity and turbulence intensity, may be attributed to the experimental error caused by
problems with flow seeding as well as the isotropic turbulence assumption inherent in the
turbulence model
(SST k − ω) used.