Including solar load in CFD analysis of temperature
distribution in a car passenger compartment

Abstract: In this thesis a numerical model has been developed that integrates solar
load when computing the temperature distribution in a passenger
compartment. The actual compartment used belongs to a Volvo S80 for which
geometry, mesh and results from tunnel tests already exists. The thesis is
divided into two sections, model development and model validation. In the
former study focus is set on means to incorporate the solar load in a
proper way and to understand the software used. In the latter study the
numerical procedure derived is applied to the test case, the Volvo S80, and
the results obtained are compared to wind tunnel tests. Three cases were
simulated throughout the thesis: a steady state ‘comfort’, a transient
soaking, and a transient cooling.

It is found that the temperature distribution for the steady state case is
strongly dependent on the solar load while realistic results from the
soaking case were not obtained due to severe divergence problems regarding
continuity. These problems can be attributed to a very coarse mesh and mesh
discrepancies in fluid zones inside doors, floor and roof. The temperatures
at several positions at the back were in many of the ‘comfort’ cases much
higher than experimental data being most likely an effect of solid cells in
the back seat. For the cooling it is even more important to use the model
developed. The validation of the model yielded that the steady-state cases
capture the trends in temperature within the compartment usually within a
few degrees. The validation of the cooling simulations was very successful
except in the front toe position for the driver. It was also shown that the
systems thermal inertia could be increased by increasing the thickness in
the sensitive areas to more realistic total masses. It is finally found
that the thermal inertia greatly affects the cooling of the compartment and
is one of the more important properties to focus on in future work.