Numerical analysis of free surface flows in the context of the water management of production cars

Christian Kussmann, Daniele Suzzi
Qpunkt

Water management and automotive engineering do not seem to have anything in common at first glance. Nevertheless, looking into detail water management plays an important role during the series development of passenger cars. There are indeed several different topics, which are related to the interaction between water and vehicle:

• HVAC systems and water separation
  
• Process air inlet for the combustion engine
  
• Tightness problems
  
• Soling problems (dirt transported by water)

qpunkt kept researching the last three years trying to cover the first two topics of the list above. The decision to research on this field was the logical consequence of our focus on development and integration of HVAC system into vehicles. Basically, one component is dedicated to fulfilling the function of separating water from the air directed to the HVAC system: the water cowl. During the standard development process, you can check the function of the water cowl while building prototypes and placing them in rain chambers. If you find problems, you have then to modify the real part and go testing again, consuming a consistent amount of time and money. This situation was the driver for us to start researching for a virtual method. After two years of development we can now present a virtual method to analyze the water separation behavior of water cowl systems. We here distinguish between the free surface analysis featuring the behavior of large amounts of water and the interaction of droplets with the air flow produced by the HVAC itself. Within this paper we will show simulation results and compare them with measurement data. The second topic we will feature is the problem of water drive. The major goal is to virtually proof water tightness, as well as the amount of water getting into the external intake duct while transporting fresh air into the air filter and then to the engine. During physical tests, vehicles are sent through water channels filled with a certain amount of water, dependent on the case you want to check. During the test, cameras film the processes under the hood and simple weighing of the air filter before and after the test is an indication for the amount of water sucked into the process air duct. Also this test needs to complete finished prototype, which can be sent through the water channel. Both topics are simulated with a multiphase Lattice-Boltzmann (LBM) solver, namely XFlow.