Wading Simulations of Complete Heavy-Duty Vehicles

Abstract: Wading is the phenomenon where a vehicle drives through water with a relatively deep water level. Sincea large portion of the vehicle is submerged in water it can affect the driveability and function of individualcomponents. Wading is therefore an important phenomenon to be aware of especially today where society moves towards alternative energy sources. This includes water sensitive components when contact with water can generate major consequences. Previous knowledge and experience of wading has been from performing physical tests, but using Computational Fluid Dynamics (CFD) to examine the phenomenon can accelerate the iterative design process. In this thesis, numerical method of wading simulations on complete heavy-duty vehicles using the software STAR-CCM+ are developed. Furthermore, the results from the numerical methods are validated against results from physical tests performed at Scania’s test facility in Södertälje. The numerical methods are divided into a simplified model of a Battery Electric Vehicle (BEV) and a detailed geometry of a gas-driven vehicle from Scania. Beside dividing the wading scenario into the geometries, two different methods are developed, Wave and Wading. The Wave-method includes the vehicle standing still while a water wave is fed in through the inlet of the domain, i.e. allowed to flush over the vehicle, with a velocity of 3.6 km/h and 8 km/h. This method is implemented for both a generic simplified BEV truck and a detailed real-life Scania truck. For the Wading-method, motion is applied to the vehicle where itis driving with a velocity of 3.6 km/h through a digital twin of the water trench available at the test facility. This method is further divided into two cases, Zero Gap and Floating, where the difference is the distance between the tires of the vehicle and ground of the domain. The Floating-case includes a 10 cm distance and the Zero Gap-case has no gap between the tires and ground. The Wading-method is only implemented for the simplified geometry due to the computational cost and complexity. All methods use the Volume of Fluid (VOF) method for multiphase modelling and the Zero Gap-case uses Overset Mesh for modelling motion. The validation of the simulations focuses on the water behaviour such as water surface topology and water flowing inside the vehicle while wading. The results for the Wave-method with both the simplified and detailed truck at 8 km/h shows similarities in the water surface topology between the numerical model and the physical test. The simulations of the Wading-method is not visualising any similarities since the visible wave pattern are few and unclear in the numerical model. An isosurface is used to visualise the surface of the water which generated a smooth topology since no other options, such as vector fields, are added. It is found that the water movement inside the vehicle will affect water sensitive areas, e.g. on the battery packs. It is concluded that the derived methods are a first draft and should be directed towards future development in optimising the methods to lower the computational cost, but also to improve the capturing of the interface between the two phases. Due to instability and computational cost the detailed geometry is not implemented in the Wading-method. The methods are adapted to use different vehicle types since the simplified and detailed geometry are a BEV and a gas-driven truck respectively.