CFD Method Development for Simulating Water Fording for a Passenger Car 2021-01-0205

The present work deals with the development of a CFD method to simulate water fording/water wading for a passenger car. Water wading of automobiles in different water depths can lead to water ingestion into the air induction snorkel. This is unfavourable as this ingested water can cause the malfunction of the engine. This takes on an added importance when designing multi-terrain vehicles, where the interest could be in wading water effectively in many scenarios. The design of the snorkel, its position and height can be important in preventing water from entering the Air Induction System (AIS) and hence the engine. So, a water fording test of a vehicle is conducted to ensure the efficacy of the AIS snorkel in preventing water entering the AIS system. The ability of numerical simulations to effectively replicate testing performed in a long water tank is put to test in this paper. The CFD method development has been done using the commercial code, Simerics-MP+^®.

In Simerics-MP+, multiphase Volume of Fluid (VOF) methodology has been used to account for capturing the water/air interaction. Simulations are performed using the explicit (VOF) multiphase approach. The simulation involves the complete vehicle CAD moving in water over a few seconds of physical time, so it can be computationally expensive. So, one of the main aims of the work is to establish a methodology that can reduce the computational time while ensuring excellent interface capturing between the water and air phases. Multiple methodologies are devised, and the results compared with each other. The numerical diffusion has been judged both qualitatively and quantitatively. The qualitative judgment has been done using the contours of volume fraction of water visualized on stream-wise planes. For the quantification of the numerical diffusion, the estimation of mass-balance error is done and is the difference of mass of water phase exiting the domain w.r.t the mass of water phase entering the domain. The developed method is used to quantify the amount of water that has entered as well as held up in the Air Induction System of the engine for a given height and car velocity. Results of the wave pattern formed around the car, and the flow around other electrical components like internal wiring and battery is also documented. The developed method has been used to simulate a passenger car wading through pool with 12 inches of water height with a speed of 10 mph. It was seen that almost negligible amount of water has entered in the AIS and ultimately engine and hence it is safe to wade the car under such conditions.