Prediction Method of Snow Ingress Amount into the Engine Air Intake Duct Employing LES and Detailed Snow Accumulation Model 2019-01-0805
When a vehicle is driven in snowy conditions, if a proper air intake design is not adopted, the snow lifted by the leading vehicles may penetrate into the engine air intake causing, in case of large snow ingress amount, a power drop. The evaluation of such risk for the intake is carried out through climatic wind tunnel tests, which cannot be conducted at the early stage of vehicle development when the prototype vehicle does not exist. In order to study that risk prior to the prototype vehicle delivery, a new simulation which predicts the snow ingress amount accurately was established with taking into account unsteady air flow and snow accumulation. Large Eddy Simulation was used to reproduce the unsteady flow, leading to a good agreement of the flow on the back side of the snow generator with the experimental one measured by Stereo-PIV. As for the snow particle behavior model, the Lagrangian method was chosen. In order to study the tracking properties of snow particles, the velocity differences between air flow and snow particles were measured by PIV, whilst super-slow snow particle motions were recorded with a high speed camera. Through comparison between experimental results and customized CFD results, non-spherical drag coefficient and turbulent dispersion are found to be fundamental to reproduce the tracking properties. Regarding the restitution coefficient at the walls, elastic-plastic deformation and surface friction were taken into account. In addition, an accumulation model was developed, in order to stop the particles and force them to accumulate at the wall when a certain criterion is satisfied. The accumulation model also takes into account the accumulation height limitation by recognizing the height of the flow path. The simulation including the new accumulation model evidences good correlation with experimental results for multiple vehicles and air intake geometries.