Modeling Flow Across a Race Car Air Filter

Air entering a NASCAR stock car travels through an air filter enclosed in an “airbox” before being mixed with fuel. To maximize the mass of air/fuel mixture delivered to the cylinders, it is desired to minimize airflow restrictions. This paper presents a preliminary model to predict pressure drop and airflow across an air filter in a simplified geometry. The model includes experimental measurements and numerical simulations using a three-dimensional finite-volume package. The simplified geometry is a 1.52-m long flow channel with 12.7 cm by 7.97 cm cross-section. Measurements of pressure drop versus air velocity were made for separate and combined elements of the filter. A curve fit to the data is used to calculate coefficients for a porous-jump boundary condition used to model flow through porous media. Numerical simulations were run using this model for each filter element in the simplified geometry to verify that measured and calculated pressure drops agreed. Finally, flow visualization techniques were used to reveal streaklines in the flow. Good agreement was found between calculated streamlines and experimental observations. Thus, the porous jump boundary condition is a valid model for the filter material. Future work will include three-dimensional, transient numerical simulations of airflow within the airbox.