Use of the immersed boundary method within the building cube method and its application to real vehicle CAD data

Methodology is developed to reduce manual work in preparing geometry for simulation when working with dirty computer-aided-design data. A method that uses arbitrary boundary representation is proposed with a dummy-cell technique based on a Cartesian grid and immersed boundary method. The complicated geometry is degenerated into celloriented values. The advantage is that the user can handle data that have a gap, overlap or sharp edge without any special preprocessing. The force term of the immersed boundary method is directly imposed on an arbitrary ghost cell by linear interpolation of the velocity, which is defined according to the distance between the cell-centered position and the crossing point with the grid line. The intersection point is obtained from the face center and normal of the characteristic wall. A calculation example of a full vehicle model provided by an automotive company is presented, and robust flow field results are obtained. The validation case of flow around sphere with low Reynolds numbers is also presented, and close agreement with results for the drag force coefficient obtained in past fundamental studies is found.