Illustration of staggered grid. Scalar properties are defined at the locations of the red dots in the center of each cell. The x, R, r component of the velocity is located at the interfaces marked with blue arrows and the y, ɀ, θ component of the velocity is calculated at the interaces marked by green arrows. Counting is indicated by the index k in the vertical or polar direction and j in the horizontal or radial direction. The location of variables at cell centers is expressed with integer indices and at cell faces with the integer $\pm \frac{1}{2}$ notation.