(25)
The calculation is advanced toward the upstream side from the outflow surface (head) where the backpressure is specified to match the pressure value of the outflow plane to the prescribed value. In other words, the pressure gradient calculated by the downstream element is preferentially used.
As shown in Eq. (15), the pressure variable is defined at the node. However, the pressure variable and the pressure gradient for recalculation based on Eq. (25) are defined for the element center. In the process of recalculating the pressure from Eq. (25) using the successive over relaxation (SOR) method, the sign of the flow rate is used to determine the downstream side. Similar to the one-dimensional calculation algorithm of the FAN method, any element calculated to have a negative or zero pressure is judged to be unfilled.
As shown in Figure 2, the edge between nodes 1, 2 or 3, 4 of the computing element are considered perpendicular to the screwz -axis. For elements aligned in the circumferential (θ ) direction, the sum of the flow rate across the axis perpendicular to the circumferential direction is equal to the extrusion flow rate,Q ext, regardless of which self-wiping section is considered.