Putting a thumb over the garden hose changes the back pressure and exit velocity of the water across the entire cross section surface area equally. If the garden hose opening is reduced, the shape of the reduced opening does not effect the exit pressure/velocity as long as the cross sectional surface area of the opening is the same (this is not to be confused with spray patterns). Likewise, the tear drop shape of an oil filter opening will have equal back pressure and exit velocity across the entire opening. Regarding the swirl effects, I highly doubt the marketing team cares to accurately portray the science. The oil is going to enter the filter perpendicular to the angle of the inlet holes, regardless of the shape. If any of this actually mattered to a measurable degree, every oil filter manufacturer would have converged onto the same design decades ago.
Originally Posted by Farnsworth
I never said I know what the flow velocity change did. Fram shows the swirling and even structure in the swirl. I didn't draw it. Don't need to study up on fluid dynamics here, just need a garden hose and a thumb to study. Based on the garden hose analogy, I learned the tear drop holes do induce changes. Learning and having an open mind are not bad things.