Dishwasher with filter assembly

A dishwasher for treating utensils according to a cycle of operation, comprising:

• a tub at least partially defining a treating chamber;
• a liquid spraying system supplying a spray of liquid to the treating chamber;
• a liquid recirculation system recirculating the sprayed liquid from the treating chamber to the liquid spraying system to define a recirculation flow path;
• a rotating filter having an upstream surface and a downstream surface and located within the recirculation flow path such that the recirculation flow path passes through the filter from the upstream surface to the downstream surface to effect a filtering of the sprayed liquid;
• a first artificial boundary spaced from and rotatable relative to one of the downstream and upstream surfaces;
• and
• a second artificial boundary spaced from and rotatable relative to the other of the downstream and upstream surfaces;
• wherein the first and second artificial boundaries have un-matched shapes and their relative rotation forms an increased shear force zone acting on the filter.