Abstract: A downhole tool assembly for use in a drilling string includes a motor, a flow head, and a flow restrictor. The flow head is coupled to the motor and comprises a plurality of ports permitting fluid communication therethrough. The flow restrictor is in fluid communication with the flow head and comprises a plurality of ports permitting fluid communication therethrough. The flow restrictor is stationary with respect to the flow head, which rotates. As the flow head rotates, one or more of the plurality of ports of the flow head enters into and out of alignment with one or more of the plurality of ports of the flow restrictor such that fluid flow through the ports of the flow head and the flow restrictor is constrained to a cyclic, polyrhythmic pattern optionally including at least one interval where the fluid flow is substantially blocked by the flow restrictor.