Effect of flow direction on circumferential velocity, radial velocity, and flow resistance characteristics of rotating gap structures

A rotating gap structure is a type of viscous flow resistance using two disks where the rotation of one disk drives the fluid within the gap, generating rotational inertia. This inertia, combined with viscous friction, determines the flow resistance characteristic curve (pressure drop vs flow rate, or Delta p-Q curve). By adjusting the disk's rotational speed, the rotational inertia and the Delta p-Q curve can be modified. This paper examines how the radial flow direction (positive and negative) affects the circumferential velocity, radial velocity, and the Delta p-Q curve of the rotating gap structure through theoretical modeling and experiments. Results show that radial flow direction and rate influence the symmetric distribution of radial velocity and the linear distribution of circumferential velocity, altering the main components of the Delta p-Q curve: the viscous flow resistance curve (Delta p(vis) -Q) and the rotational inertia flow resistance curve (Delta p(rot)-Q). The study found that the slope of the Delta p(vis)-Q curve is smaller for positive flow than for negative flow due to differences in radial velocity distribution. Additionally, the circumferential velocity is weakened in positive flow and enhanced in negative flow, resulting in a smaller slope of the Delta p rot-Q curve for positive flow. These factors cause the Delta p-Q curve to deviate from linearity, with greater deviation at higher rotational speeds. Finally, experimental verification was conducted, and the measured Delta p-Q curve closely matched the theoretical calculations.