Anomalous roughening of forced radial imbibition in a porous medium

We report forced radial imbibition of water in a porous medium in a Hele-Shaw cell. Washburn's law is confirmed in our experiment. Radial imbibition follows scaling dynamics and shows anomalous roughening dynamics when the front invades the porous medium. The roughening dynamics depend on the flow rate of the injected fluid. The growth exponents increase linearly with an increase in the flow rate while the roughness exponents decrease with an increase in the flow rate. Roughening dynamics of radial imbibition is markedly different from one dimensional imbibition with a planar interface window. Such difference caused by geometric change suggests that "universality class" for the interface growth is not universal.