Suppression of the viscous fingering instability by shear

During the viscous fingering instability, the interface between two fluids confined to a thin gap is unstable to finger formation when the less viscous fluid invades the higher viscoity one. Here, we study the instability between pairs of miscible fluids. When experiments are conducted in a radial geometry there is a period of stable growth which persists up to a critical radius that depends on the viscosity ratio of the fluids and the injection rate. The presence of fingers appears to be tied to specific interfacial structure across the small dimension of the gap. In this work we see how actively interfering with this structure formation affects the instability. By applying an oscillatory translational shear to the top plate of our Hele-Shaw cell we observe a dramatic delay in the onset of the instability. We suggest that this delay is tied to changing the curvature of the interface at the leading edge of the pattern. This phenomenon could lead to novel control techniques to suppress this instability.