Flow-induced instability of mushy layer permeability

The coupling of an external shear flow with the permeability of a solidifying mushy layer is investigated experimentally and theoretically. We grow a mushy layer from a trans-eutectic aqueous ammonium chloride solution from the base of a laboratory flume. The growth rate is constant and a laminar shear flow is applied. We find a threshold speed above which a spatiotemporal variation of the permeability of the layer appears with a planform wherein the long axis is transverse to the flow direction. Upon removal of the flow, the material returns to a uniform state. The growth of the pattern compares favorably with an analytical and numerical stability analysis which incorporates dissolution of the solid matrix.