A turbine engine ring seal for sealing gaps between turbine engine outer seal segments and turbine blade tips. The turbine engine ring segment may have an inner radial surface that defines a portion of a gap gas flow path where the inner radial surface may be formed of an abradable ceramic coating and includes a plurality of gas flow protrusions that are oriented transverse to the gap gas flow path. The gas flow protrusions may induce vortices in the gas flow in the gap gas flow path. Additionally, the gas flow protrusions may be series of peaks and depressions between two adjacent peaks, where the depressions have an approximate semicircular shape. The distance between two adjacent peaks may be equal or greater than a width of the depression and the height of a single peak may be six percent or greater than the distance between two adjacent peaks.