Rob
Ansys Employee

OK. Iso surfaces & planes use interpolated data, ie they interpolate from the nearest cell centres and then integrate/average/whatever. As a result they'll always be marginally less accurate than a defined surface from the mesh (interior, inlet, wall etc) which stores data on the facets. Assuming y=0 & y=0.06 are on the flow boundaries the interpolation may be a little worse than surfaces inside the domain as there's less data available.