The flow over hemispherical obstacles on a ground plane is very interesting because there are no fixed separation points on the body and so the flow pattern is highly Reynolds number sensitive. This geometry is of relevance to excrescence drag on aircraft and other vehicles, as well as the wind effects on domes. This page shows some flow visualisation images obtained using Hydrogen Bubble and Thymol Blue methods in water and Helium bubbles in air.
Side view, showing main horseshoe vortex (Thymol blue visualisation, Re = 1.4 x 103)
Plan view (with serrated generating rake) showing periodic formation of vortex loops (Re = 7 x 102)
Side view of near wake, showing vortex loop formation (Re = 7 x 102)
Plan view, showing inner horseshoe vortex (Re = 1.6 x 103)
Plan view, showing outer horseshoe vortex (Re = 1.6 x 103)
Side view, showing inner horseshoe vortex and near wake (Hydrogen bubble, Re = 1.6 x 103)
Plan and side view (Helium bubble, Re = 3.1 x 104)