Perspectives on the treatment of secondary flows in axial turbines

A review is presented of the main end-wall treatments for the secondary flows of axial turbines. This encompasses the use of axisymmetric and non-axisymmetric contoured end-walls, the use of fences, and of air injection and blowing. Experimental and numerical results show promise in all these techniques. Interest seems to be drawing towards the use of non-axisymmetric contoured end-walls, due to their good compatibility with current turbine passage designs and their appealing stage pressure loss reduction at design conditions and off design. An insight is provided into the flow changes from non-axisymmetric end walls and on their effect on secondary flow losses.