The complete flow fields within turbo-machinery stages, both in radial flow and axial flow machines, are significant influences on rotor vibration. Figure 6.1 illustrates the radial flow fields typical in centrifugal impeller stages. For a typical axial flow machine, Figure 6.2 shows the high-pressure turbine of the large steam-powered multiturbine unit shown in Figure 3.9. Within these machines, flow through the impellers and blade rows interacts considerably with the flow through their respective seals.