Radial means that the fluid is flowing in radial direction that is either from inward to outward or from outward to inward, with respect to the runner shaft axis. If the fluid is flowing from inward to outward then it is called outflow radial turbine.
Most practical radial outflow turbines are Reaction-type turbines, whereas the converse, radial inflow turbines can be either reaction type, impulse type (in the case of a typical turbo-supercharger), or intermediate (in the case of Francis turbines for example.)
The Main Components of Reaction Turbine are :[2]
Inward flow reaction turbine | Outward flow reaction turbine |
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Fluid enters at outer periphery of runner and flows radially inward toward the centre thus flow is radially inwards toward the centre. | Here the flow is radially outwards and the fluid gets discharged at the outer periphery of the runner |
Centrifugal head h= (u2^2 -u1^2 )/2g but u2<u1 which means that the centrifugal head imparted on fluid during the flow through runner is negative. | Centrifugal head h= (u2^2 -u1^2 )/2g but u2>u1 which means that the centrifugal head imparted on fluid during the flow through runner is positive. |
Easy speed control and load following. | Difficult to control the speed. |
Discharge is constant. | Discharge increases. |
Used in medium and high head conditions. | Used in small head conditions. |
Difference in tangential velocity between the runner inlet and outlet positively contributes to the shaft power. | Difference in tangential velocity between the runner inlet and outlet negatively impacts shaft power. |
Some of the advantages of radial outflow turbine are:
Radial flow turbines are generally more preferred in small turbines because of simpler construction. Radial flow turbine rotor does not use aerofoil sections, as a result of which the rotor of radial flow turbine has a shape very similar to a centrifugal compressor and it uses 3D shape for energy extraction. They are more conducive to being produced from a single casting or round billet as a Bladed-disk or "blisk."