A radial turbine is a turbine in which the flow of the working fluid is radial to the shaft. The difference between axial and radial turbines consists in the way the air flows through the components (compressor and turbine). Whereas for an axial turbine the rotor is 'impacted' by the air flow, for a radial turbine, the flow is smoothly orientated at 90 degrees by the compressor towards the combustion chamber and driving the turbine in the same way water drives a watermill. The result is less mechanical and thermal stress which enables a radial turbine to be simpler, more robust and more efficient (in a similar power range as axial turbines). When it comes to high power ranges (above 5 MW) the radial turbine is no longer competitive (heavy and expensive rotor) and the efficiency becomes similar to that of the axial turbines.
Read more about Radial Turbine: Advantages and Challenges, Components of Radial Turbines, Enthalpy and Entropy Diagram, Spouting Velocity, Stage Efficiency, Degree of Reaction, Stage Losses, Blade To Gas Speed Ratio, Outward-flow Radial Stages, Nikola Tesla's Bladeless Radial Turbine