Radial Turbine - Stage Losses

Stage Losses

The stage work is less than the isentropic stage enthalpy drop on account of aerodynamic losses in the stage. The actual output at the turbine shaft is equal to the stage work minus the losses due to rotor disc and bearing friction.

(a) skin friction and separation losses in the scroll and nozzle ring
They depend on the geometry and the coefficient of skin friction of these components.

(b) Skin friction and separation losses in the rotor blade channels
These losses are also governed by the channel geometry, coefficient of skin friction and the ratio of the relative velocities w₃/w₂. In the ninety degree IFR turbine stage, the losses occurring in the radial and axial sections of the rotor are sometimes separately considered.

(c) Skin friction and separation losses in the diffuser
These are mainly governed by the geometry of the diffuser and the rate of diffusion.

(d) Secondary losses
These are due to circulatory flows developing into the various flow passages and are principally governed by the aerodynamic loading of the blades. The main parameters governing these losses are b₂/d₂, d₃/d₂ and hub-tip ratio at the rotor exit.

(e) Shock or incidence losses
At off-design operation, there are additional losses in the nozzle and rotor blade rings on account of incidence at the leading edges of the blades. This loss is conventionally referred to as shock loss though it has nothing to do with the shock waves.

(f) Tip clearance loss
This is due to the flow over the rotor blade tips which does not contribute to the energy transfer.

• Losses in the rotor of an IFR turbine stage