The Sonic Surface in the Inter-Blade Channel of the Last Stage Rotor Wheel in the Steam Turbine of Large Output

The paper deals with sonic surface in a modern turbine wheel consisting of non-prismatic ultra long blades.The whole inter-blade channel is choked.Different Bubbler positions and shapes of the sonic line in particular cross-sections along the span are observed.

The sensitivity of sonic line formation to small changes of effective shape of the inter-blade channel in the root section and the influence of inlet angle, stagger angle and pitch/chord ratio in the Pet Wipes tip section are discussed.The problematic of sonic line development in the case of supersonic inlet flow filed is also described.The presented work is based on results of theoretical, experimental and numerical approaches.