Abstract
Recent trends in the electric energy market such as biomass, waste incineration or combined cycle power plants require innovative solutions in steam turbine design. Variable operating conditions cause significant changes in flow field surrounding the steam turbine last stage blades. Therefore, the enlargement of operating range for last stage blades presents new challenges in design of turbine cascades. Several turbine cascades were designed and analyzed by commercial and in-house software of CTU Prague. Selected profiles were experimentally validated in the high-speed wind tunnel for 2D cascade measurements of the Institute of Thermomechanics of the Czech Academy of Sciences which is equipped by an adjustable supersonic inlet nozzle, perforated inserts at side walls and adjustable perforated tailboard. Comparisons are presented of numerical results with optical and pneumatic measurements for a wide range of inlet and outlet Mach numbers for optimized hub and tip profile cascades.
Highlights
The last stage rotating blade is a key component of each steam turbine, directly contributing to overall efficiency of the thermal cycle
Supersonic regimes the tip cascade exhibits impressive aerodynamic performance with only very small area where the aerodynamic force acts in the opposite direction, decreasing the overall torque of the last stage blade
Advanced hub and tip profiles of ultra-long last stage blade were analyzed by both were performed in high-speed wind tunnel in the Aerodynamic Laboratory of the Institute of experimental and numerical methods
Summary
The last stage rotating blade is a key component of each steam turbine, directly contributing to overall efficiency of the thermal cycle. The proper stator blade design with advanced 3D shaping is highly important because it has significant impact on the relative velocity in the vicinity of the rotating blade. The relative Mach numbers exceeding 1 are commonly present in flow field surrounding the rotating blade due to high tangential velocities and even supersonic flow with inlet shock wave can occur, especially in the case of ultra-long full speed (3000 or 3600 RPM) last stage blades [1]. Final mechanical design must fulfill criteria of static strength which determines strict distribution of area for each section along the blade span. The combination of these requirements limits the design space and leads to the demanding process of optimal solution searching
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