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.

Aerodynamic experimental measurements and numerical simulations carried out on a model of a high-pressure valve assembly used for a nozzle governing of a turbine with 135 MW output are described in this paper. Aim of the study is to investigate effects of control valve’s strainers on pressure losses and unsteadiness in the flow field thus its effect to undesirable flow fluctuations

Last stage blades are a key element of steam turbines and in many ways determine the turbine configuration alongside with the overall turbine performance. The total efficiency of the low pressure turbine section can be increased by extending the last stage blades. The design process of such long blades involves a flutter analysis using CFD tools which have to be validated by measurements in test facilities under various operating conditions. Experimental data obtained from a subsonic wind tunnel with an oscillating turbine blade cascade, which is available at the Department of Power System Engineering at the University of West Bohemia, was compared with simulations in ANSYS CFX currently used in the Doosan Škoda Power. The paper provides a brief summary of experimental rig description, CFD tool setup and the results for the case of a travelling wave mode with the pure torsion motion of amplitude of 0.5°, Ma = 0.2, reduced frequency of 0.38 and angle of attack +5°.

A new design of an intercept valve assembly of the intermediate-pressure turbine part of greater power output is investigated in terms of pressure losses and flow fluctuations by using measurement on an experimental valve model. In addition, numerical simulations are used to further clarify measured phenomena. For such valve assemblies, it is important to exactly predict pressure

This paper describes the aerodynamic design of the scaled air test rig of axial exhaust casing. The axial exhaust casings are used to benefit steam turbines of less than 180 MW, and their design can significantly affect the performance of the last stage and thus the performance of the entire steam turbine. The proposed test rig, along with extensive CFD simulations, will help to optimize the flowing in the exhaust casing and provide the ability to reliably predict losses in the exhaust casing on real steam turbines. Part of the study will be the detection of the influence of the individual components of the velocity at the diffuser inlet, the effect of the number, shape and arrangement of the internal struts. Last but not least, the effect of a wall jet blowing into the outer diffuser wall will be studied. The aerodynamic design of the test rig itself required a lot of numerical simulations to achieve the desired velocity profile at the diffuser inlet. It has been shown that it is difficult to simulate the radial component of the velocity in experimental conditions. The desired circumferential component of the velocity can be achieved more easily by suitable shaping of the stationary blade grid at the diffuser inlet.

Modern efficient and robust steam turbines must be designed for large operating ranges and run at off-design conditions and high backpressures. Therefore, there is a danger that in some operating conditions, last-stage rotor blades can suffer from self-excited vibration (flutter), leading to severe failures of rotor blades or turbine units. In order to avoid this, the design of aerodynamically stable last stage rotor blades became a major topic for all steam turbine manufacturers and a validated numerical model for flutter prediction during the blade preliminary design phase is required. As flutter measurement is impossible in real turbines, controlled flutter tests on simplified experimental models must be used. However, experimental flutter testing facilities are rare. This paper reports on a flutter test rig enhancement to transonic flow and numerical data validation of aerodynamic stability in a linear turbine blade cascade. Aerodynamic forces and moments are estimated for different boundary conditions at pure bending, pure torsion and combined modes. The results are compared to numerical simulations performed using commercial code ANSYS CFX. Good agreement between the experiment and the numerical simulations proved a successful validation of the numerical tool.