Characteristics of a new compact valve design for steam turbines are analysed by measuring pressure losses and oscillations on the valve model. It is the model of an intercept valve of the intermediate-pressure turbine part. This valve is relatively smaller hence cheaper than usual control and intercept valves. Besides, four different valve seat angles were tested in order to investigate the valve seat angle influence. In order to further clarify measured phenomena, the wide range of numerical simulations were also carried out. Measurements were performed in the Aerodynamic laboratory of the Institute of Thermomechanics of the Czech Academy of Sciences in an air test rig installed in a modular aerodynamic tunnel. Numerical simulations were performed in the Doosan Skoda Power Company using a package of ANSYS software tools. Measurement results are compared with numerical and generalized in the form of valve characteristics and pressure oscillation maps. As a result of the pressure loss analysis, pressure losses in similar valve assemblies can be predicted with required accuracy for each new turbine where modern compact valves are used. As a result of the pressure oscillation analysis, operating conditions at which dangerous flow instabilities can occur were identified. Thanks to this, the areas of safe and dangerous operating conditions can be predicted so that the operational reliability of the valve can be guaranteed.

This paper presents the experimental research for the flow of the last stage of a turbine for saturated steam with the nominal output 1090 MW. In addition, the flows in 600, 800, and 1070 MW output turbines were also measured. Pneumatic probes were used to determine the distribution of static pressures and absolute angles at the outlets from the penultimate and the last stages of the turbine. Optical probes were used to measure wetness distribution and were placed in positions similar to the pneumatic probes. The courses of static pressures, angles, and wetness for all outputs respectively were compared and discussed. The difference between wetness courses on the left and right side of the turbine as well as before and behind last stage was minimal. Absolute angles of steam behind the last stage are strongly influenced by the vacuum level in the condenser. Big difference between the outlet angles from last stage on the left and right side of the turbine is confirmed. The influence of the tie-boss was evident in both pneumatic and wetness measurements. Differences of the flow field on the left and right sides of the turbine behind the penultimate stage are noted and discussed. These differences lead to a dynamic loading of the penultimate rotor blades and could reduce the service life.

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 losses and avoid danger of vibrations, which are caused by undesirable flow fluctuations, in order to guarantee valve’s efficiency and operational reliability. For this type of valve, it is especially important for turbine operations in partial loads (off-design conditions). Measurements were carried out in the Aerodynamic laboratory of the Institute of Thermomechanics of the Czech Academy of Sciences (IT) in a modular aerodynamic tunnel. Numerical simulations were carried out in the Doosan Skoda Power Company (DSP) by using a package of ANSYS software tools. The experimental valve model is a scaled model of a real valve assembly. It consists of an inlet pipeline, a stop valve and a control valve including its diffuser and outlet pipeline. Measured regimes were defined by a mass flow rate and a control valve cone lift which can be precisely changed. In order to investigate pressure loses, total and static pressures at valve characteristic locations were measured by using Prandtl probes and wall static pressure taps. In order to measure pressure fluctuations, Kulite fast response pressure transducers were used. They were situated near the valve throat where the flow fluctuations, which are strongly related to a flow separation, are the most visible and influential. Measurement results are compared with numerical results and locations with a flow separation were found. In order to reduce this phenomenon, different valve seat angles were also tested. As a result, a valve design could be optimized and, for a pressure loss prediction, a pressure loss model for this new intercept valve assembly could be created. Therefore, pressure losses in similar valve assemblies can be predicted with required accuracy for each new turbine where modern intercept valves are used. This helps to increase steam turbine efficiency and reduce fuel consumption. Based on pressure fluctuations results, operating conditions at which dangerous flow instabilities occur were identified. It was concluded that there is an operating condition border where the flow field starts to be unstable. As a result, the areas of safe and dangerous operating conditions can be predicted so that the operational reliability of the valve can be guaranteed.

The paper deals with experimental research of the flow and dynamics of the blades in the last stage of a steam turbine with nominal output of 34 MW and a connected axial exhaust hood. The experiments were carried out on a turbine with relatively low inlet steam parameters “- 64 bars and 445 °C. It was possible to change the operating modes of the turbine during the course of measurement so that significant ventilation would be achieved in the last stage up to the point when aerodynamic throttling occurred in the last stage. In other words the turbine output varied from about 2 to 35 MW. The output of 2 MW was for the case of the island mode turbine operation. The experiments were carried out using static pressure taps and measurements of temperatures at the root and tip limiting wall. In addition to static pressure taps and temperature measurement, it was also possible to carry out probing by pneumatic probe with a diameter of 30 mm. Blade vibration monitoring sensors, so called last stage blade tip-timing, were also installed. The blade tip-timing acquisition hardware was used to monitor rotor blades tip amplitude. Due to the obtained experimental data, it was possible to verify the behaviour of the last stage and the connected exhaust hood for four measured variants. The courses of pressures and steam angles along the length of the LSB were determined. Furthermore, basic parameters of the last stage were determined, i.e. reactions of the stage, Mach and Reynolds numbers and values of pressure recovery coefficients. Based on experimental data the boundary conditions for CFD calculations were determined. Comparison of CFD calculations done for ventilation modes and for a nominal mode was also included. Another phenomenon which occurred during the probing of the flow parameters, particularly in ventilation modes, was the inability to determine parameters of steam due to low values of measured dynamic pressure in the vortex area at the root of the blade. The probe was able to detect dynamic pressure at the level of 50 Pa and more. In other words the transition point between backward and forward flows was identified. This limit point was used for further analysis of ventilation character of the steam flow depending on the ventilation coefficient c2x/u. where c2x is the average axial velocity at the LSB outlet, calculated from volumetric mass flow and u is LSB circumferential velocity calculated at LSB middle diameter. Due to the fact that it was also possible to measure vibration amplitudes of blades using the tip-timing method for a variety of modes, the relationships between pressure ratio over the tip and root of the last moving blade and vibration amplitude were also determined. This verified that the highest amplitude of blade tips occurred just when the compression of the medium on the blade tip was maximum, i.e. c2x/u = 0.05.