A numerical study on the flow in a three stage low pressure industrial steam turbine with conical friction bolts in the last stage and lacing wires in the penultimate stage is presented and analyzed. Structured high-resolution hexahedral meshes are used for all three stages and the meshing methodology is shown for the rotor with friction bolts and blade reinforcements. Modern three-dimensional CFD with a non-equilibrium wet steam model is used to examine the aero-thermodynamic effects of the part-span connectors. A performance assessment of the coupled blades at part load, design and overload condition is presented and compared with measurement data from an industrial steam turbine test rig. Detailed flow field analyses and a comparison of blade loading between configurations with and without part-span connectors are presented in this paper. The results show significant interaction of the cross flow vortex along the part-span connector with the blade passage flow causing aerodynamic losses. This is the first time that part-span connectors are being analyzed using a non-equilibrium wet steam model. It is shown that additional wetness losses are induced by these elements.

An experimental and numerical study on the flow in a three stage low pressure (LP) industrial steam turbine is presented and analyzed. The investigated LP section features conical friction bolts in the last and a lacing wire in the penultimate rotor blade row. These part-span connectors (PSC) allow safe turbine operation over an extremely wide range and even in blade resonance condition. However, additional losses are generated which affect the performance of the turbine. In order to capture their impact on the flow field, extensive measurements with pneumatic multi-hole probes in an industrial steam turbine test rig have been carried out. State-of-the-art three-dimensional CFD applying a non-equilibrium steam (NES) model is used to examine the aero-thermodynamic effects of the PSC on the wet steam flow. A detailed comparison between measurement data and CFD results is performed for several operating conditions. The investigation shows that the applied CFD model is able to capture the three-dimensional flow field in LP steam turbine blading with PSC and the total pressure reduction due to the PSC with a generally good agreement to measured values and is therefore sufficient for engineering practice.

An experimental and numerical study on the flow in a three-stage low-pressure (LP) industrial steam turbine is presented and analyzed. The investigated LP section features conical friction bolts in the last and a lacing wire in the penultimate rotor blade row. These part-span connectors (PSC) allow safe turbine operation over an extremely wide range and even in blade resonance condition. However, additional losses are generated which affect the performance of the turbine. In order to capture the impact of PSCs on the flow field, extensive measurements with pneumatic multihole probes in an industrial steam turbine test rig have been carried out. State-of-the-art three-dimensional computational fluid dynamics (CFD) applying a nonequilibrium steam (NES) model is used to examine the aerothermodynamic effects of PSCs on the wet steam flow. The vortex system in coupled LP steam turbine rotor blading is discussed in this paper. In order to validate the CFD model, a detailed comparison between measurement data and steady-state CFD results is performed for several operating conditions. The investigation shows that the applied one-passage CFD model is able to capture the three-dimensional flow field in LP steam turbine blading with PSC and the total pressure reduction due to the PSC with a generally good agreement to measured values and is therefore sufficient for engineering practice.

Industrial steam turbines are operated over an extremely wide range of operating conditions. In order to ensure safe turbine operation, even in blade resonance condition, conical friction bolts are mounted between blade reinforcements of adjacent last stage low-pressure blades. These part-span connectors (PSC) provide blade damping and coupling. However, additional losses are generated, which affect the performance of the turbine. In this paper, a numerical and experimental study on aerodynamic optimization of PSCs is presented. State-of-the-art three-dimensional computational fluid dynamics (CFD) applying a non-equilibrium steam model is used to examine the wet steam flow in coupled last stage blading. The one-passage CFD model with parameterized PSC geometry features structured high-resolution hexahedral meshes. Experimental data of measurements with pneumatic multi-hole probes in an industrial steam turbine test rig are used for validation. According to the good agreement between measured and predicted flow field downstream of the last stage rotor blading, the CFD model is valid to capture the loss induced by the PSC. A numerical study on the aerodynamic effects of geometrical variations of PSCs concerning blockage area and shape is presented in this work. Based on this study, a performance assessment of different PSC designs is discussed and numerical results are compared to the loss coefficients predicted by Traupel's analytical correlation, which is widely used in industry.

Low-pressure last stage blades of industrial steam turbines are subjected to high dynamic loading. Especially in variable speed applications resonant blade vibration cannot be avoided. Thus, the aim of the blade layout is to reach a robust design that can cover high vibrational amplitudes while still keeping good efficiency. An effective way to keep vibration amplitudes low is the introduction of friction damping elements to the blades. In this paper the structural behavior of a low-pressure last stage blade coupled by friction bolt damping elements is described by means of linear and nonlinear Finite Element Method. Special focus is put on the nonlinear effects of the contact between blade and damping element to investigate the frictional damping performance of the system. The obtained numerical results are validated by strain gauge and tip timing measurements in a full scale test turbine under real steam conditions at the Institute of Thermal Turbomachinery and Machinery Laboratory of the University of Stuttgart.