Numerical and experimental study on aerodynamic optimization of part-span connectors in the last stage of a low-pressure industrial steam turbine

Abstract

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.

Shock wave configuration in a transonic flow through a mid-section of a last stage turbine blade cascade equipped with a part-span connector

“…Investigations of the part-span connector under subsonic flow conditions have been carried out by Bruggemann et al [1], Bin Li et al [2] and by Häfele et al [3,4]. These works by various research teams around the world showed that part-span connectors induce vorticial structures, cross flow, and increased losses.…”

Numerical and experimental analysis of low-pressure steam turbine blades coupled with lacing wire

“…Traupel 15 ) are normally used to determine the efficiency losses. More detailed numerical and experimental studies on the flow impact of part-span connectors in LP steam turbine blading have recently been published by Ha¨fele et al [16][17][18] Depending on the size and position of the elements, an efficiency decrease of several percentage points must be expected. 17…”

“…The test rig setup is shown in Figure 2. Further details can be found in Ha¨fele et al [16][17][18] The turbine is equipped with various temperature and pressure probes for a complete thermodynamic evaluation. Moreover, strain gauges are applied to several moving blades of the rows.…”