Session: 23-08 Last Stage Blades and General Design Aspects of Steam Turbines

Paper Number: 80523

80523 - Analysis of Turbulent Effects in a Low-Pressure Model Steam Turbine Operating Under Various Operating Conditions Using Detached Eddy Simulation 

Currently, the energy supply is changing. The previous energy landscape is evolving as more and more renewables are integrated into the grid. This may result in an increased flexibility requirement which can lead to possible operation of the low-pressure steam turbines under low-volume flow conditions, affecting especially the last stage rotating blade row.

In the previous paper GT2021-58704 the flow field of a low-pressure model steam turbine operating under such low volume flow conditions was analyzed. It was shown that different turbulent structures, i.e. rotating instabilities (RI), in the last stage and diffusor affected the flow field and resulting pressure fluctuations near the casing in the axial gap of the last stage. Based on the previous results, further analysis of the turbulent structures in the flow field of the turbine under low volume flow conditions has been conducted.

In order to understand and identify which turbulent structures are caused by the operation under low volume flow conditions and which can also be observed during normal operating conditions, additional operating points at higher volume flows were simulated. Pressure contours and visualizations of vortices using the Q-criterion have been used to demonstrate the similarities and differences in the flow fields between the different operating conditions. This wider operating range has also been validated using unsteady pressure fluctuations at the casing as well as time-resolved probe traverse data.

The analyzed domain consists of a three-stage low-pressure model steam turbine featuring a non-axisymmetric inlet and an axial-radial diffuser. In order to capture the asymmetry, the model spans the full annulus and comprises the inlet section, all three stages, the diffuser as well as the exhaust hood. The same numerical discretization schemes and polyhedral mesh structure described in detail in paper GT2021-58704 is being used. 

Viscous 3D CFD simulations using the Improved Delayed Detached Eddy Simulation (iDDES) model have been performed and the commercial CFD solver STAR-CCM+ is employed.

The additional detailed analysis and comparison of these flow structures helps the understanding of the complex RI phenomena and could facilitate the future implementation of constructive measures to decrease their effect on the last stage rotating blades.

Presenting Author: Ilgit Ercan Siemens Energy

Presenting Author Biography: I am a PhD student working on the analysis of rotating instabilities in low-pressure steam turbines. My PhD is a cooperation between Siemens Energy and the Institute of Thermal Turbomachinery and Machinery Laboratory at the University of Stuttgart.<br/>I have obtained my Master of Engineering degree at the University of Sheffield with a Class Two Division Honours in Mechanical engineering.

Authors:

Ilgit Ercan Siemens Energy
Damian Vogt Institute of Thermal Turbomachinery and Machinery Laboratory, University of Stuttgart