scholarly journals Flutter Analysis of a Transonic Steam Turbine Blade with Frequency and Time-Domain Solvers

2019 ◽  
Vol 4 (2) ◽  
pp. 15
Author(s):  
Christian Frey ◽  
Graham Ashcroft ◽  
Hans-Peter Kersken ◽  
Daniel Schlüß
Keyword(s):  
Steam Turbine ◽  
Time Domain ◽  
Turbine Rotor ◽  
Test Case ◽  
Nonlinear Frequency ◽  
Steam Turbines ◽  
Bending Mode ◽  
Flutter Analysis ◽  
Steam Turbine Blade ◽  
Time Marching

The aim of this study was to assess the capabilities of different simulation approaches to predict the flutter stability of a steam turbine rotor. The focus here was on linear and nonlinear frequency domain solvers in combination with the energy method, which is widely used for the prediction of flutter onset. Whereas a GMRES solver was used for the linear problem, the nonlinear methods employed a time-marching procedure. The solvers were applied to the flutter analysis of the first rotor bending mode of the open Durham Steam Turbine test case. This test case is representative of the last stage of modern industrial steam turbines. We compared our results to those published by other researchers in terms of aerodynamic damping and local work per cycle coefficients. Time-domain, harmonic balance, and time-linearised methods were compared to each other in terms of CPU efficiency and accuracy.

The Influence of Non-Equilibrium Wet Steam Effects on the Aeroelastic Properties of a Turbine Blade Row

2016 ◽  
Author(s):  
Christopher Fuhrer ◽  
Marius Grübel ◽  
Damian M. Vogt ◽  
Paul Petrie-Repar
Keyword(s):  
Steam Turbine ◽  
Turbine Blade ◽  
Ideal Gas ◽  
Test Case ◽  
Steam Turbines ◽  
Wet Steam ◽  
Flow Conditions ◽  
Flutter Analysis ◽  
Last Stage ◽  
Non Equilibrium

Turbine blade flutter is a concern for the manufacturers of steam turbines. Typically, the length of last stage blades of large steam turbines is over one meter. These long blades are susceptible to flutter because of their low structural frequency and supersonic tip speeds with oblique shocks and their reflections. Although steam condensation has usually occurred by the last stage, ideal gas is mostly assumed when performing flutter analysis for steam turbines. The results of a flutter analysis of a 2D steam turbine test case which examine the influence of non-equilibrium wet steam are presented. The geometry and flow conditions of the test case are supposed to be similar to the flow near the tip in a steam turbine as this is where most of the unsteady aerodynamic work contributing to flutter is done. The unsteady flow simulations required for the flutter analysis are performed by ANSYS CFX. Three fluid models are examined: ideal gas, equilibrium wet steam (EQS) and non-equilibrium wet steam (NES), of which NES reflects the reality most. Previous studies have shown that a good agreement between ideal gas and EQS simulations can be achieved if the prescribed ratio of specific heats is equal to the equilibrium polytropic index of the wet steam flow through the turbine. In this paper the results of a flutter analysis are presented for the 2D test case at flow conditions with wet steam at the inlet. The investigated plunge mode normal to chord is similar to a bending mode around the turbine axis for a freestanding blade in 3D. The influence of the overall wetness fraction and the size of the water droplets at the inlet are examined. The results show an increase of aerodynamic damping for all investigated interblade phase angles with a reduction of droplet size. The influence of the wetness fraction is in comparison of less importance.

Modeling Partial Admission in Control Stages of Small Steam Turbines With CFD

2018 ◽  
Author(s):  
Juri Bellucci ◽  
Filippo Rubechini ◽  
Andrea Arnone
Keyword(s):  
Steam Turbine ◽  
Three Dimensional ◽  
Admission Rate ◽  
Point Of View ◽  
Test Case ◽  
Steam Turbines ◽  
Turbine Stage ◽  
Performance Curves ◽  
Partial Admission ◽  
The Impact

This work aims at investigating the impact of partial admission on a steam turbine stage, focusing on the aerodynamic performance and the mechanical behavior. The partialized stage of a small steam turbine was chosen as test case. A block of nozzles was glued in a single “thick nozzle” in order to mimic the effect of a partial admission arc. Numerical analyses in full and in partial admission cases were carried out by means of three-dimensional, viscous, unsteady simulations. Several cases were tested by varying the admission rate, that is the length of the partial arc, and the number of active sectors of the wheel. The goal was to study the effect of partial admission conditions on the stage operation, and, in particular on the shape of stage performance curves as well as on the forces acting on bucket row. First of all, a comparison between the flow field of the full and the partial admission case is presented, in order to point out the main aspects related to the presence of a partial arc. Then, from an aerodynamic point of view, a detailed discussion of the modifications of unsteady rows interaction (potential, shock/wake), and how these ones propagate downstream, is provided. The attention is focused on the phenomena experienced in the filling/emptying region, which represent an important source of aerodynamic losses. The results try to deepen the understanding in the loss mechanisms involved in this type of stage. Finally, some mechanical aspects are addressed, and the effects on bucket loading and on aeromechanical forcing are investigated.

A generic low-pressure steam turbine test case for aeromechanics and condensation

2019 ◽  
Vol 233 (7) ◽  
pp. 953-958
Author(s):  
Christopher Fuhrer ◽  
Marius Grübel ◽  
Damian M Vogt
Keyword(s):  
Steam Turbine ◽  
Numerical Test ◽  
Low Pressure ◽  
Test Case ◽  
Test Cases ◽  
Steam Turbines ◽  
Aerodynamic Damping ◽  
Spontaneous Condensation ◽  
Pressure Steam ◽  
Turbine Design

At the Institute of Thermal Turbomachinery and Machniery Laboratory (ITSM) a generic test case was designed to investigate aeromechanical phenomena and condensation in low-pressure steam turbines. This test case, referred to as Steam turbine Test case for Aeromechanics and Condensation (STAC) consists of the two last stages of a low-pressure steam turbine and is representative for a modern steam turbine design. STAC is intended to serve as a numerical test case to allow studying the fields of aerodynamic damping and spontaneous condensation in low-pressure steam turbine last stages. The geometry of the turbine is made available online at www.itsm.uni-stuttgart.de/research/test-cases/ .

Manufacturing Experience in an Advanced 9%CrMoCoVNbNB Alloy for Ultra-Supercritical Steam Turbine Rotor Forgings and Castings

2013 ◽  
Vol 135 (6) ◽  
Author(s):  
Rod Vanstone ◽  
Ian Chilton ◽  
Pawel Jaworski
Keyword(s):  
High Temperature ◽  
Steam Turbine ◽  
Creep Strength ◽  
Stainless Steels ◽  
First Generation ◽  
Turbine Rotor ◽  
Steam Turbines ◽  
Martensitic Stainless Steels ◽  
Operating Temperatures ◽  
New Generation

Advanced 9–12%Cr martensitic stainless steels to enable extension of steam turbine operating temperatures beyond 565 °C have been under development since the 1980s. Steam turbines with operating temperatures approaching 600 °C based on the first generation of these improved alloys, which exploited optimized levels of Mo, W, V, Nb, and N, entered service in the 1990s. Around the same time, a second generation of advanced alloys was developed incorporating additions of Co and B to further enhance creep strength. These alloys have recently been exploited to enable steam turbines with operating temperatures of up to 620 °C, and this new generation of steam turbines is now beginning to enter service. This paper describes the background to the development of these alloys and the experience gained in their application to the manufacture of high temperature rotor forgings and castings.

Improvement of Steam Turbine Blade Foil With Biomimetic Design and its Influence on Aerodynamic Performance

2019 ◽  
Author(s):  
Fan Wu ◽  
Danmei Xie ◽  
Jing Zhang ◽  
Hengliang Zhang ◽  
Chun Wang
Keyword(s):  
Steam Turbine ◽  
Turbine Blade ◽  
Vortex Pair ◽  
Separated Flow ◽  
Aerodynamic Performance ◽  
Steam Turbines ◽  
Structure Amplitude ◽  
Blade Shape ◽  
Steam Turbine Blade ◽  
Flow Vortex

Abstract To improve the steam turbines’ efficiency, researchers have put their efforts on blade foil design. Aiming at improve the aerodynamic performance of steam turbine at low load, this paper will study the effect of blade foil with bionics design on steam turbine aerodynamic performance, based on humpback whale’s fin. This paper mainly discusses a bionic foil design used on steam turbine. There are three main control parameters for each tubercle structure — amplitude, wavelength, and thickness. Taking the axial torque as the decisive consideration data and combining the vorticity diagram to analyze the flow, and on this basis, the influence of the vortex pair on the flow of the turbine blade is studied. The greater the torque, the stronger the function, so the steam turbines’ efficiency is higher. The flow condition of the optimized blade shape is improved compared to the original blade shape because it fits the blade more closely and the separated flow vortex is suppressed.

scholarly journals Influence of the Tip Clearance on the Aeroelastic Characteristics of a Last Stage Steam Turbine

2019 ◽  
Vol 9 (6) ◽  
pp. 1213
Author(s):  
Tianrui Sun ◽  
Anping Hou ◽  
Mingming Zhang ◽  
Paul Petrie-Repar
Keyword(s):  
Steam Turbine ◽  
Tip Clearance ◽  
Test Case ◽  
Steam Turbines ◽  
Aeroelastic Stability ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Aerodynamic Damping ◽  
Last Stage ◽  
Gap Height

In this paper, the tip clearance effects on the aeroelastic stability of a last-stage steam turbine model are investigated. Most of the unsteady aerodynamic work contributing to flutter of the long blades of the last-stage of a steam turbine is done near the tip of the blade. The flow in this region is transonic and sensitive to geometric parameters such as the tip clearance height. The KTH Steam Turbine Flutter Test Case was chosen as the test case, which is an open geometry with similar parameters to modern free-standing last-stage steam turbines. The energy method based on 3D URANS simulation was applied to investigate the flutter characteristics of the rotor blade with five tip gap height varying from 0–5% of the chord length. The numerical results show that the global aerodynamic damping for the least stable inter-blade phase angle (IBPA) increases with the tip gap height. Three physical mechanisms are found to cause this phenomenon. The primary cause of the variation in total aerodynamic damping is the interaction between tip clearance vortex and the trailing edge shock from the adjacent blade. Another mechanism is the acceleration of the flow near the aft side of the suction surface in the tip region due to the well-developed tip leakage vortex when the tip clearance height is greater than 2.5% of chord. This causes a stabilizing effect at the least stable IBPA. The third mechanism is the oscillation of the tip leakage vortex due to the blade vibration. This has a negative influence on the aeroelastic stability.

Manufacturing Experience in an Advanced 9%CrMoCoVNbNB Alloy for USC Steam Turbine Rotor Forgings and Castings

2012 ◽  
Author(s):  
Rod Vanstone ◽  
Ian Chilton ◽  
Pawel Jaworski
Keyword(s):  
High Temperature ◽  
Steam Turbine ◽  
Creep Strength ◽  
Stainless Steels ◽  
First Generation ◽  
Turbine Rotor ◽  
Steam Turbines ◽  
Martensitic Stainless Steels ◽  
Operating Temperatures ◽  
New Generation

Advanced 9–12%Cr martensitic stainless steels to enable extension of steam turbine operating temperatures beyond 565°C have been under development since the 1980s. Steam turbines with operating temperatures approaching 600°C based on the first generation of these improved alloys, which exploited optimised levels of Mo, W, V, Nb and N, entered service in the 1990s. Around the same time a second generation of advanced alloys was developed incorporating additions of Co and B to further enhance creep strength. These alloys have recently been exploited to enable steam turbines with operating temperatures of up to 620°C and this new generation of steam turbines is now beginning to enter service. This paper describes the background to the development of these alloys and the experience gained in their application to the manufacture of high temperature rotor forgings and castings.

Sign in / Sign up

Export Citation Format

Share Document