Comparative Experimental Investigation on Aerodynamic Performance of Steam Turbine Cascades: Part I — Rotor Blades

2013 ◽  
Author(s):  
Lei Gao ◽  
Qun Zheng ◽  
Hang Chen
Keyword(s):  
Steam Turbine ◽  
Large Degree ◽  
Aerodynamic Performance ◽  
Rotor Blades ◽  
Aerodynamic Loss ◽  
Transverse Pressure ◽  
Comparative Experimental Investigation ◽  
Last Stage ◽  
Turbine Cascades ◽  
End Wall

In this paper, the static aerodynamic performance of the second to last stage rotor blades of a marine steam turbine is experimentally investigated. The experiments have been carried out for both original blade (ORI R1) and modified blade (MOD R1) annular cascades. The experimental results indicate that the straight original blade is aft-loaded type, and there is a large degree of diffusion at the tip end wall. The improvement methods include adopting twist blades, adjusting the blade profile to reach the aft-loaded as much as possible at both end walls as well as combining with the cylindrical meridian lines. It has been found in the experiment that the transverse pressure gradient of the modified decreases at both end walls, so does the loss of the flow, especially it weakens the secondary flow at the tip end wall. The aerodynamic loss coefficient of improved blades has reduced by about 25%.

Aerodynamic Performance Assessment of Part-Span Connector of Last Stage Bucket of Low Pressure Steam Turbine

2011 ◽  
Author(s):  
Hiteshkumar Mistry ◽  
Manisekaran Santhanakrishnan ◽  
John Liu ◽  
Alexander Stein ◽  
Subhrajit Dey ◽  
...  
Keyword(s):  
Steam Turbine ◽  
Low Pressure ◽  
Aerodynamic Performance ◽  
Rotor Blades ◽  
Field Analysis ◽  
Working Fluid ◽  
Steam Turbines ◽  
Structural Element ◽  
Last Stage ◽  
The Impact

Modern steam turbines often utilize very long last stage buckets (LSB’s) in their low-pressure sections to improve efficiency. Some of these LSB’s can range in the order of 5 feet long. These long buckets (aka “blades”) are typically supported at their tip by a tip-shroud and near the mid span by a part span shroud or part span connector (PSC). The PSC is a structural element that connects all the rotor blades, generally at the mid span. It is primarily designed to address various structural issues, often with little attention to its aerodynamic effects. The objective of the current work is to quantify the impact of PSC on aerodynamic performance of the last stage of a LP steam turbine by using detailed CFD analyses. A commercial CFD solver, ANSYS CFX™, is used to solve the last stage domain by setting steam as the working fluid with linear variation of specific heat ratio with temperature. A tetrahedral grid with prismatic layers near the solid walls is generated using ANSYS WORKBENCH™. The results show a cylindrical PSC reduces the efficiency of the last stage by 0.32 pts, of which 0.20 pts is due to the fillet attaching the PSC to the blade. The results also show insignificant interaction of the PSC with the bucket tip aerodynamics. The work presents a detailed flow field analysis and shows the impact of PSC geometry on the aerodynamic performance of last stage of steam turbine. Present work is useful to turbine designer for trade-off studies of performance and reliability of LSB design with or without PSC.

Comparative Experimental Investigation on Aerodynamic Performance of a Steam Turbine Cascades: Part II — Stator Vanes

2013 ◽  
Author(s):  
Lei Gao ◽  
Qun Zheng ◽  
Hang Chen
Keyword(s):  
Pressure Gradient ◽  
Steam Turbine ◽  
Aerodynamic Performance ◽  
Wake Region ◽  
Uniform Loading ◽  
Experimental Conditions ◽  
Blade Height ◽  
Comparative Experimental Investigation ◽  
Turbine Cascades ◽  
Loading Type

In this paper, the eighth and the ninth stage stator blades of a marine steam turbine are improved and the experimental research has been carried out on aerodynamic performance at 50% blade height of the original and the improved plane cascades. The experimental results indicate that both of the two original stator blades are uniform loading type, which are improved and designed as the aft-loaded. The results also show that, comparing with the original blade, the improved one can shorten the length of reverse pressure gradient, therefore the reverse pressure gradient is reduced and the adaptability of cascades to incidence variation is enhanced. Meanwhile, the thin trailing edge of aft-loaded blade not only increases the base pressure of the wake region, but also reduces the width of the wake region. In addition, the results reveal that the losses of modified blades are lower than the original ones under the experimental conditions of different exit Mach numbers and different angle of incidences.

Influence of a Cylindrical Exhaust Hood Installation on the Last Stage Rotor Blades of a Low Pressure Model Steam Turbine

2017 ◽  
Author(s):  
Fabian F. Müller ◽  
Markus Schatz ◽  
Damian M. Vogt ◽  
Jens Aschenbruck
Keyword(s):  
Flow Field ◽  
Steam Turbine ◽  
Operating Conditions ◽  
Rotor Blades ◽  
Pressure Measurements ◽  
Exhaust Hood ◽  
Blade Vibration ◽  
Time Resolved ◽  
Vibration Behavior ◽  
Last Stage

The influence of a cylindrical strut shortly downstream of the bladerow on the vibration behavior of the last stage rotor blades of a single stage LP model steam turbine was investigated in the present study. Steam turbine retrofits often result in an increase of turbine size, aiming for more power and higher efficiency. As the existing LP steam turbine exhaust hoods are generally not modified, the last stage rotor blades frequently move closer to installations within the exhaust hood. To capture the influence of such an installation on the flow field characteristics, extensive flow field measurements using pneumatic probes were conducted at the turbine outlet plane. In addition, time-resolved pressure measurements along the casing contour of the diffuser and on the surface of the cylinder were made, aiming for the identification of pressure fluctuations induced by the flow around the installation. Blade vibration behavior was measured at three different operating conditions by means of a tip timing system. Despite the considerable changes in the flow field and its frequency content, no significant impact on blade vibration amplitudes were observed for the investigated case and considered operating conditions. Nevertheless, time-resolved pressure measurements suggest that notable pressure oscillations induced by the vortex shedding can reach the upstream bladerow.

The Effect of Stage-Diffuser Interaction on the Aerodynamic Performance and Design of LP Steam Turbine Exhaust Systems

2018 ◽  
Author(s):  
Bowen Ding ◽  
Liping Xu ◽  
Jiandao Yang ◽  
Rui Yang ◽  
Yuejin Dai
Keyword(s):  
Steam Turbine ◽  
Renewable Energy Sources ◽  
Rotor Blades ◽  
Steam Turbines ◽  
Flow Conditions ◽  
Part Load ◽  
Last Stage ◽  
Load Conditions ◽  
Turbine Exhaust ◽  
Exhaust Systems

Modern large steam turbines for power generation are required to operate much more flexibly than ever before, due to the increasing use of intermittent renewable energy sources such as solar and wind. This has posed great challenges to the design of LP steam turbine exhaust systems, which are critical to recovering the leaving energy that is otherwise lost. In previous studies, the design had been focused on the exhaust diffuser with or without the collector. Although the interaction between the last stage and the exhaust hood has been identified for a long time, little attention has been paid to the last stage blading in the exhaust system’s design process, when the machine frequently operates at part-load conditions. This study focuses on the design of LP exhaust systems considering both the last stage and the exhaust diffuser, over a wide operating range. A 1/10th scale air test rig was built to validate the CFD tool for flow conditions representative of an actual machine at part-load conditions, characterised by highly swirling flows entering the diffuser. A numerical parametric study was performed to investigate the effect of both the diffuser geometry variation and restaggering the last stage rotor blades. Restaggering the rotor blades was found to be an effective way to control the level of leaving energy, as well as the flow conditions at the diffuser inlet, which influence the diffuser’s capability to recover the leaving energy. The benefits from diffuser resizing and rotor blade restaggering were shown to be relatively independent of each other, which suggests the two components can be designed separately. Last, the potentials of performance improvement by considering both the last stage rotor restaggering and the diffuser resizing were demonstrated by an exemplary design, which predicted an increase in the last stage power output of at least 1.5% for a typical 1000MW plant that mostly operates at part-load conditions.

Effect of Snubbers and Lacing Wire on Aerodynamic Performance of Last Stage Steam Turbine

2019 ◽  
Author(s):  
P. Sreekumar ◽  
Mahesh K. Varpe
Keyword(s):  
Aspect Ratio ◽  
Steam Turbine ◽  
Aerodynamic Performance ◽  
Base Line ◽  
Performance Loss ◽  
Performance Requirements ◽  
Last Stage ◽  
Lp Turbine ◽  
The Impact ◽  
Sensitive Behavior

Abstract The aerodynamics design of a steam turbine stage is an agreement between the performance requirements and the mechanical limitations. The design of last stage of the low-pressure steam (LP) turbine is the most complicated because of the blade twist and a tapered blade along with high aspect ratio due to the sharp increase in the specific volume of the steam during its expansion. The choice of higher aspect ratio for increased power generation makes the turbine blade experience the vibration due to lower modal frequencies which depend on the running speed of a turbine. Therefore, the sensitive behavior of these blades is reduced by damping the blade vibrations which comes with the penalty of aerodynamic performance. The investigation reported here discusses the impact of lacing wire and snubber mounted at 70% blade span. Both, the lacing wire and snubber aligned parallel to the rotor axis deteriorates the efficiency by 0.75% and 1.7% respectively. However, the aerodynamically shaped snubber aligned with the streamline direction recovers the efficiency to that of base line. The mechanism of streamwise aligned snubber in containing aerodynamic performance loss is quite interesting and is being discussed.

Numerical Investigations on the Aerodynamic Performance of Last Stage Bucket With Part-Span Connector

2014 ◽  
Author(s):  
Bin Li ◽  
Jun Li
Keyword(s):  
Three Dimensional ◽  
Cross Flow ◽  
Suction Side ◽  
Aerodynamic Performance ◽  
Field Analysis ◽  
Operational Conditions ◽  
Aerodynamic Loss ◽  
Three Stages ◽  
Last Stage ◽  
Flow Vortex

Long last stage bucket often utilizes part-span connector (PSC) to address various structural issues, however pay little attention to its impact on the aerodynamic performance. In this paper, the aerodynamic performance assessment of last three stages in low pressure steam turbine with PSC on last stage bucket is numerically conducted through solving the three-dimensional Reynolds-Averaged Navier-Stokes (RANS) and k-ε turbulent model based on CFD software ANSYS-CFX. Structured hexahedral grid with reasonable quality is generated for all three stages including last stage bucket with PSC. Three types of grids are used to conduct the grid number independence test. Two kinds of PSCs with different span locations are utilized in last stage bucket. Detailed flow field analysis and comparison of last three stages at designed and off-designed operational conditions without and with two different PSCs are presented. The results show that the two different part-span connectors reduce total-total isentropic efficiency by 0.11% and 0.22%. The mass flow and torque are pushed to upper and bottom as the presence of PSC. The cross flow vortex caused by pressure gradient between pressure and suction side leads to aerodynamic loss.

Numerical Analysis of the Blade Forces Caused by Wake/Blade Interaction in the Last Stage of a Steam Turbine

2007 ◽  
Author(s):  
J. C. Garci´a ◽  
J. Kubiak ◽  
F. Sierra ◽  
G. Urquiza ◽  
J. A. Rodri´guez
Keyword(s):  
Flow Field ◽  
Steam Turbine ◽  
Pressure Field ◽  
Stokes Equations ◽  
Life Time ◽  
Rotor Blades ◽  
Three Dimensions ◽  
Useful Life ◽  
Last Stage ◽  
Axial Clearance

In a steam turbine stage there is an interaction between blades and the flow field. The blades are subjected to the forces caused by the flow field, but also the flow field is affected by the blades and its movement. The nozzle wakes cause uneven pressure field downstream and produce alternating forces on blades which lead to blade vibrations. Some of the vibrations originated in this way may damage the blades and affect the turbine performance. The results of numerical computations about the forces acting on the blades as a result of the variations in the flow field in the axial clearance rotor-stator in the last stage of a 110 MW steam turbine are presented. The analysis is focused on discussing the pressure field because it is necessary for further computation of the useful life time. The flow field was resolved using computational fluids dynamics and the computed pressure field was integrated around the blades to get the forces acting on blades. These computed dynamical forces will be used in the blade useful life estimation and in the investigation to the failure causes of these blades. The Navier-Stokes equations are resolved in two and three dimensions using a commercial program based on finite-volume method. 2-D and 3-D geometry models were built to represent the dimensional aspects of the last stage of the turbine. Periodic boundary conditions were applied to both sides of a periodic segment of the 2-D and 3-D models with the purpose of reducing computational efforts. The computations were conducted in steady state and transient conditions. The results show that the force magnitude acting on blades has an harmonic pattern. Finally a Fourier analysis was used to determine the coefficients and frequency of a Fourier equation which can be used to calculate the alternating stresses on the blade in order to predict the useful life of the blades. Also, the pressure and velocity fields are shown between the diaphragm and rotor blades along the axial clearance.

A CFD Approach to Fluid Dynamic Optimum Design of Steam Turbine Stages With Stator and Rotor Blades

2010 ◽  
Author(s):  
Xin Yuan ◽  
Tadashi Tanuma ◽  
Xiaofeng Zhu ◽  
Zhirong Lin ◽  
Daisuke Nomura
Keyword(s):  
High Pressure ◽  
Steam Turbine ◽  
Optimum Design ◽  
Rotor Blade ◽  
Fluid Dynamic ◽  
Rotor Blades ◽  
Turbine Stage ◽  
Tip Leakage ◽  
Pressure Steam ◽  
End Wall

An advanced aerodynamic design optimization system for steam turbine stages considering rotor blade tip leakage and blade end-wall non-axis-symmetric contouring has been developed. Using this system, fluid dynamic optimizations were carried out for a steam turbine stage with stator and rotor blades. The system includes parametric modeling of blade and end-wall contouring, evaluation system with in-house or package CFD software and optimization strategy module. The designs of rotor blade and hub end-wall surface in a typical large-scale high-pressure steam turbine stage were optimized in order to know this design optimization impact on enhancing the stage efficiency. Results show that: from the current well designed high pressure steam turbine stage, the demonstrated efficiency enhancement with the present optimum design is around 0.2% under consideration of rotor tip leakage. Design cycle could be greatly shortened by parallel optimization algorithm and cluster PC, and especially four days could be sufficient for an optimization with one thousand iterations on 20 CPUs of 2.0G cluster PC.

Aerodynamic Optimization of the Diffuser Towards Improving the Performance of Turbine and Exhaust Hood

2014 ◽  
Author(s):  
Jing-Lun Fu ◽  
Jian-Jun Liu ◽  
Si-Jing Zhou
Keyword(s):  
Kinetic Energy ◽  
Aerodynamic Performance ◽  
Steam Turbines ◽  
Exhaust Hood ◽  
Aerodynamic Optimization ◽  
Operational Conditions ◽  
Flow Interactions ◽  
Overall Performance ◽  
Last Stage ◽  
End Wall

Exhaust hood of large steam turbines is designed to recover the leaving kinetic energy of the last stage turbine while guiding the flow from the turbine to the condenser, which is of great importance to the overall performance of the steam turbine. The influences imposed by the strong flow interactions between the last stage turbine and the non-axisymmetric exhaust hood have not been taken into account properly in the current exhaust hood design approaches. The purpose of this paper is to optimize the diffuser in order to guarantee the aerodynamic performance of the turbine and the exhaust hood under the operational conditions. Considering the flow interactions between the turbine and the exhaust hood, the profiles of the diffuser end-wall were improved. The coupled turbine and exhaust hood calculations and the experiments were carried out to validate the effects of the optimization. It’s found that the redesigned diffuser can enhance the pressure recovery ability of the exhaust hood and increase the power output of the last stage turbine.

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