Design Philosophy and Methodology of a Low Pressure Exhaust Hood for a Large Power Steam Turbine

2013 ◽  
Author(s):  
Shunsuke Mizumi ◽  
Kouji Ishibashi
Keyword(s):  
Steam Turbine ◽  
Large Scale ◽  
Design Method ◽  
Low Pressure ◽  
Influential Factors ◽  
Structural Factors ◽  
Steam Turbines ◽  
Exhaust Hood ◽  
Efficient Design ◽  
Large Power

The efficiency of a steam turbine is significantly influenced by pressure recovery performance of its low-pressure exhaust hood; hence it is important to specify the cause of loss generation and to devise improved structures. The performance of the exhaust hood is greatly influenced by many structural factors such as the size of its outer casing, design of the diffuser parts and arrangement of internal supports. Ideally, it would be preferable to take all those influential factors into consideration in designing an exhaust hood. However, it is neither cost-effective nor practicable to take everything into consideration at the same time, while it is mandatory to obtain a better shape in performance within reasonable time. For this reason, it is necessary to reach a compromise to some extent between the ideal and the realistic design methods. In the present study, we propose the efficient design method of the downstream type low-pressure exhaust hood for large-scale steam turbines, utilizing the performance charts based on the extensive CFD parameter surveys.

Performance Prediction and Optimization of Low Pressure Steam Turbine Radial Diffuser at Design and Off-Design Conditions Using Streamline Curvature Method

2017 ◽  
Vol 139 (7) ◽  
Author(s):  
Luying Zhang ◽  
Francesco Congiu ◽  
Xiaopeng Gan ◽  
David Karunakara
Keyword(s):  
Steam Turbine ◽  
Flow Separation ◽  
Large Scale ◽  
Current Method ◽  
Low Pressure ◽  
Numerical Approach ◽  
Optimization Process ◽  
Exhaust Hood ◽  
Streamline Curvature ◽  
Wide Range

The performance of the radial diffuser of a low pressure (LP) steam turbine is important to the power output of the turbine. A reliable and robust prediction and optimization tool is desirable in industry for preliminary design and performance evaluation. This is particularly critical during the tendering phase of retrofit projects, which typically cover a wide range of original equipment manufacturer and other original equipment manufacturers designs. This work describes a fast and reliable numerical approach for the simulation of flow in the last stage and radial diffuser coupled with the exhaust hood. The numerical solver is based on a streamline curvature throughflow method and a geometry-modification treatment has been developed for off-design conditions, at which large-scale flow separation may occur in the diffuser domain causing convergence difficulty. To take into account the effect of tip leakage jet flow, a boundary layer solver is coupled with the throughflow calculation to predict flow separation on the diffuser lip. The performance of the downstream exhaust hood is modeled by a hood loss model (HLM) that accounts for various loss generations along the flow paths. Furthermore, the solver is implemented in an optimization process. Both the diffuser lip and hub profiles can be quickly optimized, together or separately, to improve the design in the early tender phase. 3D computational fluid dynamics (CFD) simulations are used to validate the solver and the optimization process. The results show that the current method predicts the diffuser/exhaust hood performance within good agreement with the CFD calculation and the optimized diffuser profile improves the diffuser recovery over the datum design. The tool provides General Electric the capability to rapidly optimize and customize retrofit diffusers for each customer considering different constraints.

Numerical Investigation of Exhaust Diffuser Performances in Low Pressure Turbine Casings

2011 ◽  
Author(s):  
Tadashi Tanuma ◽  
Yasuhiro Sasao ◽  
Satoru Yamamoto ◽  
Shinji Takada ◽  
Yoshiki Niizeki ◽  
...  
Keyword(s):  
Steam Turbine ◽  
High Performance ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Measurement Data ◽  
Boundary Layer Separation ◽  
Low Pressure ◽  
Tvd Scheme ◽  
Steam Turbines ◽  
Exhaust Hood

Low pressure (LP) exhaust hoods are an important component of steam turbines. The aerodynamic loss of LP exhaust hoods is almost the same as those of the stator and rotor blading in LP steam turbines. Designing high performance LP exhaust hoods should lead further enhancement of steam turbine efficiency. This paper presents the results of exhaust hood computational fluid dynamics (CFD) analyses using last stage exit velocity distributions measured in a full-scale development steam turbine as the inlet boundary condition to improve the accuracy of the CFD analysis. One of the main difficulties in predicting the aerodynamic performance of the exhaust hoods is the unsteady boundary layer separation of exhaust hood diffusers. A highly accurate unsteady numerical analysis is introduced in order to simulate the diffuser flows in LP exhaust hoods. Compressible Navier-Stokes equations and mathematical models for nonequilibrium condensation are solved using the high-order high-resolution finite-difference method based on the fourth-order compact MUSCL TVD scheme, Roe’s approximate Riemann solver, and the LU-SGS scheme. The SST turbulence model is also solved for evaluating the eddy viscosity. The computational results were validated using the measurement data, and the present CFD method was proven to be suitable as a useful tool for determining optimum three-dimensional designs of LP turbine exhaust diffusers.

The Experimental Investigation of the Internal Support Effects on Exhaust Casing Pressure Recovery

2017 ◽  
Author(s):  
Robert Kalista ◽  
Lukáš Mrózek ◽  
Michal Hoznedl
Keyword(s):  
Steam Turbine ◽  
Axial Length ◽  
Low Pressure ◽  
Pressure Recovery ◽  
Geometrical Parameters ◽  
Structural Factors ◽  
Exhaust Hood ◽  
Last Stage ◽  
Pressure Part ◽  
Horizontal Joint

As is well known, the performance of the last stage of the low pressure part of a steam turbine is strongly influenced by the effectivity of the downstream exhaust casing. The efficiency of the exhaust hood depends on many structural factors such as the design of the diffuser parts, dimensions of the outer casing or arrangement of internal supports. The aim of this paper is the experimental study of the influence of the internal supports of the axial-radial exhaust hood on its pressure recovery factor. For one geometry of its diffuser parts a few different variations of internal supports such as T-rib, tube grid or BV were tested. The effect of reducing the width of exhaust hood in the horizontal joint and the changing of axial length of the diffuser were observed. The width of exhaust hood in horizontal joint and the axial length of the diffuser define the area in the horizontal joint of the exhaust hood. How the diffuser behaves when reducing this area is very important in retrofitting of old machines, where there are so many geometric constrains. The effect of wall jet blowing into the diffuser wall was also evaluated. In this paper we concentrate to examine the sensitivity of these certain geometrical parameters of exhaust hood on the pressure recovery of the whole exhaust system of the low pressure part of the steam turbine. The main purpose of our analysis and experimental measuring was optimising the axial-radial exhaust hood of the steam turbine. For this reason, wind tunnel facilities with relevant measuring and traversing systems were designed and built. The measurements have been performed on 1/5th scale test rig which enabled rapid and efficient evaluation of multiple geometrical variants. The observed exhaust hood was designed for an extra long 54inch last stage blade. For measurements of flow parameters was used multi-hole pneumatic pressure probes and wall pressure taps in conjunction with CFD tools to explore physics based alterations to the exhaust configuration.

Detailed Numerical Study of the Main Sources of Loss and Flow Behavior in Low Pressure Steam Turbine Exhaust Hoods

2017 ◽  
Author(s):  
Dickson Munyoki ◽  
Markus Schatz ◽  
Damian M. Vogt
Keyword(s):  
Steam Turbine ◽  
Numerical Study ◽  
Flow Behavior ◽  
Low Pressure ◽  
Operating Conditions ◽  
Pressure Recovery ◽  
Exhaust Hood ◽  
Recovery Coefficient ◽  
Pressure Steam ◽  
Underlying Mechanisms

The performance of the axial-radial diffuser downstream of the last low-pressure steam turbine stages and the losses occurring subsequently within the exhaust hood directly influences the overall efficiency of a steam power plant. It is estimated that an improvement of the pressure recovery in the diffuser and exhaust hood by 10% translates into 1% of last stage efficiency [11]. While the design of axial-radial diffusers has been the object of quite many studies, the flow phenomena occurring within the exhaust hood have not received much attention in recent years. However, major losses occur due to dissipation within vortices and inability of the hood to properly diffuse the flow. Flow turning from radial to downward flow towards the condenser, especially at the upper part of the hood is essentially the main cause for this. This paper presents a detailed analysis of the losses within the exhaust hood flow for two operating conditions based on numerical results. In order to identify the underlying mechanisms and the locations where dissipation mainly occurs, an approach was followed, whereby the diffuser inflow is divided into different sectors and pressure recovery, dissipation and finally residual kinetic energy of the flow originating from these sectors is calculated at different locations within the hood. Based on this method, the flow from the topmost sectors at the diffuser inlet is found to cause the highest dissipation for both investigated cases. Upon hitting the exhaust hood walls, the flow on the upper part of the diffuser is deflected, forming complex vortices which are stretching into the condenser and interacting with flow originating from other sectors, thereby causing further swirling and generating additional losses. The detailed study of the flow behavior in the exhaust hood and the associated dissipation presents an opportunity for future investigations of efficient geometrical features to be introduced within the hood to improve the flow and hence the overall pressure recovery coefficient.

Design Optimization of a Low Pressure Steam Turbine Radial Diffuser Using an Evolutionary Algorithm and 3D CFD

2012 ◽  
Author(s):  
Tom Verstraete ◽  
Johan Prinsier ◽  
Alberto Di Sante ◽  
Stefania Della Gatta ◽  
Lorenzo Cosi
Keyword(s):  
Design Optimization ◽  
Steam Turbine ◽  
Differential Evolution Algorithm ◽  
Low Pressure ◽  
Pressure Recovery ◽  
Strong Impact ◽  
Optimized Design ◽  
Steam Turbines ◽  
Recovery Coefficient ◽  
Lp Turbine

The design of the radial exhaust hood of a low pressure (LP) steam turbine has a strong impact on the overall performance of the LP turbine. A higher pressure recovery of the diffuser will lead to a substantial higher power output of the turbine. One of the most critical aspects in the diffuser design is the steam guide, which guides the flow near the shroud from axial to radial direction and has a high impact on the pressure recovery. This paper presents a method for the design optimization of the steam guide of a steam turbine for industrial power generation and mechanical drive of centrifugal compressors. This development is in the frame of a continuous effort in GE Oil and Gas to develop more efficient steam turbines. An existing baseline exhaust and steam guide design is first analyzed together with the last LP turbine stage with a frozen rotor full 3D Computational Fluid Dynamics (CFD) calculation. The numerical prediction is compared to available steam test turbine data. The new exhaust box and a first attempt new steam guide design are then first analyzed by a CFD computation. The diffuser inlet boundary conditions are extracted from this simulation and used for improving the design of the steam guide. The maximization of the pressure recovery is achieved by means of a numerical optimization method that uses a metamodel assisted differential evolution algorithm in combination with a 3D CFD solver. The profile of the steam guide is parameterized by a Bezier curve. This allows for a wide variety of shapes, respecting the manufacturability constraints of the design. In the design phase it is mandatory to achieve accurate results in terms of performance differences in a reasonable time. The pressure recovery coefficient is therefore computed through the 3D CFD solver excluding the last stage, to reduce the computational burden. Steam tables are used for the accurate prediction of the steam properties. Finally, the optimized design is analyzed by a frozen rotor computation to validate the approach. Also off-design characteristics of the optimized diffuser are shown.

Sequential vs Multidisciplinary Coupled Optimization and Efficient Surrogate Modelling of a Last Stage and the Successive Axial Radial Diffuser in a Low Pressure Steam Turbine

2014 ◽  
Author(s):  
Kevin Cremanns ◽  
Dirk Roos ◽  
Arne Graßmann
Keyword(s):  
Steam Turbine ◽  
Design Process ◽  
Energy Demand ◽  
Three Dimensional ◽  
Flow Simulation ◽  
Low Pressure ◽  
Steam Turbines ◽  
Low Pressure Turbine ◽  
Pressure Steam ◽  
Last Stage

In order to meet the requirements of rising energy demand, one goal in the design process of modern steam turbines is to achieve high efficiencies. A major gain in efficiency is expected from the optimization of the last stage and the subsequent diffuser of a low pressure turbine (LP). The aim of such optimization is to minimize the losses due to separations or inefficient blade or diffuser design. In the usual design process, as is state of the art in the industry, the last stage of the LP and the diffuser is designed and optimized sequentially. The potential physical coupling effects are not considered. Therefore the aim of this paper is to perform both a sequential and coupled optimization of a low pressure steam turbine followed by an axial radial diffuser and subsequently to compare results. In addition to the flow simulation, mechanical and modal analysis is also carried out in order to satisfy the constraints regarding the natural frequencies and stresses. This permits the use of a meta-model, which allows very time efficient three dimensional (3D) calculations to account for all flow field effects.

The Pressure Field at the Output From a Low Pressure Exhaust Hood and Condenser Neck of the 1090 MW Steam Turbine: Experimental and Numerical Research

2018 ◽  
Author(s):  
Michal Hoznedl ◽  
Antonín Živný ◽  
Aleš Macálka ◽  
Robert Kalista ◽  
Kamil Sedlák ◽  
...  
Keyword(s):  
Boundary Condition ◽  
Steam Turbine ◽  
Cross Section ◽  
Static Pressure ◽  
Cooling Water ◽  
Low Pressure ◽  
Maximum Temperature ◽  
Angle Distribution ◽  
Exhaust Hood ◽  
Last Stage

The paper presents the results of measurements of flow parameters behind the last stage of a 1090 MW nominal power steam turbine in a nuclear power plant. The results were obtained by traversing a pneumatic probe at a distance of about 100 mm from the trailing edges of the LSB (Last Stage Blade). Furthermore, both side walls as well as the front wall of one flow of the LP (Low Pressure) exhaust hood were fitted with a dense net of static pressure taps at the level of the flange of the turbine. A total of 26 static pressures were measured on the wall at the output from the LP exhaust hood. Another 14 pressures were measured at the output from the condenser neck. The distribution of static pressures in both cross sections for full power and 600 and 800 MW power is shown. Another experiment was measured pressure and angle distribution using a ball pneumatic probe in the condenser neck area in a total of four holes at a distance up to 5 metres from the neck wall. The turbine condenser is two-flow design. In one direction perpendicular to the axis of the turbine cold cooling water comes, it heats partially. It then reverses and it heats to the maximum temperature again. The different temperature of cooling water in the different parts of the output cross section should influence the distribution of the output static pressure. Differences in pressures may cause problems with uneven load of the tube bundles of the condenser as well as problems with defining the influential edge output condition in CFD simulations of the flow of the cold end of the steam turbine Due to these reasons an extensive 3D CFD computation, which includes one stator blade as well as all moving blades of the last stage, a complete diffuser, the exhaust hood and the condenser neck, has been carried out. Geometry includes all reinforcing elements, pipes and heaters which could influence the flow behaviour in the exhaust hood and its pressure loss. Inlet boundary conditions were assumed for the case of both computations from the measurement of the flow field behind the penultimate stage. The outlet boundary condition was defined in the first case by an uneven value of the static pressure determined by the change of the temperature of cooling water. In the second case the boundary condition in accordance with the measurement was defined by a constant value of the static pressure along all the cross section of the output from the condenser neck. Results of both CFD computations are compared with experimental measurement by the distribution of pressures and other parameters behind the last stage.

Advanced Water Droplet Erosion Protection for Modern Low Pressure Steam Turbine Steel Blades

2015 ◽  
Author(s):  
Joerg Schuerhoff ◽  
Andrei Ghicov ◽  
Karsten Sattler
Keyword(s):  
Steam Turbine ◽  
Water Droplet ◽  
Precipitation Hardening ◽  
Turbine Blades ◽  
Low Pressure ◽  
Steam Turbines ◽  
Treatment Facility ◽  
Material Loss ◽  
Pressure Steam ◽  
Steam Turbine Blades

Blades for low pressure steam turbines operate in flows of saturated steam containing water droplets. The water droplets can impact rotating last stage blades mainly on the leading edge suction sides with relative velocities up to several hundred meters per second. Especially on large blades the high impact energy of the droplets can lead to a material loss particularly at the inlet edges close to the blade tips. This effect is well known as “water droplet erosion”. The steam turbine manufacturer use several techniques, like welding or brazing of inlays made of erosion resistant materials to reduce the material loss. Selective, local hardening of the blade leading edges is the preferred solution for new apparatus Siemens steam turbines. A high protection effect combined with high process stability can be ensured with this Siemens hardening technique. Furthermore the heat input and therewith the geometrical change potential is relatively low. The process is flexible and can be adapted to different blade sizes and the required size of the hardened zones. Siemens collected many years of positive operational experience with this protection measure. State of the art turbine blades often have to be developed with precipitation hardening steels and/or a shroud design to fulfill the high operational requirements. A controlled hardening of the inlet edges of such steam turbine blades is difficult if not impossible with conventional methods like flame hardening. The Siemens steam turbine factory in Muelheim, Germany installed a fully automated laser treatment facility equipped with two co-operating robots and two 6 kW high power diode laser to enable the in-house hardening of such blades. Several blade designs from power generation and industrial turbines were successfully laser treated within the first year in operation. This paper describes generally the setup of the laser treatment facility and the application for low pressure steam turbine blades made of precipitation hardening steels and blades with shroud design, including the post laser heat treatments.

Unsteady Aerodynamics of Low-Pressure Steam Turbines Operating Under Low Volume Flow

2013 ◽  
Author(s):  
Benjamin Megerle ◽  
Timothy Stephen Rice ◽  
Ivan McBean ◽  
Peter Ott
Keyword(s):  
Unsteady Flow ◽  
Steam Turbine ◽  
Measurement Data ◽  
Unsteady Aerodynamics ◽  
Low Pressure ◽  
Rotating Stall ◽  
Stage Model ◽  
Steam Turbines ◽  
Multi Stage ◽  
Low Volume

Non-synchronous excitation under low volume operation is a major risk to the mechanical integrity of last stage moving blades (LSMBs) in low-pressure (LP) steam turbines. These vibrations are often induced by a rotating aerodynamic instability similar to rotating stall in compressors. Currently extensive validation of new blade designs is required to clarify whether they are subjected to the risk of not admissible blade vibration. Such tests are usually performed at the end of a blade development project. If resonance occurs a costly redesign is required, which may also lead to a reduction of performance. It is therefore of great interest to be able to predict correctly the unsteady flow phenomena and their effects. Detailed unsteady pressure measurements have been performed in a single stage model steam turbine operated with air under ventilation conditions. 3D CFD has been applied to simulate the unsteady flow in the air model turbine. It has been shown that the simulation reproduces well the characteristics of the phenomena observed in the tests. This methodology has been transferred to more realistic steam turbine multi stage environment. The numerical results have been validated with measurement data from a multi stage model LP steam turbine operated with steam. Measurement and numerical simulation show agreement with respect to the global flow field, the number of stall cells and the intensity of the rotating excitation mechanism. Furthermore, the air model turbine and model steam turbine numerical and measurement results are compared. It is demonstrated that the air model turbine is a suitable vehicle to investigate the unsteady effects found in a steam turbine.

E222 Development of Exhaust Hood for Axial Low Pressure Steam Turbine

2012 ◽  
Vol 2012.17 (0) ◽  
pp. 409-410
Author(s):  
Taro NOGUCHI ◽  
Hiroshi SAEKI ◽  
Tatsuro UCHIDA ◽  
Yasunori IWAI ◽  
Naoki SHIBUKAWA ◽  
...  
Keyword(s):  
Steam Turbine ◽  
Low Pressure ◽  
Exhaust Hood ◽  
Pressure Steam
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