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.

Numerical Investigation on the Aerodynamic Performance of a Low-Pressure Steam Turbine Exhaust Hood Using DOE Analysis

2020 ◽  
Author(s):  
Tommaso Diurno ◽  
Tommaso Fondelli ◽  
Leonardo Nettis ◽  
Nicola Maceli ◽  
Lorenzo Arcangeli ◽  
...  
Keyword(s):  
Flow Field ◽  
Steam Turbine ◽  
Low Pressure ◽  
Operating Conditions ◽  
Pressure Recovery ◽  
Exhaust Hood ◽  
Recovery Coefficient ◽  
Pressure Steam ◽  
Pressure Recovery Coefficient ◽  
Turbine Exhaust

Abstract Nowadays, the rising interest in using renewable energy for thermal power generation has led to radical changes in steam turbine design practice and operability. Modern steam turbines are required to operate with greater flexibility due to rapid load changes, fast start-up, and frequent shutdowns. This has given rise to great challenges to the exhaust hood system design, which has a great influence on the overall turbine performance converting the kinetic energy leaving the last stage of LP turbine into static pressure. The radial hoods are characterized by a complex aerodynamic behavior since the flow turns by 90° in a very short distance and this generates a highly rotational flow structure within the diffuser and exhaust hood outer casing, moreover, the adverse pressure gradient can promote the flow separation drastically reducing the hood recovery performance. For these reasons it is fundamental to design the exhaust system in order to ensure a good pressure recovery under all the machine operating conditions. This paper presents a Design of Experiment analysis on a low-pressure steam turbine exhaust hood through CFD simulations. A parametric model of an axial-radial exhaust hood was developed and a sensitivity of exhaust hood performance as a function of key geometrical parameters was carried out, with the aim of optimizing the pressure recovery coefficient and minimizing the overall dimensions of the exhaust casing. Since hood performance strongly depends on a proper coupling with the turbine rear stage, such a stage was modeled using the so-called mixing-plane approach to couple both stator-rotor and rotor-diffuser interfaces. A detailed analysis of the flow field in the exhaust hood in the different configurations was performed, detecting the swirling structures responsible for the energy dissipation in each simulation, as well as correlating the flow field with the pressure recovery coefficient.

Numerical Investigation on the Aerodynamic Performance of a Low-Pressure Steam Turbine Exhaust Hood Using Design of Experiment Analysis

2020 ◽  
Vol 142 (11) ◽  
Author(s):  
Tommaso Diurno ◽  
Tommaso Fondelli ◽  
Leonardo Nettis ◽  
Nicola Maceli ◽  
Lorenzo Arcangeli ◽  
...  
Keyword(s):  
Flow Field ◽  
Steam Turbine ◽  
Design Of Experiment ◽  
Low Pressure ◽  
Pressure Recovery ◽  
Exhaust Hood ◽  
Recovery Coefficient ◽  
Pressure Steam ◽  
Pressure Recovery Coefficient ◽  
Turbine Exhaust

Abstract Nowadays, the rising interest in using renewable energy for thermal power generation has led to radical changes in steam turbine design practice and operability. Modern steam turbines are required to operate with greater flexibility due to rapid load changes, fast start-up, and frequent shutdowns. This has given rise to great challenges to the exhaust hood system design, which has a great influence on the overall turbine performance converting the kinetic energy leaving the last stage of low-pressure turbine into static pressure. The radial hoods are characterized by a complex aerodynamic behavior since the flow turns by 90 deg in a very short distance and this generates a highly rotational flow structure within the diffuser and exhaust hood outer casing, moreover, the adverse pressure gradient can promote the flow separation drastically reducing the hood recovery performance. For these reasons, it is fundamental to design the exhaust system in order to ensure a good pressure recovery under all the machine operating conditions. This paper presents a design of experiment (DOE) analysis on a low-pressure steam turbine exhaust hood through computational fluid dynamics (CFD) simulations. A parametric model of an axial-radial exhaust hood was developed, and a sensitivity of exhaust hood performance as a function of key geometrical parameters was carried out, with the aim of optimizing the pressure recovery coefficient and minimizing the overall dimensions of the exhaust casing. Since hood performance strongly depends on a proper coupling with the turbine rear stage, such a stage was modeled using the so-called mixing-plane approach to couple both stator–rotor and rotor-diffuser interfaces. A detailed analysis of the flow field in the exhaust hood in the different configurations was performed, detecting the swirling structures responsible for the energy dissipation in each simulation, as well as correlating the flow field with the pressure recovery coefficient.

Numerical Investigation of the Influence of Hood Height Variation on Performance of Low Pressure Steam Turbine Exhaust Hoods

2018 ◽  
Author(s):  
Dickson Munyoki ◽  
Markus Schatz ◽  
Damian M. Vogt
Keyword(s):  
Steam Turbine ◽  
Low Pressure ◽  
Pressure Recovery ◽  
Reference Configuration ◽  
Maximum Efficiency ◽  
Parameter Study ◽  
Exhaust Hood ◽  
Pressure Steam ◽  
The Impact ◽  
Turbine Exhaust

Performance optimization of low pressure steam turbine exhaust hood has been a subject of a number of both numerical and experimental studies. This is driven by the understanding that improving the diffuser and exhaust hood outer casing performance results in a lower turbine back pressure and hence an increased plant overall output. 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 the arrangement of the internal supports. A number of studies have shown that a decrease of the hood height is detrimental to the exhaust hood performance [1, 2], however, up to now the impact of increased hood height has not been researched. In the present study, a scaled axial-radial diffuser test rig operated by ITSM is used as reference configuration for a parameter study. A total of fourteen different configurations with both increased and reduced hood height are investigated numerically. Design load at three different tip jet Mach numbers (no tip jet, tip jet Mach number of 0.4 and 1.2) is chosen as operating condition. Numerical and experimental data is available for the reference configuration and the numerical results have already been validated in a previous paper by the authors [3]. While a decrease of hood height shows the expected deterioration of efficiency, an increase of the hood height only initially results in an improved performance. After reaching a maximum efficiency, which is dependent on the tip leakage, the exhaust hood performance decreases noticeably again. Apart from the variation of pressure recovery, the results allow a better understanding of the loss mechanisms and flow phenomena in exhaust hoods, showing that the deflection of the flow coming out of the diffuser in the top part of the hood has a major impact on exhaust hood pressure recovery.

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.

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

scholarly journals Investigation on low-pressure steam turbine exhaust hood modelling through computational fluid dynamic simulations

2019 ◽  
Author(s):  
Tommaso Fondelli ◽  
Tommaso Diurno ◽  
Lorenzo Palanti ◽  
Antonio Andreini ◽  
Bruno Facchini ◽  
...  
Keyword(s):  
Steam Turbine ◽  
Computational Fluid Dynamic ◽  
Fluid Dynamic ◽  
Low Pressure ◽  
Exhaust Hood ◽  
Dynamic Simulations ◽  
Pressure Steam ◽  
Turbine Exhaust

Unsteady Flow Effect on Nonequilibrium Condensation in 3-D Low Pressure Steam Turbine Stages

2013 ◽  
Author(s):  
Satoshi Miyake ◽  
Satoru Yamamoto ◽  
Yasuhiro Sasao ◽  
Kazuhiro Momma ◽  
Toshihiro Miyawaki ◽  
...  
Keyword(s):  
Unsteady Flow ◽  
Steam Turbine ◽  
Cross Sections ◽  
Rotor Blade ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Low Pressure ◽  
Multi Stage ◽  
Pressure Steam ◽  
Nonequilibrium Condensation

A numerical study simulating unsteady 3-D wet-steam flows through three-stage stator-rotor blade rows in a low-pressure steam turbine model experimentally conducted by Mitsubishi Heavy Industry (MHI) was presented in the last ASME Turbo Expo by our group. In this study, the previous discussion is extended to the discussion how nonequilibrium condensation is influenced by unsteady wakes and corner vortices from prefaced multi-stage blade rows. Unsteady 3-D flows through three-stage stator-rotor blade rows are simulated assuming nonequilibrium condensation. Flows with a different inlet flow condition are calculated and the results are compared with each other. Instantaneous condensate mass fractions are visualized at different spans and cross sections in the three-stage stator and rotor blade rows. Also the time and space dependent values are plotted and the obtained unsteady flow characteristics are explained.

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