A Combined Numerical Model and Optimization for Low Pressure Exhaust System in Steam Turbine

2007 ◽  
Author(s):  
Tao Fan ◽  
Yonghui Xie ◽  
Di Zhang ◽  
Bi Sun
Keyword(s):  
Numerical Model ◽  
Flow Field ◽  
Exhaust System ◽  
Low Pressure ◽  
Aerodynamic Performance ◽  
Numerical Results ◽  
Steam Turbines ◽  
Exhaust Hood ◽  
Inhomogeneous Flow ◽  
Last Stage

Computational fluid dynamics is widely used in the aerodynamic performance analysis of the low pressure exhaust system (LPES) which consists of the exhaust hood and condenser neck. However, most of the former studies analyzed the exhaust system separately without considering the effect on flow field from the last stage. In order to get the detailed information of flow field in LPES of steam turbines and reduce energy loss, a numerical model includes condenser neck, exhaust hood and last stage was constructed. This model can describe the effect of unsymmetrical inlet flow on the aerodynamic performance of LPES, so the effect of the inhomogeneous flow from the last stage was taken into account. The Reynolds averaged N-S equations with RNG k-ε turbulence model were adopted to analyze the flow field in the exhaust system considering the interaction between the exhaust system and the last stage, the mixing plane approach was used. The combined model can provide more reasonable numerical results of LPES, it shows that the inhomogeneous flow from the last stage is one of the main reasons leading to flow separation in diffuser. The influence of inner low pressure heater and the diffuse function of the condenser neck structure are the main reasons for the nonuniform velocity distribution of the flow field at the LPES outlet. Furthermore, based on the numerical results, an optimal LPES which has better aerodynamic performance and more reasonable flow is obtained. The optimal structure has low steam resistance and low exhaust pressure, so it can increase the efficiency of turbine.

Numerical Investigations on the Aerodynamic Performance of Last Stage – Exhaust Hood for Steam Turbines

2011 ◽  
Author(s):  
Rui Yang ◽  
Jiandao Yang ◽  
Zeying Peng ◽  
Liqun Shi ◽  
Aping He ◽  
...  
Keyword(s):  
Working Conditions ◽  
Static Pressure ◽  
Aerodynamic Performance ◽  
Pressure Recovery ◽  
Computational Domain ◽  
Steam Turbines ◽  
Exhaust Hood ◽  
Recovery Coefficient ◽  
Last Stage ◽  
Pressure Recovery Coefficient

The aerodynamic performance and internal flow characteristics of the last stage and exhaust hood for steam turbines is numerically investigated using the Reynolds-Averaged Navier-Stokes (RANS) solutions based on the commercial CFD software ANSYS CFX. The full last stage including 66 stator blades and 64 rotor blades coupling with the exhaust hood is selected as the computational domain. The aerodynamic performance of last stage and static pressure recovery coefficient of exhaust hood at five different working conditions is conducted. The interaction between the last stage and exhaust hood is considered in this work. The effects of the non-uniform aerodynamic parameters along the rotor blade span on the static pressure recovery coefficient of the non-symmetric geometry of the exhaust hood are studied. The numerical results show that the efficiency of the last stage has the similar values ranges from 89.8% to 92.6% at different working conditions. In addition, the similar static pressure recovery coefficient of the exhaust hood was observed at five working conditions. The excellent aerodynamic performance of the exhaust hood was illustrated in this work.

Numerical Tests on the Effect Factors of the Last Stage Blade for Low Pressure Exhaust Hood Simulation

2017 ◽  
Author(s):  
Liu Meng ◽  
Chen Yang ◽  
Zhong Zhuhai ◽  
Zhang Xiaodan ◽  
Deng Guoliang ◽  
...  
Keyword(s):  
Boundary Condition ◽  
Flow Field ◽  
Jet Flow ◽  
Low Pressure ◽  
Exhaust Hood ◽  
Effect Factors ◽  
Numerical Tests ◽  
Wide Range ◽  
Last Stage ◽  
Inlet Boundary Condition

Kinetic energy recovery is a key objective for low pressure exhaust hood design and optimization. Numerical simulation of the exhaust hood helps the engineers to explore and confirm the causes of the loss in the hood. Many studies have suggested that it is necessary for the simulation to include the last stage blade to get a realistic assessment. For the sole exhaust hood study, the inlet boundary condition is hard to set precisely like the downstream flow of the last stage blade. And the studies have also shown that the performances generated from the simulations may vary evidently between the sole exhaust hood and exhaust hood with last stage blade. It is obvious that the blade influences the exhaust hood, but the exact effect factors of the blade and the way they work are not thoroughly discussed. This paper has conducted many numerical tests to audit the influence of the common effect factors of the last stage blade. The internal flow field of the exhaust hood was numerically investigated using three-dimensional Reynolds-Averaged Navier-Stokes (RANS) solutions based on the ANSYS-CFX. In the first part of the paper, the tests are conducted by changing each effect factor of the inlet boundary condition for sole exhaust hood studies. These factors include the mass flow flux, the angle of the exit flow of the last stage, both the circumferential and the radial ones, and the speed and position of the jet-flow downstream of the seal over the shroud of the bucket. The tests show that each factor has its own distinctive style and extent for influence. Some of them may maximize the performance at some certain point, and some may deteriorate the performance rapidly beyond a threshold. And some factors may change the performance insignificantly within a wide range. However, these influences are not good enough to be consistent with the difference between the sole exhaust hood and the hood with blade simulations. In the second part of this paper, the focus locates on the direction of the jet-flow of the bucket seal. The tests prove that this direction is the prominent factor to influence the exhaust hood performance. Some extra tests for the seal have also been conducted to analyze this factor. The static pressure recovery for the simulation with labyrinth seal is about only half of the sole exhaust hood simulation. The discussion of these tests show that the seal jet is the main cause for this performance dive, and explain how the seal jet direction changes the flow field of the exhaust hood. It also suggests that the procedure to optimize the seal design is not mature yet, for some nature of the jet-flow remains unclear. It may need more detailed study in the future.

Effects of the Last Stage Rotor Tip Leakage Flow on the Aerodynamic Performance of the Exhaust Hood for Steam Turbines

2013 ◽  
Author(s):  
Jun Li ◽  
Zhigang Li ◽  
Zhenping Feng
Keyword(s):  
Static Pressure ◽  
Aerodynamic Performance ◽  
Pressure Recovery ◽  
Leakage Flow ◽  
Steam Turbines ◽  
Exhaust Hood ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Last Stage ◽  
Recovery Performance

The static pressure recovery coefficient of the exhaust hood has significant impact on the aerodynamic performance of the low pressure cylinder for steam turbines. Numerical investigations on the aerodynamic performance of the exhaust hood and full last stage with consideration of the rotor tip leakage were presented in this paper. Three-dimensional Reynolds-Averaged Navier-Stokes (RANS) solutions and k–ε turbulent model were utilized to analyze the static pressure recovery performance of the exhaust hood using the commercial CFD software ANSYS-CFX. Effect of the last stage rotor tip leakage flow on the aerodynamic performance of the downstream exhaust hood was conducted by comparison of the computational domains for the exhaust hood and full last stage with and without tip clearance. The numerical results show that the last stage rotor tip leakage jet can suppress the flow separation near the diffuser wall of the exhaust hood and improve its static pressure recovery performance. The detailed flow fields of the exhaust hood with and without consideration of the rotor tip leakage flow were also illustrated and corresponding flow mechanism was discussed.

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.

Experimental Investigation of Geometrical Parameters on the Pressure Recovery of Low Pressure Steam Turbine Exhaust Hoods

2011 ◽  
Author(s):  
Conrad Finzel ◽  
Markus Schatz ◽  
Michael V. Casey ◽  
Daniel Gloss
Keyword(s):  
Exhaust System ◽  
Low Pressure ◽  
Design Flow ◽  
Pressure Recovery ◽  
Steam Turbines ◽  
Exhaust Hood ◽  
Flow Area ◽  
Pressure Steam ◽  
Joint Plane ◽  
Horizontal Joint

The three-dimensional inhomogeneous flow in the exhaust hoods of low pressure steam turbines is a major cause of losses and the design of low-loss exhaust hoods remains a challenge, particularly in retrofit units. This paper examines the sensitivity of certain geometrical exhaust hood parameters on the pressure recovery of the whole exhaust system of low pressure steam turbines. The experimental investigations are carried out in a scaled exhaust system test rig operating at full-scale Mach numbers and near design flow conditions. The measurements for all exhaust hood configurations have been performed on two axial-radial diffuser geometries at two different load points, which represent the outflow in the design point of a last stage rotor with and without shrouds. The flow measurements make use of pneumatic probes and wall pressure taps. The influence of the exhaust hood area, the flow area in the horizontal joint plane and the location of the steam inlet are examined. The sensitivity of the pressure recovery on these parameters is evaluated. The flow area in the horizontal joint plane is identified as the most sensitive geometrical parameter in the exhaust hood of low pressure steam turbines.

Unsteady Flow Field and Coarse Droplet Measurements in the Last Stage of a Low-Pressure Steam Turbine With Supersonic Airfoils Near the Blade Tip

2017 ◽  
Vol 139 (9) ◽  
Author(s):  
Ilias Bosdas ◽  
Michel Mansour ◽  
Anestis I. Kalfas ◽  
Reza S. Abhari ◽  
Shigeki Senoo
Keyword(s):  
Flow Field ◽  
Steam Turbine ◽  
Leading Edge ◽  
Low Pressure ◽  
Fast Response ◽  
Operating Conditions ◽  
Electricity Production ◽  
Test Facility ◽  
Steam Turbines ◽  
Last Stage

The largest share of electricity production worldwide belongs to steam turbines. However, the increase of renewable energy production has led steam turbines to operate under part load conditions and increase in size. As a consequence, long rotor blades will generate a relative supersonic flow field at the inlet of the last rotor. This paper presents a unique experiment work that focuses at the top 30% of stator exit in the last stage of an low pressure (LP) steam turbine test facility with coarse droplets and high wetness mass fraction under different operating conditions. The measurements were performed with two novel fast response probes: a fast response probe for three-dimensional flow field wet steam measurements and an optical backscatter probe for coarse water droplet measurements ranging from 30 μm up to 110 μm in diameter. This study has shown that the attached bow shock at the rotor leading edge is the main source of interblade row interactions between the stator and rotor of the last stage. In addition, the measurements showed that coarse droplets are present in the entire stator pitch with larger droplets located at the vicinity of the stator's suction side. Unsteady droplet measurements showed that the coarse water droplets are modulated with the downstream rotor blade-passing period. This set of time-resolved data will be used for in-house computational fluid dynamics (CFD) code development and validation.

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.

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.

Numerical Simulation of Condenser Throat Combining with Low-Pressure Exhaust Hood for 600MW Thermal Power Unit

2012 ◽  
Vol 614-615 ◽  
pp. 77-82
Author(s):  
Jian Li ◽  
Li Zhang ◽  
Si Ping Wang
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Velocity Distribution ◽  
Calculation Result ◽  
Thermal Power ◽  
Low Pressure ◽  
Exhaust Hood ◽  
Combined Model ◽  
Real Condition ◽  
Reasonable Result

In order to obtain the more real condition of the flow field at condenser throat the flow field of condenser throat is numerical simulated by the FLUENT commercial software, alone or coupling with the low-pressure exhaust hood. The results show that the flow field of condenser throat is strongly influenced by low-pressure exhaust hood, the frustum’s diffuse-angle, the low-pressure heater and the injection of the exhaust steam from the small turbine. The velocity distribution at the outlet of the throat isn’t uniform. The calculation result of combined model is also different from the single calculation result of condenser throat. Combined numerical simulation obtains more reasonable result.

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.

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