Numerical Analysis on the Swirl Flows in the Exhaust Hood of Steam Turbine and Optimization Design

2016 ◽  
Author(s):  
Mingyan Yin ◽  
Chen Yang ◽  
Liu Meng ◽  
Wei Yan ◽  
Zhong Zhuhai ◽  
...  
Keyword(s):  
Optimization Design ◽  
Static Pressure ◽  
Internal Flow ◽  
Aerodynamic Performance ◽  
Pressure Recovery ◽  
Steam Turbines ◽  
Exhaust Hood ◽  
Recovery Coefficient ◽  
Swirl Flows ◽  
Recovery Performance

A well-designed exhaust hood of large steam turbines would recover some kinetic energy from the flow between the last stage blades and condenser, which improves the efficiency of the cylinder. The internal flow field of the exhaust hood was firstly numerical investigated using three-dimensional Reynolds-Averaged Navier-Stokes (RANS) solutions based on the ANSYS-CFX. Then, the effects of the dimensions of the cylinder, bearing cone, diffuser guide, and diffuser ribs on the static pressure recovery performance of the exhaust hood were numerically conducted. The numerical results show that the cylinder length has significantly impact on the static pressure recovery coefficient of the exhaust hood by comparison of the cylinder section area at the fixed bearing cone and diffuser size. The bearing cone and diffuser were optimized to improve the aerodynamic performance of the exhaust hood. The rotationally symmetrical and enlarged diffusers show the different static pressure recovery performance of the exhaust hood. The optimized exhaust hood shows the improved aerodynamic performance by comparison of the initial design. The detailed flow pattern of the initial and optimized exhaust hood is also illustrated and discussed. This paper explicitly shows the interaction, and offers a good strategy for optimization, which has not been thoroughly discussed.

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.

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 Design of Exhaust Hood Diffuser for Steam Turbine With Three-Dimensional Reynolds-Averaged Navier-Stokes Solutions

2014 ◽  
Author(s):  
Jiandao Yang ◽  
Taowen Chen ◽  
Jun Li ◽  
Zhenping Feng
Keyword(s):  
Optimization Design ◽  
Static Pressure ◽  
Three Dimensional ◽  
Aerodynamic Performance ◽  
Navier Stokes ◽  
Exhaust Hood ◽  
Aerodynamic Optimization ◽  
Recovery Coefficient ◽  
Last Stage ◽  
Pressure Recovery Coefficient

Combined with three-dimensional parameterization method of exhaust diffuser profile, aerodynamic performance evaluation method, response surface approximation evaluation model and Hooke-Jeeves direct search approach, aerodynamic optimization design of exhaust hood diffuser for steam turbine is presented. The aerodynamic performance of exhaust hood design candidate is evaluated using three-dimensional Reynolds-Averaged Navier-Stokes (RANS) solutions. Aerodynamic optimization design of exhaust hood is conducted for the maximum of the static pressure recovery coefficient of exhaust hood. The design variables are specified by the exhaust diffuser profile parameterization method. The aerodynamic performance of the optimized exhaust hood and referenced design is numerically calibrated with consideration of the full last stage and rotor tip clearance. The static pressure recovery coefficient of the optimized exhaust hood is higher than that of the referenced design with consideration of the upstream last stage influence. Furthermore, the detailed flow pattern of the optimized exhaust hood and referenced design is also analyzed and compared.

Effects of struts profiles and skewed angles on the aerodynamic performance of gas turbine exhaust diffuser

2021 ◽  
pp. 095765092098520
Author(s):  
Yuxuan Dong ◽  
Zhigang Li ◽  
Jun Li ◽  
Liming Song
Keyword(s):  
Gas Turbine ◽  
Static Pressure ◽  
Three Dimensional ◽  
Aerodynamic Performance ◽  
Pressure Recovery ◽  
Recovery Coefficient ◽  
Flow Field Characteristics ◽  
Gas Turbine Exhaust ◽  
Pressure Recovery Coefficient ◽  
Turbine Exhaust

The strut structure directly affects the flow field characteristics and aerodynamic performance of the gas turbine exhaust diffuser. The effects of the strut profiles and strut skewed angles on the aerodynamic performance of the exhaust diffuser at different inlet pre-swirls were numerically investigated using three-dimensional Reynolds-Averaged Navier-Stokes(RANS) and Realizable k-ε turbulence model. The numerical static pressure recovery coefficient of the exhaust diffuser is in agreement with the experimental data well. The reliability of the numerical method for the exhaust diffuser performance analysis was demonstrated. Exhaust diffusers with four kinds of vertical strut profiles obtain the highest static pressure recovery coefficient at the inlet pre-swirl of 0.35. The similar static pressure recovery coefficient of exhaust diffusers with four kinds of vertical strut airfoils are observed when the inlet pre-swirl is less than 0.48. The static pressure recovery coefficient of exhaust diffusers with vertical b1 and b2 struts are higher than that with the a1 and a2 struts when the inlet pre-swirl is greater than 0.48. At the inlet pre-swirl of 0.35, The static pressure recovery coefficient of the exhaust diffuser with the a1 strut decreases with the increasing of the strut skewed angles. The static pressure recovery coefficient of the exhaust diffuser with the b1 strut increases with the increasing of the strut skewed angles, and the static pressure recovery coefficient increases by 3.6% compared with the vertical design when the skewed angle of b1 strut is 40[Formula: see text]. At the inlet pre-swirl of 0.64. The static pressure recovery coefficient of the exhaust diffuser with the a1 strut increases by 8.7% compared with the vertical design when the skewed angle of a1 strut is greater than 20°. In addition, the static pressure recovery coefficient of the exhaust diffuser with the b1 strut decreases by 3.8% compared with the vertical design when the skewed angle of b1 strut is 40°. The method to improve the aerodynamic performance of the exhaust diffuser by appropriate increase the strut maximum thickness and design the strut skewed angle is proposed in this work.

Investigations on the Flow Pattern and Aerodynamic Performance of Last Stage and Exhaust Hood for Large Power Steam Turbines

2012 ◽  
Author(s):  
Zhigang Li ◽  
Jun Li ◽  
Xin Yan ◽  
Zhenping Feng ◽  
Hiroharu Ohyama ◽  
...  
Keyword(s):  
Flow Pattern ◽  
Static Pressure ◽  
Flow Behavior ◽  
Internal Flow ◽  
Aerodynamic Performance ◽  
Meridional Plane ◽  
Computational Domain ◽  
Exhaust Hood ◽  
Large Power ◽  
Last Stage

The aerodynamic performance and internal flow behavior of the last stage and exhaust hood for large power steam turbine was numerically investigated using commercial CFD software ANSYS-CFX. The computational domain includes all stator and rotor blades of last stage and exhaust hood including bracing tubes and strengthening plates. The Reynolds-Averaged Navier-Stokes (RANS) solution was utilized to analyze aerodynamic performance of last stage and static pressure recovery coefficient of exhaust hood. For comparison, the internal flow pattern of the individual exhaust hood was also analyzed without consideration of the last stage effects. The static pressure and Mach number distribution at the meridional plane of the last stage was illustrated. The velocity vector distribution at different cross sections in the exhaust hood with and without consideration of the last stage influence was compared. In addition, the static pressure and pressure loss contours distribution in the exhaust hood were also studied. The obtained results show that the outflow of the last stage can significantly influence the aerodynamic performance and flow pattern of the exhaust hood. To obtain a reliable prediction of the aerodynamic performance of the exhaust hood, it is necessary to consider the interaction between the last stage and exhaust hood.

An Investigation of the Tapered Strut On Aerodynamic Performance of the Exhaust Diffuser Under Different Swirls

2021 ◽  
Author(s):  
Yuxuan Dong ◽  
Zhigang Li ◽  
Jun Li
Keyword(s):  
Pressure Loss ◽  
Total Pressure ◽  
Static Pressure ◽  
Aerodynamic Performance ◽  
Total Pressure Loss ◽  
Pressure Recovery ◽  
Flow Process ◽  
Loss Mechanism ◽  
Recovery Coefficient ◽  
Pressure Recovery Coefficient

Abstract The exhaust diffuser with different struts was numerically calculated by solving three-dimensional Reynolds-Averaged Navier-Stokes (RANS). The flow process and flow loss mechanism in the diffuser were analyzed, the influence of two different structures of tapered struts on the aerodynamic performance of the exhaust diffuser under different inlet pre-swirls was explored, and the aerodynamic performance of the exhaust diffuser with tapered struts was compared with a conventional exhaust diffuser with linear struts. The results show that, compared with the conventional linear strut, under different inlet pre-swirls, two different tapered struts can both weaken the flow separation in the exhaust diffuser, thereby reducing the total pressure loss. When the inlet pre-swirl is greater than 0.35, the total pressure loss coefficient of the exhaust diffuser with structure-C tapered struts decreases by up to 0.07. The two types of tapered struts also change the flow structure at the exhaust diffuser outlet, which affects the uniformity of the outlet airflow, and then affect the static pressure recovery coefficient. Under different inlet pre-swirls, two types of tapered struts can be effective to increase the static pressure recovery coefficient of the exhaust diffuser, for the exhaust diffuser with structure-C tapered struts, the static pressure recovery coefficient can be increased by up to 0.065, relative increase of 20%. The research in this paper shows that the tapered structure can significantly improve the aerodynamic performance of the exhaust diffuser under different inlet pre-swirls.

Effect of the turning angle on the flow and performance characteristics of long S-shaped circular diffusers

2003 ◽  
Vol 217 (1) ◽  
pp. 29-41 ◽  
Author(s):  
R B Anand ◽  
L Rai ◽  
S N Singh
Keyword(s):  
Total Pressure ◽  
Static Pressure ◽  
Area Ratio ◽  
Secondary Flows ◽  
Performance Characteristics ◽  
Pressure Recovery ◽  
Recovery Coefficient ◽  
Turning Angle ◽  
And Performance ◽  
Pressure Recovery Coefficient

The effect of the turning angle on the flow and performance characteristics of long S-shaped circular diffusers (length-inlet diameter ratio, L/Di = 11:4) having an area ratio of 1.9 and centre-line length of 600 mm has been established. The experiments are carried out for three S-shaped circular diffusers having angles of turn of 15°/15°, 22.5°/22.5° and 30°/30°. Velocity, static pressure and total pressure distributions at different planes along the length of the diffusers are measured using a five-hole impact probe. The turbulence intensity distribution at the same planes is also measured using a normal hot-wire probe. The static pressure recovery coefficients for 15°/15°, 22.5°/22.5° and 30°/30° diffusers are evaluated as 0.45, 0.40 and 0.35 respectively, whereas the ideal static pressure recovery coefficient is 0.72. The low performance is attributed to the generation of secondary flows due to geometrical curvature and additional losses as a result of the high surface roughness (~0.5 mm) of the diffusers. The pressure recovery coefficient of these circular test diffusers is comparatively lower than that of an S-shaped rectangular diffuser of nearly the same area ratio, even with a larger turning angle (90°/90°), i.e. 0.53. The total pressure loss coefficient for all the diffusers is nearly the same and seems to be independent of the angle of turn. The flow distribution is more uniform at the exit for the higher angle of turn diffusers.

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.

Some Studies on Low Solidity Vaned Diffusers of a Centrifugal Compressor Stage

2005 ◽  
Author(s):  
T. Ch. Siva Reddy ◽  
G. V. Ramana Murty ◽  
Prasad Mukkavilli ◽  
D. N. Reddy
Keyword(s):  
Centrifugal Compressor ◽  
Static Pressure ◽  
Pressure Ratio ◽  
Pressure Recovery ◽  
Compressor Stage ◽  
Recovery Coefficient ◽  
Vaned Diffuser ◽  
Flow Angle ◽  
Centrifugal Compressor Stage ◽  
Pressure Recovery Coefficient

Numerical simulation of impeller and low solidity vaned diffuser (LSD) of a centrifugal compressor stage is performed individually using CFX- BladeGen and BladeGenPlus codes. The tip mach number for the chosen study was 0.35. The same configuration was used for experimental investigation for a comparative study. The LSD vane is formed using standard NACA profile with marginal modification at trailing edge. The performance parameters obtained form numerical studies at the exit of impeller and the diffuser have been compared with the corresponding experimental data. These parameters are pressure ratio, polytropic efficiency and flow angle at the impeller exit where as the parameters those have been compared at the exit of diffuser are the static pressure recovery coefficient and the exit flow angle. In addition, the numerical prediction of the blade loading in terms of blade surface pressure distribution on LSD vane has been compared with the corresponding experimental results. Static pressure recovery coefficient and flow angle at diffuser exit is seen to match closely at higher flows. The difference at lower flows could be due to the effect of interaction between impeller and diffuser combinations, as the numerical analysis was done separately for impeller and diffuser and the effect of impeller diffuser interaction was not considered.

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