A Three-Dimensional Diffuser Design for the Retrofit of a Low Pressure Turbine Using In-House Exhaust Design System

2011 ◽  
Author(s):  
Sungho Yoon ◽  
Felix Joe Stanislaus ◽  
Thomas Mokulys ◽  
Gurnam Singh ◽  
Martin Claridge
Keyword(s):  
Three Dimensional ◽  
Low Pressure ◽  
Geometric Constraints ◽  
Design System ◽  
Exhaust Hood ◽  
Three Dimensional Flow ◽  
Strongly Coupled ◽  
Dimensional Flow ◽  
Flow Features ◽  
Last Stage

The performance of the last stage of a Low Pressure (LP) steam turbine is strongly coupled with the downstream exhaust hood performance. In particular, the effect of the diffuser within the exhaust hood on the pressure recovery is very important in retrofitting existing machines, which dictate many geometric constraints. Alstom’s in-house Exhaust Design System (EDS) simulates the three-dimensional flow in the exhaust hood by coupling the last stage blades and the exhaust hood. This EDS system can be used to design an LP diffuser in the exhaust hood and to achieve the required performance targets. In the first part of this paper, the EDS system is validated against measurements within model turbines, which represent both a standard machine as well as a retrofit machine. In the second part of this paper, an LP diffuser was redesigned to improve the performance using the EDS method. To begin with, an axi-symmetric diffuser was designed using numerical simulations of a passage in the last stage turbine as well as a slice of the diffuser and the exhaust hood. By carefully controlling the profile of the diffuser casing, the flow separation at the original casing walls was reduced significantly and this, in turn, improved the performance of the turbine substantially. Then, the full geometry of the exhaust hood was modeled in order to investigate the effect of the three-dimensional flow features. Based on the examined flow features, an asymmetric change was introduced to the diffuser casing to improve the three-dimensional flow structure. This new asymmetric diffuser was found to maximize the exhaust performance.

Amplification of three-dimensional perturbations during parallel vortex–cylinder interaction

2007 ◽  
Vol 573 ◽  
pp. 457-478
Author(s):  
X. LIU ◽  
J. S. MARSHALL
Keyword(s):  
Computational Study ◽  
Three Dimensional ◽  
Front Surface ◽  
Inviscid Flow ◽  
Reynolds Numbers ◽  
Three Dimensional Flow ◽  
Dimensional Flow ◽  
Flow Features ◽  
Volume Method ◽  
Proper Orthogonal

A computational study has been performed to examine the amplification of three-dimensional flow features as a vortex with small-amplitude helical perturbations impinges on a circular cylinder whose axis is parallel to the nominal vortex axis. For sufficiently weak vortices with sufficiently small core radius in an inviscid flow, three-dimensional perturbations on the vortex core are indefinitely amplified as the vortex wraps around the cylinder front surface. The paper focuses on the effect of viscosity in regulating amplification of three-dimensional disturbances and on assessing the ability of two-dimensional computations to accurately model parallel vortex–cylinder interaction problems. The computations are performed using a multi-block structured finite-volume method for an incompressible flow, with periodic boundary conditions along the cylinder axis. Growth of three-dimensional flow features is examined using a proper-orthogonal decomposition of the Fourier-transformed vorticity field in the azimuthal and axial directions. The interaction is examined for different axial wavelengths and amplitudes of the initial helical vortex waves and for three different Reynolds numbers.

Transient Growth of Three-Dimensional Vortex Perturbations During Near-Parallel Collision With a Circular Cylinder

2006 ◽  
Author(s):  
X. Liu ◽  
J. S. Marshall
Keyword(s):  
Circular Cylinder ◽  
Vortex Core ◽  
Computational Study ◽  
Three Dimensional ◽  
The Body ◽  
Transient Growth ◽  
Two Dimensional ◽  
Three Dimensional Flow ◽  
Dimensional Flow ◽  
Flow Features

A computational study is reported that examines the transient growth of three-dimensional flow features for nominally parallel vortex-cylinder interaction problems. We consider a helical vortex with small-amplitude perturbations that is advected onto a circular cylinder whose axis is parallel to the nominal vortex axis. The study assesses the applicability of the two-dimensional flow assumption for parallel vortex-body interaction problems in which the body impinges on the vortex core. The computations are performed using an unstructured finite-volume method for an incompressible flow, with periodic boundary conditions along the cylinder axis. Growth of three-dimensional flow features is quantified by use of a proper-orthogonal decomposition of the Fourier-transformed velocity and vorticity fields in the cylinder azimuthal and axial directions. The interaction is examined for different axial wavelengths and amplitudes of the initial helical waves on the vortex core, and the results for cylinder force are compared to the two-dimensional results. The degree of perturbation amplification as the vortex approaches the cylinder is quantified and shown to be mostly dependent on the dominant axial wavenumber of the perturbation. The perturbation amplification is observed to be greatest for perturbations with axial wavelength of about 1.5 times the cylinder diameter.

Flow Analysis in a Pump Diffuser—Part 1: LDA and PTV Measurements of the Unsteady Flow

1997 ◽  
Vol 119 (4) ◽  
pp. 968-977 ◽  
Author(s):  
K. Eisele ◽  
Z. Zhang ◽  
M. V. Casey ◽  
J. Gu¨lich ◽  
A. Schachenmann
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Laser Doppler Anemometry ◽  
Three Dimensional ◽  
Three Dimensional Flow ◽  
Pump Impeller ◽  
Impeller Blade ◽  
Vaned Diffuser ◽  
Dimensional Flow ◽  
Flow Features

This paper describes experimental research aimed at improving our understanding of the complex unsteady three-dimensional flow field associated with the interaction between a pump impeller and its vaned diffuser. The paper provides the results of experiments carried out using Laser Particle Tracking Velocimetry (LPTV) and Laser Doppler Anemometry (LDA), in which time-resolved details of the unsteady flow field in a vaned diffuser of a medium specific speed pump have been obtained as a function of the local position of the pump impeller blades. Detailed flow field measurements have been carried out at several measurement positions in the diffuser and at a number of operating points along the pump characteristic. The measurement results have been analyzed to elucidate some interesting flow features observed in this typical pump diffuser. These include three-dimensional flow at the impeller outlet, flow separation in the diffuser channel, unsteady recirculation of the flow from the diffuser into the impeller, the passage of vorticity in the impeller blade wakes through the diffuser, and periodic unsteadiness and turbulence in the diffuser flow channel. The relevance of these flow features to the stability of the pump characteristic is discussed.

scholarly journals The Influence of Inlet Asymmetry on Steam Turbine Exhaust Hood Flows

2013 ◽  
Vol 136 (4) ◽  
Author(s):  
Zoe Burton ◽  
Simon Hogg ◽  
Grant L. Ingram
Keyword(s):  
Steam Turbine ◽  
Flow Structure ◽  
Three Dimensional ◽  
Low Pressure ◽  
Computational Effort ◽  
Exhaust Hood ◽  
Research Activity ◽  
Computational Expense ◽  
Last Stage ◽  
Design Calculations

It has been widely recognized for some decades that it is essential to accurately represent the strong coupling between the last stage blades (LSB) and the diffuser inlet, in order to correctly capture the flow through the exhaust hoods of steam turbine low pressure cylinders. This applies to any form of simulation of the flow, i.e., numerical or experimental. The exhaust hood flow structure is highly three-dimensional and appropriate coupling will enable the important influence of this asymmetry to be transferred to the rotor. This, however, presents challenges as the calculation size grows rapidly when the full annulus is calculated. The size of the simulation means researchers are constantly searching for methods to reduce the computational effort without compromising solution accuracy. However, this can result in excessive computational demands in numerical simulations. Unsteady full-annulus CFD calculation will remain infeasible for routine design calculations for the foreseeable future. More computationally efficient methods for coupling the unsteady rotor flow to the hood flow are required that bring computational expense within realizable limits while still maintaining sufficient accuracy for meaningful design calculations. Research activity in this area is focused on developing new methods and techniques to improve accuracy and reduce computational expense. A novel approach for coupling the turbine last stage to the exhaust hood employing the nonlinear harmonic (NLH) method is presented in this paper. The generic, IP free, exhaust hood and last stage blade geometries from Burton et al. (2012. “A Generic Low Pressure Exhaust Diffuser for Steam Turbine Research,”Proceedings of the ASME Turbo Expo, Copenhagen, Denmark, Paper No. GT2012-68485) that are representative of modern designs, are used to demonstrate the effectiveness of the method. This is achieved by comparing results obtained with the NLH to those obtained with a more conventional mixing-plane approach. The results show that the circumferential asymmetry can be successfully transferred in both directions between the exhaust hood flow and that through the LSB, by using the NLH. This paper also suggests that for exhaust hoods of generous axial length, little change in Cp is observed when the circumferential asymmetry is captured. However, the predicted flow structure is significantly different, which will influence the design and placement of the exhaust hood internal “furniture.”

Three-Dimensional Flow in a Low-Pressure Turbine Cascade at Its Design Condition

1987 ◽  
Vol 109 (2) ◽  
pp. 177-185 ◽  
Author(s):  
H. P. Hodson ◽  
R. G. Dominy
Keyword(s):  
High Speed ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Low Pressure ◽  
Surface Flow ◽  
Turbine Cascade ◽  
Suction Surface ◽  
Three Dimensional Flow ◽  
Low Pressure Turbine ◽  
Dimensional Flow

This paper describes an experimental study of the three-dimensional flow within a high-speed linear cascade of low-pressure turbine blades. Data were obtained using pneumatic probes and a surface flow visualization technique. It is found that in general, the flow may be described using concepts derived from previous studies of high-pressure turbines. In detail, however, there are differences. These include the existence of a significant trailing shed vortex and the interaction of the endwall fluid with the suction surface flow. At an aspect ratio of 1.8, the primary and secondary losses are of equal magnitude.

Three-dimensional flow features in a nominally two-dimensional rectangular cavity

2013 ◽  
Vol 25 (9) ◽  
pp. 097101 ◽  
Author(s):  
G. M. Di Cicca ◽  
M. Martinez ◽  
C. Haigermoser ◽  
M. Onorato
Keyword(s):  
Three Dimensional ◽  
Rectangular Cavity ◽  
Two Dimensional ◽  
Three Dimensional Flow ◽  
Dimensional Flow ◽  
Flow Features
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