EXPERIMENTAL AND NUMERICAL RESEARCH ON FLOW IN THE LAST STAGE OF 1090MW STEAM TURBINE

The paper deals with experimental and numerical research in the last stage of real 1090MW steam turbine with the last steel blade length 1220mm placed in nuclear power station. The last stage was equipped with twelve static pressure taps. It was also possible to probe in two planes - before and behind the last stage using pneumatic or optical probes. A number of last stage flow parameters were determined at the root and tip wall for nominal turbine output. Among those parameters are static pressures, Mach and Reynolds numbers, last stage reactions and steam wetness. All the directly measured and evaluated flow parameters are taken from locally measured points and that is why even 3D CFD calculation of the whole system - last stage, diffuser and exhaust hood was implemented. Measured and calculated parameters are compared. Especially static pressures are in very good agreement; the only steam wetness has bigger difference due to different measurement position. Locally measured values are enough to estimate the flow behavior of the last stage. On the other hand, the CFD simulations with well determined boundary conditions, meshes and geometry and is effective tool to simulate even very complicated flow structures in the last stage and exhaust hood.

Download Full-text

Numerical Investigation and Validation of the 1 090 MW Steam Turbine Exhaust Hood Flow Field

Volume 8: Microturbines, Turbochargers and Small Turbomachines; Steam Turbines ◽

10.1115/gt2017-63576 ◽

2017 ◽

Cited By ~ 1

Author(s):

A. Živný ◽

A. Macálka ◽

M. Hoznedl ◽

K. Sedlák ◽

M. Hajšman ◽

...

Keyword(s):

Flow Field ◽

Steam Turbine ◽

Nuclear Power ◽

Flow Behavior ◽

Three Dimensional ◽

Exhaust Hood ◽

Recovery Coefficient ◽

Strongly Coupled ◽

Lp Turbine ◽

Turbine Exhaust

The last-stage blade (LSB) rows and exhaust hood in low-pressure (LP) steam turbine sections are key elements of the entire LP turbine part. The cold end section affects significantly the whole LP turbine efficiency and overall turbine performance due to huge steam expansion. This expansion is strongly coupled with the diffuser and exhaust hood, which transforms kinetic energy at the stage exit into potential energy. Mentioned mechanism leads to expansion line prolongation between the stage inlet and diffuser outlet and higher turbine power output. An experimental investigation of the flow field in the exhaust hood is very economically and procedurally expensive and not commonly feasible. Nowadays, capable numerical simulations can provide relatively fast and accurate results on any studied model. On the other hand, the flow behavior inside the LSB and the exhaust hood is very complex and it is still challenging to investigate the whole system using CFD codes. The purpose of this paper is to validate complex three-dimensional CFD methodology of the flow field in the operating 1 090 MW steam turbine exhaust hood with radial diffuser and condenser neck. The exceptional contribution of this paper is the fact that unique data obtained by measurement on operating Nuclear Power Plant (NPP) steam turbine are available. The comparison is focused mainly on the pressure, velocity and steam wetness distribution along the LSB height at the stage exit/diffuser inlet. Wall static pressures and the pressure recovery coefficient of the exhaust hood were also determined and compared with experimental data. The complete CFD study helps to understand the flow behavior inside the whole exhaust throat and locate critical parts that negatively affect aerodynamic design.

Download Full-text

Influence of a Cylindrical Exhaust Hood Installation on the Last Stage Rotor Blades of a Low Pressure Model Steam Turbine

Volume 8: Microturbines, Turbochargers and Small Turbomachines; Steam Turbines ◽

10.1115/gt2017-63280 ◽

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.

Download Full-text

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

Volume 8: Microturbines, Turbochargers and Small Turbomachines; Steam Turbines ◽

10.1115/gt2017-63269 ◽

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.

Download Full-text

Interaction Between Impeller and Volute of Pumps at Off-Design Conditions

Journal of Fluids Engineering ◽

10.1115/1.3242534 ◽

1986 ◽

Vol 108 (1) ◽

pp. 12-18 ◽

Cited By ~ 19

Author(s):

J. A. Lorett ◽

S. Gopalakrishnan

Keyword(s):

Analytical Solution ◽

Flow Behavior ◽

Cyclic Variation ◽

Test Results ◽

Flow Parameters ◽

Pump Output ◽

Simplifying Assumptions ◽

Radial Thrust ◽

Relative Flow ◽

Good Agreement

In a centrifugal pump of volute type, the respective characteristics of the impeller and the volute are such that at only one operating point can the flow parameters be constant along the length of the volute. At off-design conditions the mismatching of characteristics causes variations of velocity and pressure along the periphery of the impeller. This in turn forces cyclic variation of the flow in the impeller channels, introduces variations of the inlet incidence and contributes significantly to the direction and the magnitude of the radial thrust. Furthermore, below a certain pump output, a complete flow reversal occurs over a part of the impeller periphery, thus explaining the onset of recirculation. The paper describes the calculation approach used to derive this aspect of the flow behavior. Because of difficulties in obtaining a closed analytical solution, a step by step computation is employed. Beginning with arbitrarily chosen conditions at the volute tongue, the program computes the flow parameters for following segments, using the continuity and the momentum equations, until the exit from the last segment is reached. The inherent unsteadiness of the relative flow in the impeller is explicitly accounted for. Since the inflow and the velocity in the first segment depend upon the exit conditions of the last, the initial input must be modified, and the computation repeated, until the values are compatible with the exit conditions. In spite of several simplifying assumptions, the results of the calculations show very good agreement with published test results.

Download Full-text

Development of Long Rotating Blade Applied in the New Generation Nuclear Steam Turbine

Volume 2: Plant Systems, Structures, and Components; Safety and Security; Next Generation Systems; Heat Exchangers and Cooling Systems ◽

10.1115/icone20-power2012-54171 ◽

2012 ◽

Author(s):

Kai Cheng ◽

Zeying Peng ◽

Gongyi Wang ◽

Xiaoming Wu ◽

Deqi Yu

Keyword(s):

Steam Turbine ◽

Nuclear Power ◽

Power Plants ◽

Structure Design ◽

Good Reliability ◽

Pressurized Water ◽

Height Range ◽

Water Reactor ◽

Rotating Blade ◽

Last Stage

In order to meet the high economic requirement of the 3rd generation Pressurized Water Reactor (PWR) or Boiling Water Reactor (BWR) applied in currently developing nuclear power plants, a series of half-speed extra-long last stage rotating blades with 26 ∼ 30 m2 nominal exhaust annular area is proposed, which covers a blade-height range from 1600 mm to 1900 mm. It is well known that developing an extra long blade is a tough job involving some special coordinated sub-process. This paper is dedicated to describe the progress of creating a long rotating blade for a large scaled steam turbine involved in the 3rd generation nuclear power project. At first the strategy of how to determine the appropriate height for the last-stage-rotating-blade for the steam turbine is provided. Then the quasi-3D flow field quick design method for the last three stages in LP casing is discussed as well as the airfoil optimization method. Furthermore a sophisticated blade structure design and analyzing system for a long blade is introduced to obtain the detail dimension of the blade focusing on the good reliability during the service period. Thus, except for CAD and experiment process, the whole pre-design phase of the extra-long turbine blade is presented which is regarded as an assurance of the operation efficiency and reliability.

Download Full-text

A Novel Method of Coupling the Steam Turbine Exhaust Hood and the Last Stage Blades Using the Non-Linear Harmonic Method

Volume 5B: Oil and Gas Applications; Steam Turbines ◽

10.1115/gt2013-94184 ◽

2013 ◽

Cited By ~ 3

Author(s):

Zoe Burton ◽

Grant Ingram ◽

Simon Hogg

Keyword(s):

Steam Turbine ◽

Turbine Blades ◽

Computation Time ◽

Computational Effort ◽

Alternative Methods ◽

Test Case ◽

Exhaust Hood ◽

Harmonic Method ◽

Non Linear ◽

Last Stage

The exhaust hood of a steam turbine is a vital area of turbomachinery research its performance strongly influences the power output of the last stage blades. It is well known that accurate CFD simulations are only achieved when the last stage blades are coupled to the exhaust hood to capture the strong interaction. 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 of methods to reduce the computational effort without compromising solution accuracy. This work uses a novel approach, by coupling the last stage blades and exhaust hood by the Non-Linear Harmonic Method, a technique widely used to reduce calculation size in high pressure turbine blades and axial compressors. This has been benchmarked against the widely adopted Mixing Plane method. The test case used is the Generic Geometry, a representative exhaust hood and last stage blade geometry that is free from confidentiality and IP restrictions and for which first calculations were presented at last year’s conference [1]. The results show that the non-uniform exhaust hood inlet flow can be captured using the non-liner harmonic method, an effect not previously achievable with single passage coupled calculations such as the mixing plane approach. This offers a significant computational saving, estimated to be a quarter of the computation time compared with alternative methods of capturing the asymmetry with full annulus frozen rotor calculations.

Download Full-text

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

Volume 8: Microturbines, Turbochargers, and Small Turbomachines; Steam Turbines ◽

10.1115/gt2018-75248 ◽

2018 ◽

Cited By ~ 1

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.

Download Full-text

Study of Flow Behavior in a Vibrating Pipe on Offshore Platform

Volume 2: Safety and Reliability; Pipeline Technology ◽

10.1115/omae2003-37471 ◽

2003 ◽

Author(s):

Dezhong Li ◽

Ning Mei ◽

Jian Su

Keyword(s):

Flow Behavior ◽

Offshore Platform ◽

Polynomial Method ◽

Flow Parameters ◽

Pressure Distributions ◽

Incompressible Viscous Flow ◽

Fluid Properties ◽

Oscillating Fluid Mechanics ◽

The Mathematical Model ◽

Good Agreement

The purpose of this paper is to study flow behavior in a vibrating pipe on offshore platform. The mathematical model of unsteady, incompressible, viscous flow in a vibrating pipe is established according to the basic theory of oscillating fluid mechanics. The governing equations of flow are decomposed into a system for steady flow and another for flow oscillation, with the equations of the differential coefficients of flow parameters solved by using the parametric polynomial method. Velocity and pressure distributions are obtained for different flow conditions. Numerical results indicate that the flow behavior in the vibrating pipe on offshore platform is strongly affected by fluid properties and the pipe structure. A good agreement is obtained when comparing the results with the variational solution in constant cross-section, which shows that the method proposed in this work is effective for studying flow behavior in a vibrating pipe on offshore platform.

Download Full-text