Experimental and Numerical Study on Pressure Losses and Flow Fluctuations in a High-Pressure Valve Assembly of Steam Turbine Governing System

2020 ◽  
Author(s):  
Vaclav Slama ◽  
Lukas Mrozek ◽  
Bartolomej Rudas ◽  
David Simurda ◽  
Jindrich Hala ◽  
...  
Keyword(s):  
High Pressure ◽  
Flow Field ◽  
Numerical Simulations ◽  
Pressure Loss ◽  
Operational Reliability ◽  
Operating Conditions ◽  
The Real ◽  
Pressure Losses ◽  
Flow Fluctuations ◽  
Valve Assembly

Abstract Aerodynamic measurements and numerical simulations carried out on a model of a high-pressure valve assembly used for nozzle governing of a turbine with 135MW output are described in this paper. Aim of the study is to investigate effects of control valve’s strainers on pressure losses and unsteadiness in the flow field. It is an important task since undesirable flow fluctuations can lead to operational reliability issues. Measurements were carried out in the Aerodynamic laboratory of the Institute of Thermomechanics of the Czech Academy of Sciences (IT) where an aerodynamic tunnel is installed. Numerical simulations were carried out in the Doosan Skoda Power (DSP) Company using ANSYS software tools. The experimental model consists of one of two identical parts of the real valve assembly. It means it consists of an inlet pipeline, a stop valve, a valve chamber with two independent control valves, its diffusers and outlet pipelines. The numerical model consists of both assembly parts and includes also an A-wheel control stage in order to simulate the real turbine operating points. The different lifts of the main cone in each control valve for its useful combinations were investigated. Results were evaluated on the model with control valve’s strainers, which were historically used in order to stabilize the flow, and without them. The results of the experimental measurement were compared with the numerical results in the form of pressure losses prediction. From measured pressure fluctuations, it was found out where and for which conditions a danger of flow instabilities occurs. It can be concluded that there is a border, in terms of operating conditions, where the flow field starts to be unstable and this border is different dependent of the fact whether the control valve’s strainers are used or not. Therefore, the areas of safe and danger operational reliability can be predicted. The influence of the control valve’s strainers on the maximal amplitude of periodic fluctuations appears only for the cases when valves are highly overloaded. For normal operating conditions, there is no difference. As a result, the control valve’s strainers do not have to be used in standard applications of valve assemblies. Furthermore, a loss model for valve pressure loss estimation could be updated. Therefore, a pressure loss should be predicted with a sufficient accuracy for each new turbine bid with similar valve assemblies.

Investigation of Pressure Losses and Flow Fluctuations in an Intercept Valve Assembly of an Intermediate-Pressure Turbine Part

2020 ◽  
Author(s):  
Vaclav Slama ◽  
Lukas Mrozek ◽  
Bartolomej Rudas ◽  
David Simurda ◽  
Jindrich Hala ◽  
...  
Keyword(s):  
Flow Separation ◽  
Pressure Loss ◽  
Pressure Fluctuations ◽  
Control Valve ◽  
Operational Reliability ◽  
Operating Conditions ◽  
Pressure Losses ◽  
Flow Fluctuations ◽  
Valve Assembly ◽  
Valve Model

Abstract A new design of an intercept valve assembly of the intermediate-pressure turbine part of greater power output is investigated in terms of pressure losses and flow fluctuations by using measurement on an experimental valve model. In addition, numerical simulations are used to further clarify measured phenomena. For such valve assemblies, it is important to exactly predict pressure losses and avoid danger of vibrations, which are caused by undesirable flow fluctuations, in order to guarantee valve’s efficiency and operational reliability. For this type of valve, it is especially important for turbine operations in partial loads (off-design conditions). Measurements were carried out in the Aerodynamic laboratory of the Institute of Thermomechanics of the Czech Academy of Sciences (IT) in a modular aerodynamic tunnel. Numerical simulations were carried out in the Doosan Skoda Power Company (DSP) by using a package of ANSYS software tools. The experimental valve model is a scaled model of a real valve assembly. It consists of an inlet pipeline, a stop valve and a control valve including its diffuser and outlet pipeline. Measured regimes were defined by a mass flow rate and a control valve cone lift which can be precisely changed. In order to investigate pressure loses, total and static pressures at valve characteristic locations were measured by using Prandtl probes and wall static pressure taps. In order to measure pressure fluctuations, Kulite fast response pressure transducers were used. They were situated near the valve throat where the flow fluctuations, which are strongly related to a flow separation, are the most visible and influential. Measurement results are compared with numerical results and locations with a flow separation were found. In order to reduce this phenomenon, different valve seat angles were also tested. As a result, a valve design could be optimized and, for a pressure loss prediction, a pressure loss model for this new intercept valve assembly could be created. Therefore, pressure losses in similar valve assemblies can be predicted with required accuracy for each new turbine where modern intercept valves are used. This helps to increase steam turbine efficiency and reduce fuel consumption. Based on pressure fluctuations results, operating conditions at which dangerous flow instabilities occur were identified. It was concluded that there is an operating condition border where the flow field starts to be unstable. As a result, the areas of safe and dangerous operating conditions can be predicted so that the operational reliability of the valve can be guaranteed.

scholarly journals Pressure losses and oscillations in a compact valve of a steam turbine

2021 ◽  
Vol 345 ◽  
pp. 00027
Author(s):  
Václav Sláma ◽  
David Šimurda ◽  
Lukáš Mrózek ◽  
Ladislav Tajč ◽  
Jindřich Hála ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Pressure Oscillation ◽  
Operational Reliability ◽  
Operating Conditions ◽  
Steam Turbines ◽  
Valve Seat ◽  
Pressure Losses ◽  
Oscillation Analysis ◽  
Seat Angle ◽  
Wide Range

Characteristics of a new compact valve design for steam turbines are analysed by measuring pressure losses and oscillations on the valve model. It is the model of an intercept valve of the intermediate-pressure turbine part. This valve is relatively smaller hence cheaper than usual control and intercept valves. Besides, four different valve seat angles were tested in order to investigate the valve seat angle influence. In order to further clarify measured phenomena, the wide range of numerical simulations were also carried out. Measurements were performed in the Aerodynamic laboratory of the Institute of Thermomechanics of the Czech Academy of Sciences in an air test rig installed in a modular aerodynamic tunnel. Numerical simulations were performed in the Doosan Skoda Power Company using a package of ANSYS software tools. Measurement results are compared with numerical and generalized in the form of valve characteristics and pressure oscillation maps. As a result of the pressure loss analysis, pressure losses in similar valve assemblies can be predicted with required accuracy for each new turbine where modern compact valves are used. As a result of the pressure oscillation analysis, operating conditions at which dangerous flow instabilities can occur were identified. Thanks to this, the areas of safe and dangerous operating conditions can be predicted so that the operational reliability of the valve can be guaranteed.

Low Pressure Steam Turbine Exhaust Flow: Part 2 — Investigation of the Condenser Neck Flow Field and 1D Modelling

2016 ◽  
Author(s):  
Dirk Telschow ◽  
Peter Stein ◽  
Hartwig Wolf ◽  
Alessandro Sgambati
Keyword(s):  
Flow Field ◽  
Pressure Loss ◽  
Low Pressure ◽  
Combined Cycle ◽  
Operating Conditions ◽  
Computational Time ◽  
Plant Design ◽  
Pressure Losses ◽  
Design Changes ◽  
1D Modelling

Since many years the diffuser and exhaust of low pressure (LP) turbines are in focus of turbine development and accordingly broadly discussed within the scientific community. The pressure recovery gained within the diffuser significantly contributes to the turbine performance and therefore care is taken in flow investigation as well as optimization within this part of the turbine. However, on a plant level the component following the LP turbine is the condenser, which is connected by the condenser neck. Typically the condenser neck is not designed to provide additional enthalpy recovery. For plant design reasons, often numerous built-ins like stiffening struts, extraction pipes, steam dump devices and others are placed into the neck. Here it is vital to keep the pressure losses low, in order not to deteriorate performance, previously gained within the diffuser. Each mbar of total pressure loss in a condenser can reduce the plant power output up to 0.1%. As discussed in the first publication (Part 1), 3D CFD enables a deep insight into the flow field, which is costly with respect to computational time and resources. But there are phases during project execution, when geometry and/or boundary conditions are not fixed and quick estimation of pressure loss and recovery in the condenser neck is needed for benchmark of designs or design changes (e.g. tender phase). Here 1D modelling approaches can help to close the gap. Analysis of available 1D correlation of flow around obstacles has shown that these need to be adapted to the flow conditions in a condenser neck of a steam, nuclear or combined-cycle power plant. Therefore, the fluid fields, calculated and discussed in the first publication (Part 1), were analyzed regarding pressure loss created by single obstacles and interaction of built-ins of different size, number and shape. Furthermore, a 1D velocity to be used for 1D calculation was derived from the 3D velocity field. In addition, vacuum-correction-curves were implemented to cover the range of possible operating conditions. This publication discusses the development of a 1D model for calculation of pressure loss in a condenser neck and the validity of such calculations against measurement and 3D CFD data.

The Experimental Investigations of Centripetal Air Bleed With Tubed Vortex Reducer for Secondary Air System in Gas Turbine

2014 ◽  
Author(s):  
Xiao Chen ◽  
Ye Feng ◽  
Lijun Wu
Keyword(s):  
High Pressure ◽  
Flow Field ◽  
Gas Turbine ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Pressure Loss ◽  
Experimental Investigations ◽  
Pressure Losses ◽  
Nozzle Guide

In a modern gas turbine, the air bled through High Pressure Compressor (HPC) rotor drums from the main flow is transported radially inwards and then transferred to cool the High Pressure Turbine (HPT). The centripetal air flow creates a strong vortex, which results in huge pressure losses. This not only restricts the mass flow rate, but also reduces the cooling air pressure for down-stream hot components. Adding vortex reducer tubes to the centripetal air bleed can reduce the pressure loss and ensure the pressure and mass flow rate of the supply air. Design optimization of the tubed vortex reducer is essential in minimizing the pressure losses. This paper describes experimental investigations of different configurations of tubed vortex reducers at different rotational speeds and mass flow rates. Particular attention is paid to the shape of the drum hole, the length of the tubed vortex reducers at the same installation location, and the angles of the nozzle guide vane outlets. The core section of test rig is comprised of two steel disks, one drum rotor and stationary cases with nozzle guide vanes. It operates at representative engine parameters, such as the turbulent flow parameter, λT(0.2–1.8) and the Rossby number Ro(0.05–0.08). Three conclusions can be drawn based on the experimental results. 1) The shape of the drum hole is a key factor of the bleed system pressure loss. An oval hole configuration has less flow resistance and results in lower pressure losses compared with a circular hole design. 2) The tests prove that tubed vortex reducers are instrumental in minimizing centripetal air flow. These components effectively restrain the free vortex development and decrease the pressure losses in the cavity. 3) Basically, the flow field consists of a free vortex and a forced vortex. The length of the tube influences the flow field and the pressure losses at the inlet and outlet of the tubed vortex reducer. However, the tube length is less important when compared with the shape of drum hole.

Numerical Simulation of Deposition Phenomena on High-Pressure Turbine Vane Using UPACS

2019 ◽  
Author(s):  
Kenta Mizutori ◽  
Koji Fukudome ◽  
Makoto Yamamoto ◽  
Masaya Suzuki
Keyword(s):  
Numerical Simulation ◽  
High Pressure ◽  
Flow Field ◽  
Pressure Loss ◽  
Total Pressure ◽  
Total Pressure Loss ◽  
High Pressure Turbine ◽  
Pressure Loss Coefficient ◽  
Turbine Vane ◽  
Total Pressure Loss Coefficient

Abstract We performed numerical simulation to understand deposition phenomena on high-pressure turbine vane. Several deposition models were compared and the OSU model showed good adaptation to any flow field and material, so it was implemented on UPACS. After the implementation, the simulations of deposition phenomenon in several cases of the flow field were conducted. From the results, particles adhere on the leading edge and the trailing edge side of the pressure surface. Also, the calculation of the total pressure loss coefficient was conducted after computing the flow field after deposition. The total pressure loss coefficient increased after deposition and it was revealed that the deposition deteriorates aerodynamic performance.

Probabilistic and Numerical Modelling of a Lobed Mixer at Windmilling Conditions

2013 ◽  
Author(s):  
Maxime Lecoq ◽  
Nicholas Grech ◽  
Pavlos K. Zachos ◽  
Vassilios Pachidis
Keyword(s):  
Flow Field ◽  
Response Surface ◽  
Gas Turbine ◽  
Pressure Loss ◽  
Total Pressure ◽  
Engine Performance ◽  
Operating Conditions ◽  
Total Pressure Loss ◽  
Operating Point ◽  
Mixing Losses

Aero-gas turbine engines with a mixed exhaust configuration offer significant benefits to the cycle efficiency relative to separate exhaust systems, such as increase in gross thrust and a reduction in fan pressure ratio required. A number of military and civil engines have a single mixed exhaust system designed to mix out the bypass and core streams. To reduce mixing losses, the two streams are designed to have similar total pressures. In design point whole engine performance solvers, a mixed exhaust is modelled using simple assumptions; momentum balance and a percentage total pressure loss. However at far off-design conditions such as windmilling and altitude relights, the bypass and core streams have very dissimilar total pressures and momentum, with the flow preferring to pass through the bypass duct, increasing drastically the bypass ratio. Mixing of highly dissimilar coaxial streams leads to complex turbulent flow fields for which the simple assumptions and models used in current performance solvers cease to be valid. The effect on simulation results is significant since the nozzle pressure affects critical aspects such as the fan operating point, and therefore the windmilling shaft speeds and air mass flow rates. This paper presents a numerical study on the performance of a lobed mixer under windmilling conditions. An analysis of the flow field is carried out at various total mixer pressure ratios, identifying the onset and nature of recirculation, the flow field characteristics, and the total pressure loss along the mixer as a function of the operating conditions. The data generated from the numerical simulations is used together with a probabilistic approach to generate a response surface in terms of the mass averaged percentage total pressure loss across the mixer, as a function of the engine operating point. This study offers an improved understanding on the complex flows that arise from mixing of highly dissimilar coaxial flows within an aero-gas turbine mixer environment. The total pressure response surface generated using this approach can be used as look-up data for the engine performance solver to include the effects of such turbulent mixing losses.

scholarly journals Investigation of the Flow Field in the Vicinity of an Axial Flow Fan During Low Flow Rates

2014 ◽  
Author(s):  
Francois G. Louw ◽  
Theodor W. von Backström ◽  
Sybrand J. van der Spuy
Keyword(s):  
Flow Field ◽  
Numerical Simulations ◽  
Flow Rate ◽  
Axial Flow ◽  
Operating Conditions ◽  
Design Flow ◽  
Low Flow ◽  
Axial Flow Fan ◽  
Free Vortex ◽  
Flow Rates

Large axial flow fans are used in forced draft air cooled heat exchangers (ACHEs). Previous studies have shown that adverse operating conditions cause certain sectors of the fan, or the fan as a whole to operate at very low flow rates, thereby reducing the cooling effectiveness of the ACHE. The present study is directed towards the experimental and numerical analyses of the flow in the vicinity of an axial flow fan during low flow rates. This is done to obtain the global flow structure up and downstream of the fan. A near-free-vortex fan, designed for specific application in ACHEs, is used for the investigation. Experimental fan testing was conducted in a British Standard 848, type A fan test facility, to obtain the fan characteristic. Both steady-state and time-dependent numerical simulations were performed, depending on the operating condition of the fan, using the Realizable k-ε turbulence model. Good agreement is found between the numerically and experimentally obtained fan characteristic data. Using data from the numerical simulations, the time and circumferentially averaged flow field is presented. At the design flow rate the downstream fan jet mainly moves in the axial and tangential direction, as expected for a free-vortex design criteria, with a small amount of radial flow that can be observed. As the flow rate through the fan is decreased, it is evident that the down-stream fan jet gradually shifts more diagonally outwards, and the region where reverse flow occur between the fan jet and the fan rotational axis increases. At very low flow rates the flow close to the tip reverses through the fan, producing a small recirculation zone as well as swirl at certain locations upstream of the fan.

Effect of Nozzle-Rotor Clearance on Turbine Performance

2006 ◽  
Author(s):  
Eunhwan Jeong ◽  
Pyun Goo Park ◽  
Sang Hun Kang ◽  
Jinhan Kim
Keyword(s):  
High Pressure ◽  
Numerical Analysis ◽  
Pressure Loss ◽  
Performance Test ◽  
Stagnation Pressure ◽  
Operating Conditions ◽  
Impulse Turbine ◽  
Cold Air ◽  
Turbine Performance ◽  
Axial Clearance

This paper presents the results of performance test and numerical analysis of a supersonic impulse turbine. The test has been conducted using high pressure cold air. The overall turbine performance and turbine nozzle behavior for various operating conditions have been investigated. Experiment and numerical analysis also have been conducted to investigate the nozzle-rotor clearance effect on the turbine performance. It has been found that turbine performance degrades with increasing the axial clearance and this phenomenon is mainly due to the increased stagnation pressure loss in the axial clearance region.

Aerodynamic Investigation of the Performance of a Two Stage Axial Turbine at Design and Off-Design Conditions

2011 ◽  
Author(s):  
Sherif A. Abdelfattah ◽  
Hicham A. Chibli ◽  
M. T. Schobeiri
Keyword(s):  
High Pressure ◽  
Flow Field ◽  
Flow Characteristics ◽  
Operating Conditions ◽  
Numerical Dissipation ◽  
Two Stage ◽  
Engine Operation ◽  
Axial Turbine ◽  
Secondary Loss ◽  
Loss Mechanisms

This paper describes numerical aerodynamic investigations of a two-stage, high pressure axial turbine at design and off-design operating conditions. The flow field in a high pressure turbine is highly complex due to unsteadiness of the flow and the various effects of blade row interaction. Blade loss mechanisms generally include primary and secondary loss mechanisms. Examples of primary loss mechanisms include boundary layer losses, shock losses and mixing losses, whereas examples of secondary losses include tip leakage losses and end wall losses which both create secondary flow characteristics. Although modern numerical analysis techniques have provided good understanding of the flow field, it is still difficult to accurately predict impact due to the aforementioned loss effects. This is generally due to errors predicting in boundary layers, transition as well as false entropy generation due to numerical dissipation. When a turbine is operated at off-design conditions the primary and secondary loss effects are further increased and create further reductions in engine efficiency. In this study a numerical model of the two-stage axial turbine was constructed and run under boundary conditions designed to mimic the operating conditions applied during engine operation. The shear stress transport (SST) turbulence model was selected for its versatility in turbomachinery applications. A comparison was made between both experimentally measured efficiencies and numerically predicted efficiencies.

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