Transient Pressure Pulsations of a Model Pump-Turbine During Power Failure

2017 ◽  
Author(s):  
Jinhong Hu ◽  
Wei Zeng ◽  
Jiandong Yang ◽  
Renbo Tang
Keyword(s):  
Rotational Speed ◽  
Guide Vane ◽  
Dynamic Pressure ◽  
Pressure Sensors ◽  
Open Loop ◽  
Operating Conditions ◽  
Pressure Pulsations ◽  
Transient Pressure ◽  
Pump Turbine ◽  
Power Failure

Pump-turbine can operate in either pump mode or turbine mode. The quick response to load changes as well as the ability to store energy makes it essential to the stability of power grid. When a pump-turbine works in different condition, flow-induced instabilities occur, including Rotor Stator Interaction (RSI) between the runner and vanes, vortex formations and back flow regions. To understand these complicated flow dynamics, experimental and numerical investigations have been conducted by many researchers. Among these researches, many experiments on model test rigs are mainly focused on steady state, and knowledge for instabilities during transients is still lacking. In this paper, power failure experiments with constant guide van opening are conducted on an open-loop test rig. During the process, the operating point of the pump-turbine in the 4 quadrant characteristics moves from pump region through the brake region, turbine region to turbine brake region. Finally the pump-turbine settled down at runaway rotational speed. In our experiments, flow rate, rotational speed, torque, pressure in the spiral casing and the draft tube inlet are measured. Especially, dynamic pressure sensors mounted in the guide vane channels are used to measure transient pressure pulsations. Measured data are analyzed in both time domain and frequency domain. Results indicate that during power failure pressure pulsations in the vane channels vary significantly with the operating conditions. In the pump region, pressure pulsations are mainly composed of RSI. In the brake region, intensive stochastic noises occur, and the amplitude of RSI rises. In the turbine region, the magnitude of pressure pulsations drops sharply as the noise intensity goes down. In the turbine brake region, significant noises appear, and the amplitude of RSI increases dramatically.

Measurement of Unsteady Flow in Pump-Turbine for Hydropower Using PIV Method

2009 ◽  
Author(s):  
Nobuhiko Fukuda ◽  
Satoshi Someya ◽  
Koji Okamoto
Keyword(s):  
Rotational Speed ◽  
Velocity Measurement ◽  
Numerical Procedure ◽  
Hydraulic Turbine ◽  
Operating Conditions ◽  
High Time ◽  
Pump Turbine ◽  
Guide Vanes ◽  
Runner Blade ◽  
Wide Range

It is thought that the pressure fluctuation can occur due to the interaction between flow through guide vanes and flow into runner blades, resulting in a vibration of turbine and a blade cracking, in a hydraulic turbine operated in a wide range for flexible power demand. High accurate velocity measurement with high time/spatial resolution can help to clarify the mechanism of the interaction and to provide good experimental data for the validation of numerical procedure. So the aim of present study is to estimate the unstable velocity field quantitatively in the area between guide vanes and runner blades, using high time-resolved particle image velocimetry (PIV). Two types of velocity measurements were carried out, i.e., phase-locked measurement and high time sequential velocity measurement, in a pump-turbine model with 20 guide vanes and 6 runner blades. The characteristic of the flow field varied corresponding to the operating conditions such as flow rate and rotational speed. Opening angles of guide vanes were kept uniform. A clockwise vortex was generated at inside of the runner blade under smaller rotational speed. A counterclockwise vortex was separated at the backside of the runner blade under higher rotational speed. At any operating conditions, the velocity between guide vanes and runner blades oscillated periodically at the blade passing frequency.

scholarly journals Hysteresis Characteristic in Hump Region of a Pump-Turbine Model

2016 ◽  
Author(s):  
Deyou Li ◽  
Hongjie Wang ◽  
Jinxia Chen ◽  
Torbjørn K. Nielsen ◽  
Daqing Qin ◽  
...  
Keyword(s):  
Guide Vane ◽  
Pressure Sensors ◽  
Low Frequency ◽  
Rotational Frequency ◽  
Hysteresis Phenomenon ◽  
Pump Turbine ◽  
Hysteresis Characteristic ◽  
Hydraulic Losses ◽  
Measurement Direction ◽  
Turbine Model

The hump characteristic is one of the major instabilities in pump-turbines. When pump-turbines operate in the hump region, strong noise and serious fluctuations could be observed, which are harmful to the safe and stable operations and even destroy the whole unit as well as water conveyance system. In this paper, a low specific speed (nq = 36.1 min−1) pump-turbine model was experimentally investigated. Firstly, the hump characteristic was obtained under 19 mm guide vane opening. More interestingly, when the hump characteristic was measured in two directions (increasing and decreasing the discharge), the hysteresis characteristic was found during the hump region. The analysis of performance characteristics reveals that the hump instability is resultant of Euler momentum and hydraulic losses, and different Euler momentum and hydraulic losses in the two development processes lead to hysteresis phenomenon. Then, 12 pressure sensors were mounted in the different parts of the pump-turbine model to obtain the time and frequency characteristics. The analysis of fast Fourier transform confirms that the hump characteristic is related to the low-frequency (0.04–0.15 times rotational frequency) vortices. The occurrence and cease of vortices depend on the operating condition and measurement direction, which contribute to the hysteresis characteristic. Finally, the type of the low-frequency vortices was analyzed through the cross power spectrum.

A Novel Technique for Steam Turbine Exhaust Pressure Limitation Using Dynamic Pressure Sensors

2005 ◽  
Vol 219 (9) ◽  
pp. 925-932 ◽  
Author(s):  
M. S. Riaz ◽  
K. J. Barb ◽  
A Engeda
Keyword(s):  
Steam Turbine ◽  
Dynamic Pressure ◽  
Pressure Sensors ◽  
Operating Conditions ◽  
Strain Gauges ◽  
System Response ◽  
Main Concern ◽  
Finite Elements Analysis ◽  
Pressure Transducers ◽  
Last Stage

In this paper, a novel approach is presented to increase the operational flexibility of steam turbines. Exhaust pressure at the exit of the last-stage blades is one of the most important parameters that limit the operation of a steam turbine, especially on days with hot ambient conditions. The main concern in these off-design high-exhaust pressure operating conditions is that it can result in flow separation, which can lead to aeromechanics instabilities and thus to blade failure because of high-cycle fatigue. In the method proposed in this paper, dynamic pressure transducers are placed around the perimeter of the last-stage blade to measure the pressure variations caused by vibrating last-stage blades. This approach, which is applicable to condensing turbines only, will provide increased exhaust pressure limits through realtime monitoring of the pressure signal and thereby enable the power plant to produce more power during times of peak demand. Finite elements analysis was performed to predict the natural frequencies of the row of blades to distinguish between the synchronous and nonsynchronous modes of vibration. Strain gauges were placed on the blades to obtain the experimental frequency information of the system. Response from the dynamic pressure transducers was compared with responses from the strain gauges. An excellent agreement between the two sets of results proved the validity of the proposed method.

scholarly journals Analysis of Internal Flow Characteristics of a Startup Pump Turbine at the Lowest Head under No-Load Conditions

2021 ◽  
Vol 9 (12) ◽  
pp. 1360
Author(s):  
Wei Wang ◽  
Xi Wang ◽  
Zhengwei Wang ◽  
Mabing Ni ◽  
Chunan Yang
Keyword(s):  
High Speed ◽  
Pressure Pulsation ◽  
Working Condition ◽  
Guide Vane ◽  
Flow Characteristics ◽  
Internal Flow ◽  
Operating Conditions ◽  
Small Range ◽  
Pressure Balance ◽  
Pump Turbine

The instability of the no-load working condition of the pump turbine directly affects the grid connection of the unit, and will cause vibration and damage to the components of the unit in severe cases. In this paper, a three-dimensional full flow numerical model including the runner gap and the pressure-balance pipe was established. The method SST k-ω model was used to predict the internal flow characteristics of the pump turbine. The pressure pulsation of the runner under different operating conditions during the no-load process was compared. Because the rotation speed, flow rate, and guide vane opening of the unit change in a small range during the no-load process, the pressure pulsation characteristics of the runner are basically the same. Therefore, a working condition was selected to analyze the transient characteristics of the flow field, and it was found that there was a high-speed ring in the vaneless zone, and a stable channel vortex was generated in the runner flow passage. Analyzing the axial water thrust of each part of the runner, it was found that the axial water thrust of the runner gap was much larger than the axial water thrust of the runner blades, and it changed with time periodically. It was affected by rotor stator interaction. The main frequency was expressed as a multiple of the number of guide vanes, that is, vanes passing frequency, 22fn. During the entire no-load process, the axial water thrust of the runner changed slowly with time and fluctuated slightly.

Transient Pressure Analysis of a Prototype Pump Turbine: Field Tests and Simulation

2018 ◽  
Vol 140 (7) ◽  
Author(s):  
Jinhong Hu ◽  
Jiandong Yang ◽  
Wei Zeng ◽  
Jiebin Yang
Keyword(s):  
Field Tests ◽  
Water Hammer ◽  
Hydropower Plant ◽  
Pressure Pulsations ◽  
Transient Pressure ◽  
Pump Turbine ◽  
Operation Conditions ◽  
Spiral Case ◽  
Transient Events ◽  
Transient Variations

The transient behaviors of a prototype pump turbine are very important to the safe operation of a pumped-storage power plant. This is because the water hammer pressure during transient events affects the pressure surges in the spiral case (SC) and the draft tube (DT). In addition, the transient pressure pulsations in the vaneless space (VL) are important in the evaluation of the life of the runner. Although several detailed studies have been conducted on the water hammer pressure of a hydropower plant, very few have considered the transient pressure pulsations that occur in the pump turbine. The objective of the present study was to determine the characteristics of the transient pressure pulsations of a 300-MW prototype Francis pump turbine during load rejection and power failure. For this purpose, the frequency features in the steady-state were first analyzed using fast Fourier transform. A Savitzky–Golay filter was then used to extract the water hammer pressure and pulsating pressure from the acquired raw pressure signals. Further, a one-dimensional (1D) method of characteristics (MOC) mathematical model of the pump-turbine was established and used to simulate the transient variations of the flow discharge during transient events, to enable the division of the transient operation conditions into several domains. Finally, the characteristics of the transient pressure pulsations in the SC, vaneless space, and DT were investigated in the time and frequency domains. This paper also discusses the causes of the pressure pulsations that occur under different modes of operation of a pump turbine.

scholarly journals On the Rotor Stator Interaction Effects of Low Specific Speed Francis Turbines

2019 ◽  
Vol 2019 ◽  
pp. 1-11 ◽  
Author(s):  
Einar Agnalt ◽  
Igor Iliev ◽  
Bjørn W. Solemslie ◽  
Ole G. Dahlhaug
Keyword(s):  
Guide Vane ◽  
Pressure Fluctuations ◽  
Angular Position ◽  
Pressure Sensors ◽  
Pump Turbine ◽  
Blade Loading ◽  
Loading Case ◽  
Rotor Stator Interaction ◽  
Low Specific Speed ◽  
Specific Speed

The rotor stator interaction in a low specific speed Francis model turbine and a pump-turbine is analyzed utilizing pressure sensors in the vaneless space and in the guide vane cascade. The measurements are analyzed relative to the runner angular position by utilizing an absolute encoder mounted on the shaft end. From the literature, the pressure in the analyzed area is known to be a combination of two effects: the rotating runner pressure and the throttling of the guide vane channels. The measured pressure is fitted to a mathematical pressure model to separate the two effects for two different runners. One turbine with 15+15 splitter blades and full-length blades and one pump-turbine with six blades are investigated. The blade loading on the two runners is different, giving different input for the pressure model. The main findings show that the pressure fluctuations in the guide vane cascade are mainly controlled by throttling for the low blade loading case and the rotating runner pressure for the higher blade loading case.

Visualisation of Diffuser Instabilities in a Wet Gas Compressor

2015 ◽  
Author(s):  
Veronica Ferrara ◽  
Lars E. Bakken
Keyword(s):  
Oil And Gas ◽  
New Technologies ◽  
Dynamic Pressure ◽  
Pressure Sensors ◽  
Petroleum Industry ◽  
Research Programme ◽  
Open Loop ◽  
Ongoing Research ◽  
Wet Gas ◽  
Response Dynamic

The continuous demand for oil and gas pushes the petroleum industry to develop new technologies in order to increase production and exploit existing fields. The wet gas process, based on direct compression of unprocessed well stream subsea is a powerful means to expand the extraction of crude oil and gas and reach remote regions. Consequently centrifugal compressors are key elements that need to be developed in this area. Since no commercial subsea compressors are available and the liquid phase inside the standard process has to be avoided, it is essential to fully understand the machine behaviour, particularly investigate the presence of a gas-liquid mixture. Because of liquid impact, the performance of compressors and consequently the margin of stability may have to be modified. Here, delayed instability inception should be identified. An ongoing research programme is conducted at the Norwegian University of Science and Technology (NTNU) concerning the influence of wet gas on performance and aerodynamic stability. An open loop wet gas test rig is designed and employed in an experimental campaign. The main goal of this study is the visualisation of flow in a vaneless diffuser by means of special windows in Plexiglas, in correspondence with the diffuser and volute. Most attention is focused on the behaviour that leads to unstable phenomena, like stall and surge, in order to expose wet effects. Interactions between the diffuser and volute will also be taken into account. Simultaneously, the analysis will be supported by measurements from high-response dynamic pressure sensors. A fast Fourier transform (FFT) examination will be realised, in order to identify characteristic frequencies of unsteady events.

scholarly journals High Temperature Dynamic Pressure Measurements Using Silicon Carbide Pressure Sensors

2014 ◽  
Vol 2014 (HITEC) ◽  
pp. 000047-000052 ◽  
Author(s):  
Robert S. Okojie ◽  
Roger D. Meredith ◽  
Clarence T. Chang ◽  
Ender Savrun
Keyword(s):  
Silicon Carbide ◽  
Signal To Noise Ratio ◽  
Dynamic Pressure ◽  
Pressure Sensors ◽  
Operating Conditions ◽  
Thermoacoustic Instabilities ◽  
Laboratory Characterization ◽  
Dynamic Pressure Measurements ◽  
Low Sensitivity ◽  
Flow Stream

Un-cooled, MEMS-based silicon carbide (SiC) static pressure sensors were used for the first time to measure pressure perturbations at temperatures as high as 600 °C during laboratory characterization, and subsequently evaluated in a combustor rig operated under various engine conditions to extract the frequencies that are associated with thermoacoustic instabilities. One SiC sensor was placed directly in the flow stream of the combustor rig while a benchmark commercial water-cooled piezoceramic dynamic pressure transducer was co-located axially but kept some distance away from the hot flow stream. In the combustor rig test, the SiC sensor detected thermoacoustic instabilities across a range of engine operating conditions, amplitude magnitude as low as 0.5 psi at 585 °C, in good agreement with the benchmark piezoceramic sensor. The SiC sensor experienced low signal to noise ratio at higher temperature, primarily due to the fact that it was a static sensor with low sensitivity.

scholarly journals Hysteresis Characteristic in the Hump Region of a Pump-Turbine Model

2016 ◽  
Author(s):  
Deyou Li ◽  
Hongjie Wang ◽  
Jinxia Chen ◽  
Torbjørn K. Nielsen ◽  
Daqing Qin ◽  
...  
Keyword(s):  
Guide Vane ◽  
Pressure Sensors ◽  
Low Frequency ◽  
Rotational Frequency ◽  
Stable Operation ◽  
Hysteresis Phenomenon ◽  
Pump Turbine ◽  
Hydraulic Losses ◽  
Measurement Direction ◽  
Turbine Model

The hump feature is one of the major instabilities in pump-turbines. When pump-turbines operate in the hump region, strong noise and serious fluctuations can be observed, which are harmful to their safe and stable operation and can even destroy the whole unit as well as water conveyance system. In this paper, a low specific speed (nq = 36.1 min−1) pump-turbine model was experimentally investigated. Firstly, the hump characteristic was obtained under 19 mm guide vane opening conditions. More interestingly, when the hump characteristic was measured in two directions (increasing and decreasing the discharge), characteristic hysteresis was found in the hump region. The analysis of performance characteristics reveals that the hump instability is the result of Euler momentum and hydraulic losses, and different Euler momentum and hydraulic losses in the two development processes lead to the hysteresis phenomenon. Then, 12 pressure sensors were mounted in the different parts of the pump-turbine model to obtain the time and frequency characteristics. The analysis of the corresponding fast Fourier transform confirms that the hump characteristic is related to low-frequency (0.04–0.15 times rotational frequency) vortices. The occurrence and cessation of vortices depend on the operating condition and measurement direction, which contribute to the hysteresis feature. Finally, the type of the low-frequency vortices was analyzed through the cross power spectrum.

Experimentally Determining the Acoustic Damping Rates of a Combustor With a Swirl Stabilized Lean Premixed Flame

2015 ◽  
Author(s):  
Nicolai V. Stadlmair ◽  
Michael Wagner ◽  
Christoph Hirsch ◽  
Thomas Sattelmayer
Keyword(s):  
Probability Distributions ◽  
Dynamic Pressure ◽  
Pressure Sensors ◽  
Stability Margin ◽  
Open Loop ◽  
Decay Rates ◽  
Acoustic Energy ◽  
Test Rig ◽  
Acoustic Damping ◽  
Lean Premixed

In this study, we employ a method based on Bayesian statistics to determine the rate of acoustic decay from dynamic pressure measurements inside a combustor. It is common, that lean premixed flames tend to drive thermoacoustic instabilities at specific eigenfrequencies. Hence, the dissipation of acoustic energy inside the combustor, its absorption at the boundaries and its transfer over the in- and outlets must always exceed the acoustic excitation from the flame to avoid pulsations. Quantitative measures for the level of stability are of high technical relevance. In that context the occurring eigenfrequencies and their damping rates are important indicators for the stability margin of gas turbine combustors. A modular swirl burner is investigated in an atmospheric single burner test rig under lean premixed conditions. For the experimental determination of the damping rates, a siren is used to externally excite resonant frequencies of the combustion system. After interrupting the forcing abruptly, time series of the decaying signals are recorded by dynamic pressure sensors inside the combustion chamber. For the analysis of this data, an algorithm based on a Bayesian network approach, which uses a Gibbs Sampler is employed. Probability distributions of frequencies and decay rates are obtained with the Markov-Chain Monte-Carlo (MCMC) method. For the investigated configuration, the influence of the acoustic boundary conditions and the preheat temperature on eigenmodes and damping rates is evaluated. Finally, the results are compared to a network model of the test rig. With that approach, the Open-Loop Gain (OLG) is evaluated for the frequency range of interest. Eigenfrequencies as well as their corresponding damping rates are obtained from Nyquist analysis.

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