Stabilizing Pump-Turbine Operations Using Water Injection Passive Control

2019 ◽  
Author(s):  
Muhannad Altimemy ◽  
Bashar Attiya ◽  
Cosan Daskiran ◽  
I-Han Liu ◽  
Alparslan Oztekin
Keyword(s):  
Turbulent Flows ◽  
Control Strategy ◽  
Passive Control ◽  
Draft Tube ◽  
Water Injection ◽  
Large Eddy ◽  
Flow Induced Vibrations ◽  
Computational Fluid Dynamics Simulations ◽  
Dynamics Simulations ◽  
Turbine Mode

Abstract Computational fluid dynamics simulations are carried out to characterize the spatial and temporal characteristics of the velocity and pressure field of turbulent flows through a pumpturbine unit operating with the turbine mode. The high-fidelity large eddy simulations turbulence model is utilized to examine the flow-induced vibrations in the draft tube of the unit. The water injection from the runner cone is considered as the control strategy to mitigate the flow-induced fluctuations. The simulations are conducted for the turbine flow rate of 0.2 m3/s without and with the water injection at a rate of 0.008 m3/s. The pressure along the surface of the draft tube is probed at various locations to access the effectiveness of the water injection to mitigate fluctuations. Water injection at 4% rate is demonstrated to be effective in attenuating the pressure fluctuation inside the draft tube. The amplitude of fluctuations is reduced by nearly 50% by the water injection. The generated power is hardly influenced by water injection. Thus, the control strategy considered here could be employed effectively without a penalty on the power generation.

Mitigation of Flow-Induced Pressure Fluctuations in a Francis Turbine Using Water Injection

2019 ◽  
Author(s):  
Muhannad Altimemy ◽  
Bashar Attiya ◽  
Cosan Daskiran ◽  
I-Han Liu ◽  
Alparslan Oztekin
Keyword(s):  
Power Generation ◽  
Turbulent Flow ◽  
Draft Tube ◽  
Pressure Fluctuations ◽  
Water Injection ◽  
Operating Conditions ◽  
Francis Turbine ◽  
Partial Load ◽  
Flow Induced Vibrations ◽  
Dynamics Simulations

Abstract Computational fluid dynamics simulations are conducted to characterize the spatial and temporal characteristics of the turbulent flow fields inside Francis turbine operating at the design and partial load regimes. High-fidelity large eddy simulations turbulence model is applied to investigate the flow-induced vibrations in the draft tube of the unit. The water injection at 4% rate from the runner cone is implemented to control the flow-induced pressure fluctuations. The simulations are conducted at the turbine design point and two partial load operations with and without water injection. It has been demonstrated that the water injection has a profound influence in the turbulent flow structure and the pressure field inside the draft tube at the partial load operating conditions. To evaluate the effectiveness of the water injection techniques in mitigating flow-induced fluctuations, the probes at various locations along the wall of the draft tube are used to monitor the pressure signals. It appears to be a reduction in the level of pressure fluctuations by the water injection at both partial load operating regimes. However, we could not draw a firm conclusion about the level of mitigation of flow-induced vibrations. Simulations should be carried out for much longer flow time. Water injection hardly influenced the unit power generation. Hence water injection can be employed effectively without a major liability on the power generation.

scholarly journals Pumps used as turbines power recovery, energy efficiency, CFD analysis

2014 ◽  
Vol 18 (3) ◽  
pp. 1029-1040 ◽  
Author(s):  
Jasmina Bogdanovic-Jovanovic ◽  
Dragica Milenkovic ◽  
Dragan Svrkota ◽  
Bozidar Bogdanovic ◽  
Zivan Spasic
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Energy Efficiency ◽  
Operating Mode ◽  
Maximum Energy ◽  
Wide Range ◽  
Computational Fluid Dynamics Simulations ◽  
Dynamics Simulations ◽  
Power Recovery ◽  
Turbine Mode

As the global demand for energy grows, numerous studies in the field of energy efficiency are stimulated, and one of them is certainly the use of pumps in turbine operating mode. In order to reduce time necessary to determine pump characteristic in turbine operating mode problem was studied by computational fluid dynamics approach. The paper describes various problems faced during modeling (pump and turbine mode) and the approaches used to resolve the problems. Since in the majority of applications, the turbine is a pump running in reverse, many attempts have been made to predict the turbine performance from the known pump performance, but only for best efficiency point. This approach does not provide reliable data for the design of the system with maximum energy efficiency and does not allow the determination of the head for a wide range of flow rates. This paper presents an example of centrifugal norm pump operating in both (pump and turbine) regime and comparison of experimentally obtained results and computational fluid dynamics simulations.

The Effect of Natural Ventilation in a Small Room with an Unvented Gas-Fired Heater

2005 ◽  
Vol 277-279 ◽  
pp. 583-588
Author(s):  
Jaeock Yoon
Keyword(s):  
Air Pollution ◽  
Indoor Air ◽  
Natural Ventilation ◽  
Indoor Air Pollution ◽  
Passive Control ◽  
Field Measurements ◽  
Maintenance Cost ◽  
Air Contaminants ◽  
Computational Fluid Dynamics Simulations ◽  
Dynamics Simulations

In small buildings and residences in Korea, unvented or improperly vented combustion appliances are used to heat rooms. These heaters are mostly gas-fired portable equipment used for auxiliary heating. Although their maintenance cost is very low, unvented gas-fired heaters emit air contaminants such as carbon dioxide and carbon monoxide. If there is inadequate ventilation and even a little fresh air with oxygen comes into the appliances, combustion occurs less efficiently and heaters generate more air contaminants. Natural ventilation is the best way to prevent air pollution in small buildings. Outdoor air has a lot of oxygen and can reduce air pollution. The objective and scope of this research is to predict the distribution of indoor air pollution, according to the results of field measurements and CFD (Computational Fluid Dynamics) simulations. In a room of 6.4m×3.1m×2.6m in size, air contaminants (CO2 and CO) and air temperature were measured in two instances--with natural ventilation and without natural ventilation. After comparing the results obtained with computer simulation and field measurements, passive control methods to improve indoor air quality in a room are proposed.

Fully-Developed Convective Heat Transfer and Pressure Drop in a Square Duct With Baffle Inserts Using CFD Analysis

2020 ◽  
Author(s):  
Lasse U. Christensen ◽  
Stefan Holebæk ◽  
Nisanthan Thanabalasingham ◽  
Jakob Hærvig ◽  
Henrik Sørensen
Keyword(s):  
Heat Transfer ◽  
Temperature Gradient ◽  
Pressure Loss ◽  
Fully Developed Flow ◽  
Square Duct ◽  
Image Velocimetry ◽  
Large Eddy ◽  
Computational Fluid Dynamics Simulations ◽  
Dynamics Simulations ◽  
Two Parameters

Abstract The scope of this project is to investigate how the geometry of baffles affect heat transfer and pressure loss of a fluid flow at Re = 1000 through a square duct. For this purpose, Large Eddy Simulations are performed to investigate the effect of baffle height and baffle width. Focus is on the fully-developed flow that repeats itself at streamwise stations. The flow field predicted by Computational Fluid Dynamics simulations was validated using Particle Image Velocimetry. The different designs are evaluated in terms of Nusselt number, Nu and a loss coefficient, f, which are normalised using a reference geometry consisting of a square duct without baffles. The two parameters are additionally combined into a performance parameter eta η = (Nu/Nu0)/(f / f0)(1/3). It was found that adding baffles can result in a quadrupling of η. Reducing the height of baffles decreases heat transfer, while significantly reducing pressure loss and ultimately leading to a higher η. Reducing baffle height was also found to increase the temperature gradient at the upper wall and reduce it at the lower wall. Reducing baffle width resulted in the largest temperature gradient, but lead to poor heat transfer within the fluid.

Pressure Fluctuation Mitigation in a Francis Turbine With Water Injection: Computational Study

2018 ◽  
Author(s):  
Muhannad Altimemy ◽  
Cosan Daskiran ◽  
Bashar Attiya ◽  
I-Han Liu ◽  
Alparslan Oztekin
Keyword(s):  
Pressure Fluctuation ◽  
Draft Tube ◽  
Computational Study ◽  
Water Injection ◽  
Francis Turbine ◽  
Navier Stokes ◽  
Tube Surface ◽  
Vortex Rope ◽  
Central Vortex ◽  
Dynamics Simulations

Computational fluid dynamics simulations were performed on Francis turbine using Reynolds-averaged Navier-Stokes (RANS) with k-ω SST turbulence model. Simulations were conducted at the turbine’s best efficiency point with a Reynolds number of 2.01 × 107. Water injection was admitted from the runner cone in the stream-wise direction. The aim of this process was to investigate the influence of water injection on the turbine performance and the pressure pulsation. The water injection did not affect the nominal value of the turbine’s power generation. Straight vortex rope was observed at the centerline of the draft tube. Moreover, helix-shaped vortex ropes were obtained near the draft tube surface. The water injection expands the central vortex rope, but it did not suppress or disrupt the helix-shaped peripheral vortex rope near the draft tube surface. The pressure fluctuation became less regular after the water injection, but the fluctuation level remained similar.

Francis Turbine Operation at Excess Flow Rate Using Large Eddy Simulation: The Effect of Water Injection

2020 ◽  
Author(s):  
Muhannad Altimemy ◽  
Justin Caspar ◽  
Saif Watheq ◽  
Alparslan Oztekin
Keyword(s):  
Flow Rate ◽  
Draft Tube ◽  
Tube Wall ◽  
Temporal Structure ◽  
Pressure Fluctuations ◽  
Water Injection ◽  
Design Flow ◽  
Francis Turbine ◽  
Reduced Pressure ◽  
Large Eddy

Abstract High-fidelity Large Eddy Simulations (LES) were conducted to characterize the spatial and temporal structure of turbulent flows in an industrial-sized Francis turbine running at 120% of the design flow rate. Injection at a 4% and 8% flow rate is applied and investigated as a mitigation method for pressure-induced fluctuations along the draft tube. Contours of velocity and vorticity in the draft tube are presented to examine the effects of water injection. Probes placed alongside the draft tube measure the pressure signal and compare both operational regimes to characterize the pressure fluctuations. The intensity of pressure fluctuations along the draft tube wall is an order of magnitude smaller compared to that at the center. As the injection is applied, the intensity of the pressure fluctuations along the draft tube wall is increased while the intensity of pressure fluctuations in the center of the draft tube is reduced. Pressure probes in the center of the draft tube measure an 86% to 57% reduction in amplitude for 4% to 8% flow rate injection, respectively. There is a 30% to 40% increase in fluctuations along the wall for 4% to 8% flow rate injection, respectively. These changes in flow structure are due to the dissipation of the vortex rope as the injection is applied.

Large Eddy Simulations of Francis Turbine Operating at Ultra-Low Loads

2020 ◽  
Author(s):  
Muhannad Altimemy ◽  
Justin Caspar ◽  
Saif Watheq ◽  
Alparslan Oztekin
Keyword(s):  
Turbulent Flows ◽  
Structural Integrity ◽  
Draft Tube ◽  
Temporal Structure ◽  
Pressure Fluctuations ◽  
High Amplitude ◽  
Large Eddy Simulations ◽  
Francis Turbine ◽  
Partial Load ◽  
Large Eddy

Abstract High-fidelity large eddy simulations (LES) were conducted to characterize the spatial and temporal structure of turbulent flows in an industrial-sized Francis turbine. The unit operated at 50% and 40% of the best efficiency design flowrate. Contours of vorticity, velocity, pressure, and iso-surfaces of Q-Criterion were presented to characterize the effects on the draft tube. Probes placed alongside the draft tube measure the pressure signal to investigate the flow-induced pressure fluctuations inside the turbine unit. The maximum intensity of pressure fluctuations at 50% partial load was 22.66% of the turbine head, while the strength of the pressure fluctuations was 26.36% at 40% partial load. A large number of unorganized smaller vortices observed in the draft tube contribute to the creation of pressure fluctuations. Two pressure modes can be easily recognized (1) high frequency with low amplitude pressure fluctuations and (2) low frequency with high amplitude fluctuations. These pressure fluctuations could be harmful to the structural integrity of the unit and also have undesirable influences on the operational stability of the hydro-turbines.

Sign in / Sign up

Export Citation Format

Share Document