scholarly journals Transient Air-Water Flow and Air Demand following an Opening Outlet Gate

2018 ◽  
Vol 2018 ◽  
pp. 1-12 ◽  
Author(s):  
James Yang ◽  
Ting Liu ◽  
Wenhong Dai ◽  
Penghua Teng
Keyword(s):  
Water Flow ◽  
Hydraulic Jump ◽  
Three Dimensional ◽  
Cfd Simulations ◽  
Wire Ropes ◽  
Air Supply ◽  
Flow Features ◽  
Demand Rate ◽  
Air Pockets ◽  
Bottom Outlets

In Sweden, the dam-safety guidelines call for an overhaul of many existing bottom outlets. During the opening of an outlet gate, understanding the transient air-water flow is essential for its safe operation, especially under submerged tailwater conditions. Three-dimensional CFD simulations are undertaken to examine air-water flow behaviors at both free and submerged outflows. The gate, hoisted by wire ropes and powered by AC, opens at a constant speed. A mesh is adapted to follow the gate movement. At the free outflow, the CFD simulations and model tests agree well in terms of outlet discharge capacity. Larger air vents lead to more air supply; the increment becomes, however, limited if the vent area is larger than 10 m2. At the submerged outflow, a hydraulic jump builds up in the conduit when the gate reaches approximately 45% of its full opening. The discharge is affected by the tailwater and slightly by the flow with the hydraulic jump. The flow features strong turbulent mixing of air and water, with build-up and break-up of air pockets and collisions of defragmented water bodies. The air demand rate is several times as much as required by steady-state hydraulic jump with free surface.

scholarly journals Assessment and Prediction of Air Entrainment and Geyser Formation in a Bottom Outlet: Field Observations and CFD Simulation

Fluids ◽  
2020 ◽  
Vol 5 (4) ◽  
pp. 203
Author(s):  
James Yang ◽  
Penghua Teng ◽  
Junhu Nan ◽  
Shicheng Li ◽  
Anders Ansell
Keyword(s):  
Water Flow ◽  
Cfd Simulation ◽  
Three Dimensional ◽  
Air Entrainment ◽  
Cfd Modeling ◽  
Two Phase ◽  
Gate Operation ◽  
Flow Features ◽  
Air Pockets ◽  
Bottom Outlet

Air entrainment at the intake of a bottom outlet often gives rise to air pockets in its conduit and formation of geysers. The outlet in question comprises a bulkhead gate, gate shaft, horizontal conduit, and exit. Operations show that it suffers from appreciable flow fluctuations and blowouts in the tailwater, which leads to gate operation restrictions. For the purpose of understanding the hydraulic phenomenon, both prototype discharge tests and three-dimensional computational fluid dynamics (CFD) modeling of two-phase flows are performed. The operational focus of the facility are small and large gate openings. The CFD results reveal that, with air entrained in the gate shaft, continual breakup and coalescence of air bubbles in the conduit typify the flow. At small openings below 1 meter, the air–water flow is characterized by either distinct blowouts of regular frequency or continuous air release. In terms of geyser behaviors inclusive of frequency, the agreement is good between field and numerical studies. At large openings, the gate becomes fully submerged, and the flow is discharged without air entrainment and blowouts. The paper showcases the air–water flow features in a typical bottom outlet layout in Sweden, which is intended to serve as an illustration of the study procedure for other similar outlets.

scholarly journals IDDES Evaluation of Oscillating Hydraulic Jumps

2018 ◽  
Vol 40 ◽  
pp. 05067 ◽  
Author(s):  
Vimaldoss Jesudhas ◽  
Frédéric Murzyn ◽  
Ram Balachandar
Keyword(s):  
Flow Field ◽  
Hydraulic Jump ◽  
Three Dimensional ◽  
Wall Jet ◽  
Hydraulic Jumps ◽  
Vortical Structures ◽  
Instantaneous Flow Field ◽  
Type Flow ◽  
Different Types ◽  
Flow Features

This paper presents the results of three-dimensional, unsteady, Improved Delayed Detached Eddy Simulations of an oscillating and a stable hydraulic jump at Froude numbers of 3.8 and 8.5, respectively. The different types of oscillations characterised in a hydraulic jump are analysed by evaluating the instantaneous flow field. The instability caused by the flapping wall-jet type flow in an oscillating jump is distinct compared to the jump-toe fluctuations caused by the spanwise vortices in the shear layer of a stable jump. These flow features are accurately captured by the simulations and are presented with pertinent discussions. The near-bed vortical structures in an oscillating jump is extracted and analysed using the λ2 criterion.

Combined Air Supply at Fuel Pump Entrance

2014 ◽  
Author(s):  
Salimzhan Gafurov ◽  
Leonid Rodionov ◽  
Asgat Gimadiev
Keyword(s):  
Three Dimensional ◽  
Aviation Fuel ◽  
Turbine Engines ◽  
Cfd Analysis ◽  
Gas Turbine Engines ◽  
Cfd Simulations ◽  
Fuel Pump ◽  
Operating Modes ◽  
Air Supply ◽  
Series Of Experiments

Previous research has shown that aviation fuel pumps, which consist of a screw and centrifugal wheels are the most loaded units of the gas turbine engines. Thus a fuel pump is the key component that limits the reliability and endurance of the fuel system and, as a result, of the whole engine. This paper describes the results of CFD simulations of the process getting free gas to enter the combined pump. The CFD analysis has been used to calculate an unsteady three-dimensional viscous flow of multi-component fluid in the fuel pump. The calculations have been used to determine unsteady loads of fuel pump in different operating modes. To examine the efficiency of the CFD analysis, we conducted a series of experiments. The experimental results proved the accuracy of the numerical model. The results can help to develop measures for the reduction of dynamic loads in aviation fuel pumps in case where combined air is at entrance to pump.

Angle-of-Attack Effects on Counter-Rotating Propellers at Take-Off

2012 ◽  
Author(s):  
Tobias Brandvik ◽  
Cesare Hall ◽  
Anthony B. Parry
Keyword(s):  
Flow Field ◽  
Angle Of Attack ◽  
Three Dimensional ◽  
Linear Increase ◽  
Tip Vortex ◽  
Cfd Simulations ◽  
Installation Effects ◽  
Flow Features ◽  
High Angles Of Attack ◽  
Unsteady Lift

Due to their potential for significant fuel consumption savings, Counter-Rotating Open Rotors (CRORs) are currently being considered as an alternative to high-bypass turbofans. When CRORs are mounted on an aircraft, several ‘installation effects’ arise which are not present when the engine is operated in isolation. This paper investigates how flow features arising from one such effect — the angle-of-attack of the engine centre-line relative to the oncoming flow — can influence the design of CROR engines. Three-dimensional full-annulus unsteady CFD simulations are used to predict the time-varying flow field experienced by each rotor and emphasis is put on the interaction of the front-rotor wake and tip vortex with the rear-rotor. A parametric study is presented that quantifies the rotor-rotor interaction as a function of the angle-of-attack. It is shown that angle-of-attack operation significantly changes the flow field and the unsteady lift on both rotors. In particular, a frequency analysis shows that the unsteady lift exhibits sidebands around the rotor-rotor interaction frequencies. Further, a non-linear increase in the total rear-rotor tip unsteadiness is observed for moderate and high angles-of-attack. The results presented in this paper demonstrate that common techniques used to mitigate CROR noise, such as modifying the rotor-rotor axial spacing and rear-rotor crop, can not be applied correctly unless angle-of-attack effects are taken into account.

Performance enhancement of Savonius wind turbine by blade shape and twisted angle modifications

2021 ◽  
pp. 095765092098794
Author(s):  
Ahmed M Nagib Elmekawy ◽  
Hassan A Hassan Saeed ◽  
Sadek Z Kassab
Keyword(s):  
Wind Turbine ◽  
Performance Enhancement ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Vertical Axis ◽  
Cfd Simulations ◽  
Sliding Mesh ◽  
Blade Shape ◽  
Rotor Shape ◽  
Twisting Angle

Three-dimensional CFD simulations are carried out to study the increase of power generated from Savonius vertical axis wind turbines by modifying the blade shape and blade angel of twist. Twisting angle of the classical blade are varied and several proposed novel blade shapes are introduced to enhance the performance of the wind turbine. CFD simulations have been performed using sliding mesh technique of ANSYS software. Four turbulence models; realizable k -[Formula: see text], standard k - [Formula: see text], SST transition and SST k -[Formula: see text] are utilized in the simulations. The blade twisting angle has been modified for the proposed dimensions and wind speed. The introduced novel blade increased the power generated compared to the classical shapes. The two proposed novel blades achieved better power coefficients. One of the proposed models achieved an increase of 31% and the other one achieved 32.2% when compared to the classical rotor shape. The optimum twist angel for the two proposed models achieved 5.66% and 5.69% when compared with zero angle of twist.

scholarly journals Radial Turbine Design for Solar Chimney Power Plants

Energies ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 674
Author(s):  
Paul Caicedo ◽  
David Wood ◽  
Craig Johansen
Keyword(s):  
Power Plants ◽  
Reference Frames ◽  
Three Dimensional ◽  
Discrete Ordinates ◽  
Large Area ◽  
Solar Chimney ◽  
Cfd Simulations ◽  
Radial Turbine ◽  
Design Changes ◽  
Turbine Design

Solar chimney power plants (SCPPs) collect air heated over a large area on the ground and exhaust it through a turbine or turbines located near the base of a tall chimney to produce renewable electricity. SCPP design in practice is likely to be specific to the site and of variable size, both of which require a purpose-built turbine. If SCPP turbines cannot be mass produced, unlike wind turbines, for example, they should be as cheap as possible to manufacture as their design changes. It is argued that a radial inflow turbine with blades made from metal sheets, or similar material, is likely to achieve this objective. This turbine type has not previously been considered for SCPPs. This article presents the design of a radial turbine to be placed hypothetically at the bottom of the Manzanares SCPP, the only large prototype to be built. Three-dimensional computational fluid dynamics (CFD) simulations were used to assess the turbine’s performance when installed in the SCPP. Multiple reference frames with the renormalization group k-ε turbulence model, and a discrete ordinates non-gray radiation model were used in the CFD simulations. Three radial turbines were designed and simulated. The largest power output was 77.7 kW at a shaft speed of 15 rpm for a solar radiation of 850 W/m2 which exceeds by more than 40 kW the original axial turbine used in Manzanares. Further, the efficiency of this turbine matches the highest efficiency of competing turbine designs in the literature.

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