scholarly journals Numerical Study on Flow Characteristics in a Francis Turbine during Load Rejection

Energies ◽  
2019 ◽  
Vol 12 (4) ◽  
pp. 716 ◽  
Author(s):  
Daqing Zhou ◽  
Huixiang Chen ◽  
Jie Zhang ◽  
Shengwen Jiang ◽  
Jia Gui ◽  
...  
Keyword(s):  
Geometric Modeling ◽  
Numerical Study ◽  
Numerical Models ◽  
Experimental Testing ◽  
Pressure Fluctuations ◽  
Load Condition ◽  
Numerical Results ◽  
Francis Turbine ◽  
Labyrinth Seals ◽  
Load Rejection Process

Labyrinth seals are not usually included in the numerical models of hydraulic machinery to simplify the geometric modeling, and thereby reduce the calculation burden. However, this simplification affects the numerical results, especially in the load rejection process, because disc friction losses, volume losses, and pressure fluctuations in the seal ring (SR) clearance passage are neglected. This paper addresses the issue by considering all of the geometrical details of labyrinth seals when conducting multiscale flow simulations of a high head Francis turbine under a transient load rejection condition using the commercial software code. A comparison of the numerical results that were obtained with the experimental testing data indicates that the calculated values of both torque and mass discharge rate are 8.65% and 5% slightly less than the corresponding values that were obtained from experimental model testing, respectively. The obtained pressure fluctuations of the Francis turbine in the vaneless zone and the draft tube appear to more closely match with the experimental test data when including SR clearance. Moreover, the flow rates through SR clearance passages were very small, but the pressure fluctuations among them were significantly enhanced under the minimal load condition. The numerical model with SR clearance can more accurately reflect the fact that the water thrust on the runner only fluctuates from 800 N to 575 N during the load rejection process, even though the water thrust on the blades varies from −220 N to 1200 N. Therefore, multiscale flow study is of great significance in understanding the effect of clearance flow on the load rejection process in the Francis turbine.

Performance of Francis Turbine Operating at Excess Load Condition

2020 ◽  
Author(s):  
Muhannad Altimemy ◽  
Justin Caspar ◽  
Alparslan Oztekin
Keyword(s):  
Flow Field ◽  
Draft Tube ◽  
Turbine Blades ◽  
Pressure Fluctuations ◽  
Load Condition ◽  
Operating Conditions ◽  
Francis Turbine ◽  
Partial Load ◽  
Dynamics Simulations ◽  
Excess Load

Abstract Computational fluid dynamics simulations are conducted to characterize the spatial and temporal characteristics of the flow field inside a Francis turbine operating in the excess load regime. A high-fidelity Large Eddy Simulation (LES) turbulence model is applied to investigate the flow-induced pressure fluctuations in the draft tube of a Francis Turbine. Probes placed alongside the wall and in the center of the draft tube measure the pressure signal in the draft tube, the pressure over the turbine blades, and the power generated to compare against previous studies featuring design point and partial load operating conditions. The excess load is seen during Francis turbines in order to satisfy a spike in the electrical demand. By characterizing the flow field during these conditions, we can find potential problems with running the turbine at excess load and inspire future studies regarding mitigation methods. Our studies found a robust low-pressure region on the edges of turbine blades, which could cause cavitation in the runner region, which would extend through the draft tube, and high magnitude of pressure fluctuations were observed in the center of the draft tube.

Numerical study on characteristics of unsteady flow in a centrifugal pump volute at partial load condition

2015 ◽  
Vol 32 (6) ◽  
pp. 1549-1566 ◽  
Author(s):  
Lei Tan ◽  
Baoshan Zhu ◽  
Yuchuan Wang ◽  
Shuliang CAO ◽  
Shaobo Gui
Keyword(s):  
Flow Field ◽  
Centrifugal Pump ◽  
Numerical Study ◽  
Pressure Fluctuations ◽  
Load Condition ◽  
Dominant Frequency ◽  
Content Type ◽  
Cavitation Effect ◽  
Partial Load ◽  
Large Pressure Gradient

Purpose – The purpose of this paper is to elucidate the detailed flow field and cavitation effect in the centrifugal pump volute at partial load condition. Design/methodology/approach – Unsteady flows in a centrifugal pump volute at non-cavitation and cavitation conditions are investigated by using a computation fluid dynamics framework combining the re-normalization group k-e turbulence model and the mass transport cavitation model. Findings – The flow field in pump volute is very complicated at part load condition with large pressure gradient and intensive vortex movement. Under cavitation conditions, the dominant frequency for most of the monitoring points in volute transit from the blade passing frequency to a lower frequency. Generally, the maximum amplitudes of pressure fluctuations in volute at serious cavitation condition is twice than that at non-cavitation condition because of the violent disturbances caused by cavitation shedding and explosion. Originality/value – The detailed flow field and cavitation effect in the centrifugal pump volute at partial load condition are revealed and analysed.

scholarly journals Numerical and Experimental Investigation into the Aerodynamic Benefits of Rotorcraft Formation Flight

2021 ◽  
Author(s):  
Ramon Duivenvoorden ◽  
Mark Voskuijl ◽  
Lars Morée ◽  
Jan de Vries ◽  
Finbar van der Veen
Keyword(s):  
Wind Tunnel ◽  
Numerical Study ◽  
Numerical Models ◽  
Wind Tunnel Experiment ◽  
Numerical Results ◽  
Formation Flight ◽  
Total Power ◽  
Small Scale ◽  
Main Rotor ◽  
Rotor Disk

The use of formation flight to achieve aerodynamic benefit applied to rotorcraft has, unlike its fixed-wing counterpart, received little attention in the literature. This document presents a proof-of-concept of rotorcraft formation flight from two independent investigations: a numerical study of a fully articulated helicopter influenced by an upstream helicopter wake and a wind-tunnel experiment featuring two small-scale helicopter models with fixed-pitch blades. Both cases feature a representation of two helicopters in a diagonal, staggered formation aligned on the advancing side of the main rotor, but do not simulate directly comparable flight conditions. The vertical and lateral alignment of the two helicopters is varied in order to observe the achievable reductions in main rotor power required during cruise flight. The wind-tunnel experiment data yield an estimated maximum total power reduction for the secondary aircraft of approximately 24%, while the numerical models yield reductions between 20% and 34% dependent on flight velocity. Both experiments predict a higher potential for aerodynamic benefit than generally observed for fixed-wing formations, which is attributed to the asymmetric velocity profile induced by the wake of the upstream rotor. Optimal lateral alignment of both experimental and numerical results is found to feature overlap of the rotor disk areas, rather than tip-to-tip alignment, as a result of the circular rotor disk area. Experimental data show an optimal vertical alignment of the secondary rotorcraft below the primary, due to the self-induced vertical displacement of the rotor wake, which is absent from the numerical results due to the application of a flat wake assumption. The results show a promising potential for rotorcraft formation flight, though due to the limited nature of the models used, conclusions cannot be generalized. The potential aerodynamic benefit indicated by the present study invites further research in the field of rotorcraft formation flight.

scholarly journals Development of Impact-Echo Multitransducer Device for Automated Concrete Homogeneity Assessment

Materials ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2144
Author(s):  
Bartłomiej Sawicki ◽  
Tomasz Piotrowski ◽  
Andrzej Garbacz
Keyword(s):  
Nondestructive Testing ◽  
Numerical Study ◽  
Numerical Models ◽  
Experimental Testing ◽  
Experimental Tests ◽  
Impact Echo ◽  
University Of Technology ◽  
Homogeneity Assessment

A combination of multiple nondestructive testing (NDT) methods speeds up the assessment of concrete and increases the precision. This is why the UIR-Scanner was developed at Warsaw University of Technology. The scanner uses an Impact-Echo (IE) method with a unique arrangement of multiple transducers. This paper presents the development of the IE module using numerical models validated with experimental testing. It was found that rectangular arrangement of four transducers with the impactor in the middle is optimal for quick scanning of area for faults and discontinuities, changing the method from punctual to volumetric. A numerical study of void detectability depending on its position with respect to the IE module is discussed as well. After confirmation of the findings of models using experimental tests, the module was implemented into the scanner.

Numerical Simulation of Pressure Fluctuation in Draft Tube of Large Francis Turbine

2007 ◽  
Author(s):  
Cuilin Liao ◽  
Fujun Wang ◽  
Xiaoqin Li ◽  
Yuliang Zhu
Keyword(s):  
Pressure Fluctuation ◽  
Swirling Flow ◽  
Transport Model ◽  
Draft Tube ◽  
Numerical Study ◽  
Hydraulic Turbine ◽  
Dominant Frequency ◽  
Numerical Results ◽  
Francis Turbine ◽  
Pressure Amplitude

The pressure fluctuation caused by swirling flow in draft tube is one of the main reasons of vibration in hydraulic turbine. It directly affects the steady operation of hydraulic turbine unit. The pressure fluctuation in draft tube of a large Francis turbine can’t be obtained accurately by similarity law from model test, and prototype test is difficult to carry out and costs too much. Therefore, it is necessary to predict pressure fluctuation in draft tube numerically and provide scientific reference for mitigating and suppressing pressure fluctuation. This paper describes a numerical study of unsteady flow in the draft tube of a large Francis turbine in a Hydropower Station of China by using the Reynolds averaged Navier–Stokes (RANS) approach with a Reynolds stress transport model (RSM), validating the numerical results against experimental data. The numerical results successfully represent the vortex rope. The pressure fluctuation patterns in different parts of the draft tube including the cone, elbow and diffuser are analyzed. The pressure fluctuation in the cone and elbow is relative steady, and it has an obvious dominant frequency which is approximately 0.28 and 0.3 times of the runner rotational frequency. These results show very good agreement with experiments. The largest pressure amplitude appears in the draft tube cone downstream side and the draft elbow inside. The pressure fluctuation in the diffuser is stochastic, and the amplitude is small. Additionally, the pressure distributions on the horizontal computational section of the draft tube are analyzed.

Experimental and Numerical Study on the Motion Characteristics of Cylinder Oil and the Suppressing Methods for Abnormal Combustion in Low-Speed Dual-Fuel Marine Engine

2020 ◽  
Author(s):  
Zhen Gong ◽  
Wenjing Qu ◽  
Min Pan ◽  
Liyan Feng
Keyword(s):  
Natural Gas ◽  
Numerical Study ◽  
Load Condition ◽  
Numerical Results ◽  
Exhaust Valve ◽  
Dual Fuel ◽  
Cylinder Wall ◽  
Oil Droplets ◽  
Low Speed ◽  
Auto Ignition

Abstract The auto-ignition of cylinder oil droplets could trigger pre-ignition, the most threatening abnormal combustion in low-speed two-stroke Otto cycle dual-fuel engines. In this study, both the experiment of cylinder oil stripping and numerical simulation of in-cylinder charge motion were conducted to reveal the motion state of cylinder oil near scavenging ports and its spatial distribution after entering combustion chamber. Further, a measure to suppress the occurrence of abnormal combustion was also investigated by numerical study. Experimental results illuminate that cylinder oil both in the form of film and single droplet would strip under the flow velocity of engine’s scavenging ports, which demonstrated the oil stripping near scavenging ports was one of its pathways into cylinder. Numerical results indicate that at high-load condition, the gathered region of oil-vapor mainly located near cylinder wall. In contrast, at low-load condition, gathered region of oil-vapor distributed near cylinder wall and the dead-region under exhaust valve. Auto-ignition of oil and pre-ignition of natural-gas were more likely to occur in these gathered regions of oil-vapor. Decreasing engine load reduced scavenging pressure, which raised the residual mass of in-cylinder oil. And the reduction of the diameter of stripped cylinder oil droplets promoted oil evaporation, which increased the oil concentration in the gathered region of oil-vapor. These two factors could further intensify the occurrence tendency of auto-ignition of cylinder oil. Moreover, numerical results also show that the combination of proper increase of downward angle of natural-gas injector and the advance of injection timing could significantly improve the mixture homogeneity and decrease the escaping ratio of natural-gas. The rich-fuel region near cylinder wall and under exhaust valve reduced apparently as well, which meant fuel concentration in gathered regions of oil-vapor decreased. The reduction of pre-mixture concentration in gathered region of oil-vapor could decrease the occurrence possibility of auto-ignition of cylinder oil. Thus the occurrence tendency of pre-ignition of natural-gas and subsequent severe abnormal combustion could also be inhibited.

A Numerical Study of Francis Turbine Operation at No-Load Condition

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Hossein Hosseinimanesh ◽  
Christophe Devals ◽  
Bernd Nennemann ◽  
Marcelo Reggio ◽  
François Guibault
Keyword(s):  
Numerical Study ◽  
Guide Vane ◽  
Flow Behavior ◽  
Full Range ◽  
Load Condition ◽  
Francis Turbine ◽  
Maximum Pressure ◽  
Complex Flow ◽  
Time Step ◽  
Interface Models

This paper presents a numerical methodology to study Francis turbines at no-load condition, an important operating condition regarding static and dynamic stresses. The proposed methodology uses unsteady Reynolds-averaged Navier–Stokes (RANS) simulations that have been integrated with a user subroutine to compute and return the value of runner speed, time step, and friction torque. The modeling tool is the commercial software ansys-cfx 14. The research compares the simulations that were performed using transient rotor–stator (TRS) and stage interface models and validate the results through experiments over the full range of admissible guide vane angles (GVAs). Both TRS and stage interface models yielded similar trends for all turbine runner parameters during the no-load process. Results show sizable differences in the average and maximum pressure on the blades between TRS and stage simulations. Analysis of the flow behavior in TRS simulation demonstrates complex flow phenomena involving a vortex breakdown within the draft tube, and strong vortices blocking the runner inlet, which dissipate the input energy into the turbine and yield a near zero-torque at no-load condition.

scholarly journals Numerical models development for unidirectional air flow diffusers with lobed and circular orifices

2019 ◽  
Vol 111 ◽  
pp. 01049
Author(s):  
Laurentiu Tacutu ◽  
Ilinca Nastase ◽  
Florin Bode ◽  
Cristiana Croitoru ◽  
Catalin Lungu
Keyword(s):  
Numerical Simulation ◽  
Boundary Conditions ◽  
Numerical Study ◽  
Numerical Models ◽  
Ventilation System ◽  
Numerical Results ◽  
Airflow Distribution ◽  
Numerical Grid ◽  
Computational Resources ◽  
Real Scale

In order to achieve more realistic boundary conditions on the inlet of a ventilation system it is necessary to study the influences of the air diffuser orifices geometry on the airflow distribution in the enclosure. Integrating these orifices directly in a real scale air diffuser for a numerical study will result in a huge computational grid which will translate in huge computational resources and a much larger calculation time. The solution, in this case, was the numerical simulation of the airflow through small parts of the studied air diffuser. Later, the numerical results will be implemented as boundary conditions in the unidirectional diffuser of a numerical simulation that represents a real scale operating room (OR). In the current study two diffusers with different orifices were studied, one having circular („O”) and the other one lobbed („+”) orifices. The initial numerical model had 25 orifices on the diffuser, but because of the very large numerical grid resulted for the initial meshes (>35 million tetrahedral cells), a solution with only 4 orifices was chosen for this study. A mesh independency study was made for these two types of air diffusers. The numerical studies were made using RANS method, with SST k-ω turbulence model in steady state conditions. The numerical results obtained with the first step models showed very good agreement with the PIV stereoscopic experimental measurements.

Using Ansys for Design and Numerical Study of a Specific Fixed Wing UAV

2018 ◽  
Vol 55 (4) ◽  
pp. 652-657 ◽  
Author(s):  
Gabriel Murariu ◽  
Razvan Adrian Mahu ◽  
Adrian Gabriel Murariu ◽  
Mihai Daniel Dragu ◽  
Lucian P. Georgescu ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Unmanned Aerial Vehicle ◽  
Numerical Study ◽  
Flight Time ◽  
Cluster System ◽  
Numerical Results ◽  
Operational Performance ◽  
Gliding Flight ◽  
Aerial Vehicle ◽  
Constant Altitude

This article presents the design of a specific unmanned aerial vehicle UAV prototype own building. Our UAV is a flying wing type and is able to take off with a little boost. This system happily combines some major advantages taken from planes namely the ability to fly horizontal, at a constant altitude and of course, the great advantage of a long flight-time. The aerodynamic models presented in this paper are optimized to improve the operational performance of this aerial vehicle, especially in terms of stability and the possibility of a long gliding flight-time. Both aspects are very important for the increasing of the goals� efficiency and for the getting work jobs. The presented simulations were obtained using ANSYS 13 installed on our university� cluster system. In a next step the numerical results will be compared with those during experimental flights. This paper presents the main results obtained from numerical simulations and the obtained magnitudes of the main flight coefficients.

Sign in / Sign up

Export Citation Format

Share Document