scholarly journals Stereo-PIV investigation of the unsteady flow in the draft tube of a model hydro turbine

2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Ivan Litvinov ◽  
Dmitry Sharaborin ◽  
Sergey Shtork ◽  
Vladimir Dulin ◽  
Sergey Alekseenko ◽  
...  
Keyword(s):  
Velocity Field ◽  
Unsteady Flow ◽  
Swirling Flow ◽  
Flow Instability ◽  
Draft Tube ◽  
Pressure Pulsations ◽  
Mean Velocity ◽  
Hydro Turbine ◽  
Operation Conditions ◽  
Wide Range

Varying the generator load of a hydro turbine results in short-term changes in the rotation frequency of the runner, leading inevitably to flow instability and strong flow swirling behind the turbine. This may lead to the formation of unsteady flow regimes featured by vortex instability of the swirling flow behind the runner, known as the precessing vortex core (PVC) Dorfler et al. (2012). This effect causes dangerous periodic pressure pulsations that propagate throughout the water column in the draft tube. The present study reports on stereo PIV measurements of the air flow field inside a transparent draft tube of a model hydro turbine for a wide range of operation conditions. The research is focused on the time-averaged flow properties (mean velocity field and the second-order moments of velocity fluctuations), pressure pulsations and coherent flow structures in the velocity field.

scholarly journals Manipulation of the swirling flow instability in hydraulic turbine diffuser by different methods of water injection

2018 ◽  
Vol 180 ◽  
pp. 02090 ◽  
Author(s):  
Pavel Rudolf ◽  
Jiří Litera ◽  
Germán Alejandro Ibarra Bolanos ◽  
David Štefan
Keyword(s):  
Swirling Flow ◽  
Flow Instability ◽  
Draft Tube ◽  
Water Injection ◽  
Hydraulic Turbine ◽  
Operating Conditions ◽  
Francis Turbine ◽  
Necessary Condition ◽  
Vortex Rope ◽  
Wide Range

Vortex rope, which induces substantial pressure pulsations, arises in the draft tube (diffuser) of Francis turbine for off-design operating conditions. Present paper focuses on mitigation of those pulsations using active water jet injection control. Several modifications of the original Susan-Resiga’s idea were proposed. All modifications are driven by manipulation of the shear layer region, which is believed to play important role in swirling flow instability. While some of the methods provide results close to the original one, none of them works in such a wide range. Series of numerical experiments support the idea that the necessary condition for vortex rope pulsation mitigation is increasing the fluid momentum along the draft tube axis.

Studies of the Effect of Vortex-Control Grooves on Pressure Oscillations in a Francis Turbine Draft Tube

2015 ◽  
Author(s):  
Yu An ◽  
Luo Xianwu ◽  
Ji Bin
Keyword(s):  
Swirling Flow ◽  
Draft Tube ◽  
Francis Turbine ◽  
Pressure Oscillations ◽  
Hydro Turbine ◽  
Vortex Control ◽  
Operation Conditions ◽  
Calculation Results ◽  
Sst Turbulence Model ◽  
Load Conditions

In case of the hydro turbine operated deviated from the designed condition, vortex ropes usually occur in the draft tube, and consequently generate large pressure oscillations. This kind of unsteady flow phenomenon is believed to be harmful for hydropower stations. In this paper, the authors designed a runner with vortex-control grooves and numerically simulate the flow in a Francis hydro turbine using the SAS-SST turbulence model. The pressure oscillations induced by the vortex rope under several operation conditions were analyzed based on the calculation results. It is indicated that the runner with vortex-control grooves can alleviate the pressure fluctuation at part load conditions. However, vortex-control grooves may enhance the swirling flow, and cause a small hydraulic performance drop at full load conditions. Thus, the design optimization of vortex-control grooves is necessary and will be conducted in the future.

Unsteady regimes and pressure pulsations in draft tube of a model hydro turbine in a range of off-design conditions

2018 ◽  
Vol 91 ◽  
pp. 410-422 ◽  
Author(s):  
Ivan Litvinov ◽  
Sergey Shtork ◽  
Evgeny Gorelikov ◽  
Andrey Mitryakov ◽  
Kemal Hanjalic
Keyword(s):  
Draft Tube ◽  
Pressure Pulsations ◽  
Hydro Turbine ◽  
Unsteady Regimes

A Batchelor Vortex Model for Mean Velocity of Turbulent Swirling Flow in a Macroscale Multi-Inlet Vortex Reactor

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
Zhenping Liu ◽  
Rodney O. Fox ◽  
James C. Hill ◽  
Michael G. Olsen
Keyword(s):  
Reynolds Number ◽  
Simple Model ◽  
Velocity Field ◽  
Swirling Flow ◽  
Stereoscopic Particle Image Velocimetry ◽  
Mean Velocity ◽  
Vortex Model ◽  
Nonlinear Curve Fitting ◽  
Image Velocimetry ◽  
Vortex Reactor

The velocity field in a macroscale multi-inlet vortex reactor (MIVR) used in “flash nanoprecipitation (FNP)” process for producing functional nanoparticles was investigated using stereoscopic particle image velocimetry (SPIV). Based on the experimental data, a simple model was proposed to describe the average velocity field within the reactor. In the model, the axial and azimuthal velocities could be well described by the combination of two coflowing Batchelor vortices. In this model, six dimensionless coefficients are identified by nonlinear curve fitting, and their dependence on Reynolds number can be linearly described. This simple model is able to accurately predict the mean velocity field within the confined turbulent swirling flow based purely on Reynolds number.

scholarly journals Study on flow instability and countermeasure in a draft tube with swirling flow

2014 ◽  
Vol 22 (3) ◽  
pp. 032007
Author(s):  
T Nakashima ◽  
R Matsuzaka ◽  
K Miyagawa ◽  
K Yonezawa ◽  
Y Tsujimoto
Keyword(s):  
Swirling Flow ◽  
Flow Instability ◽  
Draft Tube

Spatiotemporal Characterization of a Conical Swirler Flow Field Under Strong Forcing

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
A. Lacarelle ◽  
T. Faustmann ◽  
D. Greenblatt ◽  
C. O. Paschereit ◽  
O. Lehmann ◽  
...  
Keyword(s):  
Flow Field ◽  
Swirling Flow ◽  
Flow Instability ◽  
Laser Doppler Anemometry ◽  
Helical Structure ◽  
Mean Velocity ◽  
Flow Measurements ◽  
Natural Flow ◽  
Flow Frequency

In this study, a spatiotemporal characterization of forced and unforced flows of a conical swirler is performed based on particle image velocimetry (PIV) and laser Doppler anemometry (LDA). The measurements are performed at a Reynolds number of 33,000 and a swirl number of 0.71. Axisymmetric forcing is applied to approximate the effects of thermoacoustic instabilities on the flow field at the burner inlet and outlet. The actuation frequencies are set at the natural flow frequency (Strouhal number Stf≈0.92) and two higher frequencies (Stf≈1.3 and 1.55) that are not harmonically related to the natural frequency. Phase-averaged measurement are used as a first step to visualize the coherent flow structures. Second, proper orthogonal decomposition (POD) is applied to the PIV data to characterize the effect of the actuation on the fluctuating flow. Measurements indicate a typical natural flow instability of helical nature in the unforced case. The associated induced pressure and flow oscillations travel upstream to the swirler inlet where generally fuel is injected. This observation is of critical importance with respect to the stability of the combustion. Harmonic actuation at different frequencies and amplitudes does not affect the mean velocity profile at the outlet, while the coherent velocity fluctuations are strongly influenced at both the inlet and outlet. On one hand, the dominant helical mode is replaced by an axisymmetric vortex ring if the flow is forced at the natural flow frequency. On the other hand, the natural flow frequency prevails at the outlet under forcing at higher frequencies and POD analysis indicates that the helical structure is still present. The presented results give new insight into the flow dynamics of a swirling flow burner under strong forcing.

Homogeneity of turbulence generated by static-grid structures

2010 ◽  
Vol 654 ◽  
pp. 473-500 ◽  
Author(s):  
Ö. ERTUNÇ ◽  
N. ÖZYILMAZ ◽  
H. LIENHART ◽  
F. DURST ◽  
K. BERONOV
Keyword(s):  
Reynolds Number ◽  
Velocity Field ◽  
Numerical Simulations ◽  
Direct Numerical Simulations ◽  
Uniform Grid ◽  
Reynolds Stresses ◽  
Hot Wire ◽  
Mean Velocity ◽  
Wide Range ◽  
The Mean

Homogeneity of turbulence generated by static grids is investigated with the help of hot-wire measurements in a wind-tunnel and direct numerical simulations based on the Lattice Bolztmann method. It is shown experimentally that Reynolds stresses and their anisotropy do not become homogeneous downstream of the grid, independent of the mesh Reynolds number for a grid porosity of 64%, which is higher than the lowest porosities suggested in the literature to realize homogeneous turbulence downstream of the grid. In order to validate the experimental observations and elucidate possible reasons for the inhomogeneity, direct numerical simulations have been performed over a wide range of grid porosity at a constant mesh Reynolds number. It is found from the simulations that the turbulence wake behind the symmetric grids is only homogeneous in its mean velocity but is inhomogeneous when turbulence quantities are considered, whereas the mean velocity field becomes inhomogeneous in the wake of a slightly non-uniform grid. The simulations are further analysed by evaluating the terms in the transport equation of the kinetic energy of turbulence to provide an explanation for the persistence of the inhomogeneity of Reynolds stresses far downstream of the grid. It is shown that the early homogenization of the mean velocity field hinders the homogenization of the turbulence field.

scholarly journals Stereo-PIV study of unsteady flow in a laboratory air hydro turbine model over a wide range of operating regimes

2021 ◽  
Vol 774 (1) ◽  
pp. 012044
Author(s):  
I V Litvinov ◽  
D K Sharaborin ◽  
E U Gorelikov ◽  
D A Suslov ◽  
S I Shtork
Keyword(s):  
Unsteady Flow ◽  
Hydro Turbine ◽  
Wide Range ◽  
Operating Regimes ◽  
Turbine Model

scholarly journals Study on Flow Instability and Countermeasure in a Draft tube with Swirling flow

2015 ◽  
Vol 8 (4) ◽  
pp. 230-239 ◽  
Author(s):  
Takahiro Nakashima ◽  
Ryo Matsuzaka ◽  
Kazuyoshi Miyagawa ◽  
Koichi Yonezawa ◽  
Yoshinobu Tsujimoto
Keyword(s):  
Swirling Flow ◽  
Flow Instability ◽  
Draft Tube
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