| 1. |
- Agustin, Sanchez-Arcilla, et al.
(författare)
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Introduction
- 2008
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Ingår i: Journal of Hydraulic Research. - 0022-1686. ; 46:2, s. 179-182
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 2. |
- Amiri, Kaveh, et al.
(författare)
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Experimental investigation of the hydraulic loads on the runner of a Kaplan turbine model and the corresponding prototype
- 2015
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Ingår i: Journal of Hydraulic Research. - : Informa UK Limited. - 0022-1686 .- 1814-2079. ; 53:4, s. 452-465
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports on unsteady pressure measurements on the runner blades of a Kaplan turbine model as well as torque and radial load bearing measurements on the corresponding prototype at several operating points to investigate the sources of periodic loads exerted on the runner when operating at the best efficiency point and off design. Pressure measurements on the model runner blades indicated that the spiral casing delivers a poorly conditioned flow to the guide vanes close to the lip-entrance junction, resulting in flow separation on the guide vanes. The asymmetric flow delivered to the runner induces large oscillations with respect to the guide vane passing frequency, runner frequency and its harmonics to the runner blades. The torque measurements on the prototype also revealed an asymmetric flow at the distributor outlet. The bearing radial load measurements performed on the prototype support the torque measurement results. The asymmetric hydraulic loads on the runner result in shaft wobbling, and the oscillatory forces exerted on the blades are transferred to the main shaft and bearings. Another source of oscillating forces exerted on the runner blades is the rotating vortex rope (RVR) formation that occurs at part-load operation of the turbine and induces pressure fluctuations at two sub-synchronous frequencies to the runner.
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| 3. |
- Amiri, Kaveh, et al.
(författare)
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Unsteady pressure measurements on the runner of a Kaplan turbine during load acceptance and load rejection
- 2016
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Ingår i: Journal of Hydraulic Research. - : Informa UK Limited. - 0022-1686 .- 1814-2079. ; 54:1, s. 56-73
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Tidskriftsartikel (refereegranskat)abstract
- The paper addresses unsteady pressure measurements on the blades and stationary parts of a Kaplan turbine model (Porjus U9) during load variation. The turbine was studied in various load acceptance and load rejection scenarios in off-cam mode to investigate the effect of the transients on the turbine performance. The formation and mitigation processes for the rotating vortex ropes and their effects on the forces exerted on the runner were also investigated. The results show a smooth transition during load variations between high load and the best efficiency point, at which no rotating vortex ropes form in the draft tube. However, load variation to part load resulted in a draft tube surge and the formation of a rotating vortex rope with two fluctuating components: rotating and plunging. The rotating vortex ropes began to form at the end of the draft tube cone during the closure of the guide vanes and travelled upstream with further guide vane closure. The plunging mode induced flow oscillation throughout the entire turbine conduit, whereas the rotating mode resulted in local pressure fluctuations. The rotating vortex ropes induced wide-band pressure fluctuations on the suction side of the runner close to the hub section. The formation of the rotating vortex ropes near the runner resulted in a sudden change in the pressure exerted on the suction side of the blades, whereas the rotating vortex rope mitigation process proceeded in a smooth manner.
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| 4. |
- Andersson, L. Robin, et al.
(författare)
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Localized roughness effects in non-uniform hydraulic waterways
- 2021
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Ingår i: Journal of Hydraulic Research. - : Taylor & Francis. - 0022-1686 .- 1814-2079. ; 59:1, s. 100-108
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Tidskriftsartikel (refereegranskat)abstract
- Hydropower tunnels are generally subject to a degree of rock falls. Studies explaining this are scarce and the current industrial standards offer little insight. To simulate tunnel conditions, high Reynolds number flow inside a channel with a rectangular cross-section is investigated using Particle Image Velocimetry and pressure measurements. For validation, the flow is modelled using LES and a RANS approach with k - ε turbulence model. One wall of the channel has been replaced with a rough surface captured using laser scanning. The results indicate flow-roughness effects deviating from the standard non-asymmetric channel flow and hence, can not be properly predicted using spatially averaged relations. These effects manifest as localized bursts of velocity connected to individual roughness elements. The bursts are large enough to affect both temporally and spatially averaged quantities. Both turbulence models show satisfactory agreement for the overall flow behaviour, where LES also provided information for in-depth analysis.
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| 5. |
- Andreasson, Patrik
(författare)
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Energy conversions in turbulent wind-induced countercurrent flow
- 1992
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Ingår i: Journal of Hydraulic Research. - : Informa UK Limited. - 0022-1686 .- 1814-2079. ; 30:6, s. 783-800
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Tidskriftsartikel (refereegranskat)abstract
- A detailed analysis of energy conversions and fluxes in wind-induced countercurrent flow is provided. At the free surface mechanical energy is supplied to the waterbody by the wind. Via stages of pressure-volume work and kinetic energy (divided into a mean and a fluctuating part), the energy will ultimately leave the flow as a surface heat flux. The analysis is based on mathematical modelling, supported by order-of-magnitude estimates and comparisons with reported experimental studies. A Reynolds-stress model, extended into the viscous sublayers, was required to predict adequately the mean velocity and turbulence structure of countercurrent flow.
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| 6. |
- Billstein, Mats, et al.
(författare)
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A numerical evaluation of air bubbles as a potential explanation to the higher than expected pore pressures in the core of WAC Bennett Dam
- 2002
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Ingår i: Journal of Hydraulic Research. - : Informa UK Limited. - 0022-1686 .- 1814-2079. ; 40:5, s. 623-630
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this study is to numerically evaluate if the Air Hypothesis is a potential explanation of the unusual pressure behaviour of the core at WAC Bennett Dam. Up to now, the pore pressures have exceeded the expected normal steady state distribution for about 25 years. The Air Hypothesis describes the influence of air bubbles on the pressure distribution in the core. An increased water pressure will compress the air bubbles and increases the amount of air that can go into solution at the upstream side of the core. At the downstream side, the situation is reversed, i.e. the air volume will increase and cause a hydraulic blockage. A one-dimensional numerical model, that is based on relevant conservation laws, physical laws (Darcy's, Boyle's, and Henry's laws) and the relationships between the relative hydraulic conductivity and water saturation level, is able to predict the pressure evolution in both a qualitative and quantitative way. The model is applied to both a hypothetical core and the core of WAC Bennett Dam. Results from a plug flow analysis on the dissolution of the air in the hypothetical core are in fair agreement with the numerical results. Comparisons with pressure measurements from WAC Bennett Dam show that the Air Hypothesis is a potential explanation to the unusual pressure distribution in the core
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| 7. |
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| 8. |
- Cervantes, Michel, et al.
(författare)
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Pulsating turbulent flow in a straight asymmetric diffuser
- 2008
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Ingår i: Journal of Hydraulic Research. - : Informa UK Limited. - 0022-1686 .- 1814-2079. ; 46:Suppl. 1, s. 112-128
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Tidskriftsartikel (refereegranskat)abstract
- Pulsating turbulent flow is studied for four regimes: steady, quasi-steady, relaxation, and quasi-laminar in a rectangular straight asymmetric diffuser, a generic model of the diffuser found at the end of most Kaplan and Francis type hydropower turbines. The flow entering the diffuser is a developing duct flow at Reynolds number 20 000, based on mean streamwise velocity and hydraulic diameter. The time averaged velocity and turbulent quantities are not affected by the forced oscillation. The regimes prevail in the diffuser, but are shifted due to the decreasing friction velocity. The oscillating quantities are affected by the adverse pressure gradient in the same way as the time averaged quantities, but with a decreasing effect for higher forcing frequencies. The amplitude of the oscillating wall shear stress is found to be signicantly lower than the Stokes solution in the quasi-laminar regime. The regime is confirmed by the behaviour of several other quantities. The pressure recovery is found to be 30 % higher in the relaxation regime than in the other regimes. Results are compared with experiments in channels and turbulent boundary layers, with and without an adverse pressure gradient, and with large-eddy simulations.
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| 9. |
- Cervantes, Michel, et al.
(författare)
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Unsteadiness and viscous losses in hydraulic turbines
- 2006
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Ingår i: Journal of Hydraulic Research. - : Informa UK Limited. - 0022-1686 .- 1814-2079. ; 44:2, s. 249-258
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Tidskriftsartikel (refereegranskat)abstract
- The variation of the mechanical energy for the mean, oscillating and turbulent flows are considered. Their mean point out the contribution of the unsteadiness to the viscous losses and the turbulent production. A two-dimensional turbulent pulsating flow is investigated for different unsteady regimes to illustrate the effects of unsteadiness on the overall losses.
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| 10. |
- Dargahi, Bijan
(författare)
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Flow characteristics of bottom outlets with moving gates
- 2010
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Ingår i: Journal of Hydraulic Research. - : Informa UK Limited. - 0022-1686 .- 1814-2079. ; 48:4, s. 476-482
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates the discharge characteristics of a bottom outlet with a moving gate by Flow3D. Experimental results for a scale model outlet of the Aswan Dam, Egypt, were used. Two different flow features were found. Pressurized flow established if the flume was filled and then the gate was slowly opened. However, a free surface flow occurred if the gate was fully opened and the entire flume was slowly flooded with water. The numerical simulations successfully captured the two flow patterns as well as the discharges and water surface profiles. The discharges were predicted with sufficient accuracy using the first-order momentum advection scheme. In comparison with the k-epsilon turbulence model, the Re-Normalization Group model yields the best agreement with the experiments. The model performed with similar accuracy for both model and prototype cases.
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