| 1. |
- Amiri, Kaveh
(författare)
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An experimental investigation of flow in a Kaplan runner : steady-state and transient
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Water turbines are since some years widely used for grid stabilization purposes according to their exceptional load variation capability which gives them the ability to compensate grid fluctuations initiated by the customer’s consumption or intermittent electricity production systems such as wind and solar power. Different renewable power generation technologies can be combined in mini-grids to electrify isolated villages and extend existing grid networks. In these occasions, small hydro units are also a good option to reduce the overall variability of supply to low levels and provide low‑cost, local electrification solutions. Hence, initially designed hydropower turbines for steady operation at on-design operating condition experience many off-design, start/stop and load variations during their life time according to the nowadays on-demand energy market and introduction of intermittent power generation systems to the electricity market.Start/stop and load variations can be harsh for the turbines due to the time dependent forces exerted on different parts of the turbines, especially rotating parts. Off-design performance of hydropower systems may also result in unfavorable and harmful periodic forces on the rotating parts. Therefore, investigations are required to study these working conditions and consider them in design of new hydropower plants and refurbished turbines. This was the motivation for the experimental investigation of a Kaplan turbine during on-design, off-design and transient operations with focus on the turbine’s rotor. The test case was a 1:3.1 scaled model of Porjus U9; a Kaplan turbine. The first paper deals with pressure measurements on the runner blades of the model under steady state operating conditions to find and quantify the sources of pressure fluctuations exerted on the runner at different operating points. The goal was to investigate the turbine’s performance at the best efficiency point with concentration on the performance of the water supply system and compare it to operations at high load and part load for a constant blades angle. The model results are compared with prototype measurements to corroborate the findings. The second paper presents the model investigations during load acceptance and load rejection. The model was investigated with pressure measurement on the stationary and rotating parts of the turbine under different load variations between part load, high load and best efficiency point. The third paper focuses on velocity measurements in the runner blade channels and at the runner outlet under on-design and off-design operating conditions. The velocity measurements are performed with a laser Doppler anemometry (LDA) system. The results of the model investigations along two propeller curves are presented to investigate the runner blade angle effects on the turbine’s performance.
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| 2. |
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| 3. |
- Amiri, Kaveh, et al.
(författare)
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Effects of flow unsteadiness on the wall shear stress
- 2012
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Ingår i: 26th IAHR Symposium on Hydraulic Machinery and Systems. - : IOP Publishing Ltd. ; , s. 62033-
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Konferensbidrag (refereegranskat)abstract
- Measurements were performed on pulsating fully turbulent flows in a pipe test rig with a diameter of 100 mm. Sinusoidal oscillatory flow at different frequencies was superimposed on a mean flow of averaged Reynolds number Re=20000 based on the pipe diameter. The measurements have been performed at different forcing frequencies (0.001 < ω+ < 0.08) covering all the oscillatory regimes; quasi-steady, relaxation, quasi laminar and high frequency. The amplitude of the flow oscillation was small enough to allow a linear response in the measurements, i.e., all flow parameters showed an oscillatory behavior at the frequency of the flow. The amplitude of the oscillatory flow was about 10% of the mean velocity in all cases. The results include mean and phase averaged values of different parameters. The centerline velocity was measured by a 2D LDA system. Hot film and constant temperature anemometry system was used to determine the wall shear stress. Bulk velocity and pressure gradient along the pipe were also acquired. The results showed a good agreement with the previous analytical, experimental and numerical results available in the literature.
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| 4. |
- Amiri, Kaveh, et al.
(författare)
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Effects of load variation on a Kaplan turbine runner
- 2016
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Ingår i: The International Journal of Fluid Machinery and Systems. - 1882-9554. ; 9:2, s. 182-193
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Tidskriftsartikel (refereegranskat)abstract
- Introduction of intermittent electricity production systems like wind and solar power to electricity market together with the deregulation of electricity markets resulted in numerous start/stops, load variations and off-design operation of water turbines. Hydraulic turbines suffer from the varying loads exerted on their stationary and rotating parts during load variations they are not designed for such operating conditions. Investigations on part load operation of single regulated turbines, i.e., Francis and propeller, proved the formation of a rotating vortex rope (RVR) in the draft tube. The RVR induces pressure pulsations in the axial and rotating direction called plunging and rotating modes, respectively. This results in oscillating forces with two different frequencies on the runner blades, bearings and other rotating parts of the turbine. This study investigates the effect of transient operations on the pressure fluctuations exerted on the runner and mechanism of the RVR formation/mitigation. Draft tube and runner blades of the Porjus U9 model, a Kaplan turbine, were equipped with pressure sensors for this purpose. The model was run in off-cam mode during different load variations. The results showed that the transients between the best efficiency point and the high load occurs in a smooth way. However, during transitions to the part load a RVR forms in the draft tube which induces high level of fluctuations with two frequencies on the runner; plunging and rotating mode. Formation of the RVR during the load rejections coincides with sudden pressure change on the runner while its mitigation occurs in a smooth way.
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| 5. |
- Amiri, Kaveh, et al.
(författare)
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Effects of upstream flow conditions on runner pressure fluctuations
- 2017
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Ingår i: Journal of Applied Fluid Mechanics. - : Isfahan University of Technology. - 1735-3572 .- 1735-3645. ; 10:4, s. 1045-1059
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Tidskriftsartikel (refereegranskat)abstract
- The rotor-stator interaction and the corresponding pressure fluctuations represent one of the sources of pressure and load fluctuations on the rotating parts of rotating machineries. The high-Reynolds flow is subject to rotation in the comparably large vaneless space of axial turbines, causing wake interaction and wake dissipation in this region. This increases the level of flow complexity in this region. This study examined the effect of the flow condition entering the spiral casing on the flow condition within the distributor and the runner and the physical source of pressure fluctuations exerted on the runner of a Kaplan turbine model. Simulations were performed within the water supply system, including the upstream tank, penstock, and the Francis turbines, the level of entering the spiral casing; the results were compared with laser Doppler anemometry (LDA) results. The results were considered as the inlet boundary condition for simulation of the turbine model from the spiral inlet to the draft tube outlet to investigate the flow condition within the distributor and the runner. The CFD simulations showed that the water supply system induces inhomogeneity to the velocity distribution at the spiral inlet. However, the flow condition does not affect the pressure fluctuations exerted on the runner blades due to the rotor-stator interactions. Moreover, the dominant frequencies exerted on the runner blades were accurately approximated although the amplitudes of the fluctuations were underestimated.
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| 6. |
- Amiri, Kaveh
(författare)
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Experimental investigation of a Kaplan runner under steady-state and transient operations
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Hydropower is a key part in electricity production nowadays. Hydropower electricity production rose to 3579.5 TWh in 2013, ranked as the second source of electricity production in the world after fossil fuels. It is the principle source of renewable electricity production, producing 16.2% of the electricity in 2013, accounting for 78% of the renewable electricity production in the world. Specifically in Sweden, hydropower is the main source of electricity production producing 47.5% of the required electricity. Nuclear, biomass, and wind placed in the following positions in the ranking in 2013 with 38.4%, 6.5%, and 4.3%, respectively.Besides meeting electricity demand with an environmental-friendly method, hydropower has a unique and important role which is grid regulation: balancing electricity production and consumption. Gas turbines and hydraulic turbines called “Primary reserves” are the only electricity production systems that can be used for fast regulations due to their short start-up time from 1 to 60 s. The obvious environmental problems, air pollution, and costs associated with gas turbines make hydropower a prime alternative whenever applicable. In Sweden, the share of fossil fuels in electricity production is small; 2.8% in 2012 with an average annual growth of -0.7% in the period 2002-2012. Hence, hydropower is practically the only available source used to regulate the grid fluctuations resulting from deregulated market and fast growth of intermittent power generation systems, i.e., solar and wind energy. Hydraulic turbines are subject to frequent off-design and transient operations because of their grid regulation responsibility. Such operating conditions decrease turbine’s efficiency and affect its lifetime significantly. Off-design and transient operation of hydraulic turbines may induce unpredicted pressure fluctuations on the stationary and rotating parts of the turbine. Special attention should be dedicated to the effects of such phenomena on the runner blades because of their importance on the efficiency of the turbine, and their vulnerability to the pressure fluctuations.This thesis presents an experimental investigation on the effects of off-design and transient operation of an axial hydraulic turbine on velocity fields and pressure fluctuations exerted on the runner and the draft tube of a turbine. The investigation was performed on a 1:3.1 scaled model of a Kaplan turbine known as Porjus U9. The main objective was to investigate the effect of operating point on pressure and velocity fluctuations in the runner and the draft tube. Another objective was to study the effect of transient operation on pressure fluctuations exerted on the runner and the draft tube, to investigate the formation and mitigation process of a rotating vortex rope (RVR) within the draft tube. Finally, the effect of the swirl leaving the runner and the draft tube bend on the performance of the turbine was investigated. The study involves pressure measurements on the runner blades and draft tube walls of the turbine, laser Doppler anemometry (LDA) measurements within and after the runner, and particle image velocimetry (PIV) measurements within the draft tube.The pressure and LDA results acquired during steady state operation of the turbine showed different sources of fluctuations on the runner at different operating points resulting in symmetric and asymmetric fluctuating forces on the runner. The pressure measurements during transient operating conditions exhibited pressure fluctuations exerted on the runner during load variations and elucidated some aspects of formation and mitigation process of RVR within the draft tube. The PIV measurements performed after the draft tube bend of the turbine focuses on the physical phenomena resulting in flow asymmetry after the draft tube bend of hydraulic turbines affecting their efficiency.
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| 7. |
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| 8. |
- 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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| 9. |
- Amiri, Kaveh, et al.
(författare)
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Experimental Investigation of the Interblade Flow in a Kaplan Runner at Several Operating Points Using Laser Doppler Anemometry
- 2016
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Ingår i: Journal of Fluids Engineering. - : ASME International. - 0098-2202 .- 1528-901X. ; 138:2
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents laser Doppler anemometry (LDA) measurements within the runner blade channels and at the runner outlet of a Kaplan turbine model. The model was investigated at six operating points located on two propeller curves of the turbine to study the flow condition during on-cam and off-cam operations. Main and secondary flows within and after the runner were analyzed, and the effects of the hub and tip clearances on the velocity fields within and after the runner were evaluated. Operation of the turbine at flow rates that are lower than the designed rate for the corresponding propeller curve resulted in vortex breakdown and the formation of a rotating vortex rope (RVR). The RVR formation produced an asymmetrical velocity distribution within and after the runner. The results demonstrated the occurrence of an oscillating flow with the same frequency as the vortex rope within the blade channels located upstream of the RVR. This results in an asymmetric flow through the runner and oscillating forces on the runner blades. The measured velocities indicated that the geometrical asymmetries in the runner manufacturing process resulted in various flow asymmetries at the measured sections. The asymmetries were up to 3% within the runner and 7% at the runner outlet
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