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  • 1.
    Jonsson, Pontus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Flow and pressure measurements in low-head hydraulic turbines2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Hydropower is a clean and sustainable energy resource that has been developed and used since the late 19th century. In Sweden, power plants have been constructed over the entire 20th century, with a peak in the period of 1950-1970. Currently, many of the older plants are in need of refurbishment. A modern hydropower turbine can have efficiency up to 95%. By upgrading older turbines, substantial gain can be achieved.As part of this thesis, a detailed experimental investigation of the flow in a Kaplan turbine model has been performed with a main focus on the draft tube. Besides the goal of describing the flow, the result will serve as validation data for CFD simulations and for scale-up studies (corresponding prototype is available for similar measurements). The investigation is performed with time-resolved pressure measurements in which different periodic flow phenomena are captured. The turbine is investigated at three different loads: part load, best efficiency point and near full load.During the refurbishment of a turbine, site efficiency tests are common practice to verify the improvements. A key feature of many methods regarding efficiency tests is flow rate measurements. Several commonly used methods exist for this task, such as current meter, Gibson's and ultrasonic (acoustic) methods. These methods can provide trustworthy results, but the difficulty to obtain satisfactory accuracy for low-head machines, below 50 m, is common to most of them. Gibson's method is rather economical and is easily performed on site. However, it has some limitations that make it difficult to apply to low-head turbines, such as short and non-uniform water passages. This thesis also aims to extend Gibson's method for use on low-head machines, i.e., outside the criteria stated in the IEC 41 standard. The investigation is performed with both numerical and experimental methods. In the numerical investigation, the physical quantities in rapidly decelerated flows are studied in detail. Unsteady friction terms are implemented in Gibson's method to enhance the accuracy under non-preferred conditions. A test rig was developed at the Norwegian University of Science and Technology in Norway for investigation with Gibson's method outside the criteria stated in the standard, as well as the validation of the numerical model and the updated Gibson method.

  • 2.
    Jonsson, Pontus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Numerical and experimental investigation of the Gibson’s method2009Licentiate thesis, comprehensive summary (Other academic)
  • 3.
    Jonsson, Pontus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Cervantes, Michel
    Pressure measurements in the spiral casing of a Kaplan turbine model2010In: 13th International Symposium on Transport Phenomena and Dynamics of Rotating Machinery 2010 (ISROMAC-13): Honolulu, Hawaii, USA, 4 - 7 April 2010, Red Hook, NY: Curran Associates, Inc., 2010, p. 79-84Conference paper (Refereed)
    Abstract [en]

    This paper presents an investigation of time-dependent pressure measurements in the spiral casing of a Kaplan turbine model. The work is part of a project with the purpose of investigating unsteady flow phenomena in hydro-power turbines. Three different loads were investigated: part load, best efficiency point, and high load. Several locations on the spiral casing were investigated. The results are compared with measurements in the draft tube cone. The mean values of the pressure around the spiral casing outlet indicates a nearly uniform distribution of the pressure to the runner. The runner frequency is one of the dominating frequencies. The corresponding amplitude is similar for all loads and decreases on the outer part of the spiral casing. At part load, a rotating vortex rope with precessional movement occurs in the draft tube. The rope generates an acoustic propagation upstream of the runner, which amplitude is ∼1/5 of the amplitude in the draft tube.

  • 4.
    Jonsson, Pontus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Cervantes, Michel
    Tidsupplösta tryckmätningar på en Kaplan modellturbin2009In: Svenska mekanikdagarna: Södertälje 2009, Stockholm: Svenska nationalkommittén för mekanik , 2009, p. 69-Conference paper (Other academic)
  • 5.
    Jonsson, Pontus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Cervantes, Michel
    Time resolved pressure measurements on a Kaplan model2009In: Water engineering for sustainable environment: 33rd IAHR congress ; 9 - 14 August 2009, Vancouver, British Columbia, Canada ; co-located with the 19th Canadian Hydrotechnical Conference, Madrid: IAHR , 2009Conference paper (Refereed)
  • 6.
    Jonsson, Pontus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Utveckling av Gibsons metod med transient friktion2011Conference paper (Refereed)
  • 7.
    Jonsson, Pontus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Cervantes, Michel
    Finnström, Marie
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Numerical investigation of the Gibson's method2007In: Svenska Mekanikdagar 2007: Program och abstracts / [ed] Niklas Davidsson; Elianne Wassvik, Luleå: Luleå tekniska universitet, 2007, p. 52-Conference paper (Other academic)
  • 8. Jonsson, Pontus
    et al.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Finnström, Marie
    Numerical investigation of the Gibson's method: effects of connecting tubing2007In: Proceedings of the 2nd IAHR International Meeting of the Workgroup on Cavitation and Dynamic Problems in Hydraulic Machinery and Systems, Timisoara,Romania, October 24-26, 2007 / [ed] R. Susan-Resiga; S. Bernad; S. Muntean, Timişoara, 2007, p. 305-310Conference paper (Refereed)
    Abstract [en]

    In order to calculate the efficiency of a hydro power plant some quantities needs to be measured. One of them is the flow rate, which can be difficult to measure with good accuracy. There are several methods for that task. Gibson's method is one of them and has the advantage to be economical and easily installed at the site. In order to achieve accurate results with this method, some criterions must be fulfilled. Two of these criterions are the measuring length must be larger than 10 m and the mean initial velocity times the measuring length should be larger than 50 m2/s. These criterions are rarely fulfilled in low head hydro power plants.This paper presents a numerical analysis of the effects of the connecting tubing between the pressure taps at the conduit and the differential pressure sensor. A one dimensional code programmed in Matlab is used for the numerical simulations where the governing equations, continuity and equation of motion, are discretizised with a second order Godunov-type scheme. The simulations are made for different initial flow rates and different valve closures. The result shows that the tubing has an overall small influence on the calculated flow rate error. A positive bias error appears in all tested cases and has a maximum (1.2 to 1.3 % depending on the test case) at the smallest Reynolds number.

  • 9. Jonsson, Pontus
    et al.
    Mulu, Berhanu
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Experimental investigation of a Kaplan draft tube: Part II: Off-design conditions2012In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 94, no 2, p. 71-83Article in journal (Refereed)
    Abstract [en]

    Off-design conditions of hydropower turbines are becoming more frequent with the deregulation of electricity markets and the introduction of renewable energy resources. Originally, turbines were not built to operate under such conditions. It is evident that there is a need to develop turbines that can operate under off-design conditions while attaining high efficiency. This may be achieved with computational fluid dynamics (CFD). However, the complexity of Kaplan turbine flows is challenging to treat using CFD. Therefore, detailed experimental investigations are necessary to validate and develop CFD. This paper presents an investigation of a modern design Kaplan turbine model. The measurements were performed in the draft tube with laser Doppler anemometry and flush-mounted pressure sensors, with a focus on the part load and high load operation of the turbine. Mean and phase-averaged quantities are presented for the velocity and pressure along several sections. A contra-rotating flow region was observed under high load operation. Under part load operation, a rotating vortex rope (RVR) develops due to vortex breakdown. The presence of the RVR significantly reduces the draft tube performance.

  • 10. Jonsson, Pontus
    et al.
    Ramdal, J.
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Development of the Gibson method – unsteady friction2012In: Flow Measurement and Instrumentation, ISSN 0955-5986, E-ISSN 1873-6998, Vol. 23, no 1, p. 19-25Article in journal (Refereed)
    Abstract [en]

    The Gibson method is commonly used for discharge measurements at hydropower plants to estimate turbine efficiency. This paper presents a detailed numerical study of this method in order to estimate the physical quantities of importance in the method. Additionally, a modification of the Gibson method is proposed that adds temporal acceleration to the calculation procedure. The modification is numerically and experimentally validated for Reynolds numbers ranging from ≈0.6×106 to 1.7×106. Using both simulations and experimental data, it is shown that the modified method, the unsteady Gibson method, can reduce the flow estimation error by as much as 0.4% compared to the standard Gibson method. Depending on the conditions, the unsteady Gibson method corrects, or partly corrects, both under- and overestimations of the flow rate that are calculated when using the standard Gibson method.

  • 11. Jonsson, Pontus
    et al.
    Ramdal, J.
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Experimental investigation of the Gibson's method outside standards2008In: Hydro technology and the evironment for the new century: 24th IAHR Symposium on Hydraulic Machinery and Systems, October 27 - 31, 2008, Foz do Iguassu, Brazil, Foz do Iguassu, 2008Conference paper (Refereed)
    Abstract [en]

    Gibson's method, also known as pressure time method, is used to measure the discharge in hydropower plants. It is an accurate and economical method which is suitable for site efficiency tests. However, it has some limitations. The present paper presents an experimental survey of Gibson's method used outside these limitations, i.e. with a measuring length and an initial flow velocity that are below the criterions stated by the IEC 41. In the experiments pressure is measured with two types of sensors; absolute pressure sensors and differential pressure sensors, to see the influence of the connecting tubing. The measurements are compared to an accurate reference flow meter and also to calculations from 1-D water hammer simulations. The results show, for both types of sensors, a positive bias error of the discharge which increases with decreasing initial velocity. The uncertainty for most of the measurements lies within ±1.5% at a 95% confidence level. The absolute sensors give a slightly larger random error than the differential. The numerical result shows a similar pattern as the experiments but with a smaller magnitude of the error.

  • 12.
    Jonsson, Pontus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Ramdal, Jørgen
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Cervantes, Michel
    Dahlhaug, Ole Gunnar
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Nielsen, Torbjørn
    Norwegian University of Science and Technology (NTNU), Trondheim.
    The pressure-time measurements project at LTU and NTNU2010In: The 8th International Conference on Hydraulic Efficiency Measurement, 2010Conference paper (Other academic)
  • 13.
    Mulu, Berhanu
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Jonsson, Pontus
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Experimental investigation of a Kaplan draft tube: Part I: best efficiency point2012In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 93, p. 695-706Article in journal (Refereed)
    Abstract [en]

    Hydropower, originally designed as a base electrical power, is now used to balance grid fluctuations that are primarily produced by market deregulation and the introduction of other renewable energy resources. New turbine designs must account for such constraints while also achieving high efficiency. Computational fluid dynamics, now an integrated tool in the hydraulic industry, requires accurate and detailed experimental data for validation purposes.The present work presents the investigation of a modern Kaplan turbine model combined with laser Doppler anemometry and flush-mounted pressure sensors, with a focus on the draft tube at the best turbine efficiency. Mean and phase-resolved quantities are presented for the velocity and pressure at several locations. The results demonstrate the strong influence of the swirl leaving the runner for a well-functioning draft tube as well as the negative impact of the draft tube cone. The blade-hub clearance is also found to have an impact on the flow beneath the runner cone.

  • 14.
    Ramdal, Jorgen
    et al.
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Jonsson, Pontus
    Nielsen, Torbjorn
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Finding inertia time constants for bends related to a modified Gibson's method2009In: Proceedings of the 3rd IAHR International Meeting of the Workgroup on Cavitation and Dynamic Problems in Hydraulic Machinery and Systems, Brno, October 14-16, 2009 / [ed] Pavel Rudolf, Brno: Brno University of Technology , 2009, p. 541-550Conference paper (Refereed)
  • 15.
    Ramdal, Jørgen
    et al.
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Jonsson, Pontus
    Dahlhaug, Ole Gunnar
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Nielsen, Torbjørn
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Uncertainties for pressure-time efficiency measurements2010In: The 8th International Conference on Hydraulic Efficiency Measurement, 2010Conference paper (Other academic)
    Abstract [en]

    In connection with the pressure-time project at the Norwegian University of Science and Technology and Luleå University of Technology, a number of tests with the pressure-time method have been performed at the Waterpower Laboratory in Trondheim, Norway. The aim is to lower the uncertainty and improve usability of the method. Also a field test at the Anundsjoe power plant in Sweden has been performed. The pressure-time measurement is affected by random uncertainty. To minimize the effect of the random behavior it is found that a correct integration end limit in the integration of the differential pressure is essential. An analysis using 100 different end points for integration show a possible random error as large as 0.6%. A filtration method for finding an appropriate end point is developed and presented. In laboratory, the random behavior of the method can be described since many tests can be performed. During field measurements, this may not be feasible. However, the random uncertainty can be included if the efficiency curve can be described by polynomial regression curves. This method is presented with the Anundsjoe Power Plant measurements.

  • 16.
    Ramdal, Jørgen
    et al.
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Jonsson, Pontus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Nielsen, Torbjørn
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Influence from bends on a pressure-time measurement2010In: 25th IAHR Symposium on Hydraulic Machinery and Systems :: 20-24 September 2010 'Politehnica' University of Timişoara, Timişoara, Romania, London: IOP Publishing Ltd , 2010Conference paper (Refereed)
    Abstract [en]

    One of the criteria for using the pressure-time method is that there is a straight pipe between the measurement cross sections. If the physical influences from a bend were known the method could be expanded for use over bends and hence on more power plants. At the Norwegian University of Science and Technology (NTNU) a test rig suited for experiments on the pressure-time method has been built. In addition to earlier experiments performed on straight pipe and double 90 degree bend, experiments on double 45 degree bend has been performed. This is done in order to try to find out if there is a clear relationship between bend geometry and its influence on the pressure time curve. To further develop the knowledge a full scale test in the field has been conducted on a 5 MW 58 meter head machine with a vertical penstock and a 90 degree bend. In the laboratory a double 90 degree bend caused an underestimation of the flow of about 1 % compared to a straight pipe, while for a double 45 degree bend a conclusion can not be found as the spread around the mean and uncertainty bands is within the range for the straight pipe. The field measurements with a 90 degree bend showed that the underestimation became 8.5%. When measuring pressure difference over bends the resulting calculation will give an underestimation of the flow. This should imply that the measured transient pressure is damped. (Regardless if this is the correct term it is here chosen to call this damping.) The question is if the damping is caused by friction or kinetic effects. The rapid deceleration of the water masses will give transient friction. How transient friction behaves is a topic of interest in hydraulic research. Bends will also cause skewed velocity and pressure profile on inlet and outlet of the bend as well as secondary flows. How this affects the transient pressure is also an interesting parameter.

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