| 1. |
- Cervantes, Michel, et al.
(författare)
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Reformulation of the pressure-time method for application without flow rate cut-off
- 2022
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Ingår i: Measurement. - : Elsevier. - 0263-2241 .- 1873-412X. ; 188
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Tidskriftsartikel (refereegranskat)abstract
- The paper presents a reformulation of the standard pressure-time method for flow rate measurement in closed conduits. According to the IEC 60041 standard, the method is used with turbines flow rate cut-off. Its current formulation requires complete closure of the turbine shut-off device, generally guide vanes for reaction turbines and valves for impulse turbines, which may cause wear and tear on the machine. Any leakage through the closed shut-off device also needs to be measured. In the present work, a new formulation of the pressure-time method is derived, extending the actual use. The newly formulated method allows the determination of the flow rate at any instant of time from a load variation and, thus, the initial, incremental, and final flow rate. The load variation may be positive or negative. Measurements of any leakage flow are eliminated. Numerical and experimental cases are used to assess the validity and applicability of the proposed formulation. The numerical results demonstrate the correctness of the derivation. The experimental results exemplify the applicability of the method. Limitations of the derived methodology are discussed.
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| 2. |
- Kranenbarg, Jelle, 1996-, et al.
(författare)
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Modeling an axial turbine: a parametric study
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Numerical simulations of axial hydraulic turbines away from the best efficiency point are challenging. Especially previous studies show difficulties predicting the tangential velocity at part-load operating conditions where the swirl is high. Moreover, there is a lack of knowledge about the ability of eddy viscosity turbulence models to predict the runner inter-blades flow. Therefore, a parametric study is performed to address these points. Specifically, the effects of the blade clearance, blade angle, flow rate, and different turbulence models are studied on these issues. Results are analyzed by comparing the predicted axial and tangential velocity profiles and torque to experimentally obtained values. In addition, the physical phenomena responsible for head losses are studied in detail. Results show that the model can predict the flow relatively well at optimal flow conditions with low swirl but has problems at part load; the tangential velocity between the runner blades is underestimated by ~20%. The undervalued head losses are the root cause. They result in an overestimation of the axial velocity and an overestimation of the torque which is connected to the runner extracting too much swirl from the flow, hence the low tangential velocity. Furthermore, the blade clearance is found to be important as high-velocity jets that originate from the clearances affect the flow field, especially close to the hub. The torque prediction is also affected. Therefore, the clearance should be carefully measured during an experimental campaign, especially at the leading and trailing edge. A small modeling error of 0.5° in the blade angle and a change of 3% in the flow rate significantly affect the tangential velocity and torque prediction. The studied parameters must be considered carefully when building a numerical model. However, part of the deviation can also be explained by the insensitivity of eddy viscosity models to anisotropy, swirling flow with streamline curvature and runner mesh density.
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| 3. |
- Kranenbarg, Jelle, et al.
(författare)
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Sensitivity analysis of a swirling flow to the GEKO model
- 2022
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Ingår i: 31st IAHR Symposium on Hydraulic Machinery and Systems 26/06/2022 - 01/07/2022 Trondheim, Norway. - : Institute of Physics Publishing (IOPP).
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Konferensbidrag (refereegranskat)abstract
- Accurate numerical models for hydraulic turbine applications are highly coveted. They must be able to correctly capture the swirling flow found at off-design operating conditions in the turbine draft tube. The GEKO model is a relatively fast and flexible eddy viscosity turbulence model with adjustable coefficients to tune the model to different flow scenarios. In this study, the GEKO model is tested on a swirling flow inside a diffusor similar to the flow conditions found at part-load operation of a propeller turbine. The diffusor investigated corresponds to the Porjus U9 draft tube cone section, including the runner cone. Results showed that the near-wall coefficient, with a value of 2, increased the wall shear stress and moved the separation point from the runner cone further downstream. Moreover, with a value of 0.7, the separation coefficient increased the eddy viscosity, which also moved the separation point from the runner cone further downstream. Both coefficients gave velocity profiles closer to experimental values and increased the swirl number at the outlet of the diffusor by up to 36.9 % compared to the GEKO default model. Overall, the near-wall coefficient with a value of 2 gave the best results. The GEKO model provides an opportunity to tweak numerical models to swirling flow.
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| 4. |
- Kranenbarg, Jelle, et al.
(författare)
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Uncertainty in the numerical prediction of the tangential velocity in axial turbines at part load operations: A parametric study
- 2023
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Ingår i: Energy Reports. - : Elsevier. - 2352-4847. ; 10, s. 2597-2611
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Tidskriftsartikel (refereegranskat)abstract
- Numerical simulations of axial hydraulic turbines away from the best efficiency point are challenging. Previous studies especially show difficulties predicting the tangential velocity at Part Load (PL) operating conditions, where the swirl is high, in comparison to experiments. This is a reoccurring problem, and it is essential to understand, as the high tangential velocity is a fundamental characteristic of the flow in hydraulic turbines and is directly related to the swirling flow stability and the turbine's power output. The objective of this study is to numerically investigate and understand the origin of the tangential velocity deviation from experimental results by performing simulations with the finite volume method of an axial turbine operated at PL. A parametric study is performed to address the abovementioned. Specifically, the effects of the blade clearance, blade angle, flow rate, and different turbulence models are studied on this issue. Results are analyzed by comparing the predicted axial and tangential velocity profiles and torque to experimentally obtained values. Primarily the runner inter-blades flow is studied as there is a knowledge gap. In addition, the physical phenomena responsible for head losses are studied in detail. Results show that the model can predict the flow relatively well at optimal flow conditions with low swirl but has problems at part load; the tangential velocity between the runner blades is underestimated by ∼20%. The undervalued head losses are the root cause. They result in an overestimated torque and an underestimated tangential velocity as the runner extracts too much energy from the fluid. A small modeling error of 0.5° in the blade angle and a change of 3% in the flow rate significantly affect the tangential velocity and torque prediction. The studied parameters must be considered carefully when building a numerical model.
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| 5. |
- Aaltonen, T., et al.
(författare)
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Combination of CDF and D0 measurements of the W boson helicity in top quark decays
- 2012
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Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 85:7, s. 071106-
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Tidskriftsartikel (refereegranskat)abstract
- We report the combination of recent measurements of the helicity of the W boson from top quark decay by the CDF and D0 collaborations, based on data samples corresponding to integrated luminosities of 2.7-5.4 fb(-1) of p (p) over bar collisions collected during Run II of the Fermilab Tevatron collider. Combining measurements that simultaneously determine the fractions of W bosons with longitudinal (f(0)) and right-handed (f(+)) helicities, we find f(0) = 0.722 +/- 0.081[+/- 0.062(stat) +/- 0.052(syst)] and f(+) = -0.033 +/- 0.046[+/- 0.034(stat) +/- 0.031(syst)]. Combining measurements where one of the helicity fractions is fixed to the value expected in the standard model, we find f(0) = 0.682 +/- 0.057[+/- 0.035(stat) +/- 0.046(syst)] for fixed f(+) and f(+) = -0.015 +/- 0.035[+/- 0.018(stat) +/- 0.030(syst)] for fixed f(0). The results are consistent with standard model expectations.
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| 6. |
- Aaltonen, T., et al.
(författare)
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Combination of CDF and D0 W-Boson mass measurements
- 2013
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Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 88:5, s. 052018-
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Tidskriftsartikel (refereegranskat)abstract
- We summarize and combine direct measurements of the mass of the W boson in root s = 1.96 TeV proton-antiproton collision data collected by CDF and D0 experiments at the Fermilab Tevatron Collider. Earlier measurements from CDF and D0 are combined with the two latest, more precise measurements: a CDF measurement in the electron and muon channels using data corresponding to 2.2 fb(-1) of integrated luminosity, and a D0 measurement in the electron channel using data corresponding to 4.3 fb(-1) of integrated luminosity. The resulting Tevatron average for the mass of the W boson is M-W = 80387 +/- 16 MeV. Including measurements obtained in electron-positron collisions at LEP yields the most precise value of M-W = 80385 +/- 15 MeV.
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| 7. |
- Aaltonen, T., et al.
(författare)
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Combination of measurements of the top-quark pair production cross section from the Tevatron Collider
- 2014
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Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 89:7
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Tidskriftsartikel (refereegranskat)abstract
- We combine six measurements of the inclusive top-quark pair (t(sic)) production cross section (sigma(t)(sic)) from data collected with the CDF and D0 detectors at the Fermilab Tevatron with proton-antiproton collisions at root s = 1.96 TeV. The data correspond to integrated luminosities of up to 8.8 fb(-1). We obtain a value of sigma tt = 7.60 +/- 0.41 pb for a top-quark mass of m(t) = 172.5 GeV. The contributions to the uncertainty are 0.20 pb from statistical sources, 0.29 pb from systematic sources, and 0.21 pb from the uncertainty on the integrated luminosity. The result is in good agreement with the standard model expectation of 7.35(-0.33)(+0.28) pb at next-to-next-to-leading order and next-to-next-to leading logarithms in perturbative QCD.
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| 8. |
- Aaltonen, T., et al.
(författare)
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Combined Forward-Backward Asymmetry Measurements in Top-Antitop Quark Production at the Tevatron
- 2018
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Ingår i: Physical Review Letters. - : AMER PHYSICAL SOC. - 0031-9007 .- 1079-7114. ; 120:4
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Tidskriftsartikel (refereegranskat)abstract
- The CDF and D0 experiments at the Fermilab Tevatron have measured the asymmetry between yields of forward- and backward-produced top and antitop quarks based on their rapidity difference and the asymmetry between their decay leptons. These measurements use the full data sets collected in proton-antiproton collisions at a center-of-mass energy of root s = 1.96 TeV. We report the results of combinations of the inclusive asymmetries and their differential dependencies on relevant kinematic quantities. The combined inclusive asymmetry is A(FB)(t (t) over bar) = 0.128 +/- 0.025. The combined inclusive and differential asymmetries are consistent with recent standard model predictions.
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| 9. |
- Aaltonen, T., et al.
(författare)
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Evidence for a Particle Produced in Association with Weak Bosons and Decaying to a Bottom-Antibottom Quark Pair in Higgs Boson Searches at the Tevatron
- 2012
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 109:7, s. 071804-
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Tidskriftsartikel (refereegranskat)abstract
- We combine searches by the CDF and D0 Collaborations for the associated production of a Higgs boson with a W or Z boson and subsequent decay of the Higgs boson to a bottom-antibottom quark pair. The data, originating from Fermilab Tevatron p (p) over bar collisions at root s = 1.96 TeV, correspond to integrated luminosities of up to 9.7 fb(-1). The searches are conducted for a Higgs boson with mass in the range 100-150 GeV/c(2). We observe an excess of events in the data compared with the background predictions, which is most significant in the mass range between 120 and 135 GeV/c(2). The largest local significance is 3.3 standard deviations, corresponding to a global significance of 3.1 standard deviations. We interpret this as evidence for the presence of a new particle consistent with the standard model Higgs boson, which is produced in association with a weak vector boson and decays to a bottom-antibottom quark pair.
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| 10. |
- Aaltonen, T., et al.
(författare)
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Higgs boson studies at the Tevatron
- 2013
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Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 88:5, s. 052014-
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Tidskriftsartikel (refereegranskat)abstract
- We combine searches by the CDF and D0 Collaborations for the standard model Higgs boson with mass in the range 90-200 GeV/c(2) produced in the gluon-gluon fusion, WH, ZH, t (t) over barH, and vector boson fusion processes, and decaying in the H -> b (b) over bar, H -> W+W-, H -> ZZ, H -> tau(+)tau(-), and H -> gamma gamma modes. The data correspond to integrated luminosities of up to 10 fb(-1) and were collected at the Fermilab Tevatron in p (p) over bar collisions at root s = 1.96 TeV. The searches are also interpreted in the context of fermiophobic and fourth generation models. We observe a significant excess of events in the mass range between 115 and 140 GeV/c(2). The local significance corresponds to 3.0 standard deviations at m(H) = 125 GeV/c(2), consistent with the mass of the Higgs boson observed at the LHC, and we expect a local significance of 1.9 standard deviations. We separately combine searches for H -> b (b) over bar, H -> W+W-, H -> tau(+)tau(-), and H -> gamma gamma. The observed signal strengths in all channels are consistent with the presence of a standard model Higgs boson with a mass of 125 GeV/c(2).
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