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- Gyllenram, Walter, 1971, et al.
(författare)
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Numerical Investigations of Swirling flow in a Conical Diffuser
- 2004
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Ingår i: 22nd IAHR Symposium, Stockholm, Sweden, June 29 - July 2, 2004. ; A, s. A09-2 (1-10)-
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Konferensbidrag (refereegranskat)abstract
- When a hydraulic power plant is operating at off-design, a swirling flow exits the runner and is convected through the draft tube. The swirling flow gives rise to several features that decrease the efficiency and/or may damage the construction. As a step towards making reliable numerical predictions of the swirling flow in draft tubes, steady computations in an idealised model have been carried out. The model geometry is a straight conical diffuser and O. G. Dahlhaug of NTNU, Trondheim, Norway, has provided experimental data. In this paper, numerical 3D RANS investigations are quantitatively compared to the available experimental data. Good agreement with experimental data was obtained. The discrepancies are partly reminiscent of the nature of the k-omega turbulence model that was used in this work. Given symmetric geometry and boundary conditions, a fluid flow is most often thought to behave in an equally symmetric manner. If the flow is swirling, this is not generally true. Due to the unstable properties of the symmetric solutions for the averaged Navier-Stokes equations, the flow will collapse into an asymmetric mode. In the first computational cases of this paper, the disturbance that triggers the instability is shown to be imperfections in the CAD-geometry. Also included is a discussion concerning the development of counter-rotating vortices in the boundary layer of swirling flow in a circular pipe.
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| 2. |
- Nilsson, Anders, et al.
(författare)
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Temporally fluctuating prey and coexistence among unequal conspecific interferers
- 2003
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Ingår i: Oikos. - : Wiley. ; 101:2, s. 411-415
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Tidskriftsartikel (refereegranskat)abstract
- Coexistence among unequal conspecific interferers should be unlikely to persist if stronger interferers always experience a relative fitness increment from their higher foraging rates. In this study, we suggest that decreased relative costs to weaker interferers with increasing temporal fluctuations in prey availability may be a mechanism enhancing coexistence of unequal conspecific interferers. Previous work on fluctuation and coexistence has dealt with oscillations over a time-scale measured in generations of competitor species and their resources, while our work shows that fluctuations in prey availability facilitate coexistence of different phenotypic strategies within species and generations, and over short time-scales. With increasing amplitude of temporal fluctuation about an average prey density, cumulative intakes for differently strong interferers are affected differently. Because of the prey-dependent effect of interference, high amplitudes of fluctuation allow for relatively lower foraging-rate costs in weaker interferers, which decreases the difference in foraging success between strong and weaker interferers. This decreased difference in foraging success could thus significantly relax the conditions allowing for unequal interferer coexistence.
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| 8. |
- Nilsson, Håkan, 1971
(författare)
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Numerical Investigations of Turbulent Flow in Water Turbines
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis investigates turbulent flow in water turbines, focusing onthe flow in the vicinity of reaction water turbine runners such as theKaplan runner and the Francis runner. The method of investigationis principally numerical although some experimental observations andmeasurements made in the present work and elsewhere are included.A major part of the present work was to implement an efficient andgeneral CFD (Computational Fluid Dynamics) code that could resolvethe complicated geometry of a water turbine. A parallel multiblockfinite volume CFD code, CALC-PMB (Parallel MultiBlock), was developed.The main features of the code are the use of conformal blockstructured boundary fitted coordinates, a pressure correction scheme(SIMPLEC), Cartesian velocity components as the principal unknownsand a collocated grid arrangement together with Rhie and Chow interpolation.The turbulence is modeled using a low-Reynolds k-omega turbulencemodel. The parallel multiblock algorithm employs two ghost cellplanes at the block interfaces. The message passing at the interfacesis done using either PVM (Parallel Virtual Machine) or MPI (MessagePassing Interface).Three water turbine runners are used for the investigations, two Kaplanrunners and one Francis runner. One of the Kaplan runners wasused during the development of the CFD code. This runner could notbe used to validate the CFD code but the work on this runner still gavevaluable insights on CFD in water turbines. The other Kaplan runneris a model of the runners installed in the H¨olleforsen power plant inIndals¨alven in Sweden. The computational results of the H¨olleforsenwicket gate and runner flow are validated against the thorough experimentalinvestigations from the Turbine 99 workshops and additionalLDV (Laser Doppler Velocimetry) measurements made in the presentwork. The Francis runner model investigated here was used as a testcase at a GAMM workshop in 1989. The present computational results of the GAMM Francis runner are validated against measurements atboth the best efficiency operating condition and four off-design operatingconditions. Several important flow features are visualized to makecomparisons with experimental observations and to better understandthe flow in water turbine runners. The validations against both detailedmeasurements and experimental observations show that the flowis captured qualitatively correctly.A method for numerical verification of the computational results hasbeen derived and applied to the computational results of the presentwork. The method is based on the conservation of a sub-set of the angularmomentum equations that is particularly important to swirlingflow in water turbines. The method is based on the fact that the discretizedangular momentum equations are not necessarily conservedwhen the discretized linear momentum equations are solved. The methodshows that the first-order hybrid discretization scheme cannot beused and that the second-order Van Leer discretization scheme needsimprovement to give quantitatively correct results in these kinds ofapplications.
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| 12. |
- Oliveira de Souza, Luis C. Eduardo, et al.
(författare)
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Assessment of turbulence modelling for CFD simulations into hydroturbines: spiral casings
- 2003
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Ingår i: 17th International Mechanical Engineering Congress (COBEM 2003) at São Paulo (Brazil).
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Konferensbidrag (refereegranskat)abstract
- Spiral casings are applied to distribute the water, as evenly as possible, to the stay vanes and wicket gates and then to the turbine runner. In a well-designed spiral casing, the pressure head of the fluid should be made available to the runner with minimum loss, hence the analysis of the flow through a spiral casing is important for the design of efficient hydraulic turbines. The goal of this work is based on turbo machines spiral casings three-dimensional flow modeling, simulation and characterization. Governing equations related to their study are used in the mathematical modeling part. Therefore, several turbulence models available will be tested with a finite volume method based commercial software CFX 5.5.1 which generates default tetrahedral meshing. Qualitative and quantitative results validation are proved by workshop benchmark experiments already done, in order these results can obtain a turbulence model that represents better the flow complexity inside spiral casings.
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| 13. |
- Schmitt, Anneli, 1971, et al.
(författare)
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Radiation therapy of small cell lung cancer with 177Lu-DOTA-Tyr3-octreotate in an animal model
- 2004
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Ingår i: Journal of nuclear medicine. - 0161-5505. ; 45:9, s. 1542-8
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Tidskriftsartikel (refereegranskat)abstract
- Small cell lung cancer (SCLC) is a tumor of neuroendocrine (NE) origin with very low survival rate. Somatostatin receptor scintigraphy using 111In-DTPA-octreotide (DTPA is diethylenetriaminepentaacetic acid) is a well-established method for the visualization of somatostatin receptor-expressing NE tumors. Recently, new combinations of radionuclides and somatostatin analogs have been investigated for therapeutic purposes. In this study, the somatostatin analog DOTA-Tyr3-octreotate (DOTA is 1,4,7,10-tetraazacyclododecane-N,N',N",N"'-tetraacetic acid), labeled with the medium-energy electron emitter 177Lu (maximal electron energy = 498 keV, half-life = 6.6 d), was used for radiation therapy of human SCLC in an animal model. METHODS: Nude mice, bearing tumors from the human SCLC cell line NCI-H69, were injected intravenously with 177Lu-DOTA-Tyr3-octreotate. Groups of animals (n = 5 or 6) were injected with 45-, 60-, and 120-MBq fractions and two 45-MBq fractions 48 h apart. Furthermore, 1 control group was treated with unlabeled DOTA-Tyr3-octreotate and another control group was not treated. RESULTS: In both control groups, the tumor volumes were increased 2-fold in approximately 5 d. Treatment with 177Lu-DOTA-Tyr3-octreotate resulted in marked tumor regression with statistically significant tumor volume reduction after 1 wk (P < 0.001). The tumor growth delay time was dependent on the amount of injected activity for the groups with single injections, 26 d for 60 MBq and 40 d for 120 MBq. The best therapeutic effect was obtained in mice injected with 2 fractions of 45 MBq. The relative tumor volume after 1 mo was 0.004 +/- 0.004. CONCLUSION: Radiation therapy with 177Lu-DOTA-Tyr3-octreotate on SCLC-bearing mice was successful. Since the experiments were performed on a human SCLC cell line xenografted to nude mice, the results may be clinically relevant and treatment with 177Lu-DOTA-Tyr3-octreotate could be a treatment alternative in this tumor disease that normally has a dismal prognosis.
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