| 1. |
- Holmström, Henrik, Doktorand, 1995-
(författare)
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Mitigation of Pressure Pulsations in Axial turbine draft tube with jet injection or solid rod protrusion: A Numerical investigation
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The introduction of intermittent renewable energy sources, such as wind and solar power, to the power grid, demands some hydraulic turbines to operate at unfavorable operating conditions not initially designed for. Strong swirl develops at loads below the best efficiency point, (BEP) due to angle mismatch between the guide vanes and the fixed runner blades typical for Francis and Propeller turbines. A rotating vortex rope (RVR) is developed at part load (PL) operation as a consequence of the strong swirl exiting the runner for the aforementioned turbines. The RVR is associated with harmful pressure pulsations, decreasing turbine efficiency, and increasing maintenance time. Thus, it is of great interest to develop and investigate methods to mitigate the RVR. Methods to mitigate the adverse effect associated with the RVR at PL are studied in the presented research. An active mitigation method was numerically studied for a down-scaled propeller turbine, named "injection of pulsating momentum" (IPM). IPM aimed to locally disrupt the RVR by injecting pulsating momentum horizontally into a local part of the quasi-stagnant region in the draft tube. Numerical results indicate a significant reduction of the pressure pulsations associated with the RVR using approximately 5% of the runner flow. A passive mitigation method was also studied on a numerical model of the Porjus U9 Prototype using stationary rods radially protruded into the draft tube flow field. Solid rod protrusion aims to alter the mean flow properties in the draft tube cone, disrupting the formation of the RVR. Numerical results of stationary rod protruding to the RVR shear layer region indicates a complete reduction of the RVR plunging component and a significant reduction of the RVR rotating component due to an increased swirl at the draft tube center.
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| 2. |
- Holmström, Henrik, Doktorand, 1995-, et al.
(författare)
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Vortex rope interaction with radially protruded solid bodies in an axial turbine : a numerical study
- 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
- Radially protruded solid rods and their interaction with the rotating vortex rope at part load condition are investigated numerically on an axial model turbine. The commercially available software ANSYS CFX was used to perform the simulation, and the test case was the Porjus U9 Kaplan turbine model operating at a fixed runner blade angle at part load condition. Four rods, with a rod diameter equal to 15% of the runner diameter were evenly distributed in a horizontal plane in the draft tube cone and protruded to a length set to intercept the RVR in its unperturbed trajectory. It is shown that the RVR plunging (synchronous) mode is completely mitigated upstream and downstream of the protruded rods. The RVR rotating (asynchronous) mode is reduced by 47% and 63% at the two monitor positions located upstream of the protruding rods, while only a minor reduction occurs to the first RVR harmonic at the monitor positions located downstream of the protruded rods. The perturbed RVR experiences an increased angular velocity due to the flow area decrease caused by the protruding rods, thus increasing the RVR frequency by approximately 53% compared to the unperturbed value. Investigation of the swirling flow indicates a locally increased swirl in the center of the draft tube downstream of the protruded rods which could explain the reduction of the RVR pressure amplitude. The overall turbine efficiency with solid rods protruded causes a marginally efficiency reduction of 0.85%. However, as the RVR pressure pulsations are reduced significantly, a more comprehensive investigation of the rods impact on the turbine performance and life time should be performed to elucidate the suitability of using solid rod protrusion for RVR mitigation.
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| 3. |
- Holmström, Henrik, Doktorand, 1995-, et al.
(författare)
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Vortex rope mitigation with azimuthal perturbations: A numerical study
- 2021
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Ingår i: 30th IAHR Symposium on Hydraulic Machinery and Systems (IAHR 2020). - : Institute of Physics Publishing (IOPP).
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Konferensbidrag (refereegranskat)abstract
- A novel method to mitigate the rotating vortex rope is investigated numerically on a propeller turbine using ANSYS CFX. Pulsating momentum is injected in a horizontal plane in the diffuser cone from four evenly spaced jets. Three mitigation strategies are tested; M1 in which the momentum is injected perpendicular to the axial flow direction, M2, which exhibit a 12 degree angle against the tangential velocity in the diffuser cone, and finally M3, which exhibit the same horizontal angle as M2 but at a 15 % higher flow rate. It is shown that mitigation attempts M1, M2 and M3 decrease the amplitude of the rotating mode by 51%,96% and 97%, respectively. The amplitude of the plunging mode, on the other hand, increase for all mitigation attempts. However, the amplitude of the plunging mode of the unperturbed RVR is an order of magnitude smaller than the rotating mode, and thus, the overall amplitude of the pressure fluctuations in the diffuser decreases significantly. The more efficient mitigation using attempt M2 and M3 are explained using velocity contour in the diffuser cone, which show that the RVR is significantly reduced downstream of the injection plane in between injections, which is not the case for attempt M1.
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| 4. |
- Thrane, Karl Julius, et al.
(författare)
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Spectrum of Fontan-associated liver disease assessed by MRI and US in young adolescents
- 2021
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Ingår i: Abdominal Radiology. - : Springer Science and Business Media LLC. - 2366-004X .- 2366-0058. ; 46:7, s. 3205-3216
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: Patients with Fontan circulation are at risk of developing hepatic fibrosis/cirrhosis. The mechanisms and disease development are unclear and early secondary liver cancer is a concern. This study will describe hepatic imaging findings in a national cohort of adolescents with Fontan circulation. Methods: The patients prospectively underwent abdominal contrast enhanced magnetic resonance imaging (MRI) including diffusion-weighted imaging. Images were assessed for criteria of fibrosis/cirrhosis including characterization of hepatic nodules. These nodules were in addition, assessed by ultrasonography (US). Nodules ≥ 1 cm were investigated and monitored to evaluate malignant transformation. Clinical and hepatic serological data were recorded. Results: Forty-six patients, median age of 16.5 years (15.4–17.9 years) were enrolled. All patients underwent US examination and MRI was performed in 35/46 patients. On MRI, 60% had hepatomegaly and 37% had signs of fibrosis/cirrhosis. Seven patients had together 13 nodules ≥ 1 cm in diameter. Only 4/13 (17%) where seen on US. Nodules had variable MRI signal characteristics including hepatobiliary contrast enhancement and two nodules revealed portal venous phase ‘wash-out’ on the first examination. No further imaging signs of malignancy were revealed during the follow-up period of median 24.4 (7–42) months. Conclusion: The majority of adolescents with Fontan circulation had imaging findings of fibrosis/cirrhosis of varying severity. US had low detection rate of hepatic nodules compared to MRI. The imaging work-up before transition to adult cardiology care did not reveal findings suggestive of malignancy. However, the high prevalence of Fontan-associated liver disease calls for surveillance strategies even in childhood.
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| 5. |
- Tanghöj, Gustaf, 1979-
(författare)
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Young children with atrial septal defect
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Background: Secundum atrial septal defect (ASD II), situated within the fossa ovalis, is the third most common congenital heart defect and even more common among preterm children. Spontaneous closure usually occurs during the first year of life. Most children with an ASD II remain asymptomatic during early childhood. Guidelines recommend ASD II closure in the presence of a significant left-to-right shunt. Percutaneous device closure, which is most commonly used, and surgery are both considered safe, with few major adverse events.In Sweden, approximately 6% of all children are born preterm. The morbidity of preterm children includes increased risk of chronic pulmonary disease and altered cardiac morphology and function which remain into adulthood. Most studies on ASD II incidence and interventional and surgical risks following ASD II closure are based on otherwise healthy children. Preterm children are a special subset of patients with ASD II and the hypothesis in this thesis is that preterm birth may be associated with increased risks of ASD II diagnosis and adverse events following closure.Aim: The overall aim of this thesis was to assess the incidence of ASD II, independent risk factors associated to ASD II diagnosis, and adverse events following ASD II interventional closure.Methods: Paper I: A retrospective case-control study assessing associated risk factors for adverse events after percutaneous device closure among children with an interventional weight of less than 15 kg. Paper II: A cohort study assessing a preterm and a term cohort and time to first adverse event within one month or one year after ASD II closure, as well as number of events. Paper III: A retrospective case-control study assessing the association between major and minor adverse events after ASD II closure, and potential paediatric risk factors. Paper IV: A national registry-based retrospective incidence and case-control study calculating the incidence of ASD II diagnosis among term and preterm children and assessing potential maternal, neonatal, and paediatric risk factors for ASD II.Results: Paper I: No independent risk factor was associated with adverse events after percutaneous device closure. However, major adverse events occurred in 11 (10%) of the children weighing less than 15 kg, compared with six (4%) children weighing over 15 kg (p = 0.04). Paper II: There was no difference between the preterm and term cohorts in time to first adverse event or in multiple adverse events within one month or within a year, neither in number of major events (p = 0.69) nor in number of minor events (p = 0.84). However, the preterm cohort was younger (2.1 versus 3.4 years, p < 0.01), lighter (11.6 versus 15.1 kg, p < 0.01), had a smaller ASD II size (12.0 versus 13.0 mm, p< 0.01), and a larger ASD II size to weight ratio (1.1 versus 0.8, p < 0.01) compared with the term cohort. Paper III: ASD II with significant clinical symptoms was associated with both minor OR = 2.18, (CI 95% 1.05–8.06) and major OR = 2.80 (CI 95% 1.23–6.37) adverse events following closure. Paper IV: The yearly overall incidence of ASD II was 150 per 100,000 live births. However, this incidence ranged from 449 to 1,737 per 100,000 live births, with higher incidence in preterm children. ASD II was associated with a presence of persistent ductus arteriosus; OR = 8.11 (CI 95% 2.80–16.69), female gender; OR = 1.39 (CI 95% 1.18–1.63), and being small for gestational age; OR = 1.86 (CI 95% 1.29–2.68). Being born preterm was also associated with ASD II diagnosis: born at 32–36 gestational weeks; OR = 3.21 (CI 95% 2.46–4.19), and born at < 32 gestational weeks; OR = 4.02 (CI 95% 2.80–7.12).Conclusions: Preterm children have a high incidence of ASD II diagnosis, increasing with lower gestational age at birth, and is an independent risk factor for ASD II diagnosis. Few adverse events occurred among children following ASD II closure, and there were no neonatal or paediatric risk factors (including procedural body weight and gestational age) associated with adverse events. There was an association between clinical symptomatic ASD II and major adverse events. Despite younger procedural age, larger ASD II size to weight ratio and increased comorbidity, preterm children appeared to have similar risks of adverse events during the first year after ASD II closure when compared with term children.Preterm children and children with symptomatic ASD II need careful management both prior to and after ASD II closure. A new, structured follow-up programme with assessment of indication and timing of treatment and closure should be considered for children born preterm.
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| 6. |
- Hjortshøj, Cristel M Sørensen, et al.
(författare)
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Past and current cause-specific mortality in Eisenmenger syndrome.
- 2017
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Ingår i: European Heart Journal. - : Oxford University Press (OUP). - 0195-668X .- 1522-9645. ; 38:26, s. 2060-2067
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Tidskriftsartikel (refereegranskat)abstract
- Aims: Eisenmenger syndrome (ES) is associated with considerable morbidity and mortality. Therapeutic strategies have changed during the 2000s in conjunction with an emphasis on specialist follow-up. The aim of this study was to determine the cause-specific mortality in ES and evaluate any relevant changes between 1977 and 2015.Methods and results: This is a retrospective, descriptive multicentre study. A total of 1546 patients (mean age 38.7 ± 15.4 years; 36% male) from 13 countries were included. Cause-specific mortality was examined before and after July 2006, 'early' and 'late', respectively. Over a median follow-up of 6.1 years (interquartile range 2.1-21.5 years) 558 deaths were recorded; cause-specific mortality was identified in 411 (74%) cases. Leading causes of death were heart failure (34%), infection (26%), sudden cardiac death (10%), thromboembolism (8%), haemorrhage (7%), and peri-procedural (7%). Heart failure deaths increased in the 'late' relative to the 'early' era (P = 0.032), whereas death from thromboembolic events and death in relation to cardiac and non-cardiac procedures decreased (P = 0.014, P = 0.014, P = 0.004, respectively). There was an increase in longevity in the 'late' vs. 'early' era (median survival 52.3 vs. 35.2 years, P < 0.001).Conclusion: The study shows that despite changes in therapy, care, and follow-up of ES in tertiary care centres, all-cause mortality including cardiac remains high. Patients from the 'late' era, however, die later and from chronic rather than acute cardiac causes, primarily heart failure, whereas peri-procedural and deaths due to haemoptysis have become less common. Lifelong vigilance in tertiary centres and further research for ES are clearly needed.
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| 7. |
- Hjortshøj, Cristel Sørensen, et al.
(författare)
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Epidemiological changes in Eisenmenger syndrome in the Nordic region in 1977-2012
- 2017
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Ingår i: Heart. - : BMJ Publishing Group Ltd. - 1355-6037 .- 1468-201X. ; 103:17, s. 1353-1358
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: Improved diagnostic tools, timely closure of the shunt and a better understanding of the complexity of Eisenmenger syndrome (ES) have led to improved care and treatment in tertiary centres. These may have decreased the incidence of ES and improved survival of patients with ES, although evidence is still lacking. The aim of this study was to investigate temporal changes in incidence, prevalence and mortality in patients with ES for 35 years in the Nordic region.METHODS: This was a retrospective population-based study including 714 patients with ES. Survival analysis was performed based on all-cause mortality and accounting for immortal time bias.RESULTS: The incidence of ES decreased from 2.5/million inhabitants/year in 1977 to 0.2/million inhabitants/year in 2012. Correspondingly, prevalence decreased from 24.6 to 11.9/million inhabitants. The median survival was 38.4 years, with 20-year, 40-year and 60-year survival of 72.5%, 48.4%, and 21.3%, respectively. Complex lesions and Down syndrome were independently associated with worse survival (HR 2.2, p<0.001 and HR 1.8, p<0.001, respectively). Age at death increased from 27.7 years in the period from 1977 to 1992, to 46.3 years from July 2006 to 2012 (p<0.001).CONCLUSIONS: The incidence and prevalence of ES in the Nordic region have decreased markedly during the last decades. Furthermore, the median age at death increased throughout the study period, indicating prolonged life expectancy in the ES population. However, increasing age represents decreased incidence, rather than improved survival. Nonetheless, longevity with ES is still shorter than in the background population.
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