45 research outputs found

    Flow modeling in Pelton turbines by an accurate Eulerian and a fast Lagrangian evaluation method

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    The recent development of Computational Fluids Dynamics (CFD) has allowed the flow modeling in impulse hydro turbines that includes complex phenomena like free surface flow, multi fluid interaction, and unsteady, time dependent flow. Some commercial and open-source CFD codes, which implement Eulerian solving methods, have been validated against experimental results showing satisfactory accuracy. Nevertheless, further improvement of the flow analysis accuracy is still a challenge, while the computational cost is very high and unaffordable for multi-parametric design optimization of the turbine’s runner. In the present work, a CFD Eulerian approach is applied at first, in order to simulate the flow in the runner of a Pelton turbine model installed at the laboratory. Then, a particulate method, the Fast Lagrangian Simulation (FLS), is used for the same case, which is much faster than the Eulerian approach, and hence potentially suitable for numerical design optimization, providing that it can achieve adequate accuracy. The results of both methods for various operation conditions of the turbine, as also for modified runner and bucket designs, are presented and discussed in the paper. In all examined cases the FLS method shows very good accuracy in predicting the hydraulic efficiency of the runner, although the computed flow evolution and torque curve during the jet-runner interaction exhibit some systematic differences from the Eulerian results

    The role of surgical resection in Unicentric Castleman’s disease: a systematic review

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    Introduction: Castleman’s disease is a rare benign lymphoproliferative disorder of unknown etiology. The disease occurs in twoclinical forms with different prognoses, treatments and symptoms: a unicentric form (UCD), which is solitary, localized, and a multicentricform characterized by generalized lymphadenopathy and systemic symptoms. This article aims to review the currentliterature to consolidate the evidence surrounding the curative potential of surgical treatment to the unicentric type.Material and methods: A systematic review of English-language literature was performed and databases (Medline, Pubmed,the Cochrane Database and grey literature) were searched to identify articles pertaining to the treatment of unicentric form ofCastleman’s disease. Each article was critiqued by two authors using a structured appraisal tool, and stratified according to thelevel of evidence.Results: After application of inclusion criteria, 14 studies were included. There were no prospective randomized control studiesidentified. One meta-analysis including 278 patients with UCD reported that resective surgery is safe and should be consideredthe gold standard for treatment. Seven retrospective studies enhance this standpoint. Radiotherapy (RT) has been used in sixstudies with controversial results.Conclusions: We conclude that surgical resection appears to be the most effective treatment for Unicentric Castleman’s Diseaseof the thoracic cavity. Radiotherapy can also achieve clinical response and cure in selected patients

    Rola resekcji chirurgicznej w leczeniu zlokalizowanej postaci choroby Castlemana — przegląd systematyczny

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    Choroba Castlemana jest rzadką, łagodną chorobą limfoproliferacyjną o nieznanej etiologii. Schorzenie występuje w dwóch postaciach klinicznych o różnym rokowaniu, sposobie leczenia i objawach: postaci zlokalizowanej (UCD) oraz wieloogniskowej, charakteryzującej się powiększeniem węzłów chłonnych oraz objawami ogólnymi. Celem pracy był przegląd piśmiennictwa, a także analiza dowodów na skuteczność resekcji chirurgicznej w zlokalizowanej postaci choroby. Przeprowadzono przegląd systematyczny piśmiennictwa angielskojęzycznego oraz baz danych (Medline, Pubmed, Cochrane i źródeł dodatkowych) w poszukiwaniu artykułów dotyczących leczenia zlokalizowanej postaci choroby Castlemana. Każdy artykuł oceniony był przez dwóch autorów przy użyciu ustrukturyzowanego narzędzia oceny, a następnie skategoryzowany zgodnie z siłą dowodu. Zgodnie z kryteriami włączenia, do badania zakwalifikowano 14 badań. Nie znaleziono prospektywnych, randomizowanych badań z grupą kontrolną. W jednej metaanalizie, obejmującej 278 chorych na UCD, stwierdzono, że resekcja chirurgiczna jest bezpieczna i powinna być traktowana jako „złoty standard” w leczeniu. Wnioski zawarte w siedmiu badaniach retrospektywnych potwierdzały ten punkt widzenia. Radioterapia (RT) była stosowana w sześciu badaniach, z różnym efektem. W leczeniu choroby Castlemana zlokalizowanej w klatce piersiowej resekcja chirurgiczna wydaje się metodą o najwyższej skuteczności. Ponadto, pozytywną odpowiedź kliniczną można w niektórych przypadkach osiągnąć przy zastosowaniu radioterapii.Choroba Castlemana jest rzadką, łagodną chorobą limfoproliferacyjną o nieznanej etiologii. Schorzenie występuje w dwóch postaciach klinicznych o różnym rokowaniu, sposobie leczenia i objawach: postaci zlokalizowanej (UCD) oraz wieloogniskowej, charakteryzującej się powiększeniem węzłów chłonnych oraz objawami ogólnymi. Celem pracy był przegląd piśmiennictwa, a także analiza dowodów na skuteczność resekcji chirurgicznej w zlokalizowanej postaci choroby. Przeprowadzono przegląd systematyczny piśmiennictwa angielskojęzycznego oraz baz danych (Medline, Pubmed, Cochrane i źródeł dodatkowych) w poszukiwaniu artykułów dotyczących leczenia zlokalizowanej postaci choroby Castlemana. Każdy artykuł oceniony był przez dwóch autorów przy użyciu ustrukturyzowanego narzędzia oceny, a następnie skategoryzowany zgodnie z siłą dowodu. Zgodnie z kryteriami włączenia, do badania zakwalifikowano 14 badań. Nie znaleziono prospektywnych, randomizowanych badań z grupą kontrolną. W jednej metaanalizie, obejmującej 278 chorych na UCD, stwierdzono, że resekcja chirurgiczna jest bezpieczna i powinna być traktowana jako „złoty standard” w leczeniu. Wnioski zawarte w siedmiu badaniach retrospektywnych potwierdzały ten punkt widzenia. Radioterapia (RT) była stosowana w sześciu badaniach, z różnym efektem. W leczeniu choroby Castlemana zlokalizowanej w klatce piersiowej resekcja chirurgiczna wydaje się metodą o najwyższej skuteczności. Ponadto, pozytywną odpowiedź kliniczną można w niektórych przypadkach osiągnąć przy zastosowaniu radioterapii

    Investigating the influence of the jet from three nozzle and spear design configurations on Pelton runner performance by numerical simulation

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    This paper reports the initial results of three dimensional CFD simulations of the jet – runner interactions in a twin jet horizontal axis Pelton turbine. More specifically, the analysis examines the impact of the nozzle and spear valve configuration on the performance of the runner. Previous research has identified that injectors with notably steeper nozzle and spear angles attain a higher efficiency than the industry standard. However, experimental testing of the entire Pelton system suggests that there appears to be an upper limit beyond which steeper angled designs are no longer optimal. In order to investigate the apparent difference between the numerical prediction of efficiency for the injector system and the obtained experimental results, four different jet configurations are analysed and compared. In the first configuration, the interaction between the runner and an ideal axisymmetric jet profile is investigated. In the final three configurations the runner has been coupled with the jet profile from the aforementioned injectors, namely the Standard design with nozzle and spear angles of 80° & 55° and two Novel designs with angles 110° & 70° and 150° & 90° respectively. The results are compared by examining the impact the jet shape has on the runner torque profile during the bucket cycle and the influence this has on turbine efficiency. All results provided incorporate the Reynolds-averaged Navier Stokes (RANS) Shear Stress Transport (SST) turbulence model and a two-phase Volume of Fluid (VOF) model, using the ANSYS® FLUENT® code. Therefore, this paper offers new insights into the optimal jet – runner interaction

    Experimental investigation and analysis of the spear valve design on the performance of Pelton turbines:3 case studies

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    The impact of the nozzle and spear valve configuration on the performance of a Pelton turbine is investigated both experimentally and computationally. A previously published computational fluid dynamics (CFD) study has shown that injectors with noticeably steeper nozzle and spear angles, 110° and 70° respectively, attain a higher efficiency than the industry standard 80° and 55°. As a result, three injector design cases were manufactured for experimental testing. Two of those cases were the standard (80/55) design, with nozzle and spear tip angles of 80° and 55° and the Novel 1 design (110/70) with nozzle and spear tip angles of 110° and 70° based on previously published CFD optimisation studies. These studies showed that increasing the nozzle and spear angles to the upper limit of the investigated test plan gave higher efficiencies. The response surfaces suggested that the optimum nozzle and spear angles could be even steeper. That is why, an additional case, a third design (Novel 2) with even steeper angles (150/90) was also manufactured and tested. The experimental tests were carried out in a single jet operation using the upper injector on the Gilkes Pelton runner with series Z120 buckets. The results show that two novel injector design cases produce higher efficiencies than the standard design, when tested with a Pelton runner. An important gain of about 1% in efficiency is achieved at the Best Efficiency Point of the turbine. Furthermore, the improvement is even more pronounced at lower flow rates, where the spear valve opening is smaller and the geometry of the injector has even larger effect. To discuss and analyse these experimental observations, a further 2D axisymmetric CFD analysis is performed. This analysis shows a similar trend to the experimental results. The CFD results show that the largest amount of energy is lost at the region upstream of the nozzle exit, where the static pressure is converted into the dynamic pressure. This conversion starts earlier in case 1, the Standard injector design, at about twice the distance compared to the Novel designs, cases 2 and 3. Consequently, the flow must travel in this region at an increased velocity and it is shown that this region is longer in the Standard injector. Hence, its friction losses are higher. However, the differences between the designs calculated in CFD are about a factor of 2 lower than the experimental results, indicating that the 3D secondary flow mechanisms arising from the geometry upstream of the nozzle and spear tip also affect the performance of the spear valve and the Pelton runner. The mismatch between the efficiency increase magnitude observed experimentally and modelled using the axisymmetric case suggests that the steeper angle injectors cope better with secondary velocities in the flow

    Experimental investigation and analysis of three spear valve designs on the performance of Turgo impulse turbines

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    Several numerical investigations into the impact of the spear and nozzle configuration of impulse turbine injectors can be found in the literature, however there is little or no experimental data available for the effect on Turgo impulse turbine performance. A recent 2D numerical Design of Experiments (DoE) study found that much steeper nozzle and spear angles than the industry standard produced higher efficiencies. This work was extended to compare the performance of an industry standard injector (with nozzle and spear angles of 80° and 55°) and an improved injector with much steeper angles of 110° and 70° using a full 3D simulation of the injector, guide vanes and first branch pipe. The impact of the jets produced by these injectors on the performance of a Turgo runner was also simulated. The results for both CFD tools used suggest that steeper injector nozzle and spear angles reduce the injector losses, showing an increase in efficiency of 0.76% for the Turgo 3D injector. In order to investigate the numerical results from the previous studies further, three Turgo impulse turbine injectors were manufactured by Gilbert Gilkes & Gordon Ltd for testing on the 9” Gilkes HCTI Turgo rig at the Laboratory of Hydraulic Machines, National Technical University of Athens (NTUA). The injector designs tested were the standard (80/55) design, with nozzle and spear tip angles of 80° and 55° and the Novel 1 design (110/70) with nozzle and spear tip angles of 110° and 70° based on previously published CFD optimisation studies. The optimisations in the previous studies showed that the nozzle and spear angles in the upper limit of the investigated test plan, which was much higher than current industry guidelines, gave higher efficiencies. The DoE response surfaces in that study suggested that the optimum nozzle and spear angles may be even steeper and therefore an additional, third design (Novel 2) with even steeper angles (150/90) was also manufactured and tested. This paper presents the experimental data obtained for the three injector designs which were tested in a Turgo model turbine at various rotating speeds and flow rates. The 70 kW Turgo was coupled to a 75kW DC generator which allowed continuous speed regulation. The inlet conditions into the Turgo model turbine were controlled by a high head adjustable speed multistage pump of nominal operation point Q=290 m3/h, H=130 m (coupled via a hydraulic coupler to a 200 kW induction motor) which pumped water from the 320 m3 main reservoir of the Lab. The tests were carried out in single jet and twin jet operation. Testing and calibration of all the sensors was carried out according to testing standard IEC 60193 Hydraulic turbines, storage pumps and pump-turbines – Model acceptance tests (IEC 60193:1999). The results show that the Novel 2 injector performs best overall, which is consistent with the results obtained in previous 2D injector simulations. The achieved turbine efficiency with this injector is of the order of 0.5-1% higher than the Standard design, for both single and twin jet operation. The Novel 1 injector’s performance is between the Standard and Novel 2 injectors overall. Some images of the jets were also taken at various openings and are presented to qualitatively analyse the impact of each injector design on the disturbances on the outside of the jet. A further 2D axisymmetric CFD analysis is carried out to validate the measurements and to analyse the mechanisms which lead to injector losses. The results found that the majority of the losses occur in the region just upstream of the nozzle exit, where the static pressure is converted into dynamic pressure and the flow accelerates. In the Standard design, this conversion begins sooner and the flow travels over a longer distance at higher velocities leading to an increase in the losses. The CFD results found the differences between the designs to be smaller than the experiments however the trend of the results was similar, suggesting that the steeper angle injectors achieve higher efficiencies and better jet quality. The next stage of this research is to carry out a CFD analysis of the three injector designs in 3D, including the guide vanes and branch pipes, to investigate the impact of the steeper angles on the secondary velocities within the jet and the impact this has on the runner performance

    Investigating the influence of the jet from three nozzle and spear design configurations on Pelton runner performance by numerical simulation

    Get PDF
    This paper reports the initial results of three dimensional CFD simulations of the jet – runner interactions in a twin jet horizontal axis Pelton turbine. More specifically, the analysis examines the impact of the nozzle and spear valve configuration on the performance of the runner. Previous research has identified that injectors with notably steeper nozzle and spear angles attain a higher efficiency than the industry standard. However, experimental testing of the entire Pelton system suggests that there appears to be an upper limit beyond which steeper angled designs are no longer optimal. In order to investigate the apparent difference between the numerical prediction of efficiency for the injector system and the obtained experimental results, four different jet configurations are analysed and compared. In the first configuration, the interaction between the runner and an ideal axisymmetric jet profile is investigated. In the final three configurations the runner has been coupled with the jet profile from the aforementioned injectors, namely the Standard design with nozzle and spear angles of 80° & 55° and two Novel designs with angles 110° & 70° and 150° & 90° respectively. The results are compared by examining the impact the jet shape has on the runner torque profile during the bucket cycle and the influence this has on turbine efficiency. All results provided incorporate the Reynolds averaged Navier Stokes (RANS) Shear Stress Transport (SST) turbulence model and a two-phase Volume of Fluid (VOF) model, using the ANSYS® FLUENT® code. Therefore, this paper offers new insights into the optimal jet – runner interaction

    Cavernous Malformations of the Central Nervous System: An International Consensus Statement

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    Introduction: Cavernous malformations (CM) of the central nervous system constitute rare vascular lesions. They are usually asymptomatic, which has allowed their management to become quite debatable. Even when they become symptomatic their optimal mode and timing of treatment remains controversial. Research question: A consensus may navigate neurosurgeons through the decision-making process of selecting the optimal treatment for asymptomatic and symptomatic CMs. Material and methods: A 17-item questionnaire was developed to address controversial issues in relation to aspects of the treatment, surgical planning, optimal surgical strategy for specific age groups, the role of stereotactic radiosurgery, as well as a follow-up pattern. Consequently, a three-stage Delphi process was ran through 19 invited experts with the goal of reaching a consensus. The agreement rate for reaching a consensus was set at 70%. Results: A consensus for surgical intervention was reached on the importance of the patient’s age, symptomatology, and hemorrhagic recurrence; and the CM’s location and size. The employment of advanced MRI techniques is considered of value for surgical planning. Observation for asymptomatic eloquent or deep-seated CMs represents the commonest practice among our panel. Surgical resection is considered when a deep-seated CM becomes symptomatic or after a second bleeding episode. Asymptomatic, image-proven hemorrhages constituted no indication for surgical resection for our panelists. Consensus was also reached on not resecting any developmental venous anomalies, and on resecting the associated hemosiderin rim only in epilepsy cases. Discussion and conclusion: Our Delphi consensus provides an expert common practice for specific controversial issues of CM patient management

    The genomic landscape of ANCA-associated vasculitis: Distinct transcriptional signatures, molecular endotypes and comparison with systemic lupus erythematosus

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    IntroductionAnti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitides (AAVs) present with a complex phenotype and are associated with high mortality and multi-organ involvement. We sought to define the transcriptional landscape and molecular endotypes of AAVs and compare it to systemic lupus erythematosus (SLE).MethodsWe performed whole blood mRNA sequencing from 30 patients with AAV (granulomatosis with polyangiitis/GPA and microscopic polyangiitis/MPA) combined with functional enrichment and network analysis for aberrant pathways. Key genes and pathways were validated in an independent cohort of 18 AAV patients. Co-expression network and hierarchical clustering analysis, identified molecular endotypes. Multi-level transcriptional overlap analysis to SLE was based on our published data from 142 patients.ResultsWe report here that “Pan-vasculitis” signature contained 1,982 differentially expressed genes, enriched in leukocyte differentiation, cytokine signaling, type I and type II IFN signaling and aberrant B-T cell immunity. Active disease was characterized by signatures linked to cell cycle checkpoints and metabolism pathways, whereas ANCA-positive patients exhibited a humoral immunity transcriptional fingerprint. Differential expression analysis of GPA and MPA yielded an IFN-g pathway (in addition to a type I IFN) in the former and aberrant expression of genes related to autophagy and mRNA splicing in the latter. Unsupervised molecular taxonomy analysis revealed four endotypes with neutrophil degranulation, aberrant metabolism and B-cell responses as potential mechanistic drivers. Transcriptional perturbations and molecular heterogeneity were more pronounced in SLE. Molecular analysis and data-driven clustering of AAV uncovered distinct transcriptional pathways that could be exploited for targeted therapy.DiscussionWe conclude that transcriptomic analysis of AAV reveals distinct endotypes and molecular pathways that could be targeted for therapy. The AAV transcriptome is more homogenous and less fragmented compared to the SLE which may account for its superior rates of response to therapy

    Efficacy of canakinumab in patients with Still's disease across different lines of biologic therapy: real-life data from the International AIDA Network Registry for Still's Disease

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    Introduction: The effectiveness of canakinumab may change according to the different times it is used after Still's disease onset. This study aimed to investigate whether canakinumab (CAN) shows differences in short- and long-term therapeutic outcomes, according to its use as different lines of biologic treatment.Methods: Patients included in this study were retrospectively enrolled from the AutoInflammatory Disease Alliance (AIDA) International Registry dedicated to Still's disease. Seventy-seven (51 females and 26 males) patients with Still's disease were included in the present study. In total, 39 (50.6%) patients underwent CAN as a first-line biologic agent, and the remaining 38 (49.4%) patients were treated with CAN as a second-line biologic agent or subsequent biologic agent.Results: No statistically significant differences were found between patients treated with CAN as a first-line biologic agent and those previously treated with other biologic agents in terms of the frequency of complete response (p =0.62), partial response (p =0.61), treatment failure (p >0.99), and frequency of patients discontinuing CAN due to lack or loss of efficacy (p =0.2). Of all the patients, 18 (23.4%) patients experienced disease relapse during canakinumab treatment, 9 patients were treated with canakinumab as a first-line biologic agent, and nine patients were treated with a second-line or subsequent biologic agent. No differences were found in the frequency of glucocorticoid use (p =0.34), daily glucocorticoid dosage (p =0.47), or concomitant methotrexate dosage (p =0.43) at the last assessment during CAN treatment.Conclusion: Canakinumab has proved to be effective in patients with Still's disease, regardless of its line of biologic treatment
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