Turbine-Diffusor-Interaktion

Diffusers increase the power output and cycle efficiency of gas turbines by reducing the back pressure of the turbine, thus, increasing the work extracted from the fluid by the turbine. They are, however, challenging to design. This is due to the inherent predisposition of the flow to separate under the adverse pressure gradients generated by diffusers, hence negating their benefit. This condition of imminent flow separation is aggravated because diffuser designers seek ever-shorter diffusers with correspondingly steeper opening angles and, thus, higher adverse pressure gradients, to reduce frictional losses and costs. This work presents a novel theory of turbine–diffuser interaction. More specifically, this theory addresses the stabilisation of diffuser boundary layers induced by tip-leakage vortices from an upstream rotor. The theory provides a framework to characterise tip-leakage vortices based upon integral stage-design parameters. The stage parameters loading coefficient, flow coefficient, swirl an- gle, and non-dimensional blade-passing frequency have been identified as the determinants for the intensity, orientation, and duty cycle of the tip-leakage vortices. These parameters have been condensed into the stabilisation number as a predictor for the inflow-dependent diffuser performance. Several hypotheses are derived from the theory and subsequently confirmed using partially scale-resolving simulations and experimental data. Additionally, a prediction method for the vortex-induced boundary-layer stabilisation in annular diffusers has been developed. The results of the prediction method are shown to be consistent with the theory presented.Diffusoren steigern die Leistung sowie den Wirkungsgrad von Gasturbinen, indem sie den Gegendruck der Turbine herabsenken und somit den Arbeitsumsatz in der Turbine erhöhen. Jedoch ist die Auslegung von Diffusoren herausfordernd. Dies ist auf die inhärente Neigung von Strömungen zurückzuführen, unter Einwirkung adverser Druckgradienten, wie sie in Diffusoren vorliegen, abzulösen und somit den Nutzen des Diffusors zunichte zu machen. Dieser Umstand wird dadurch verschärft, dass kürzere Diffusoren mit folglich größeren Öffnungswinkeln und somit ausgeprägteren adversen Druckgradienten wünschenswert sind, um Totaldruckverluste und Kosten zu senken. Die bisherige Forschung hat gezeigt, dass die Sekundärströmungsstrukturen in der Ab- strömung der Turbine durchaus positiv auf die Grenzschicht des Diffusors einwirken können. In dieser Arbeit wird eine neuartige Theorie der Turbine-Diffusor-Interaktion vorgestellt. Genauer gesagt, adressiert diese Theorie die Stabilisation der Diffusor-Grenzschichten durch Radialspaltwirbel eines stromauf liegenden Rotors. Die Theorie liefert ein Grundgerüst für die Charakterisierung des Radialspaltwirbels basierend auf integralen Stufenkennzahlen. Die Stufenkennzahlen Leistungszahl, Durch- flusszahl, Abströmwinkel und dimensionslose Schaufelwechselfrequenz wurden als die ausschlaggebenden Faktoren der Intensität, Orientierung sowie des Tastgrads der Radi- alspaltwirbel identifiziert. Diese Parameter wurden zu einer Stabilisationskennzahl zusam- mengeführt, welche als Vorhersagewerkzeug für die zuströmbedingungsabhängige Leis- tungsfähigkeit des Diffusors dient. Eine Reihe an Hypothesen wird aus der Theorie abgeleitet und anschließend anhand partiell skalenauflösender Simulationen sowie experimenteller Daten bestätigt. Zusätzlich wurde eine Vorhersagemethode für die wirbelinduzierte Grenzschichtstabilisa- tion in Ringdiffusoren entwickelt. Es wird gezeigt, dass deren Ergebnisse zur vorgestellten Theorie konsistent sind

Loss assessment of the axial-gap size effect in a low-pressure turbine

The aim of this work is the decomposition, quantification, and analysis of losses related to the axial-gap size effect in a 1.5-stage low-pressure turbine. Both experimental data and unsteady RANS calculations are investigated for axial gaps equal to 20%, 50% and 80% of the stator axial chord. A framework for identifying sources of loss typically encountered in turbomachinery is derived and utilized for the low-pressure turbine presented. The analysis focuses on the dependency between these losses and the axial-gap vari-ation. It is found that two-dimensional profile losses increase for smaller gaps due to higher wake-mixing losses and unsteady wake-blade interaction. Losses in the end-wall regions, however, decrease for smaller gaps. The total system efficiency can be described by a superposition of individual loss con-tributions, the optimum of which is found for the smallest gap investigated. It is concluded that these loss contributions are characteristic for the medium aspect-ratio airfoils and operating conditions investigated. This establishes a deeper physical understanding for future investigations into the axial-gap size effect and its interdependency with other design parameters

Tailored Porous Transport Layers for Optimal Oxygen Transport in Water Electrolyzers: Combined Stochastic Reconstruction and Lattice Boltzmann Method

The porous transport layer (PTL) plays an integral role for the mass transport in polymer electrolyte membrane (PEM) electrolyzers. In this work, a stochastic reconstruction method of titanium felt-based PTLs is applied and combined with the Lattice Boltzmann method (LBM). The aim is to parametrically investigate the impact of different PTL structures on the transport of oxygen. The structural characteristics of a reconstructed PTL agree well with experimental investigations. Moreover, the impact of PTL porosity, fiber radius, and anisotropy parameter on the structural characteristics of PTLs are analyzed, and their impact on oxygen transport are elucidated by LBM. Eventually, a customized graded PTL is reconstructed, exhibiting almost optimal mass transport performance for the removal of oxygen. The results show that a higher porosity, larger fiber radius, and smaller anisotropy parameter facilitate the formation of oxygen propagation pathways. By tailoring the fiber characteristics and thus optimizing the PTLs, guidelines for the optimal design and manufacturing can be obtained for large-scale PTLs for electrolyzers

Nomogram predicting the probability of spontaneous stone passage in patients presenting with acute ureteric colic

Objectives: To develop a nomogram that could predict spontaneous stone passage (SSP) in patients presenting with acute ureteric colic who are suitable for conservative management. Patients and Methods: A 2517 patient dataset was utilised from an international multicentre cohort study (MIMIC, A Multi-centre Cohort Study Evaluating the role of Inflammatory Markers In Patients Presenting with Acute Ureteric Colic) of patients presenting with acute ureteric colic across 71 secondary care hospitals in the UK, Ireland, Australia, and New Zealand. Inclusion criteria mandated a non-contrast computed tomography of the kidneys, ureters, and bladder. SSP was defined as the ‘absence of the need for intervention’. The model was developed using logistic regression and backwards selection (to achieve lowest Akaike's information criterion) in a subset from 2009–2015 (n = 1728) and temporally validated on a subset from 2016–2017 (n = 789). Results: Of the 2517 patients, 1874 had SSP (74.5%). The mean (SD) age was 47 (14.7) years and 1892 were male (75.2%). At the end of the modelling process, gender: male (odds ratio [OR] 0.8, 95% confidence interval [CI] 0.64–1.01, P = 0.07), neutrophil count (OR 1.03, 95% CI 1.00–1.06, P = 0.08), hydronephrosis (OR 0.79, 95% CI 0.59–1.05, P = 0.1), hydroureter (OR 1.3, 95% CI 0.97–1.75, P = 0.08), stone size >5–7 mm (OR 0.2, 95% CI 0.16–0.25, P 7 mm (OR 0.11, 95% CI 0.08–0.15, P < 0.001), middle ureter stone position (OR 0.59, 95% CI 0.43–0.81, P = 0.001), upper ureter stone position (OR 0.31, 95% CI 0.25–0.39, P < 0.001), medical expulsive therapy use (OR 1.36, 95% CI 1.1–1.67, P = 0.001), oral nonsteroidal anti-inflammatory drug (NSAID) use (OR 1.3, 95% CI 0.99–1.71, P = 0.06), and rectal NSAID use (OR 1.17, 95% CI 0.9–1.53, P = 0.24) remained. The concordance-statistic (C-statistic) was 0.77 (95% CI 0.75–0.80) and a nomogram was developed based on these. Conclusion: The presented nomogram is available to use as an on-line calculator via www.BURSTurology.com and could allow clinicians and patients to make a more informed decision on pursuing conservative management vs early intervention

Co-localization of GSTP1 and JNK in transitional cell carcinoma of urinary bladder

Transitional cell carcinoma (TCC) of urinary bladder belongs to glutathione S-transferase P1 (GSTP1) overexpressing tumors. Upregulated GSTP1 in TCC is related to apoptosis inhibition. This antiapoptotic effects of GSTP1 might be mediated through protein:protein interaction with c-Jun NH2 -terminal kinase (JNK). Herein, we analyzed whether a direct link between GSTP1 and JNK exists in TCC. The presence of GSTP1/JNK complexes was analyzed by immunoprecipitation and Western blotting in 20 TCC specimens, obtained after surgery. Co-localization of GSTP1 and JNK was also investigated in the 5637 TCC cell line by immunofluorescence confocal microscopy. By means of immunoprecipitation we show for the first time the presence of GSTP1/JNK complexes in all TCC samples studied. A co-localization of GSTP1 and JNK was also demonstrated in the 5637 TCC cell line by means of confocal microscopy. Protein-protein interactions, together with co-localization between GSTP1 and JNK provide evidence that GSTP1 most probably inhibits apoptosis in TCC cells by non-covalent binding to JNK

Outcomes and re-interventions after one-stage repair of transposition of great arteries and aortic arch obstruction

Objectives: One-stage repair of transposition of great arteries (TGA) and aortic arch obstruction (AAO) is currently advocated, but carries formidable surgical challenges. This report presents our experience and re-interventions for residual lesions over the last 10 years. Methods: Twenty-two patients (19.5±42.4 days; range 2-206; median 10 days, 3.5±0.6kg) diagnosed with TGA (nine patients) or double outlet right ventricle (DORV) (13 patients) and AAO underwent one-stage repair. Of the nine TGA patients (two with intact ventricular septum), AAO were: two patients hypoplastic arch, one patient discrete coarctation, four patients hypoplastic arch with coarctation and two patients interrupted aortic arch. The 13 DORV patients were all of Taussig-Bing type and one showed multiple ventricular septal defects (VSDs). The degree of AAO ranged from hypoplastic arch in five patients, coarctation two patients, combined four patients and interrupted aortic arch (IAA) two patients. Arterial switch with Lecomte±VSD repair was performed during cooling, and aortic arch repair was performed under deep hypothermic circulatory arrest (DHCA) (35±14min at 16.9±0.7°C). Our preference was to use homograft patch-plasty for arch and direct end-to-side anastomosis for coarctation repair. Aortic-cross-clamp time was 124±24min and cardiopulmonary bypass (CPB) time 215±84min. Results: Early survival was 19/22 (86%) up to 30 days without mortality in the second half of our series. Three patients required extracorporeal membrane oxygenation (ECMO) support and renal support was needed in three and preferred permanent pace maker (PPM) implantation in two. Length of stay was 21.9±22.1 days. There was one late death and overall survival was 18/22 (82%) for the follow-up period of 4.8 years (0.2-9.8 years). Eight patients (44%) required re-intervention for re-coarctation. Four patients required right ventricular outflow tract (RVOT)/pulmonary artery re-interventions. At follow-up, there was no requirement for aortic valve replacement, residual VSD closure and no evidence of ventricular dysfunction. Conclusions: One-stage repair of TGA/DORV and AAO can be performed safely with a good survival rate. Three important lessons that we have learnt are as follows: (1) the subpulmonary VSD may have a perimembraneous component, (2) late re-coarctation is not infrequent and (3) late residual right-sided cardiac lesions remain an issue in complex TGA repai

Combining shape‑adaptive blades and active fow control in a multi‑stage axial compressor: a numerical study

Shape adaption (SA) via piezo-ceramic actuation, and active flow control (AFC) by means of fluid injection and aspiration, are investigated within the Cluster of Excellence for Sustainable and Energy-Efficient Aviation (SE2A) with the goal of increasing the efficiency of multi-stage compressors—particularly at part-load, and of extending their operating range. Although both technologies have shown to be beneficial for the compressor off-design operation, drawbacks are still apparent at the aerodynamic design point when a single rotor or stator is equipped with SA or AFC, because of wake disturbances, which increase the incidence angle of the following row. Especially matching an improved component with its respective stage counterpart poses a major challenge in both research areas and is, therefore, addressed within this investigation. This work focuses on the first two stages of a high-pressure compressor, to compare and evaluate different combinations of shape adaption and active flow control. By considering structural requirements, such as a minimum blade thickness for the actuator application, and aerodynamic sensitivities, such as flow incidence and deviation due to off-design operation, a suitable configuration is derived and investigated in further detail

Die Flugzeuge von morgen : Energieeffizientes und nachhaltiges Fliegen

[no abstract available