13 research outputs found
Mapping Flexibility Region through Three-phase Distribution Optimal Power Flow at TSO-DSO Point of Interconnection
No full textIn the coming years, distributed energy resources (DERs) located at medium voltage (MV) and low voltage (LV) level will be employed as flexible resources to face the uncertainties and the operative problems introduced by renewable energy sources (RES) in power system management. Nevertheless, to unlock the potential of such resources, a coordinated operation between transmission (TSO) and distribution (DSO) system operators is needed. The methodology of flexibility region estimation well fits such need, since it allows to calculate active and reactive power that can be aggregated and released from the DSO to the TSO at the interface point, without violating any steady-state distribution grid constraint. This paper investigated the feasibility of implementing a flexibility region estimation routine based on formulation of an unbalanced three-phase optimal power flow (TOPF), suitable to deal also with LV resources and unbalanced distribution networks. The methodology is tested considering the detailed representation of a portion of an Italian distribution grid, comprising about six hundred MV/LV buses. The availability of both active and reactive flexibility resources has been considered
Numerical and Experimental Analysis of the Tip Leakage Flow in a Squealer Low-Pressure Turbine Blade for Different Operating Conditions
No full textThis study combines experiments and numerical simulations (3D-Reynolds-averaged Navier-Stokes (RANS)) to achieve a deep understanding of the effects induced by varying key parameters affecting tip leakage flow in a highly loaded low-pressure turbine (LPT) rotor blade. Specifically, results for flat tip configurations are compared with a squealer tip geometry for different clearance heights and mass flow ratios simulating coolant flow ejected from the tip. Experimental results map the effects of these parameters on loss generation, while detailed insights into the interaction between the tip vortex and other vortical structures within the passage are discussed through computational fluid dynamic (CFD) simulations. Available experimental data include 2D distributions of total pressure and flow angles measured with a five-hole pressure probe downstream of the cascade for different operating conditions, enabling comparison with numerical simulations. The RANS solver provides visualizations of streamlines developing close to the tip region, offering a clear interpretation of the mechanism by which cross flow motion in the tip region interacts with the pressure gradient to generate the tip leakage vortex. The study explores how these processes vary with tip gap height and different mass flow ratios, providing a comprehensive view on the development of the secondary flow system. Finally, additional simulations with moving endwall are conducted to evaluate the impact of the relative motion between the blade and casing in the current application
Study of the turbulent flow downstream of a gas turbine combustor simulator
No full textLAUREA MAGISTRALENegli ultimi anni, a seguito della crescente attenzione globale verso l'ambiente, le aziende
del settore aeronautico hanno adottato dei nuovi tipi di combustori per le turbine a gas.
Questi combustori bruciano il carburante utilizzando una miscela magra, ottenendo una
elevata efficienza di combustione che consente la riduzione dei consumi di carburante e
delle emissioni di inquinanti. Nonostante questi vantaggi, i combustori a miscela magra
richiedono flussi molto vorticosi per ottenere una miscela uniforme di aria e combustibile
ed raggiungere quindi una combustione completa. Questo flusso vorticoso, in
combinazione con le non uniformità di temperatura create dagli iniettori di combustibile,
fluisce verso la turbina modificandone il funzionamento e il relativo rendimento. Negli
ultimi anni, i ricercatori hanno iniziato a studiare gli effetti sulle turbine cercando di ricreare
le condizioni a valle del combustore. Nel laboratorio LFM del politecnico di Milano
un simulatore del combustore è stato appositamente costruito per ricreare condizioni non
stazionarie di temperature e di velocità. Un'importante caratteristica del flusso prodotto
da questi combustori è l'elevato livello di turbolenza, che è stato misurato in questa tesi
tramite un anemometro a filo caldo. Il simulatore è stato fatto funzionare in diverse condizioni,
analizzando come l'iniezione di onde d'entropia influenza la formazione del vortice
e l'evoluzione dei rispettivi livelli di turbolenza. In particolare, la differenza di intensità
di turbolenza e la vorticità sono state confrontate in quattro casi differenti:
EWG off
Hot-streak continuo
EWG on 10 Hz
EWG on 110 Hz
che sono stati scelti sia per analizzare gli effetti dell'introduzione delle onde d'entropia,
sia per determinare il ruolo della frequenza di iniezione in questo fenomeno.In the last fifteen years, the growing environmental concerns have lead the aviation industry
to adopt lean burning combustors for gas turbine engines. These combustors permit
to obtain higher combustion efficiency, which leads to a reduction of both pollutant emission
and fuel consumption. Despite this advantage, lean-burn combustors require highly
swirling flow to achieve an uniform air-fuel mixture and a complete combustion. This
swirled flow, combined with the temperature non-uniformity created by the fuel injectors,
travel towards the turbine affecting its performance and the overall engine e ciency. Researchers
have started to investigate these effects in the last years by trying to simulate
the conditions created by the combustor. In the LFM, a combustor simulator, called
EWG, has been built specifically to create combined temperature and velocity instationarities.
One main characteristic of the flow released by the combustor is the high level of
turbulence, which has been recreated through the combustor simulator and analyzed with
a Hot wire anemometer. Different working conditions of the EWG have been analyzed
with the aim to understand how the injection of an entropy wave affects the swirling
flow formation and evolution and the respective level of turbulence. In particular, the
difference in vortex and turbulence intensity have been compared for four different cases:
EWG off
Continuous Hot-streak,
EWG on 10 Hz
EWG on 110 Hz
The conditions have been selected to analyze the effects of the entropy wave and to
determine whether the injection frequency plays a relevant role in this phenomenon
Comparison among 18FDG-PET/CT semiquantitative parameters for evaluation of neoadjuvant chemoradiotherapy in low rectal cancer.
No full text18FDG-PET/CT qualitative analysis for evaluation of neoadjuvant chemoradiotherapy in low rectal cancer; can be it useful by itself? Assessment by Mandard’s Tumor Regression and (y)pTNM staging
No full textProspective analysis of 18F-FDG PET/CT’ predictive value in patients with low rectal cancer treated with neoadjuvant chemoradiotheraphy and conservative surgery
No full textOptimized radiofrequency lesions through local impedance guidance for effective CTI ablation in right atrial flutter
No full textBackground: Although radiofrequency (RF) catheter ablation of cavo-tricuspid isthmus (CTI) is an established treatment for typical right atrial flutter (RAFL), it remains to be established whether local tissue impedance (LI) is able to predict effective CTI ablation and what LI drop values during ablation should be used to judge a lesion as effective. We aimed to investigate the ability of LI to predict ablation efficacy in patients with RAFL.Methods: RF delivery was guided by the DirectSense (TM) algorithm. Successful single RF application was defined according to a defragmentation of atrial potentials (DAP), reduction of voltage (RedV) by at least 80% or changes on unipolar electrogram (UPC). The ablation endpoint was the creation of bidirectional conduction block (BDB) across the isthmus.Results: 392 point-by-point RF applications were analyzed in 48 consecutive RAFL patients. The mean baseline LI was 105.4 +/- 12 Omega prior to ablation and 92.0 +/- 11 Omega after ablation (p < 0.0001). According to validation criteria, absolute drops in impedance were larger at successful ablation sites than at ineffective ablation sites (DAP: 17.8 +/- 6 Omega vs. 8.7 +/- 4 Omega; RedV: 17.2 +/- 6 Omega vs. 7.8 +/- 5 Omega; UPC: 19.6 +/- 6 Omega vs. 10.1 +/- 5 Omega, all p < 0.0001). LI drop values significantly increased according to the number of criteria satisfied (ranging from 7.5 Omega to 19.9). BDB was obtained in all cases. No procedure-related adverse events were reported.Conclusions: A LI-guided approach to CTI ablation was safe and effective in treating RAFL. The magnitude of LI drop was associated with effective lesion formation and BDB and could be used as a marker of ablation efficacy
Experimental and Numerical Investigation of Suction-Side Fences for Turbine NGVs
No full textThis work presents an extensive experimental and numerical analysis, aimed at investigating the impact of shelf-like fences applied on the suction side of a turbine nozzle guide vane. The cascade is constituted of vanes characterized by long chord and low aspect ratio, which are typical features of some LPT first stages directly downstream of an HPT, hence presenting high channel diffusion, especially near the tip. In particular, the present study complements existing literature by highlighting how blade fences positioned on the suction side can reduce the penetration of the large passage vortex. This is particularly effective in applications where flow turning is limited, the blades are lightly loaded at the front, and the horseshoe vortex is weak. The benefits of the present fence design in terms of losses and flow uniformity at the cascade exit plane have been demonstrated by means of a detailed experimental campaign carried out on a large-scale linear cascade in the low-speed wind tunnel installed in the Aerodynamics and Turbomachinery Laboratory of the University of Genova. Measurements mainly focused on the characterization of the flow field upstream and downstream of straight and fenced vane cascades using a five-hole pressure probe, to evaluate the impact of the device in reducing secondary flows. Furthermore, experiments were also adopted to validate both low-fidelity (RANS) and high-fidelity (LES) simulations and revealed the capability of both simulation approaches to accurately predict losses and flow deviation. Moreover, the accuracy in high-fidelity simulations has enabled an in-depth investigation of how fences act mitigating the effects of the passage vortex along the blade channel. By comparing the flow fields of the configurations with and without fences, it is possible to highlight the mitigation of secondary flows within the channel
Gorham-Stout Disease Management during Pregnancy
No full textAbstractGorham-Stout Disease (GSD) is a rare lymphatic disorder affecting children or young adults with no predilection of sex. It is generally associated with vanishing bone osteolytic lesions, thoracic and abdominal involvement, and diffuse pulmonary lymphangiomatosis. Chylous effusions and chylothorax, consequent to the abnormal proliferation of lymphatic vessels, may induce respiratory failure with a high mortality risk. Extrapulmonary alterations may include chylous ascites, lymphopenia, and destructing bone disease for overgrowth of lymphatic vessels. Here, we report the case of a young woman who developed a severe and recalcitrant GSD with persistent unilateral chylothorax during pregnancy. The complex management of this patient during and after pregnancy was discussed and compared with literature data to contribute to the definition of a correct diagnostic and therapeutic approach to this rare lymphatic disease.</jats:p
Modalities of treatment and 30-day outcomes of unselected patients older than 75 years with acute ST-elevation myocardial infarction: data from the BLITZ study
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