Impact of Stretch and Heat Loss on Flame Stabilization in a Lean Premixed Flame approaching Blow-off

Abstract The accurate prediction of the turbulent combustion process in lean burn flames is of primary importance in the design of gas turbine low-emission combustors. In this framework, the correct account for high strain levels, combined with the heat loss of the flame, by numerical tools is of high technical relevance in order to improve the operational flexibility while reducing emissions. In fact, in high Reynolds lean combustion modelling, the quenching effects due to flame front distortion are expected to govern flame behaviour. The present work presents an assessment of the modelling strategies to introduce the stretch effects on the flame in Flamelet Generated Manifold (FGM) model, in both the framework of Reynolds-Averaged Navier-Stokes (RANS) and Large-Eddy Simulation (LES). At this purpose a premixed swirl burner experimentally studied at Cambridge University was chosen, consisting of a strongly swirling, confined natural gas flame. Results highlight that LES-FGM, coupled with an extended Turbulence Flame Closure model (TFC), succeeds in predicting the main characteristics of the flame at different operating conditions approaching blow-off, thus representing a valid tool to investigate lean burn flames in such context

Numerical simulation of a swirl stabilized methane-air flame with an automatic meshing CFD solver

International audience; The reliable prediction of the turbulent combustion processes in lean flames is nowadays of crucial importance in the design of gas turbine combustors. This work presents an assessment of the capabilities of Flamelet Generated Manifold (FGM) in the framework of Large-Eddy Simulation (LES), as implemented in the commercial CFD solver CONVERGE. One of the main characteristic of the code is the Adaptive Mesh Refinement (AMR) technique, namely the use of a dynamic mesh where elements size varies during the simulation. For validation purposes, the TECFLAM swirl burner, consisting of a strongly swirling, unconfined natural gas flame, has been chosen. Results highlight the advantages of AMR in describing turbulent flames, leading to a successful prediction of the main characteristics of the reacting flow field

methane swirl stabilized lean burn flames assessment of scale resolving simulations

Abstract The reliable prediction of the turbulent combustion process in lean flames is of paramount importance in the design of gas turbine combustors. The present work presents an assessment of the capabilities of Flamelet Generated Manifold (FGM) in the framework of Reynolds-Averaged Navier-Stokes (RANS) and Large-Eddy Simulation (LES) At this purpose the TECFLAM swirl burner consisting of a strongly swirling, unconfined natural gas flame was chosen. Results highlight that RANS-FGM succeeds in predicting the main characteristics of the reacting flow field and species concentrations. However, only LES is capable of reproducing the actual turbulent mixing between swirling flow and co-flow, thus leading to appreciable enhancements with respect to RANS results

modelling soot production and thermal radiation for turbulent diffusion flames

Abstract This paper presents a systematic investigation on the strategies required for modelling soot when performing CFD simulations of turbulent flames. The first test case consists in a 3D enclosure containing a mixture of N 2 , CO 2 , H 2 O and soot (Coelho, 2003). Results obtained with the gray implementation of the Discrete Ordinate Method in ANSYS Fluent are compared against literature data, assessing different formulations for the absorption coefficient of soot. These considerations are exploited through reactive RANS simulations accounting for radiative heat transfer, with the purpose to test different models for soot formation process on a turbulent non-premixed kerosene-air flame (Young et al., 1994)

Heat Transfer Investigation on an Internal Cooling System of a Gas Turbine Leading Edge Model

Abstract A scaled up test model simulating a realistic leading edge cooling system of a high pressure gas turbine blade was designed with the aim of performing heat transfer measurements in static and rotating conditions. The test model is composed by a trapezoidal supply channel which feeds three large racetrack holes, generating coolant impingement on the internal concave leading edge surface. Four big fins allow to confine the impingement jets impact zones. Air is then extracted through 4 rows of 6 holes each, two of showerhead (SH) and two of film cooling (FC). The test model is installed on a rotating test rig, which allows to reach jet Reynolds numbers (Re j ) up to 40000 and rotation numbers (Ro j ) up to 0.05. The effect of cross-flow in the supply channel is also considered. The heat transfer coefficient (HTC) distribution on the internal concave surface was evaluated by means of a steady state technique, using wide band thermochromic liquid crystals (TLCs) to measure the wall temperature and an electrically heated Inconel sheet to provide a constant heat flux to the investigated surface. This paper reports experimental results obtained in static conditions for Re j 10000 and 30000 and for two cross-flow cases representative of blade tip and hub sections. The effects of different mass flow extraction between pressure and suction side is also investigated by varying the mass flow rate through FC and SH holes. The effect of the coolant extraction holes geometry on the Nusselt number distribution is analyzed by comparing the experimental results, reported as 2D Nusselt number (Nu) maps, with a previous investigation on an analogous test model with similar impingement geometry. A CFD campaign was also carried out on the present test rig, exploiting a previously validated computational model. Both numerical and experimental results reveal that the effects of differentiated mass flow extraction and extraction area modification are secondary with respect to the effects of Re j and crossflow variation

Comparison of image processing techniques for nonviable tissue quantification in late gadolinium enhancement cardiac magnetic resonance images

Purpose: The aim of this study was to compare the performance of quantitative methods, either semiautomated or automated, for left ventricular (LV) nonviable tissue analysis from cardiac magnetic resonance late gadolinium enhancement (CMR-LGE) images. Materials and Methods: The investigated segmentation techniques were: (i) n-standard deviations thresholding; (ii) full width at half maximum thresholding; (iii) Gaussian mixture model classification; and (iv) fuzzy c-means clustering. These algorithms were applied either in each short axis slice (single-slice approach) or globally considering the entire short-axis stack covering the LV (global approach). CMR-LGE images from 20 patients with ischemic cardiomyopathy were retrospectively selected, and results from each technique were assessed against manual tracing. Results: All methods provided comparable performance in terms of accuracy in scar detection, computation of local transmurality, and high correlation in scar mass compared with the manual technique. In general, no significant difference between single-slice and global approach was noted. The reproducibility of manual and investigated techniques was confirmed in all cases with slightly lower results for the nSD approach. Conclusions: Automated techniques resulted in accurate and reproducible evaluation of LV scars from CMR-LGE in ischemic patients with performance similar to the manual technique. Their application could minimize user interaction and computational time, even when compared with semiautomated approaches

The link of biocompatibility to cytokine production

The link of biocompatibility to cytokine production. Recent studies suggest that chronic inflammation plays a role in the pathogenesis of cardiovascular disease. Cytokines released from jeopardized tissues stimulate the liver to synthesize acute phase proteins, including C-reactive protein (CRP). Baseline levels of CRP in apparently healthy persons or in persons with unstable angina constitute an independent risk factor for cardiovascular events. More recently, it has been suggested that CRP is useful not only as a marker of the acute phase response, but is also involved in the pathogenesis of the disease. CRP may, in fact, directly interact with the atherosclerotic vessels or ischemic myocardium by activation of the complement system, thereby promoting inflammation and thrombosis. Several studies in uremic patients have implicated CRP as a marker of malnutrition, resistance to erythropoietin, and chronic stimulation in hemodialysis. An increased cytokine production secondary to blood interaction with bioincompatible dialysis components has been reported by several studies; interleukin-1 (IL-1), tumor necrosis factor-α (TNF-α), and mainly IL-6 are the three proinflammatory cytokines involved in the pathogenesis of hemodialysis-related disease. We have provided evidence for the occurrence of high CRP and IL-6 levels in chronic dialytic patients exposed to contaminate dialysate and suggest that backfiltration may induce a chronic, slowly developing inflammatory state that may be abrogated by avoiding backfiltration of contaminate dialysate. Therefore, CRP is implicated as a marker linking bioincompatibility associated with backfiltration and increased cytokine production with a clinical state of chronic inflammation

Position-based dynamics simulator of vessel deformations for path planning in robotic endovascular catheterization

A major challenge during autonomous navigation in endovascular interventions is the complexity of operating in a deformable but constrained workspace with an instrument. Simulation of deformations for it can provide a cost-effective training platform for path planning. Aim of this study is to develop a realistic, auto-adaptive, and visually plausible simulator to predict vessels’ global deformation induced by the robotic catheter’s contact and cyclic heartbeat motion. Based on a Position-based Dynamics (PBD) approach for vessel modeling, Particle Swarm Optimization (PSO) algorithm is employed for an auto-adaptive calibration of PBD deformation parameters and of the vessels movement due to a heartbeat. In-vitro experiments were conducted and compared with in-silico results. The end-user evaluation results were reported through quantitative performance metrics and a 5-Point Likert Scale questionnaire. Compared with literature, this simulator has an error of 0.23±0.13% for deformation and 0.30±0.85mm for the aortic root displacement. In-vitro experiments show an error of 1.35±1.38mm for deformation prediction. The end-user evaluation results show that novices are more accustomed to using joystick controllers, and cardiologists are more satisfied with the visual authenticity. The real-time and accurate performance of the simulator make this framework suitable for creating a dynamic environment for autonomous navigation of robotic catheters

Predictive value of HDL function in patients with coronary artery disease: relationship with coronary plaque characteristics and clinical events

BACKGROUND: HDL is endowed with several metabolic, vascular, and immunoinflammatory protective functions. Among them, a key property is to promote reverse cholesterol transport from cells back to the liver. The aim of this study was to estimate the association of scavenger receptor class B type I (SR-BI)- and ATP binding cassette transporter A1 (ABCA1)-mediated cholesterol efflux (the two major routes for cholesterol efflux to HDL) with the presence, extent, and severity of coronary artery disease (CAD), vascular wall remodelling processes, coronary plaque characteristics, and the incidence of myocardial infarction in the different subgroups of patients from the CAPIRE study. METHODS: Patients (n = 525) from the CAPIRE study were divided into two groups: low-risk factors (RF), with 0–1 RF (n = 263), and multiple-RF, with ≥2 RFs; within each group, subjects were classified as no-CAD or CAD based on the segment involvement score (SIS) evaluated by coronary computed tomography angiography (SIS = 0 and SIS > 5, respectively). SR-BI- and ABCA1-mediated cholesterol efflux were measured using the plasma of all patients. RESULTS: SR-BI-mediated cholesterol efflux was significantly reduced in patients with CAD in both the low-RF and multiple-RF groups, whereas ABCA1-mediated cholesterol efflux was similar among all groups. In CAD patients, multivariable analysis showed that SR-BI-mediated cholesterol efflux <25(th) percentile predicted cardiovascular outcome (odds ratio 4.1; 95% CI: 1.3–13.7; p = .019), whereas ABCA-1-mediated cholesterol efflux and HDL-C levels significantly did not. Despite this finding, reduced SR-BI-mediated cholesterol efflux was not associated with changes in high-risk plaque features or changes in the prevalence of elevated total, non-calcified, and low-attenuation plaque volume. CONCLUSION: KEY MESSAGES: Increased cholesterol efflux capacity, an estimate of HDL function, is associated with a reduced CVD risk, regardless of HDL-C levels. HDL-C levels are significantly lower in patients with CAD. Lower SR-BI-mediated cholesterol efflux capacity is observed in patients with diffuse coronary atherosclerosis and is associated with the worst clinical outcomes in patients with CAD, independently of atherosclerotic plaque features

Comparison of the diagnostic performance of 64-slice computed tomography coronary angiography in diabetic and non-diabetic patients with suspected coronary artery disease

<p>Abstract</p> <p>Background</p> <p>Diabetics have high prevalence of subclinical coronary artery disease (CAD) with typical characteristics (diffuse disease, large calcifications). Although 64-slice multidetector computed tomography (MDCT) coronary angiography has high diagnostic accuracy to detect CAD, its diagnostic performance in diabetics with suspected CAD is unknown. To compare the diagnostic performance of 64-slice MDCT between diabetics and non-diabetics with suspected CAD scheduled for invasive coronary angiography (ICA).</p> <p>Methods</p> <p>We enrolled one hundred and five diabetic patients (92 men, age 65 +/- 9 years, Group 1) and 105 non-diabetic patients (63 men, age 63+/-5 years, Group 2) with indication to ICA for suspected CAD undergoing coronary 64-slice MDCT before ICA.</p> <p>Results</p> <p>In Group 1, the overall feasibility of coronary artery visualization was 93.8%. The most frequent artifact was blooming due to large coronary calcifications (54 artifacts, 67%). In Group 2, the overall feasibility was significantly higher vs. Group 1 (97%, p < 0.0001). In Group 1, the segment-based analysis showed a MDCT sensibility, specificity, positive predictive value, negative predictive value and accuracy for the detection of ≥50% luminal narrowing of 77%, 90%, 70%, 93% and 87%, respectively. In Group 2, all these parameters were significantly higher vs. Group 1. In the patient-based analysis, specificity, negative predictive value and accuracy were significantly lower in Group 1 vs. Group 2.</p> <p>Conclusions</p> <p>Although MDCT has high sensitivity for early identification of significant CAD in diabetics, its diagnostic performance is significantly reduced in these patients as compared to non-diabetics with similar clinical characteristics.</p