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An artificial neural network (ANN) is trained on moderate or intense low- oxygen dilution (MILD) combustion to predict the sub-grid filtered density function (FDF) in large eddy simulation (LES). For wide usability, a new quantity ψ is calculated by scaling the filtered mixture fraction using the stoichiometric value and a logarithmic function, which is used as an input feature of the ANN. Self-testing on MILD combustion is first conducted for validation and determining the best layout of ANN. An ANN with 4 hidden layers and the activation function of rectified linear unit (ReLU) has the highest accuracy. This ANN is subsequently tested on five different premixed combustion cases. Overall predictions of the progress variable FDF are sat- isfactory, and the filtered chemical source term modelled by the FDFs is in good agreement with the DNS data for each case. However, an underpredic- tion of the filtered reaction rate occurs for the hydrogen–air flames, and the ANN accuracy is lower than that of a presumed β-FDF approach. DNS data of one premixed flame are then added to the training datasets, and newly trained ANNs are tested on remaining premixed flame cases. When the test- ing cases are similar to the added training dataset, improved predictions of marginal FDFs are observed, and the modelled progress variable source terms show good comparisons with the corresponding DNS data. Compared to the presumed β-FDF method, the new ANN shows an improved accuracy and serves as a viable alternative for FDF-based combustion modelling in the LES of turbulent flames.

Simulations of two cases in a novel multi-regime burner configuration are undertaken using a presumed joint probability density function (PDF) approach with tabulated chemistry. The flame conditions are varied by changing the central jet equivalence ratio, which produces different multi-regime combustion modes in the non-premixed inner flame. An outer premixed flame and recirculation zone behind a bluff body are present to supply heat and combustion products to stabilise the inner flame. A two-progress variable approach is tested to improve predic- tions of carbon monoxide (CO) in the post-flame regions, where CO oxidation occurs. The large eddy simulation set-up and sub-grid combustion model are assessed through comparisons with time-averaged measurements for radial profiles at different streamwise locations. The jet break-up length, the shear layers and the mixture fraction distribution are well captured. The temperature distribution is well captured for the inner flame in each case but the temperature and mixture fraction are over predicted in the downstream regions of the outer premixed flame, which is due to increased dilatation that suppresses air entrainment. Improved predictions of the CO mass fraction are obtained for the outer premixed flames with the two-progress variable approach. Over predictions are seen in the upstream regions of the inner flame when the CO mass fraction is obtained from a look-up table, suggesting that the CO mass fraction should be transported to include the convection/diffusion balance in regions where there is no flame. Furthermore, transporting the CO mass fraction with a one-progress variable approach produces over predictions in the burnt regions, suggesting a two-progress variable model is needed to capture the consumption region of CO. The multi-regime combustion behaviour is observed to be stronger in flame MRB26b, where non- premixed and rich premixed combustion is present. For flame MRB18b, the non-premixed contribution is smaller and weak stratified combustion is observed.

Multi-scale analysis of turbulence-flame interaction is performed using experimental data sets from three methane- and propane-fired premixed, turbulent V-flames, at an approach flow turbulent Reynolds number of 450 and a ratio of r.m.s. fluctuating velocity from the mean to laminar flame speed of between 2.1 and 3.0, straddling the border between corrugated flamelets and thin reaction zone in the Borghi-Peters diagram. The measurements were made in the plane of a single laser sheet using stereo particle image velocimetry SPIV and planar laser-induced fluorescence to measure three orthogonal components of velocity and flame OH. Methods to approximate the remaining, unmeasured, out of plane derivatives are described. The instantaneous SPIV images were bandpass filtered at user-specified characteristic length scales Lω and Ls (for vorticity and strain rate, respectively) resulting in instantaneous bandpass-filtered velocity fields, u̲bLω and u̲bLs, which were further analysed to give the bandpass filtered vorticity field, ω̲Lω=∇×u̲bLω, the strain-rate field, eijLs, and the tangential strain rate field aTLs. This work quantifies two aspects of turbulence-flame interaction. The first aspect is that of the flame interaction of eddies of size Ls on the turbulence, as found by the statistics of the alignment of vorticity with strain rate. We find that vortical eddies with scale about Lω=2δth (where δth is the flame thickness) are stretched by Ls structures which are larger than about 2 Lω, with this factor broadly true also for vortical eddies of scales Lω=4δth and Lω=6δth. Within the limitations of the data set, these findings are consistent with those in the literature on reacting and non-reacting flows, suggesting that the premixed flame has had little influence on the vortex stretching mechanism. The second aspect of turbulence-flame interaction examined is that of flame surface-averaged tangential strain rate imparted by eddies. Eddies with length scales Ls smaller than 3 or 4δth are likely to have the strongest individual contribution but eddies of this length scale and smaller may contribute only about 1/5th of the total tangential strain rate. This is to be compared with the value of 10% that has been reported in the literature based on analysis of DNS predictions of premixed flames at turbulent Reynolds numbers up to 110. Eddies with length scale Ls larger than about 20δth contribute a negligible amount to the total tangential strain rate. We have found no evidence that the Lewis number up to about 1.8 has an observable effect, but this may reflect the limitations of the current experiment. In the context of large eddy simulations (LES) of premixed combustion, these results are preliminary experimental evidence supporting the suggestion that resolving turbulence scales down to a few multiples of δth might be adequate to capture much of the flame straining caused by turbulence.

This is Book chapter Vijayraghavan P V, Ravichandran L, Swaminathan N. Institutional Strategies to Promote Scholarship in Health Professions Education. Adkoli BV, Ray A, editors. Medical Education Research - Theory, Practice, Publication and Scholarship. 1st Edition. Amritsar: MEUINDIA ; 2022. p. 343-52

Atrial Septal Defect by virtue of its left to right shunt induces geometric and electrical remodeling of the right sided chambers of the heart which produces prototypical changes in the Electrocardiogram. Various patterns produced by ASD in the ECG can give a clue in diagnosing the defect. Reversal of remodeling after the shunt closure and its accompanying changes in ECG are also helpful in follow up of these patients Methodology: This is a retrospective cohort analysis, wherein, ECG of the patients who have undergone ASD closure by percutaneous device closure or surgical closure during the study period,were obtained from hospital records and they were followed up. After screening, 60 patients met the inclusion criteria and were included in the study. ECG of the patients before closure of ASD and on immediate post procedure day, 2 weeks, 1month, 3 months, 6 months and 1year were obtained and analyzed.Mean age of the study population was 28.4 ± 09 years. In analysis of ECG after closure of ASD, the mean QRS axis reduced from 108 ± 10 to 70 ±12 degrees (P = 0.016), mean QRS duration reduced from 123 ± 30 ms to 80 ± 27 ms (P= 0.28). Mean PR interval reduced from 188 ± 30 ms to 123 ± 24 ms (P value= 0.09). The Crochetage Sign disappeared in the 2 patients who had it before closure of the defect. The amplitude of R' wave in rSR' in right precordial leads reduced over 2 years. rR' and qR pattern in right precordial leads reverted to rSr' pattern in 10 out of 12 patients. The other 2 patients who did not show reversal had residual shunt. No clinically significant complete heart block was observed in any patient.ECG forms as an easily available tool for diagnosis of ASD as well as in assessing the success of closure in the follow up after the closure of ASD by surgical or percutaneous device therapy. Failure of reversal of electrocardiographic signs of ASD after the closure should prompt search for residual shunt or pulmonary complications.