Numerical Simulation of Dam-Break Problem Using an Adaptive Meshing Approach

Abstract The numerical simulation of free-surface flows is a vast topic, with applications to various fields of engineering such as aerospace, automotive, nuclear, etc. The Volume of Fluid (VOF) method represents a suitable technique to simulate free surface flows, tracking the air-liquid interface within the calculation domain. However this method requires a very fine mesh to successfully reconstruct the liquid surface, leading to very high computational costs. In this paper, VOF simulations of three-dimensional dam-break problem have been carried out using an adaptive meshing approach. Unsteady calculations have been performed exploiting the adaptive mesh feature implemented in ANSYS Fluent. In particular, a grid adaptation strategy has been defined as a way of significantly reducing the numerical effort. The main idea is to keep high resolution only locally at the air-liquid interface, minimizing numerical diffusion, and to maintain a coarse mesh size elsewhere. The dam-break problem was analyzed because it has been widely studied experimentally and numerically, representing a benchmark problem for verifying numerical models involving free-surface flows. The accuracy of the method has been assessed comparing simulation results with experimental data

Numerical Identification of a Premixed Flame Transfer Function and Stability Analysis of a Lean Burn Combustor

AbstractCombustion instabilities represent a long known problem in combustion technology. The environment-friendly lean premixed gas turbines exhibit an increased risk of occurrence of thermo-acoustically induced combustion oscillations. In the present work the stability of a lean premixed swirl-stabilized combustor, experimentally studied at Technische Universität of Munich, has been investigated. The complex interaction between the system acoustics and the turbulent swirling flame is studied using unsteady CFD simulations with Flamelet-Generated Manifolds combustion model. Results were validated against experimental data. Perturbations are introduced in the system imposing a broadband excitation as inlet boundary condition. The flame response to the perturbation is then computed and described exploiting system identification techniques. The identified Flame Transfer Function (FTF) shows quantitative agreement with experiment for amplitude and phase, especially for the low frequency range. At higher frequencies the phase prediction slightly deteriorates while the gain is still well described. The obtained results are implemented into a finite element model of the combustor in order to analyze the stability of the system. Results are compared with available experimental data showing a satisfactory agreement. The advantage introduced by a more sophisticated model for FTF is further evidenced comparing the results with those obtained with analytical formulation found in literature

Large Eddy Simulation of a Bluff Body Stabilized Lean Premixed Flame

The present study is devoted to verify current capabilities of Large Eddy Simulation (LES) methodology in the modeling of lean premixed flames in the typical turbulent combustion regime of Dry Low NOx gas turbine combustors. A relatively simple reactive test case, presenting all main aspects of turbulent combustion interaction and flame stabilization of gas turbine lean premixed combustors, was chosen as an affordable test to evaluate the feasibility of the technique also in more complex test cases. A comparison between LES and RANS modeling approach is performed in order to discuss modeling requirements, possible gains, and computational overloads associated with the former. Such comparison comprehends a sensitivity study to mesh refinement and combustion model characteristic constants, computational costs, and robustness of the approach. In order to expand the overview on different methods simulations were performed with both commercial and open-source codes switching from quasi-2D to fully 3D computations

Hidden relationships between metalloproteins unveiled by structural comparison of their metal sites

Metalloproteins account for a substantial fraction of all proteins. They incorporate metal atoms, which are required for their structure and/or function. Here we describe a new computational protocol to systematically compare and classify metal-binding sites on the basis of their structural similarity. These sites are extracted from the MetalPDB database of minimal functional sites (MFSs) in metal-binding biological macromolecules. Structural similarity is measured by the scoring function of the available MetalS(2) program. Hierarchical clustering was used to organize MFSs into clusters, for each of which a representative MFS was identified. The comparison of all representative MFSs provided a thorough structure-based classification of the sites analyzed. As examples, the application of the proposed computational protocol to all heme-binding proteins and zinc-binding proteins of known structure highlighted the existence of structural subtypes, validated known evolutionary links and shed new light on the occurrence of similar sites in systems at different evolutionary distances. The present approach thus makes available an innovative viewpoint on metalloproteins, where the functionally crucial metal sites effectively lead the discovery of structural and functional relationships in a largely protein-independent manner

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