Large Eddy Simulations of a Low-Swirl Gaseous Partially Premixed Lifted Flame in Presence of Wall Heat Losses

The use of lifted flames presents some very promising advantages in terms of pollutant emissions and flame stability. The focus here is on a specific low-swirl injection system operated with methane and derived from an air-blast atomizer for aero-engine applications, which is responsible for flame lift-off. The key feature of this concept is the interaction between the swirling jet and the confinement walls, leading to a strong outer recirculation zone and thus to an upstream transport of combustion products from the main reaction region to the flame base. Here, the representation of the physics involved is challenging, since finite-rate effects govern the lift-off occurrence, and only a few numerical studies have been carried out on this test case so far. The aim of the present work is therefore to understand the limits of some state-of-the-art combustion models within the context of LES. Considering this context, two different strategies are adopted: the Flamelet-Generated Manifold (FGM) approach and the Thickened Flame (TF) model. A modified version of the FGM model including stretch and heat loss effects is also applied as an improvement of the standard model. Numerical results are compared with the available experimental data in terms of temperature and chemical species concentration maps, showing that the TF model can better reproduce the lift-off than the FGM approach

Bamboo trusses with low cost and high ductility joints

Innovative solutions of joints for bamboo trusses are presented. Experimental tests show the performances and the high level of ductility of the proposed technique, joined with simplicity in the concept of the joints, low level of technology and low cost of all used materials. It can permit a proper dissemination and a sustainable maintenance in developing countries

Probabilistic models for the erosion rate in embankments and reliability analysis of earth dams

Probabilistic models for the concentrated leak erosion of earthen water retaining structures are presented. The models predict the values of the critical shear stress, the coefficient of erosion and the pipe radius enlargement, starting from other measurable soil properties and the geometrical dimensions of the embankment. The models account for both the non-cohesive and cohesive contributions to the erosion behavior. A Bayesian approach is used for the treatment of the unknown parameters. An importance sampling simulation is adopted to calibrate the models and estimate the posterior distribution of the unknown model parameters using laboratory and in situ experimental data. The new proposed probabilistic model for the pipe radius is then used to develop fragility curves that capture the pipe enlargement as a function of time for a given earth dam

Draft tube discharge fluctuation during self-sustained pressure surge: fluorescent particle image velocimetry in two-phase flow

Hydraulic machines play an increasingly important role in providing a secondary energy reserve for the integration of renewable energy sources in the existing power grid. This requires a significant extension of their usual operating range, involving the presence of cavitating flow regimes in the draft tube. At overload conditions, the self-sustained oscillation of a large cavity at the runner outlet, called vortex rope, generates violent periodic pressure pulsations. In an effort to better understand the nature of this unstable behavior and its interaction with the surrounding hydraulic and mechanical system, the flow leaving the runner is investigated by means of particle image velocimetry. The measurements are performed in the draft tube cone of a reduced scale model of a Francis turbine. A cost-effective method for the in-house production of fluorescent seeding material is developed and described, based on off-the-shelf polyamide particles and Rhodamine B dye. Velocity profiles are obtained at three streamwise positions in the draft tube cone, and the corresponding discharge variation in presence of the vortex rope is calculated. The results suggest that 5-10% of the discharge in the draft tube cone is passing inside the vortex rop

CFD Analysis of NOx Emissions of a Natural Gas Lean Premixed Burner for Heavy Duty Gas Turbine

AbstractThe present work presents a numerical analysis of a low NOx partially premixed burner for heavy duty gas turbine. The first part of the paper is focused on the study of the premixing process inside the burner using standard RANS CFD approach. The resulting profiles at different test points have been used to perform reactive simulations of an experimental test rig, where exhaust NOx emissions were measured. A reliable numerical setup was found comparing predicted and measured NOx emissions at different operating conditions and split ratios between main and pilot fuel. The calibrated numerical setup was then employed to explore possible modifications to fuel injection criteria and fuel split, with the aim of minimizing exhaust NOx emissions. This preliminary numerical screening of new fuel injection strategies, allowed defining a set of advanced configurations to be investigated in future experimental tests

A Master\u27s Recital in Percussion

This recital was given in partial fulfillment of a Master of Music degree in Percussion Performance at the University of Northern Iowa. The selections included in this program are works which are representative of both the historical and contemporary styles of percussion composition. The following abstract provides discussion in the historical background, compositional styles, systems of notation, and performance techniques used in each of the works from the program

STRATEGI PENGAWAS SEKOLAH DASAR DALAM MELAKSANAKAN PENGAWASAN KE SEKOLAH BINAAN

The purpose of this research is to analyze and describe the strategy of primary school supervisors in carrying out supervision of the target schools in the City of Palangka Raya, which focuses on: (1) the mechanism of supervision by school supervisors in the target schools; and (2) the obstacles faced by school supervisors in carrying out supervision in the target schools. The approach used is qualitative with a case study design. Data was collected by observation, interviews and documentation. Data analysis was carried out by adopting an interactive pattern from Miles et al (2014). The results showed that the primary school supervisor's strategy in carrying out the supervision of the target schools had been going well and regularly scheduled so that it had a positive impact both for teachers and principals in particular and for schools in general