Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Phd by thesis

Dynamics and stability of lean-premixed swirl-stabilized combustion

Large-eddy simulation (LES) of turbulent combustion is a relatively new research field. Much research has been carried out over the past years, but to realize the full predictive potential of combustion LES, many fundamental questions still have to be addressed, and common practices of LES of nonreacting flows revisited. The focus of the present review is to highlight the fundamental differences between Reynolds-averaged Navier-Stokes (RANS) and LES combustion models for nonpremixed and premixed turbulent combustion, to identify some of the open questions and modeling issues for LES, and to provide future perspectives.

/pdf/large-eddy-simulation-of-turbulent-combustion-39umcykkan.pdf

Large-eddy simulation of turbulent combustion

Fluid dynamic turbulence is one of the most challenging computational physics problems because of the extremely wide range of time and space scales involved, the strong nonlinearity of the governing equations, and the many practical and important applications. While most linear fluid instabilities are well understood, the nonlinear interactions among them makes even the relatively simple limit of homogeneous isotropic turbulence difficult to treat physically, mathematically, and computationally. Turbulence is modeled computationally by a two-stage bootstrap process. The first stage, direct numerical simulation, attempts to resolve the relevant physical time and space scales but its application is limited to diffusive flows with a relatively small Reynolds number (Re). Using direct numerical simulation to provide a database, in turn, allows calibration of phenomenological turbulence models for engineering applications. Large eddy simulation incorporates a form of turbulence modeling applicable when the large-scale flows of interest are intrinsically time dependent, thus throwing common statistical models into question. A promising approach to large eddy simulation involves the use of high-resolution monotone computational fluid dynamics algorithms such as flux-corrected transport or the piecewise parabolic method which have intrinsic subgrid turbulence models coupled naturally to the resolved scales in the computed flow. The physical considerations underlying and evidence supporting this monotone integrated large eddy simulation approach are discussed.

New insights into large eddy simulation

Metal-based reactive nanomaterials

Effect of particle size on combustion of aluminum particle dust in air

The effect of inlet swirl on the flow development and combustion dynamics in a lean-premixed swirl-stabilized combustor has been numerically investigated using a large-eddy-simulation (LES) technique along with a level-set flamelet library approach. Results indicate that when the inlet swirl number exceeds a critical value, a vortex-breakdown-induced central toroidal recirculation zone is established in the downstream region. As the swirl number increases further, the recirculation zone moves upstream and merges with the wake recirculation zone behind the centerbody. Excessive swirl may cause the central recirculating flow to penetrate into the inlet annulus and lead to the occurrence of flame flashback. A higher swirl number tends to increase the turbulence intensity, and consequently the flame speed. As a result, the flame surface area is reduced. The net heat release, however, remains almost unchanged because of the enhanced flame speed. Transverse acoustic oscillations often prevail under the effects of strong swirling flows, whereas longitudinal modes dominate the wave motions in cases with weak swirl. The ensuing effect on the flow/flame interactions in the chamber is substantial.

Effect of swirl on combustion dynamics in a lean-premixed swirl-stabilized combustor

A comprehensive numerical study of the combustion dynamics in a lean-premixed swirl-stabilized combustor is described. The analysis treats the conservation equations in three dimensions and takes into account e niterate chemical reactions and variable thermophysical properties. Turbulence closure is achieved using a largeeddy-simulation technique. The compressible-e ow version of the Smagorinsky model is employed to describe subgrid-scale turbulent motions and their effect on large-scale structures. A level-set e amelet library approach is used to simulatepremixed turbulent combustion. The governing equationsand theassociated boundary conditions aresolvedbymeansofafour-stepRunge‐ Kuttaschemealongwithimplementationofthemessagepassinginterface parallel computing architecture. The analysis allows for a detailed investigation into the interaction between turbulent e ow motions and oscillatory combustion of a swirl-stabilized combustor. Several physical processes responsible for driving combustion instabilities in the chamber have been identie ed and quantie ed, including the mutual coupling between acoustic wave motions, vortex shedding, and e ame oscillations. In particular, the mechanisms of energy transfer from chemical reactions in the e ame zone to acoustic motions in the bulk of chamber are carefully studied.

http://www.yang.gatech.edu/publications/Journal/JPP%20(2003,%20Huang,%20ref%201,%20color).pdf

Large-Eddy Simulation of Combustion Dynamics of Lean-Premixed Swirl-Stabilized Combustor

The combustion of bimodal nano/micron-sized aluminum particles with air is studied both analytically and experimentally in a well-characterized laminar particle-laden flow. Experimentally, an apparatus capable of producing Bunsen-type premixed flames was constructed to investigate the flame characteristics of bimodal-particle/air mixtures. The flame speed is positively affected by increasing the mass fraction of nano particles in the fuel formulation despite the lower flame luminosity and thicker flame zone. Theoretically, the flames are assumed to consist of several different regimes for fuel-lean mixture, including the preheat, flame, and post flame zones. The flame speed and temperature distribution are derived by solving the energy equation in each regime and matching the temperature and heat flux at the interfacial boundaries. The analysis allows for the investigation of the effects of particle composition and equivalence ratio on the burning characteristics of aluminum-particle/air mixtures. Reasonable agreement between theoretical results and experimental data was obtained in terms of flame speed. The flame structure of a bimodal particle dust cloud may display either an overlapping or a separated configuration, depending on the combustion properties of aluminum particles at different scales. At low percentages of nano particles in the fuel formulation, the flame exhibits a separated spatial structure with a wider flame regime. At higher nano-particle loadings, overlapping flame configurations are observed.

http://www.yang.gatech.edu/publications/Journal/Combust%20Inst%20(Huang,%202007).pdf

Ying Huang

Papers

Dynamics and stability of lean-premixed swirl-stabilized combustion

Effect of particle size on combustion of aluminum particle dust in air

Effect of swirl on combustion dynamics in a lean-premixed swirl-stabilized combustor

Large-Eddy Simulation of Combustion Dynamics of Lean-Premixed Swirl-Stabilized Combustor

Combustion of bimodal nano/micron-sized aluminum particle dust in air