A Numerical Study of Forest Fire Progression and Fire Suppression by Aerial Fire Fighting

Forest fires are of common occurrence all over the world, which cause severe damages to valuable natural resources and human lives. In the recent California Fire, which burned 300,000 hectors of land, the disaster danger could reasonably be predicted, but early control of fires by means of aerial fire fighting might have been failed in that situation. Also in Japan, there are similar problems in the aerial fire fighting. Most forest fires occur in the daytime and the fires are freely in progress without any control during the nighttime. Therefore, it is important to attack the fires when there is daylight. The water dropped by helicopters is not always sufficient to control fires, since the quantity of water that can be carried aloft is a critical issue. Large amount of water can be dropped from aircrafts, but the high-speed flight of aircrafts may be dangerous in the mountain, where tall trees and steel towers with electric wires may exist. Therefore, those aircrafts have to fly at much higher altitudes than helicopters, while the water drop at high altitudes changes water into mist in the air. The objective of this study is to examine the methods to prevent the ignition by firebrands in the downwind area by applying water through the aerial fire fighting. However, tests by real aircrafts to obtain such information would be too costly. Therefore, the patterns of water drop from aircrafts were examined in CFD simulations, together with the investigation of needed water drop rate based on the forest fire statistics, the previous real aircraft tests and laboratory experiments. It has been found in the simulations that the water supply with the water density of 2 L/m2 is effective to control fires and the patterns of dropping water are reasonable.

Modeling of Combustion of Mono-Carbon Fuels Using the Rate-Controlled Constrained-Equilibrium Method

Modeling of a non-equilibrium combustion process involves the solution of large systems of differential equations with as many equations as species present during the process. The process of chemical reaction and combustion is complicated since it may be governed by hundreds, sometimes thousands of microscopic rate processes. Integration of these equations simultaneously becomes more difficult with the complexity of the combustible. In order to reduce the size of these systems of equations, the Rate-Controlled Constrained-Equilibrium method (RCCE) has been proposed to model non-equilibrium combustion processes. This method is based on the Second Law of Thermodynamics, assuming that the evolution of a complex system can be described by a small number of rate-controlling reactions which impose slowly changing constraints on all allowed states of the system, therefore a non-equilibrium system will relax to its final equilibrium state through a sequence of rate controlled constrained equilibrium states. Oxidation induction times and concentration of species during a combustion process are found in a less complicated way with this method, as equations for constraints rather than for species determine the composition and evolution of the system. The time evolution of the system can be reduced since the number of constraints is much smaller than the number of species presents, so the number of equations to solve. The RCCE method has been applied to the stoichiometric combustion of mono-carbon fuels using 29 chemical species and 139 chemical reactions at different sets of pressure and temperature, ranging from 1 atm to 100 atm, and from 900 K to 1600 K respectively. Results of using 8, 9, 10 and 11 constraints compared very well to those of the detailed calculations at all conditions for the cases of formaldehyde (H2CO), methanol (CH3OH) and methane (CH4). For these systems, ignition delay times and major species concentrations were within 5% of the values given by detailed calculations, and computational saving times up to 50% have been met.

An H-Adaptive Finite Element Model for Constructing 3-D Wind Fields

Calculating wind velocities accurately and efficiently is the key to successfully assessing wind fields over irregular terrain. In the finite element method, decreasing individual element size (increasing the mesh density) and increasing shape function interpolation order are known to improve accuracy. However, computational speed is typically impaired, along with tremendous increases in computational storage. This problem becomes acutely obvious when dealing with atmospheric flows. An h-adaptation scheme, which allows one to start with a coarse mesh that ultimately refines in high gradients regions, can obtain high accuracy at reduced computational time and storage. H-adaptation schemes have been shown to be very effective in compressible flows for capturing shocks [1], but have found limited use in atmospheric wind field simulations [2]. In this paper, an h-adaptive finite element model has been developed that refines and unrefines element regions based upon velocity gradients. An objective analysis technique is applied to generate a mass consistent 3-D flow field utilizing sparse meteorological data. Results obtained from the PSU/NCAR MM5 atmospheric model are used to establish the initial velocity field in lieu of available meteorological tower data. Wind field estimations for the northwest area of Nevada are currently being examined as potential locations for wind turbines.

Numerical Simulation of a High Pressure Supersonic Multiphase Jet Flow Through a Gaseous Medium

Computational Fluid Dynamics (CFD) analysis is used to numerically study the structure and dynamics of a high-pressure, high-speed jet of a gas/liquid mixture through a gaseous medium close to the nozzle region. The complex structure of the jet near the nozzle region is captured before it breaks-up downstream. A new multiphase model based on a mixture formulation of the conservation laws for a multiphase flows is used in the simulation. The model does not require ad-hoc closure for the variation of mixture density with pressure and yields thermodynamically accurate acoustic propagation for multiphase mixtures. The numerical formulation has been implemented to a multi-physics unstructured code “RocfluMP” that solves the modified three-dimensional time-dependent Euler/Navier-Stokes equations for a multiphase framework in integral form. The Roe’s approximate Riemann solver is used to allow capturing of shock waves and contact discontinuities. For a very steep gradient, an HLLC scheme is used to resolved the isolated shock and contact waves. The developed flow solver provides a general coupled incompressible-compressible multiphase framework that can be applied to a variety of supersonic jet flow problems including fuel injection systems, thermal and plasma spray coating, and liquid-jet machining. Preliminary results for shock tube analysis and gas/liquid free surface jet flow through a gaseous medium are presented and discussed.

Pre-Delivery Testing of Centrifugal Compressors Within the Petroleum Industry: A User’s View

In oil and gas applications where centrifugal compressors play a central role, their availability is essential for continued production; typically the loss of a day’s revenue can far exceed the capital value of the machine. Performing more rigorous inspection and testing prior to accepting delivery of centrifugal compressors can reveal a fairly large percentage of mechanical and performance failures. This paper is devoted to illustrate the crucial importance of centrifugal compressors testing within the petroleum industry with a special attention to the performance test and complete-unit test.

CFD Analysis of the Combustion of Hydrogen in a Simulated Two Dimensional Scramjet Engine

The purpose of this research is to accurately simulate combustion in a scramjet engine using a CFD (Computational Fluid Dynamics) software package called Fluent and to validate the results with existing experimental data from NASA Langley Research Center[1]. The use of a particular engine characteristic called compression ramp injection was used to increase the mixing of air and fuel inside the combustion duct as well as provide the necessary compression of the fuel/air mixture. The duct length and other pertinent dimensions were also determined by published data from NASA [1]. The engine model used is relatively small and, at this stage, can be thought of as a two dimensional combustor duct rather than a true engine. The scope of this project involves the simultaneous calculations and analysis of both combustion and high-speed compressible flow. Thermodynamic data was used to create hydrogen fuel in a Fluent module called prePDF (probability density function), which calculates the look-up tables and chemical reactions for the fuel. Non-premixed combustion at Mach 2 was carried out using various equivalence ratios, (ratio of actual fuel/air mixture to stoichiometric fuel/air mixture) ranging from .4 to 1.4. The basic characteristics of the numerical model are as follows: steady state; non-premixed combustion; hydrogen fuel PDF model with 4 species; k-epsilon viscous model. Results of the numerical analysis include a comparison of combustion efficiencies for various equivalence ratios to the combustion efficiencies and equivalence ratios obtained by NASA in their experimental ground test facility at Langley Research Center [1].

Coalescence Criterion of Part-Through Wall Cracks in Steam Generator Tubes of Nuclear Power Plants

In scheduling inspection and repair of nuclear power plants, it is important to predict failure pressure of cracked steam generator tubes. Nondestructive evaluation (NDE) of cracks often reveals two neighboring cracks. If two neighboring part-through cracks interact, the tube pressure, under which the ligament between the two cracks fails, could be much different than the critical burst pressure of an individual equivalent part-through crack. The ability to accurately predict the ligament failure pressure, called “coalescence pressure,” is important. The coalescence criterion, established earlier for 100% through cracks using nonlinear finite element analyses [1–3], was extended to two part-through-wall axial collinear and offset cracks cases. The ligament failure is caused by local instability of the radial and axial ligaments. As a result of this local instability, the thickness of both radial and axial ligaments decreases abruptly at a certain tube pressure. Good correlation of finite element analysis with experiments (at Argonne National Laboratory’s Energy Technology Division) was obtained. Correlation revealed that nonlinear FEM analyses are capable of predicting the coalescence pressure accurately for part-through-wall cracks. This failure criterion and FEA work have been extended to axial cracks of varying ligament width, crack length, and cases where cracks are offset by axial or circumferential ligaments. The study revealed that rupture of the radial ligament occurs at a pressure equal to the coalescence pressure in the case of axial ligament with collinear cracks. However, rupture pressure of the radial ligament is different from coalescence pressure in the case of circumferential ligament, and it depends on the length of the ligament relative to crack dimension.

Effect of Vortex Flow on Heat Transfer to Combustion Chamber Wall

A new experimental facility was designed, fabricated and tested to model and study the effect of bidirectional swirl flow on the rate of heat transfer to combustion chamber walls in many applications. Heat transfer to combustion chamber walls is an unwanted phenomenon. Reduction of this heat transfer can result in time and cost saving methods in design and fabrication of combustion chambers. The experimental study was performed by using propane and air with oxygen as fuel and oxidizer respectively. The location of injection ports and geometry of combustion chamber are flexible and could be varied. Tests were performed with different mass flow rates of fuel and oxidizer. For the same flow rates and with the presence of bidirectional flow, a wall temperature reduction of up to 50% was observed. In cases where only some of the oxidizer was injected from the chamber end to generate the bidirectional swirl flow, highest efficiency and lowest wall temperature existed. This can be due to better mixing of fuel and oxidizer and absence of hot spots in the combusting core. Further development of this technique enables combustion chamber manufacturers in a wide spectrum of industries such as gas turbine manufacturers to use less expensive and more available material in their production of combustors.

Development of Systems Engineering Model for Spent Fuel Extraction Process

The mission of the Transmutation Research Program (TRP) at University of Nevada, Las Vegas (UNLV) is to establish a nuclear engineering test bed that can carry out effective transmutation and advanced reactor research and development effort. Chemical Engineering Division, Argonne National Laboratories (ANL) is in charge the design, modeling, and demonstration of countercurrent solvent-extraction process for treating high-level liquid waste, such as U and Tc. The Nevada Center for Advanced Computational Methods (NCACM) at UNLV is developing a systems engineering model that provides process optimization through the automatic adjustment on input parameters, such as feed compositions, stages, flow rates, etc., based on the extraction efficiency of components and concerned output factors. An object-oriented programming (OOP) is considered. Previously designed Microsoft (MS) Excel macro-based program, Argonne Model for Universal Solvent Extraction (AMUSE) code, based on firm understanding of the chemistry and thermodynamics, is the core module for Uranium Extraction process (UREX). Currently AMUSE is the only available module. The Transmutation Research Program System Engineering Model Project (TRPSEMPro) consists of task manager, task integration and solution/monitor modules. A MS SQL server database is implemented for managing large data flow from optimization processing. Task manager coordinates and interacts with other two modules. Task integration module works as a flowsheet constructor that builds task hierarchy, input parameter values and constrains. Task solution/monitor component presents both final and in-progress outputs in tabular and graphical formats. The package also provides a multiple-run process that executes a design matrix without invoking the optimization module. Experimental reports can be generated through database query and formatting.

Verify Results of a Combustion Chamber Model for One Type of Fuel

The focus of this paper is the validation of a Computational Fluid Dynamic (CFD) code with respect to combustion processes. To perform this validation, the emission results from a numerical model of a simple combustor are compared to experimental results obtained from a physical model that has the exact same dimensions and configuration as the numerical model. FLUENT was the numerical CFD code used for this study. Both the numerical model and the experimental apparatus are two-dimensional, vertical combustors that inject methane through a 2 mm slot at the combustor base. Air is injected through 6 mm slots placed 6 mm on each side of the fuel injection slot. The combustion chamber is a 300 mm long tube that has a wall thickness of 5 mm. For both the experimental and numerical results, the equivalence ratio was varied from 1 to 1.5 The results obtained at the exit of the chamber show that the temperature predictions match the model within 2.5%, the CO predictions match the model within 14.75%, and the CO2 predictions match the model within 15.91%. This study shows that the results from FLUENT are consistent with the experimental results. The percentage error shows a slight difference between the numerical and physical results, but these errors are acceptable because of the assumptions made and the nature of numerical modeling.