The study of the turbulent burning velocity by imaging the wrinkled flame surface

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76129/1/AIAA-2002-482-348.pd

DDDAS for Fire and Agent Evacuation Modeling of the Rhode Island Nightclub Fire

Abstract. A Dynamic Data Driven Application System (DDDAS) was created to study interaction between fire and agent models during a fire evacuation. The analysis from that research can be used to validate proposed ideas in evacuation and building designs to ensure safety of buildings given various agent behav-iors. Two separate models were used to simulate the components of the emer-gency situation: fire and agent. The independent models were able to run using data computed by the other interacting models, allowing careful examination of real-time interactions in a situation. Through study of the interactions, a better understanding is gained of how individual variables such as exit position and width affect the evacuation process and escape rate in the given scenario. Exits can be relocated and changed to quickly assess the effect on the model. The re-sults can be used for improving building design and regulations as well as train-ing first responders.

Tunneling spectroscopy measurement of the superconductor gap parameter of MgB_2

Cryogenic scanning tunneling microscopy and magnetization measurements were used to study the superconducting properties of MgB_2. The magnetization measurements show a sharp superconductor transition onset at T_c = 38.5 K, in agreement with previous works. The tunneling spectra exhibit BCS gap structures, with gap parameters in the range of 5 to 7 meV, yielding a ratio of 2delat/KT_c ~ 3-4. This suggests that MgB_2 is a conventional BCS (s-wave) superconductor, either in the weak-coupling or in the `intermediate-coupling` regimeComment: accepted to PRB, revised versio

Numerical Simulation of a Laboratory-Scale Turbulent SlotFlame

We present three-dimensional, time-dependent simulations ofthe flowfield of a laboratory-scale slot burner. The simulations areperformed using an adaptive time-dependent low Mach number combustionalgorithm based on a second-order projection formulation that conservesboth species mass and total enthalpy. The methodology incorporatesdetailed chemical kinetics and a mixture model for differential speciesdiffusion. Methane chemistry and transport are modeled using the DRM-19mechanism along with its associated thermodynamics and transportdatabases. Adaptive mesh refinementdynamically resolves the flame andturbulent structures. Detailedcomparisons with experimental measurementsshow that the computational results provide a good prediction of theflame height, the shape of the time-averaged parabolic flame surfacearea, and the global consumption speed (the volume per second ofreactants consumed divided by the area of the time-averaged flame). Thethickness of the computed flamebrush increases in the streamwisedirection, and the flamesurface density profiles display the same generalshapes as the experiment. The structure of the simulated flame alsomatches the experiment; reaction layers are thin (typically thinner than1 mm) and the wavelengths of large wrinkles are 5--10 mm. Wrinklesamplify to become long fingers of reactants which burn through at a neckregion, forming isolated pockets of reactants. Thus both the simulatedflame and the experiment are in the "corrugated flameletregime.

Experimental Measurement of Local Burning Velocity Within a Rotating Flow

The final publication is available at link.springer.com.The work presented in this paper details the implementation of a new technique for the measurement of local burning velocity using asynchronous particle image velocimetry. This technique uses the local flow velocity ahead of the flame front to measure the movement of the flame by the surrounding fluid. This information is then used to quantify the local burning velocity by taking into account the translation of the flame via convection. In this paper the developed technique is used to study the interaction between a flame front and a single toroidal vortex for the case of premixed stoichiometric methane and air combustion. This data is then used to assess the impact of vortex structure on flame propagation rates. The burning velocity data demonstrates that there is a significant enhancement to the rate of flame propagation where the flame directly interacts with the rotating vortex. The increases found were significantly higher than expected but are supported by burning velocities [22-24] found in turbulent flames of the same mixture composition. Away from this interaction with the main vortex core, the flame exhibits propagation rates around the value recorded in literature for unperturbed laminar combustion [18-21]

Study of turbulent burning velocity using laser diagnostics in turbulent premixed flames.

Turbulent burning velocity plays an important role in turbulent premixed combustion. After many years of study it still remains an unresolved problem. One goal of the present study was to determine if the burning velocity curve has nonlinear bending as turbulence intensity level increases and to study reasons why the non-linear behavior exists. The nonlinear dependence of the turbulent burning velocity on the mean flow velocity and the turbulence intensity level was studied using Mie scattering technique. A stoichiometric methane-air slot burner with 2-D mean flow and surrounding outer flames was used. Mean velocity was varied from 3 to 12 m/s and turbulent intensity levels were varied from 5 to 25%. Images of the wrinkled flame surface were recorded. It was found that nonlinear bending behavior does occur. Mean velocity was found to be a governing parameter in addition to turbulent intensity level. To understand stretch effects and possible extinction processes that can contribute to the bending phenomenon simultaneous CH-PLIF/PIV diagnostics were employed. The technique allowed studying the flame interaction with the reactant flow. The CH layer images show that flame surface loss by local extinction does not occur, and thus is not a cause of the bending observed. The average CH layer thickness was about the same for all cases studied. Flame-vortex interactions were observed: pairs of counter-rotating vortices exerted strain on the flame in ways similar to a counterflow flame; single vortices made the flame roll around them straining the flame. The stretch effects were investigated along the flame for different flow conditions.Ph.D.Aerospace engineeringApplied SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/123584/2/3096091.pd

The through optimization of fail-safe branched injection trajectories of launch vehicles in view of aerodynamic load constraints on the basis of the maximum principle

A problem of through optimization of fail-safe branched trajectories of launchers in view of aerodynamic load constraints and restrictions on ground impact areas of separated parts (SP) is considered. The failsafety is regarded to the possibility of a recoverable vehicle (RV) to return from any point of the ascent trajectory to landing points without excess of allowable g-loads. So, the purpose is determination of the launcher optimal control in view of constraints on all trajectory branches: the main, corresponding to an active injection leg, and side branches, corresponding to SP fall trajectories and imaginary RV emergency trajectories, which form a continuum. The problem solution is based on the Pontryagin maximum principle (PMP)