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Agoura Hills, CA, United States

Potturi A.S.,Metacomp Technologies, Inc. | Edwards J.R.,North Carolina State University
Combustion and Flame

In this study, a hybrid large-eddy/Reynolds-averaged Navier-Stokes (LES/RANS) method is used to simulate ethylene combustion inside a cavity flameholder. The cavity flameholder considered is Configuration E of University of Virginia's Scramjet Combustion Facility, which consists of a Mach 2 inlet nozzle, a constant-area isolator, a combustor, and an extender, through which the exhaust gases are vented to the atmosphere. To increase the fuel-residence time, a cavity is fitted along the upper wall inside the combustor section of the flameholder. The configuration has the capability of injecting ethylene through a series of ports located upstream of and inside the cavity along the upper wall the combustor. In the simulations, ethylene combustion is modeled using a 22-species ethylene oxidation mechanism. Also, a synthetic eddy method is used to introduce turbulence at the inflow plane of the flameholder. For an equivalence ratio of 0.15, a cavity stabilized flame is predicted. Predictions are compared with line-of-sight temperature, water column-density, water mole-fraction, CO column-density, and CO2 column-density measurements at three stations within and downstream of the cavity. Agreement with experiment is generally good within the cavity. Downstream of the cavity, the simulations predict higher temperatures near the wall. Analysis of the flame structure predicted by the LES/RANS method indicates that the flame propagates into a stoichiometric to fuel-rich mixture near the cavity. Flame angles captured in the simulation are in close agreement with those predicted through classical premixed turbulent flame-speed estimates. Further downstream, the flame structure is non-premixed in character, and near complete conversion of CO to CO2 is observed by the time the flame reaches the combustor exit. © 2014 The Combustion Institute. Source

Agency: Department of Defense | Branch: Air Force | Program: SBIR | Phase: Phase II | Award Amount: 749.99K | Year: 2009

Metacomp Technologies proposes to take advantage of the achieved enhancements to  computational fluid dynamics capabilties and opportunities presented by developments in related disciplines, to proceed with the development of a unified multiphysics capability for scramjet applications that will drastically reduce the overall process time spanning geometry definition to analysis results.  The application scenario includes coupled fluid dynamics and structural mechanics with the necessary mesh generation.  The operational envelope includes incompressible and compressible turbulent reacting flows with heat tranfer to the structures, in combination with the resulting deflection and deformation of these structures. BENEFIT: Anticipated benefits include drastic reduction in time from problem definition to first results, from weeks to within a day.  Another benefit will be the accessiblity of complex simulation technology to an expanded class of users who will be able to focus on the exploitation of the available results and not on any tortuous process to obtain  results.  The benefits will accrue immediately to the propulsion systems currently on the table for hypersonic vehicles.

Agency: Department of Defense | Branch: Missile Defense Agency | Program: SBIR | Phase: Phase I | Award Amount: 100.00K | Year: 2009

Metacomp Technologies proposes to explore, evaluate, select and implement several improvements in fidelity and computational effectiveness to enhance continuum modeling approaches for near-transitional flow regime.

Agency: Department of Defense | Branch: Air Force | Program: SBIR | Phase: Phase I | Award Amount: 99.99K | Year: 2009

When using the current state-of-the-art in spatial discretization, numerical flux functions and temporal integration techniques, the amount of effort required for simulations in general geometries is prohibitively large for most unsteady flow simulations in multi-element rocket engines. In addition, current numerical techniques, while effective for stationary flows, have a potential for spurious reflections at interfaces, where grid sizes change abruptly. These limitations render present day approaches less than successful for unsteady flows. Following an exhaustive search for an efficient method to push rocket engine flow simulations to the next level, both in terms of fidelity and turnaround time, Metacomp Technologies proposes to employ an innovative application of high resolution methodologies in the CFD++ framework.   BENEFITS: The proposed technology will result in a dramatic reduction in computational effort to achieve a desirable level of fidelity in the simulation of unsteady flow in rocket engines. The proposed development will lead to a modern, high fidelity rocket engine flow simulation capability that can predict the onset of instability as well as transient response of the flow in the combustion chamber to disturbances.  The proposed research will complement other developments at Metacomp and CFD++, Metacomps flow solver, and will become a useful tool for DoD agencies to explore new designs for high performance rocket engines.  Concurrently, rocket engines are increasingly used in the commercial, non-military, market. Examples are the various Earth-to-Space rocket-powered payload carriers, some of which are government-sponsored, others privately owned.  Recent years have seen the birth of commercial space travel. While still in its infancy, increased activity in this area indicates a potentially big market in the near future. Since all these vehicles must be able to travel in vacuum, most of them will resort to chemically fueled rocket engines, which will encounter the same transient problems associated with military rocket motors. Consequently, the current proposal has potential for a diverse usage, benefitting both military and commercial sectors.

Agency: Department of Defense | Branch: Air Force | Program: STTR | Phase: Phase I | Award Amount: 100.00K | Year: 2010

The occurrence of combustion instability has long been a matter of serious concern in the development of liquid-propellant rocket engines due to the high rate of energy release in a confined volume in which energy losses are relatively small. Shear layer instabilities and intermittent growth rates of the mixing layer cause fluctuations in the burning rates and result in acoustic waves triggering flow instabilities. These flow oscillations may grow uncontrolled if there is a positive feedback between the oscillatory heat release at the combustion front and acoustic waves within the combustion chamber. The proposed work will focus on shear layers and mixing around single and multiple jets under acoustic excitation. Conditions that lead to positive feedback between the acoustic waves and shear layers will be identified and the influence of amplitude and frequency of excitation on shear layer development will be quantified. BENEFIT: The study of shear layer development around fuel jets in the presence of acoustic excitation will furnish useful information concerning the instability mechanisms in rocket engines. It will extend experimental data and enable identification of cause and effect relationships between flow features evolving in three-dimensional, unsteady fields. The outcome of the proposed research has the potential to help build stable liquid propellant rocket engines. The proposed work will support the experimental investigation at AFRL. The experimental results will serve as a validation of the proposed methodology. The simulation will augment the experimental observations by providing a complete, three dimensional view of the evolving flow.

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