On recessed cavity flame-holders in supersonic cross-flows

Flame-holding in a recessed cavity is investigated experimentally in a Mach 2.5 preheated cross-flow for both stable and unstable combustion, with a relatively low preheating. Self-sustained combustion is investigated for stagnation pressures and temperatures reaching 1.4 MPa and 750 K. In particular, cavity blowout is characterized with respect to cavity aspect ratio (L/D =2.84 - 3.84), injection strategy (floor - ramp), aft ramp angle (90 deg - 22.5 deg) and multi-fuel mixture (CH₄-H₂ or CH₄-C₂H₄ blends). The results show that small hydrogen addition to methane leads to significant increase in flame stability, whereas ethylene addition has a more gradual effect. Since the multi-fuels used here are composed of a slow and a fast chemistry fuel, the resulting blowout region has a slow (methane dominant) and a fast (hydrogen or ethylene dominant) branch. Regardless of the fuel composition, the pressure at blowout is close to the non-reacting pressure imposed by the cross-flow, suggesting that combustion becomes potentially unsustainable in the cavity at the sub-atmospheric pressures encountered in these supersonic studies. The effect of preheating is also investigated and results show that the stability domain broadens with increasing stagnation temperature. However, smaller cavities appear less sensitive to the cross-flow preheating, and stable combustion is achieved over a smaller range of fuel flow rate, which may be the result of limited residence and mixing time. The blowout data point obtained at lower fuel flow rate fairly matches the empirical model developed by Rasmussen et al. for floor injection phi = 0.0028 Da^-.8, where phi is the equivalence ratio and Da the Damkohler number. An alternate model is proposed here that takes into account the ignition to scale the blowout data. Since the mass of air entrained into the cavity cannot be accurately estimated and the cavity temperature is only approximated from the wall temperature, the proposed scaling has some uncertainty. Nevertheless the new phi-Da scaling is shown to preserve the subtleties of the blowout trends as seen in the current experimental data.PhDCommittee Chair: Suresh Menon; Committee Member: David Scarborough; Committee Member: Jechiel Jagoda; Committee Member: Jerry Seitzman; Committee Member: Robert Pit

Detection of Surface Corrosion by Ultrasonic Backscattering

Corrosion often occurs in the inner aluminum lining of the HB-53 helicopter external fuel tank, resulting in fuel leaks. This project centers on developing an in-situ ultrasonic inspection technique to detect corroded areas inside the fuel tank. Due to the complexity of the composite structure of the tank, the ultrasonic inspection is carried out from inside the tank using a monostatic backscattering technique. The backscattered field contains information related to the insonified surface properties (surface roughness scales). Numerical predictions are implemented with a simplified model of backscattered intensity (Ogilvy, 1991). Experimental results are obtained on artificially corroded plates, and on the actual fuel tank of the HB-53 helicopter. Signal processing techniques (Envelope Correlation and Inverse Technique) are used to detect corroded surfaces with data obtained with a focused 10 MHz pulsed transducer.M.S.Committee Chair: Yves H. Berthelot; Committee Member: Jennifer E. Michaels; Committee Member: Peter H. Roger

A Systematic Concept Exploration Methodology Applied to Venus In Situ Explorer

This presentation was part of the session : Probe Missions to the Giant Planets, Titan and VenusSixth International Planetary Probe WorkshopA critical task in any design process is the initial conversion of customer or program objectives into a baseline system architecture. This task becomes particularly important for space exploration systems that have unique requirements which, in many cases, have never been met before. A useful tool to the space systems engineer would be a methodology which helps to make this objectives-to-design conversion more systematic and efficient. Presented in this paper is such a methodology frequently used at the Georgia Institute of Technology, and in this paper the methodology is applied to initial concept formulation for the Venus In Situ Explorer (VISE) mission. VISE is one of six New-Frontiers-class missions to occur within the next 30 years that NASA addresses in its Solar System Exploration Roadmap. VISE is envisioned as an aerial mission that will study Venus' atmospheric composition as well as descend briefly to the surface to acquire samples for later analysis at more benign altitudes. Common to both VISE and its successor, Venus Mobile Explorer, is the challenge to operate under the extreme temperatures (about 730 K) and pressures (about 90 atm) present at the Venusian surface. In order to establish a baseline mission and vehicle concept for VISE, the methodology presented here begins with problem definition and the generation of functional and operational architectures. Customer requirements and engineering targets are set through an established set of tools known as the seven management and planning tools and through the use of a quality function deployment (QFD). A morphological matrix is used to identify 12.4 billion potential solutions in the concept space. From this concept space, six representative designs are chosen to demonstrate how alternatives from the morphological matrix may be ranked through multi-attribute decision making (MADM) techniques such as the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) and Pugh concept selection matrices. Two of the six concepts are eliminated based on these MADM techniques, and the remaining four concepts are recognized as requiring more in-depth study to allow definitive rankings to be assigned. A notional modeling and simulation framework for this problem is formed which could be used to complete such an in-depth, quantitative study. This paper principally serves to illustrate an example of how a systematic objectives definition, concept generation, and downselection methodology can be applied to advanced interplanetary missions (specifically in the example of Venus In Situ Explorer). The methodology and tools presented here are shown as a helpful guide and addition to the toolbox of the space systems engineer during the advanced planning stages of design.Georgia Institute of Technology ; National Institute of Aerospac