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Kishwar HossainGlendale, CaliforniaDoctoral Research:Three-dimensional Numerical Study of Flames Supported by a Rotating BurnerAbstract
The evolution of non-uniform flames is typically a manifestation of the intrinsic instabilities of the system. These instabilities lead to dynamics that are unique and offer insight into the conditions necessary for the sustainability of the flame. In this study non-uniform methane diffusion flames, formed from a porous plug burner spinning in quiescent air are investigated numerically in a three-dimensional context. Flames are simulated for Damkohler numbers on the upper branch of the S-response curve close to the extinction point. Multi-dimensional instabilities appear at these near extinction Damkohler numbers, as observed in experimental studies of flames sustained by a rotating fuel disk [1] or by a rotating porous burner [2], [3].
Simulation results from the constant density and constant viscosity model suggest that the non-uniform flames are a result of thermodiffusional instabilities and are a function of the Damkohler number. Non-uniform flames simulated in this study include flame holes, single armed spirals and double armed spirals. The flame holes have stationary edges and the radius of these holes is found to increase as the Damkohler number is lowered. The single and double spirals have edges that rotate about the axis of the burner. It is found that the velocity of the single spiral relative to the flow is considerably higher than that of the double spiral. It is also found that the shapes of the spirals are affected by the velocity vectors and by interactions between distinct spiral arms. Analyses of the scalar dissipation and cross-scalar dissipation rates of these flames show that the flames are primarily diffusion flames with some premixing near the edges. Factors, other than the Damkohler number, that are found to significantly affect the stability of the spinning porous plug burner included the mixture strength and the exit velocity at the burner surface. The range of Damkohler number within which the system exhibits non-uniform behaviour is larger at higher values of exit velocity and lower values of mixture strength. [1] V. Nayagam and F. A. Williams. Rotating Spiral Edges in Von Karman Swirling Flows, Physical Review Letters 84, 3 (2000). [2] V. Nayagam and F. A. Williams. Pattern Formation in Diusion Flames Embedded in Von Karman Swirling Flows, NASA/CP 2001-21082 (2001). [3] V. Nayagam and F. A. Williams. Pattern Formation in Diusion ames Embedded in Von Karman Swirling Flows, NASA/CR 2006-214057 (2006).
Papers: Masters Research:Open Loop Longitudinal Envelope Protection for Aircraft in Icing EncountersAbstractIn-flight
icing has been recognized as a safety threat to aircraft operations
since
the 1930’s. Although significant progresses have been made over
the
past 70 years in improving flight safety in icing conditions, recent
accident
and incident reports analyzed for the Aviation Safety Program (AvSP)
showed
that 13% of all weather-related accidents were due to airframe
icing.
Thus, further developments are necessary in order to reduce the number
of
icing related incidents and accidents.
The goal of this research was to improve aircraft safety through enhancing the envelope protection capabilities of an aircraft in icing conditions. To accomplish this goal, an open loop envelope protection algorithm was developed to ensure the safe operation of an iced aircraft during the manual mode of flight. The Iced Aircraft Envelope Protection system (IAEP), developed as a part of the Smart Icing Systems (SIS) research project at the University of Illinois, was based on data from wind tunnel tests, flight tests and iced aircraft simulations obtained from a six-degree-of-freedom computational flight dynamics model. The system consisted of estimative and predictive methods for approximating, and avoiding the envelope boundaries. Simulation results demonstrated that IAEP was capable of successfully avoiding incidents and accidents during flight in icing conditions.
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