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  • 1
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    Reversal in Spreading of a Tabbed Circular Jet Under Controlled Excitation (1997)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Detailed flow field measurements have been carried out for a turbulent circular jet perturbed by tabs and artificial excitation. Two "delta tabs" were placed at the nozzle exit at diametricall opposite y locations. The excitation condition involved subharmonic resonance that manifested in a periodic vortex pairing in the near flow field. While the excitation and the tabs independently increased jet spreading, a combination of the two diminished the effect. The jet spreading was most pronounced with the tabs but was reduced when excitation was applied to the tabbed jet. The tabs generated streamwise vortex pairs that caused a lateral spreading of the jet in a direction perpendicular to the plane containing the tabs. ne excitation, on the other hand, organized the azimuthal vorticity into coherent ring structures whose evolution and pairing also increased entrainment by the jet. In the tabbed case, the excitation produced coherent azimuthal structures that were distorted and asymmetric in shape. The self-induction of these structures produced an effect that opposed the tendency for the lateral spreading of the streamwise vortex pairs. The passage of the distorted vortices, and their pairing, also had a cancellation effect on the time-averaged streamwise vorticity field. These led to the reduction in jet spreading.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: Physics of Fluids; Volume 9; No. 12; 3733-3741
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  • 2
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    An Experimental Study of Nonlinear Standing Waves in Resonators with Numerical Comparison (2002)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: Lawrenson et. al. [Journal of the Acoustic Society of America, Nov. 1998] described the generation of shock-free high-amplitude pressure waves in closed cavities using large equipment and resonators to produce the reported effects. An attempt is made to generate shock-free high-amplitude pressure waves using relatively small resonators. Ambient air is used as the working fluid. A small cylindrical resonator is tested resulting in the lack of a shocked waveform while a larger model of the same shape produces shock waves. A small conical resonator produces shock-free pressure waves at resonance, but the amplitude of these waves is small. A larger cone resonator model produces shock-free pressure waves of higher amplitude. A large horn-cone resonator also produces shock-free high amplitude pressure waves, A numerical model is used to compare the experimental results to theoretical results. The effects of structural resonances on the production of shock-free high-amplitude pressure waves are discussed, especially concerning difficulties encountered when these resonances were in the frequency ranges of interest. Identifying features of a structural resonance are presented.
    Keywords: Fluid Mechanics and Thermodynamics
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  • 3
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    Effect of Controlled Excitation on a Tabbed Jet (1997)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Detailed flowfield measurements have been carried out for a turbulent circular jet perturbed by tabs and artificial excitation. The excitation condition involved subharmonic resonance which manifested in a periodic vortex pairing in the near flowfield. While the excitation and the tabs independently increased jet spreading, a combination of the two diminished the effect. The jet spreading was the most with the tabs, but was reduced when excitation was applied to the tabbed jet. The self-induction of the distorted azimuthal vortex rings during the pairing process weakened the streamwise vortices produced by the tabs to cause this effect.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: AIAA Paper 97-0216 , Aerospace Sciences; Jan 06, 1997 - Jan 10, 1997; Reno, NV; United States
    Format: text
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  • 4
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    Quadrature Moments Method for the Simulation of Turbulent Reactive Flows (2003)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: A sub-filter model for reactive flows, namely the DQMOM model, was formulated for Large Eddy Simulation (LES) using the filtered mass density function. Transport equations required to determine the location and size of the delta-peaks were then formulated for a 2-peak decomposition of the FDF. The DQMOM scheme was implemented in an existing structured-grid LES solver. Simulations of scalar shear layer using an experimental configuration showed that the first and second moments of both reactive and inert scalars are in good agreement with a conventional Lagrangian scheme that evolves the same FDF. Comparisons with LES simulations performed using laminar chemistry assumption for the reactive scalar show that the new method provides vast improvements at minimal computational cost. Currently, the DQMOM model is being implemented for use with the progress variable/mixture fraction model of Pierce. Comparisons with experimental results and LES simulations using a single-environment for the progress-variable are planned. Future studies will aim at understanding the effect of increase in environments on predictions.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: Center for Turbulence Research Annual Research Briefs 2003; 261-275
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  • 5
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    Simulation of SRAM SEU Sensitivity at Reduced Operating Temperatures (2009)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A new NanoTCAD-to-Spectre interface is applied to perform mixed-mode SEU simulations of an SRAM cell. Results using newly calibrated TCAD cold temperature substrate mobility models, and BSIM3 compact models extracted explicitly for the cold temperature designs, indicate a 33% reduction in SEU threshold for the range of temperatures simulated.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: Government Microcircuit Applications and Critical Technology Conference (GOMAC); Mar 16, 2009 - Mar 19, 2009; Orlando, FL; United States
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