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Multiscale modeling of the anisotropic shock response of β-HMX molecular polycrystals
Zamiri, Amir R.,De, Suvranu Techno-Press 2011 Interaction and multiscale mechanics Vol.4 No.2
In this paper we develop a fully anisotropic pressure and temperature dependent model to investigate the effect of the microstructure on the shock response of ${\beta}$-HMX molecular single and polycrystals. This micromechanics-based model can account for crystal orientation as well as crystallographic twinning and slip during deformation and has been calibrated using existing gas gun data. We observe that due to the high degree of anisotropy of these polycrystals, certain orientations are more favorable for plastic deformation - and therefore defect and dislocation generation - than others. Loading along these directions results in highly localized deformation and temperature fields. This observation confirms that most of the temperature rise during high rates of loading is due to plastic deformation or dislocation pile up at microscale and not due to volumetric changes.
Zamiri, A.,Lee, B.J.,Taek Chung, J. ELSEVIER PARIS 2017 AEROSPACE SCIENCE AND TECHNOLOGY Vol. No.
Three-dimensional, compressible, unsteady Navier-Stokes equations are solved to investigate the flow field of a transonic centrifugal compressor with high compression ratio. The computational domain is consisted of an inlet bell mouth and an impeller with splitter blades, followed by a two-dimensional wedge vaned diffuser. The numerical method was validated by comparing the results with those of experiments in terms of aerodynamic compressor performance and flow field within the compressor passages. A detailed analysis of instantaneous and time-averaged flow field was conducted in the impeller and diffuser passages. The present study focuses on the pressure fluctuations and entropy production within the impeller and diffuser passages at the compressor design point. It is shown that the interaction between the impeller and diffuser blades leads to unsteadiness at the interface region and a pulsating behavior within the diffuser passages. Pressure waves with different convective velocities, generated by the impeller-diffuser interaction and pseudo-periodic unsteady separation bubbles, are captured in the time/space domain along the diffuser blade surfaces. The pressure fluctuation spectra were evaluated to analyze the noise characteristics of the centrifugal compressor as the main source of blade passing frequency noise. It is expected that the current unsteady Reynolds-Averaged Navier-Stokes (URANS) approach can be used as a tool for the prediction of unsteady flow and compressor noise characteristics with a proper turbulence model and well-resolved grids.
Ali Zamiri,이병주,정진택 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.11
Three-dimensional, compressible, Reynolds-averaged Navier-Stokes equations were solved to investigate the influence of the inclined leading edge diffuser vanes on the flow field and performance of a transonic centrifugal compressor with a high compression ratio. Diffuser vanes with leading edge inclined at different angles (10 different cases) were numerically modeled to investigate the effects that the inclined leading edge of the diffuser vane had on the diffuser pressure recovery and total pressure loss characteristics of the compressor. Diffuser vanes with an inclined leading edge reduce the interaction between the impeller discharge flow and the leading edge of the diffuser, which results in a reduced separation inside the diffuser passages. A maximum diffuser pressure recovery coefficient of 0.7185, was observed at a 30-degree inclination angle from hub-to-shroud. Moreover, in the case of inclination angles greater than 60 degrees for both hub-to-shroud and shroud-to-hub, there is a significant reduction in the pressure recovery, efficiency and pressure ratio.