10,260 research outputs found
A second-order accurate parabolized Navier-Stokes algorithm for internal flows
A parabolized implicit Navier-Stokes algorithm which is of second-order accuracy in both the cross flow and marching directions is presented. The algorithm is used to analyze three model supersonic flow problems (the flow over a 10-degree edge). The results are found to be in good agreement with the results of other techniques available in the literature
Numerical study of hydrogen-air supersonic combustion by using elliptic and parabolized equations
The two-dimensional Navier-Stokes and species continuity equations are used to investigate supersonic chemically reacting flow problems which are related to scramjet-engine configurations. A global two-step finite-rate chemistry model is employed to represent the hydrogen-air combustion in the flow. An algebraic turbulent model is adopted for turbulent flow calculations. The explicit unsplit MacCormack finite-difference algorithm is used to develop a computer program suitable for a vector processing computer. The computer program developed is then used to integrate the system of the governing equations in time until convergence is attained. The chemistry source terms in the species continuity equations are evaluated implicitly to alleviate stiffness associated with fast chemical reactions. The problems solved by the elliptic code are re-investigated by using a set of two-dimensional parabolized Navier-Stokes and species equations. A linearized fully-coupled fully-implicit finite difference algorithm is used to develop a second computer code which solves the governing equations by marching in spce rather than time, resulting in a considerable saving in computer resources. Results obtained by using the parabolized formulation are compared with the results obtained by using the fully-elliptic equations. The comparisons indicate fairly good agreement of the results of the two formulations
Implementation of uniform perturbation method for potential flow past axisymmetric and two-dimensional bodies
The aerodynamic characteristics of potential flow past an axisymmetric slender body and a thin airfoil are calculated using a uniform perturbation analysis method. The method is based on the superposition of potentials of point singularities distributed inside the body. The strength distribution satisfies a linear integral equation by enforcing the flow tangency condition on the surface of the body. The complete uniform asymptotic expansion of its solution is obtained with respect to the slenderness ratio by modifying and adapting an existing technique. Results calculated by the perturbation analysis method are compared with the existing surface singularity panel method and some available analytical solutions for a number of cases under identical conditions. From these comparisons, it is found that the perturbation analysis method can provide quite accurate results for bodies with small slenderness ratio. The present method is much simpler and requires less memory and computation time than existing surface singularity panel methods of comparable accuracy
The sulfur budget of the troposphere
A one dimensional photochemical tropospheric model was used to calculate the vertical profiles of tropospheric species. Particular attention is focused on the recent inclusion of the chemistry of the sulfur group, which consists of 13 species involving a total of 45 chemical reactions. It is found that the chemistry of the sulfur species, because it is largely anthropogenic, plays an increasingly important role in the distribution of tropospheric gases. The calculated vertical profiles were compared to available measurements and generally found to be in good agreement
Magnetoconductance signatures of chiral domain-wall bound states in magnetic topological insulators
Recent magnetoconductance measurements performed on magnetic topological
insulator candidates have revealed butterfly-shaped hysteresis. This hysteresis
has been attributed to the formation of gapless chiral domain-wall bound states
during a magnetic field sweep. We treat this phenomenon theoretically,
providing a link between microscopic magnetization dynamics and butterfly
hysteresis in magnetoconductance. Further, we illustrate how a spatially
resolved conductance measurement can probe the most striking feature of the
domain-wall bound states: their chirality. This work establishes a regime where
a definitive link between butterfly hysteresis in longitudinal
magneto-conductance and domain-wall bound states can be made. This analysis
provides an important tool for the identification of magnetic topological
insulators.Comment: v2: Final published version; 7 pages, 3 figure
Switchable valley filter based on a graphene - junction in a magnetic field
Low-energy excitations in graphene exhibit relativistic properties due to the
linear dispersion relation close to the Dirac points in the first Brillouin
zone. Two of the Dirac points located at opposite corners of the first
Brillouin zone can be chosen as inequivalent, representing a new valley degree
of freedom, in addition to the charge and spin of an electron. Using the valley
degree of freedom to encode information has attracted significant interest,
both theoretically and experimentally, and gave rise to the field of
valleytronics. We study a graphene - junction in a uniform out-of-plane
magnetic field as a platform to generate and controllably manipulate the valley
polarization of electrons. We show that by tuning the external potential giving
rise to the - junction we can switch the current from one valley
polarization to the other. We also consider the effect of different types of
edge terminations and present a setup, where we can partition an incoming
valley-unpolarized current into two branches of valley-polarized currents. The
branching ratio can be chosen by changing the location of the - junction
using a gate.Comment: 8 pages, 7 figure
Chemoviscosity modeling for thermosetting resins
A chemoviscosity model, which describes viscosity rise profiles accurately under various cure cycles, and correlates viscosity data to the changes of physical properties associated with structural transformations of the thermosetting resin system during cure, was established. Work completed on chemoviscosity modeling for thermosetting resins is reported
Studies on chemoviscosity modeling for thermosetting resins
A new analytical model for simulating chemoviscosity of thermosetting resins has been formulated. The model is developed by modifying the well-established Williams-Landel-Ferry (WLF) theory in polymer rheology for thermoplastic materials. By introducing a relationship between the glass transition temperature Tg(t) and the degree of cure alpha(t) of the resin system under cure, the WLF theory can be modified to account for the factor of reaction time. Temperature dependent functions of the modified WLF theory constants C sub 1 (t) and C sub 2 (t) were determined from the isothermal cure data. Theoretical predictions of the model for the resin under dynamic heating cure cycles were shown to compare favorably with the experimental data. This work represents progress toward establishing a chemoviscosity model which is capable of not only describing viscosity profiles accurately under various cure cycles, but also correlating viscosity data to the changes of physical properties associated with the structural transformation of the thermosetting resin systems during cure
- …