Low-energy e^−-CO scattering in the static-exchange approximation

This paper presents a theoretical study of e^−-CO scattering at collision energies from 1 to 7 eV in the static-exchange approximation. The T-matrix discrete-basis-set approach to electron-molecule scattering introduced by Rescigno, McCurdy, and McKoy is used together with the variational correction method of Fliflet and McKoy. The authors show the behavior of the ^2Σ and ^2Π channel eigenphases and extract the width and position of the ^2Π shape resonance. Comparison is made with other theoretical and semiempirical results and with the corresponding resonance parameters for e^−-N_2 scattering. The momentum-transfer cross section is calculated and compared with the experimental data of Land and with other theoretical results

Discrete-basis-set approach to the minimum-variance method in electron scattering

We show that the minimization of the variance integral provides a method for the determination of scattering wave functions which uses discrete basis functions exclusively. By using a separable representation of the scattering potential only one new class of matrix elements appears in the evaluation of the variance integral which is not already required in the diagonalization of the Hamiltonian. The choice of Gaussian basis functions for the expansion of the scattering wave function should make the method particularly applicable to electron-molecule scattering. Some advantages and limitations of the method are discussed

Factors influencing flow steadiness in laminar boundary layer shock interactions

The Direct Simulation Monte Carlo method has been used to model laminar shock wave boundary interactions of hypersonic flow over a 30/55-deg double-wedge and “tick-shaped” model configurations studied in the Hypervelocity Expansion Tube facility and T-ADFA free-piston shock tunnel, respectively. The impact of thermochemical effects on these interactions by changing the chemical composition from nitrogen to air as well as argon for a stagnation enthalpy of 8.0 MJ/kg flow are investigated using the 2-D wedge model. The simulations are found to reproduce many of the classic features related to Edney Type V strong shock interactions that include the attached, oblique shock formed over the first wedge, the detached bow shock from the second wedge, the separation zone, and the separation and reattachment shocks that cause complex features such as the triple point for both cases. However, results of a reacting air flow case indicate that the size of the separation length, and the movement of the triple point toward to the leading edge is much less than the nitrogen case

Modeling of near-continuum laminar boundary layer shocks using DSMC

The hypersonic flow of nitrogen gas over a double wedge was simulated by the DSMC method using two-dimensional and three-dimensional geometries. The numerical results were compared with experiments conducted in the HET facility for a high-enthalpy pure nitrogen flow corresponding to a free stream Mach number of approximately seven. Since the conditions for the double wedge case are near-continuum and surface heat flux and size of the separation are sensitive to DSMC numerical parameters, special attention was paid to the convergence of these parameters for both geometries. At the beginning of the simulation, the separation zone was predicted to be small and the heat flux values for the 2-D model were comparable to the experimental data. However, for increasing time, it was observed that the heat flux values and shock profile strongly deviated from the experiment. Investigation of a three-dimensional model showed that the flow is truly three-dimensional and the side edge pressure relief provides good agreement between simulations and the experiment

Prediction of Thermal Protection System Material Permeability and Hydraulic Tortuosity Factor Using Direct Simulation Monte Carlo

Carbon preforms used in Thermal Protection System (TPS) materials are 80 to 90% porous, allowing for boundary layer and pyrolysis gases to flow through the porous regions. The bulk material properties such as permeability and hydraulic tortuosity factor affect the transport of the boundary layer gases. The use of Direct Simulation Monte Carlo along with the Klinkenberg permeability formulation allows us to compute the continuum permeability and Knudsen correction factor for flow in the transition regime. In this work, we have computed the permeability for two types of carbon preforms, namely, Morgan Felt and FiberForm, and assessed the effect of orientation on the permeability. Since both the materials are anisotropic, the permeability was found to depend on orientation, wherein, the materials are more permeable in the in-plane orientation than the through-thickness orientation. The through-thickness orientation was also more tortuous compared to the in-plane material orientation. Compared to Morgan Felt, FiberForm is less permeable, in both, through thickness and in-plane directions

Development of a Water Cluster Evaporation Model using Molecular Dynamics

Abstract. A Monte Carlo simulation using the SPC potential model has been used to determine the potential energy and constant volume heat capacity of water dimers and trimers. It was found that the potential energy almost follows a linear trend versus temperature. The heat capacity fluctuates around 10 cal/mol/K and reaches a maximum around 220 K for the dimer and 240 K for the trimer. The Molecular Dynamics simulation has been used to evaporate water dimers and trimers. The cumulative evaporation probabilities were calculated for temperatures ranging from 240 K to 300 K. The cluster evaporation rates were calculated using Weerashinge's equation, and they were compared with the UDT rates. Both values were found to be in good agreement. Finally, vibrational frequencies were computed