Analytical RS-GBSM-Based Nonstationary Low-Altitude Air-to-Air Channel Modeling over Open Area

Aerial communication is very flexible due to almost no restrictions on geographical conditions. In recent years, with the development and application of the unmanned aerial vehicle, the air-to-air communication attracts dense interests from the researchers. More accurate and precise channel modeling for air-to-air communication is a new hot topic because of its essential role in the performance evaluation of the systems. This paper presents an analytical nonstationary regular-shaped geometry-based statistical model for low-altitude air-to-air communication over an open area with considerations on ground scattering. Analytical expressions of the channel impulse response and the autocorrelation functions based on the three-ray model are derived. Based on the assumption of uniform distribution of the ground scatterers, the distributions of the channel coefficients such as time delay and path attenuation are derived, simulated, compared, and fitted. The nonstationary characteristics of the channel are observed through the time-variant distributions of the channel coefficients as well as the time-variant autocorrelated functions and time-variant Doppler power spectrum density.

Local thermal non-equilibrium conjugate forced convection and entropy generation in an aircraft cabin with air channel partially filled porous insulation

Purpose The purpose of this study is to numerically investigate heat transfer and entropy generation between airframe and cabin-cargo departments in an aircraft. The conjugate forced convection and entropy generation in a cylindrical cavity within air channel partly filled with porous insulation material as simplified geometry for airframe and cabin-cargo departments are considered under local thermal non-equilibrium condition. Design/methodology/approach The non-dimensional governing equations for fluid and porous media discretized by finite volume method are solved using the SIMPLE algorithm with pressure and velocity correction. Findings The effects of the following parameters on the problem are investigated; Reynolds number, Darcy number, the size of inlet and exit cross-section, thermal conductivity ratio for solid and fluid phases, angle between the vertical symmetry axis and the end of channel wall exit and the gap between adiabatic channel wall and horizontal adiabatic wall separating cabin and cargo sections. Originality/value This paper can provide a basic perspective and framework for thermal design between the fuselage and cabin-cargo sections. The minimum total entropy generation number is calculated for various Reynolds numbers and thermal conductivity ratios. It is observed that the channel wall temperature increases for high Reynolds number, low Darcy number, narrower exit cross-section and wider the gap between channel wall and horizontal.

Numerical analysis of the effect of trapezoidal baffles inside fuel and air channels on the performance of a planar-type Solid Oxide Fuel Cell

The present paper investigates the effect of trapezoidal baffles inside a planar-type solid oxide fuel cell. To achieve the objective, four cases are proposed: 1) simple planar geometry as base case, 2) trapezoidal baffles inside the fuel channel, 3) trapezoidal baffles inside the air channel and 4) trapezoidal baffles in both fuel and air channels. The height of the trapezoidal baffles inside the channels of the solid oxide fuel cell increases along the direction of the fluid flow. The numerical investigation is based on a three-dimensional computational fluid dynamics (CFD) model that takes into account the phenomenon of mass transfer, heat transfer, species transport and electrochemical reactions. A detailed comparison of the performance between the four cases of the fuel cell is provided in terms of power density, fluid flow, species concentration, temperature distributions and electric fields at a variable current density and a fixed power density of 3000 W/m2. The results show that the power density, the velocity, the availability of the hydrogen and oxygen species on the electrodes-electrolyte interfaces increases for the case 2, case 3 and case 4, respectively, in comparison to the case 1. Finally, the average temperature of the electrode-electrolyte interface is reduced with the baffles and it is concluded that the configuration with baffles inside air channel (case 3) shows better results in terms of the increment of the power density and the decrement of the average temperature.