Thermophysics and Aeromechanics最新文献

This paper presents a summary of a numerical study of mixed convection in a two-dimensional ventilated square cavity; it discusses the impact of the fresh inlet fluid jet on the flow and temperature structures. A saturated porous partition of thickness E_p = H/5 is positioned at the center of the cavity bottom with a height H_p between H/5 and H, while the vertical walls are kept adiabatic and impervious, the bottom horizontal wall is subject to a vertical thermal gradient. The momentum conservation equation uses the Darcy model with an energy equation, including the Brinkman extension, the multi-relaxation time collision factor based lattice Boltzmann method is used to solve the set of coupled equations. The numerical results present and discuss flow patterns and thermal field structures, reveal important physical quantities, such as the local and mean Nusselt value on the bottom wall. The parametric study presents the effects of Reynolds and Rayleigh numbers with respect to a given Darcy number and porous wall height. For a high Darcy number, the porous medium increases the surface of action of the cold fluid. In addition, by increasing the height of the porous wall, the thermal draft (Ra) has little influence on the Nusselt values.

An innovative method for rapid calculation of engine infrared signatures was proposed and integrated into the component-level model. Subsequently, the multiple-objective particle swarm optimization algorithm was utilized to optimize the infrared characteristics and fuel economy under the constraint of constant thrust during high-altitude penetration state. According to the Pareto solution sets, the exhaust system’s infrared radiation intensity decreased by 6 % to 23 % compared with the baseline engine while keeping the fuel consumption rate unchanged. When designing thermodynamic cycle parameters, a higher pressure ratio is beneficial for reducing infrared characteristics. The combination of high bypass ratio and high turbine inlet total temperature would strike a compromise between fuel economy and low infrared performance. Reducing the bypass ratio and turbine inlet total temperature while decreasing the nozzle throat area would further decrease the infrared radiation intensity of the exhaust system, but also lead to an increase in infrared radiation from jet flow, while enlarging the nozzle throat area would have the opposite effect. These findings have important implications for the development of more efficient designs and contribute to the advancement of thermal management.

A modeling study was performed for excitation of streamwise structures in a boundary layer with combustion. Modeling for undisturbed flow in a boundary layer is based on locally self-similar solutions for a boundary layer flow; these solutions account for streamwise pressure gradients and a heat source in the boundary layer with combustion that comply to simulated data. This undisturbed flow solution is a basis for solving a problem of interacting the external vorticity with a boundary layer (for the case of hydrogen-air combustion). We demonstrated that this type of interaction with the boundary layer generates intensive streamwise structure with velocity inhomogeneity in the lateral direction. These structures have the level of velocity higher than for the external vorticity velocity by factor of tens. Meanwhile, a maximum value of temperature inhomogeneity is much higher than for the velocity maldistribution.

The current research conducted experimental inquiries into convective heat transfer of different serpentine minichannel heat exchangers used to cool an electronic component. The working fluid used in all the experiments aimed at both minichannels was deionized water. The experimental investigation reported the thermal performance of the cooling minichannels, introducing the effect of several operating parameters. The findings revealed that the heat transfer enhancement achieved with the 2-mm long cooling serpentine minichannel exceeded that of the 3-mm long cooling minichannel; however, the overall thermal resistance derived from the heat exchanger with five minichannels was also greater than that obtained from the ten serpentine minichannels. In addition, at the same imposed volume flow rate used in these experimental investigations, the average convective heat transfer rate estimated from the 2-mm heat sink was 2.5 times greater than that obtained from the 3-mm heat sink. Furthermore, the utilization of U-shaped serpentine minichannel heat exchangers underscores their significance as a crucial element in efficiently cooling electronic components, particularly at low flow rates. Based on the experimental data, distinct correlations emerge among temperature differentials, overall thermal resistance, and average heat transfer coefficients.

The presented research has made progress in describing sea spray and understanding the associated processes in terms of its physical properties, as well as the resulting fluxes from the ocean to the atmosphere, its influence on the development of ocean storms, and related problems and issues. The main results were obtained during laboratory experiments on wind-wave flumes using high-speed photography. Descriptions of studies related to the identification of the dominant type of spray generation (the bag-breakup type) and the statistics of these phenomena in a wide range of conditions depending on the wind-wave Reynolds number characterizing small-scale processes are given. Convolution of this statistics with the droplet size distribution from a single phenomenon of spray generation of the specified type, obtained from data of a special experiment, yields the spray generation function.

The paper presents the results of dilatometric measurements for thermal expansion of monocrystalline silicon for the temperature range of 100 – 1373 K. The temperature dependencies for thermal properties of material are calculated. The look-up tables for a wide temperature range for a solid state are calculated.

A simple CFD modeling method is presented which is adapted for a problem of liquid atomization by a pressure swirl nozzle. The method is based on the VOF method and several assumptions; this approach enables calculating the spray characteristics during a reasonable computation time. The primary testing results confirmed the possibility of using this simulation method.

Based on the previously developed method for constructing the equation of state (EOS) for liquid and vapor, the thermodynamically consistent analytical equation of state for liquid and gaseous nitrogen (in the molecular phase) is obtained. While constructing the equation of state, the Mie – Gruneisen form was used as a sum of potential and thermal components for pressure and internal energy. The potential components are described by a potential of the Born–Meyer type. For the thermal components, a simplifying approximation is adopted that follows from the condition for the constant average heat capacity and the dependence of Gruneisen function on the volume. When deriving the equation of state for nitrogen vapor and liquid phases, the tables calculated from equations approximating experimental data on isothermal compressibility, adiabatic speed of sound (including the critical region and phase equilibrium line) were used. The obtained equation of state for nitrogen can be useful in studying the phenomena associated with the processes of nitrogen evaporation and condensation in multiphase flows. This modeling takes into account the interfacial heat and mass transfer under conditions of low pressures and cryogenic temperatures.

Results of experimental measurements of aerodynamic forces acting on a finite-size cylindrical body in a compressible flow are reported. The flow around a transversely aligned cylinder and the influence of yaw angle variation in the interval β = 0 – 9° are studied. For each position of the cylinder, several locations of the blowing hole along the cylinder radius are considered. The force measurements are performed with the use of strain gauges. The changes in the drag force, lift force, yaw moment, and roll moment are investigated. New experimental data are obtained in the study on the influence of blowing on aerodynamic characteristics of a finite-size cylindrical body in a compressible flow. The data are analyzed and interpreted.

The effect of peripheral flow swirling in a cylindrical channel on the local flow structure and heat transfer in a turbulent gas-droplet flow was numerically studied with variations in the initial mass concentration of water droplets in the range M_L1 = 0 – 0.1 and the initial droplet diameter d₁ = 10 – 100 µm. It is shown that adding droplets leads to a significant increase in heat transfer (more than 2.5 times) in comparison with a single-phase swirling flow. The heat transfer patterns in gas-droplet flows with and without swirling are qualitatively similar. The effect of heat transfer intensification due to gas-droplet flow swirling reaches 50 % at M_L1 = 0.1. Initially, with an increase in the droplet size, a significant intensification of heat transfer in the swirling flow occurs. Maximum heat transfer is obtained at d₁ ≈ 50 µm for all swirling intensities of the two-phase flow. Then the value of heat transfer decreases and its dependence on the droplet size becomes more gradual.