Analysis Method of Transient Temperature Field for Fuel Tank ofHigh-Altitude Large UAV

Based on the analysis of factors affecting transient temperature field of aircraft fuel tank and coupled heat transfer mechanism, a mathematical model of transient coupled heat transfer, including the dynamic- change of fuel quality, the internal heat transfer, the external aerodynamic convection and the radiation heat transfer, is established. Taking the aerodynamic convection and radiation heat transfer outside the tank as the third kinds of thermal boundary conditions for the thermal analysis of the fuel tank, calculation of internal and external coupling heat of fuel tank is decoupled. Ther^nal network method combined with hierarchical dynamic- grid is used to deal with the fuel consumption, and carry on the heat transfer analysis of the fuel tank. The numerical method for the transient temperature field of aircraft fuel tank is established. Through the simulation calculation, the transient temperature distribution of the fuel tank under different flight conditions is obtained, and the influence of the fuel mass and the external thermal environment on the temperature field is analyzed.

Numerical exploration on the thermal invasion characteristics of two typical gap-cavity structures subjected to hypersonic airflow

In this paper,numerical investigation of hypersonic gas flow over two typical gap-cavity structures is carried out using all-speed preconditioned density-based solver.Such structures filled with porous seal in the gap are often present at the joint locations of control surfaces of the hypersonic vehicles.Single-domain approach is adopted to integrate the governing equations for both porous and fluid regions.The basic thermal invasion characteristic is first illustrated using the maze gap-cavity structure without sealing.Then,the influence of seal filling depth on the thermal invasion characteristic is investigated for the structure with sealing.Finally,a comparison of thermal invasion characteristics between maze and straight gap-cavity structures is performed to examine the influence of gap bending.Results show that the main source of hot airflow invading into the gap is from the millimeter scale gas layer within the boundary layer.And the invasion characteristic presents approximate stationary behavior.A primary vortex occurs in the gap adjacent to the leeward wall,which is ascribed to the impinging effect between the separate boundary flow and the windward wall.This effect is also the main driving force of thermal invasion.A treatment of filling the seal in certain depth inside the gap can significantly reduce the thermal load of seal and maintain an acceptable level of the invading mass flow rate.Additionally,it is found that the gap bending exerts a limited block effect on the thermal invasion without sealing,and this effect can be ignored with sealing.These results can provide a reference for optimizing the seal gap-cavity structure configuration.

Thermal conductivity of micro/nano-porous polymers: Prediction models and applications

Micro/nano-porous polymeric material is considered a unique industrial material due to its extremelylow thermal conductivity, low density, and high surface area. Therefore, it is necessary to establishan accurate thermal conductivity prediction model suiting their applicable conditions and provide atheoretical basis for expanding their applications. In this work, the development of the calculationmodel of equivalent thermal conductivity of micro/nano-porous polymeric materials in recent yearsis summarized. Firstly, it reviews the process of establishing the overall equivalent thermal conductivity calculation model for micro/nanoporous polymers. Then, the predicted calculation models ofthermal conductivity are introduced separately according to the conductive and radiative thermalconductivity models. In addition, the thermal conduction part is divided into the gaseous thermalconductivity model, solid thermal conductivity model and gas-solid coupling model. Finally, it isconcluded that, compared with other porous materials, there are few studies on heat transfer of micro/nanoporous polymers, especially on the particular heat transfer mechanisms such as scale effectsat the micro/nanoscale. In particular, the following aspects of porous polymers still need to be furtherstudied: micro scaled thermal radiation, heat transfer characteristics of particular morphologies at thenanoscales, heat transfer mechanism and impact factors of micro/nanoporous polymers. Such studieswould provide a more accurate prediction of thermal conductivity and a broader application in energyconversion and storage systems.