Thermal Analysis And Flow Field Simulation Of An Unmanned Helicopter Main Gearbox

In the long flight of unmanned helicopter,the friction pairs such as gears and bearings of the main gearbox will produce a lot of friction heat.Sufficient lubrication and reasonable heat dissipation structure can effectively reduce the operating temperature of the main gearbox and improve the performance of the unmanned helicopter.At the same time,the unmanned helicopter has no cockpit restrictions,and its aerodynamic layout and structure design are more free.It can further reduce the working temperature of the main gearbox by improving the air distribution around the main gearbox.In order to reduce the working temperature of the main gearbox,researches are carried out based on the thermal network method and the Fluent.The main contents are as follows:(1)The calculation methods of heat generation of gear,bearing and other heating parts and the calculation methods of convective heat transfer coefficient of gear,bearing,shaft and main gearbox case are described in detail.The calculation software of power loss and convective heat transfer coefficient of gear is designed.The influence of gear speed,lubricant viscosity and oil immersion depth on meshing power loss and convective heat transfer coefficient are studied by numerical example analysis.(2)The generation of the heat source,the heat conduction resistance and the convective heat transfer resistance are calculated under a given working condition.The steady-state heat balance equations are listed according to the thermal network diagram,and the steady-state temperature distribution of the main gearbox is obtained by solving the equations.On the basis of theoretical research,the thermal analysis software of the main gearbox is developed based on modularization.The interface of the software supports visual parameter input and graphical and textual display of the results.By comparing and analyzing the results of temperature field of gears and bearings in domestic and foreign literatures,it is proved that the study is reliable.(3)The fluid model in the main gearbox cabin is established,then the grid is divided by ICEM,and the grid is imported into Fluent.The external flow field and temperature field of the main gearbox of unmanned helicopter are simulated by using the fan model and radiator model of Fluent.The influence of the inlet air velocity on the direction of air flow passing through the fan and the temperature of the main gearbox is analyzed.By adjusting the shape of the guide hood,the distance between the fan,the main gearbox and the distance between the radiator and the fan,the cooling system of the main gearbox is simulated and analyzed,and the temperature distribution of the radiator under different schemes is obtained,which provides a reference for improving the heat dissipation performance of the main gearbox cooling system.