Metodologia para análises aerodinâmicas de hélices

Abstract

Propellers are widely used for various purposes in our daily lives. They are rotating devices that can generate thrust for a system when coupled to an engine, or, when driven by the wind, capable of transforming its kinetic energy of rotation into another type of energy that is of interest to the user. Due to its importance, aerodynamic analyzes are necessary to assess the thrust and torque that the propellers are capable of absorbing or delivering. Among the tools available for this purpose, the computational fluid dynamics (CFD - Computational Fluid Dynamics) stands out, which was used because it is the most complete and capable to incorporate more information in the modeling process. In general, the main concerns with the use of CFD are found in the complexity of its geometry, which most of the time is not available by the manufacturer, in the generation of the mesh and in the use of the appropriate numerical methods to solve the problem. The use of CFD to obtain propeller thrust and torque is the main objective of this research. For this, the free and open software OpenFOAM was used. When it comes to this, the computational domain is subdivided into two subdomains, the rotating domain that comprises the propeller and a stationary external region. The computational tool must be able to capture the movement of the rotating domain of the propeller and transfer the information to the rest of the computational domain, which is stationary. At the interfaces between both, there is no perfect fit between the nodes and the elements from one mesh to the other. However, the numerical technique used ensures the correct transfer of information. In addition, due to the flow characteristics, turbulence models must be incorporated to represent the entire behavior of the system properly. The methodology proposed here consists of using the CFD and comparing the responses in terms of thrust and torque for some operational conditions of three examples of propellers. In comparisons, when relevant, boundary conditions and similar numerical techniques are adopted. There are also comparisons with results in a wind tunnel and with mathematical models to validate the methods and verify the quality of the results. In general, there was a good correlation between the results of this work and the literature. From these analyzes, it was possible to evidence the contribution of the methodology used for the aerodynamic analysis of propellers in comparison to other methodologies.