C.F.D. SIMULATION OF TAKE OFF OFAN AMPHIBIAN AIRCRAFT UNDER VARIOUS ATMOSPHERIC CONDITIONS

Abstract

Amphibious aircrafts are specialised aircrafts designed to operate on both water and land. They are capable of taking-off and landing on water as well as air. Compared to conventional airplanes, these are small in size and have low aerodynamic efficiency. Relatively they are heavier due to additional components which are used to provide amphibian characteristics. Additional components impose weight and drag. Compared to helicopters, they are efficient and provide long range operations. In this article, CFD analysis of LISA Akoya, a French commercial amphibious aircraft is done. Solid geometry is created using SOLID WORKS. Using ANSYS 15.0 with VOF model, k-w SST model for turbulence, and its motion on water surface and take-off process is simulated. Its motion during process of landing is also simulated but main focus is on take-off analysis. Total drag forces on aircraft are calculated at different speeds, different meshes and different degrees of freedom throughout the simulations. Owing to dynamic mesh, it is quite a complicated Fluid Structure Interaction problem. To overcome difficulties faced in such a problem, care is taken in choosing correct parameters: like mesh size, time step, relaxation factors and solvers to provide accurate and converging solution. Using Volume of Fluid method to trace air-water interface and Dynamic mesh requires precise values of setup parameters. Otherwise solution diverges or shows negative mesh volume error. Drag force variation during take-off follows expected curves and pressure contours are plotted for the process. Grid-independence test is done for steady state cruising analysis of aircraft. Using three levels of meshes it is found that force values are close to each other. Drag coefficient is also calculated using this analysis and its value is comparable to classical seaplanes. Their values are available through literature review.