Efficient finite element methods for aircraft engine noise prediction

Abstract

Aircraft noise has a negative environmental impact. One of the ways in which it can be mitigated is by placing acoustic liners inside the aircraft's engines. These liners can be optimised for noise reduction. A cost effective way to optimise acoustic liners is to make use of numerical modelling. However, there is room for improvement of the efficiency of current modelling methods. This thesis is concerned with the efficient numerical prediction of noise emitted from modern aircraft engines. Four high order finite element methods are used to solve the convected wave equation, and their performances are compared. The benefit of using the hierarchic Lobatto finite element method to solve this type of problem is demonstrated. A scheme which optimises the efficiency of the high order method is developed. The scheme automatically chooses the most efficient order for a given element, depending on the element size, and the problem parameters on that element. The computational cost of using the standard quadratic finite element method to solve a typical engine intake noise problem, is compared to the cost of the proposed adaptive-order method. A significant improvement in terms of efficiency is demonstrated when using the proposed method over the standard method. Furthermore, a new formulation based on potential flow theory for the solution of vortex sheet problems (typically encountered when dealing with exhaust noise problems) is presented..

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