Date of Award

9-12-2019

Publication Type

Master Thesis

Degree Name

M.A.Sc.

Department

Mechanical, Automotive, and Materials Engineering

Keywords

Body Force, Design, Fan, Model

Supervisor

Defoe, J.

Rights

info:eu-repo/semantics/openAccess

Abstract

Modern aircraft design is seeing an increase in inflow distortions entering the engines as a consequence of modifying the size, shape, and placement of the engine and/or nacelle casing to increase propulsive efficiency and reduce weight and drag. This could take the form of increasing the fan diameter, which generally leads to a decrease in intake length to maintain lower nacelle weight, or fuselage-embedded engines. It is important to be able to predict how these changes will affect the external flow-fan interaction. High computational costs as well as a limited access to detailed fan geometry has impaired the ability of airframers to investigate these interactions. In this thesis, the objective is to present a process, which is used to create a simplified numerical model, known as a body force model, and which produces, within the framework of a fluid flow simulation, a desired fan performance without the need for detailed geometry. This body force approach uses volumetric source terms and a compressibility correction to model the blade rows. The main advantage of using this approach is that it allows for steady calculations to capture distortion effects; compared to traditional bladed unsteady calculations it reduces the computational cost by two orders of magnitude. The process determines the requirements for the fluid simulations using both a 1D analysis through the fan stage, as well as simplified blade camber shapes, and is enabled by making a series of simplifying assumptions. An example fan stage representative of one seen in modern large bypass ratio engines was created using this process, and was found to produce the desired performance to within 1%. The process is also used to create a stage which mimics the performance of NASA Stage 67. This newly created stage, as well as NASA Stage 67 are inserted into a nacelle and used to predict flow separation at varying crosswind speeds. The simplified stage was capable of reproducing the overall trends well; it over predicted the separation velocity by approximately 6% compared to NASA Stage 67.

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