Project Abstract

Abstract
Aerodynamic analysis plays a crucial role in the design of various engineering systems such as aircraft, automobiles, and wind turbines. The ability to accurately predict aerodynamic forces and moments is essential for optimizing the performance and efficiency of these systems. In this project, we developed a preliminary design tool for aerodynamic analysis that combines computational fluid dynamics (CFD) simulations with empirical methods to provide rapid and accurate predictions of aerodynamic performance. The preliminary design tool consists of two main components a CFD solver and an empirical database. The CFD solver is used to compute the flow field around the geometry of interest and calculate the aerodynamic forces and moments. The empirical database contains correlations and empirical formulas that relate the geometric parameters of the system to its aerodynamic performance. By coupling these two components, the preliminary design tool is able to leverage the accuracy of CFD simulations while reducing the computational cost associated with detailed simulations. To validate the accuracy of the preliminary design tool, we conducted a series of case studies on airfoil shapes and vehicle bodies. The results of these case studies demonstrated that the tool was able to predict aerodynamic forces and moments with good accuracy compared to experimental data. Additionally, the tool was able to provide design recommendations for improving the aerodynamic performance of the systems under study. Furthermore, the preliminary design tool was used to optimize the aerodynamic performance of a small-scale unmanned aerial vehicle (UAV). By varying the geometric parameters of the UAV, the tool was able to identify an optimal design configuration that minimized drag and maximized lift. This optimization process showcased the capability of the tool to assist engineers in quickly exploring design alternatives and identifying the most efficient configurations. Overall, the developed preliminary design tool represents a valuable asset for engineers and designers working on aerodynamic analysis and optimization. By combining the strengths of CFD simulations and empirical methods, the tool provides a practical and efficient approach for predicting aerodynamic performance and guiding the design process. Future work will focus on expanding the capabilities of the tool to include more complex geometries and flow conditions, as well as integrating it into existing design workflows for seamless integration into engineering practice.

Project Overview

The aim of this study was to develop a potential flow calculation model which includes computation of flow around aircraft bodies (fuselage, engines) and a boundary layer method which calculates the viscous effects over the aircraft wings. The models developed will be merged with an already existing panel program developed by Saab, Linköping, Sweden.

Different methods have been studied but the basis of this work has been to develop a model using a panel method which can provide results from a simple geometry description, with short calculation time and hence be used in early design phases. In this thesis Matlab has been used as programming language, ensure that future development and maintenance is possible.

The body model uses a panel method where the flow domain is divided into an inner and an outer part where the outer problem uses a three dimensional panel description while the inner problem performs two dimensional calculations. The inner and outer problems are separated by an arbitrarily shaped reference box. The inner area is divided into a number of cross sections which are described by line segments. With the help of these the two dimensional cross flow is obtained. This result is connected to the outer part through boundary conditions and the entire three dimensional flow domain can be determined.

The resulting body program is limited to aircraft bodies with a slenderness ratio less than 1/5. Higher values violate the model assumption. The number of cross sections needed to describe a body of one unit length is between 80-150 and the number of line segments needed for one cross sections is 20 for the inner boundary and 40 line segments for the outer. This configuration gives results with acceptable accuracy within a computation time less than 15 seconds/body.

The viscous effects around the aircraft wings are modelled with a two dimensional boundary layer model where the boundary layer displacement thickness over the wing profile is calculated with two different methods depending on if the flow in the boundary layer is laminar or turbulent. The computed displacement thickness is then added to the wing profile geometry and new pressure distributions are computed on the modified geometry.

The computed pressure distributions including the viscous effects show better agreement with results from experimental wind tunnel tests than the inviscid without boundary layer contribution. Separation is not modelled and neither are the large effects this has on the pressure distribution. The model gives usable results up to 15-20 degrees angle of attack; at higher angles the separated regions are so large that the model is not valid anyway.