Introduction

Table of Contents

• xFoil AIM Overview
• Assumptions
  • Airfoils in ESP
• Examples

xFoil AIM Overview

A module in the Computational Aircraft Prototype Syntheses (CAPS) has been developed to interact (through input files) with the subsonic airfoil analysis tool xFoil [1]. xFoil is an open-source tool and may be freely downloaded from http://web.mit.edu/drela/Public/web/xfoil/ . At this time only a subsection of xFoil's capabilities are exposed through the AIM. Furthermore, only version 6.99 of xFoil have been tested against.

An outline of the AIM's inputs and outputs are provided in AIM Inputs and AIM Outputs, respectively.

Upon running preAnalysis the AIM generates two files: 1. "xfoilInput.txt" which contains instructions for xFoil to execute and 2. "caps.xfoil" which contains the geometry to be analyzed.

The xFoil AIM can automatically execute xfoil, with details provided in AIM Execution.

Assumptions

xFoil inherently assumes the airfoil cross-section is in the x-y plane, if it isn't an attempt is made to automatically rotate the provided body.

Airfoils in ESP

Within OpenCSM there are a number of airfoil generation UDPs (User Defined Primitives). These include NACA 4 series, a more general NACA 4/5/6 series generator, Sobieczky's PARSEC parameterization and Kulfan's CST parameterization. All of these UDPs generate EGADS FaceBodies where the Face's underlying Surface is planar and the bounds of the Face is a closed set of Edges whose underlying Curves contain the airfoil shape.

Important Airfoil Geometry Assumptions

• There must be a Node that represents the Leading Edge point
• For a sharp trailing edge, there must be a Nodes at the Trailing Edge
• For a blunt trailing edge, the airfoil curve may be open, or closed by a single Edge connecting the upper/lower Nodes
• For a FaceBody, the airfoil coordinates traverse counter-clockwise around the Face normal. The OpenCSM REORDER operation may be used to flip the Face normal.
• For a WireBody, the airfoil coordinates traverse in the order of the loop

Note: Additional spurious Nodes on the upper and lower Edges of the airfoil are acceptable.

It should be noted that general construction in either OpenCSM or even EGADS will be supported as long as the topology described above is used. But care should be taken when constructing the airfoil shape so that a discontinuity (i.e., simply C⁰) is not generated at the Node representing the Leading Edge. This can be done by splining the entire shape as one and then intersecting the single Edge to place the LE Node.

Examples

An example problem using the xFoil AIM may be found at xFoil AIM Example .