Airfoil Lift Calculation Using Wind Tunnel Wall Pressures

TL;DR

This paper presents an experimental wind tunnel method using wall pressures to calculate lift, analyzing its sensitivity to test section size, airfoil chord, and thickness, and validating its accuracy against reference data.

Contribution

It introduces a chord sensitivity parameter and establishes guidelines for optimal test section and airfoil sizing for the wall-pressure measurement method.

Findings

WPM method's accuracy depends on airfoil chord and thickness.

A chord sensitivity parameter ($CSP$) was formulated and validated.

WPM can effectively replace traditional lift measurement techniques.

Abstract

An experimental method to calculate lift using static pressure ports on the wind tunnel walls and its associated limits has been explored in this paper. While the wall-pressure measurement (WPM) technique for lift calculation has been implemented by other researchers, there is a lack of literature on the sensitivity of the WPM method to test section size, airfoil chord, and model thickness. Chord sensitivity studies showed that the airfoil chord plays an important role in the accuracy of the measurements and needs to be appropriately sized for a given test section dimensions for optimum performance of the WPM method. A chord sensitivity parameter ($CSP$) was formulated and a lower limit ($=0.025$) was established to relate the ideal chord-length to wind tunnel test-section dimensions to ensure best lift measuring capabilities. Finally, a combination of symmetric and cambered airfoils with thicknesses varying from $6\%-21\%$ were tested and successfully validated against reference data for a freestream chord Reynolds number range of 100,000 to 550,000. The WPM method was found to be sensitive to varying surface flow conditions and airfoil thickness and has been shown to be a viable replacement to traditional lift measurement techniques using load balances or surface pressure ports.