A Study of a Wind Tunnel Measurement System for Unsteady Pressures Using Pneumatic Transmission Lines

摘要

The application of pneumatic transmission lines theory to a tube-scanning valve system for unsteady pressure measurements in the AFIT 5-foot wind tunnel is investigated. Transfer gains of various tube-scanning valve configurations were experimentally measured and the validity of a theoretical model verified for a frequency range of 20 Hz to 140 Hz. The selected system having a 0.0625-in. ID flexible tube of 84 in. length connected to a scanning valve was installed in the wind tunnel. Unsteady pressures introduced over an 18 percent airfoil at zero angle of attack were measured with this system. Data were collected for 0, 40, 60, 80, 100, and 150 mph for a frequency range of 30 Hz to 55 Hz. Comparison of theoretical and experimental results for one data point revealed the dependence of the verification of the system measurement accuracy on the wind tunnel speeds and flow perturbation characteristics. Theoretical predictions were verified for 30, 35, and 40 hz only. (Author)