Wind Tunnel Data Acquisition System

Abstract

A team of mechanical engineering students at Western Kentucky University designed a subsonic wind tunnel data acquisition system through LabVIEW to analyze the forces acting on an object in external air flow. The experimental setup provides future fluid mechanics laboratory students a hands-on procedure to study aerodynamic forces such as lift and drag. The physical models tested include two 3D-printed cylinders and a NACA 0012 airfoil placed in the wind tunnel test section. The cylinder shape was chosen, because it provides a simple flow field that can easily be used to verify the accuracy of the system, and the NACA 0012 was selected for the simplicity of symmetric airfoil theory calculations. Pressure transducers were used to measure pitot tube velocity readings as well as the pressure at 16 points around the upper 180 degrees of the objects. The resulting pressure distribution on the surface of the bodies was then applied to calculate lift and drag forces acting on the objects. A force balance was also designed to securely mount objects in the wind tunnel while directly measuring the total lift and drag forces, calculating the moment about the leading edge, and monitoring the angle of attack. The force balance results can be used to verify the experimental results from the pressure distribution data. A LabVIEW program was written to communicate directly with data acquisition hardware (NI CompactDAQ), set experimental parameters such as air flow speed and sample rate, record data, and interpret the results through a single user interface. Inviscid theory was used to theoretically predict the ideal drag acting on the cylinder, and symmetric thin airfoil theory was used to predict the ideal lift acting on the airfoil. Along with theoretical models, CFD analysis was performed to simulate a controlled experiment and validate the experimental results. Though experimental data has not yet been collected, the LabVIEW code has been tested using simulated data, and the accuracy of the pressure transducers has been confirmed by comparing pressure readings to controlled manometer readings. The system is expected to provide accurate data limited to the maximum speed of the subsonic wind tunnel currently owned by the Thermofluids Laboratory at Western Kentucky University. Future improvements of this project could include purchasing a more capable wind tunnel to run experiments in the turbulent flow regime, as well as a larger test section to avoid error from wall effects. This experimental set up has laid the groundwork for a multitude of future studies. It can be used to observe aerodynamic forces acting on more complex NACA airfoil shapes, rotating plates, cylinders and spheres, wind turbine blades, ground vehicles, airplanes and more.