Flow Physics Facility Drag Plate Design and Validation

This project involves the design and validation of a drag plate for the Flow Physics Facility (FPF) at University of New Hampshire. The purpose of this sensor is to accurately measure the wall shear stress in turbulent flows up to high Reynolds numbers. The wall shear stress is a primary contribution to the drag force on streamline bodies, such as aircraft. By reducing this force airlines could save tens of billions of dollars per year. The wall shear stress measurement is also used to obtain the friction velocity, which is a scaling number needed in turbulence theory. The completion and validation of the drag plate will allow for future research in these areas of importance. The drag plate was built to be lightweight, rigid, and differentially ballasted replacing the previous drag plate that was heavy, required many people to and equipment to setup, used a glycerin liquid to float, and could not be easily modified. These features allow for easy installation and modification, frictionless movement in water, and it to be level with the surrounding tunnel floor. Validation procedures using a velocity profile using a pitot static tube and Preston tube experiment at wind speeds ranging from 6 m/s to 10 m/s were compared to the wall shear stress found using the drag plate at the same wind speeds at a location of 59 m from the start of the wind tunnel test section. Here we report on the performance of the drag plate, and the experimental procedures developed for its use to accurately determine the surface shear stress