Novel measurement techniques for the study of unsteady flow phenomena: Shear sensitive paint and pressure sensitive microspheres

The goal of this project was to develop novel techniques for the measurement of unsteady, or turbulent, flow phenomena. The project involved two parts: the first being the development of a shear stress sensor based upon real time dynamic birefringence measurements of a liquid crystal coating, and the second being the development and application of pressure sensitive polystyrene microspheres that can simultaneously measure pressure and velocity within aerodynamic flows. The shear stress sensor is a combination of a chiral nematic liquid crystal coating that exhibits birefringence that changes upon application of a shear flow. The change in birefringence is measured in real time using a new instrument known as Shearpol. Additionally, Shearpol is capable of determining the extinction angle of the sample, which reveals the direction of the applied shear stress. The theory behind Shearpol's operation, as well as its implementation towards shear stress measurements of a flow over a flat plate and an impinging wall jet are presented. The pressure sensitive polystyrene microspheres, known as PSBeads, are based upon pressure sensitive paint (PSP) technology. Here work is presented demonstrating the ability of PSBeads to measure changes in oxygen concentration in the gas phase between 0 and 25% using intensity-based measurements. In addition, it will be shown that lifetime-based measurements can provide pressure data with a precision of 0.1 to 1% of 1 atm. Interrogated flows include emanating jets containing varying levels of oxygen concentrations, as well as flow trapped within the walls of square syringe as the plunger of the syringe is moved in and out. A shock tube facility was also constructed to determine the response time of PSBeads to large pressure jumps. The polystyrene-based PSBeads displayed a response time of 3.15 ms. A new generation of pressure sensitive silicon dioxide microspheres were also tested, and their response times were found to be between 13.6 and 18.9mus.