Doctor of Philosophy (PhD), Wright State University, 2011, Engineering PhD

Low Reynolds number boundary layer separation causes reduced aerodynamic performance in a variety of applications such as MAVs, UAVs, and turbomachinery. The inclusion of a boundary layer separation control system offers a way to improve efficiency in conditions that would otherwise result in poor performance. Many effective passive and active boundary layer control methods exist. Active methods offer the ability to turn on, off, or adjust parameters of the flow control system with either an open loop or closed loop control strategy using sensors. This research investigates the use of a unique sensor called Surface Stress Sensitive Film (S3F) in a closed loop, low Reynolds number separation control system. S3F is an elastic film that responds to flow pressure gradients and shear stress along its wetted surface, allowing optical measurement of wall pressure and skin friction. A new method for installing the S3F sensor to assure a smooth interface between the wall and wetted S3F surface was investigated using Particle Image Velocimetry techniques (PIV). A Dielectric Barrier Discharge (DBD) plasma actuator is used to control laminar boundary layer separation on an Eppler 387 airfoil over a range of low Reynolds numbers. Several different DBD plasma actuator electrode configurations were fabricated and characterized in an open loop configuration to verify separation control of the Eppler 387 boundary layer. The open loop study led to the choice of a spanwise array of steady linear vertical jets generated by DBD plasma as the control system flow effecter. Operation of the plasma actuator resulted in a 33% reduction in section drag coefficient and reattachment of an otherwise separated boundary layer. The dissertation culminates with an experimental demonstration of S3F technology integrated with a control system and flow effecter for closed loop, low Reynolds number separation control. A simple On/Off controller and Proportional Integral (PI) controller were used to clos (open full item for complete abstract)

Committee: Mitch Wolff PhD (Advisor); Rolf Sondergaard PhD (Committee Member); James Menart PhD (Committee Member); Mark Reeder PhD (Committee Member); Joseph Shang PhD (Committee Member) Subjects: Aerospace Engineering; Engineering; Fluid Dynamics; Mechanical Engineering

Doctor of Philosophy (PhD), Wright State University, 2007, Engineering PhD

This dissertation is a design and validation study of the high-lift low-pressure turbine (LPT) blade designated L2F. High-lift LPTs offer the promise of reducing the blade count in modern gas turbine engines. Decreasing the blade count can reduce development and maintenance costs and the weight of the engine, but care must be taken in order to maintain turbine section performance with fewer blades. For an equivalent amount of work extracted, lower blade counts increase blade loading in the LPT section. The high-lift LPT presented herein allows 38% fewer blades with a Zweifel loading coefficient of 1.59 and maintains the same inlet and outlet blade metal angles of conventional geometries in service today while providing an improved low-Reynolds number characteristic. The computational design method utilizes the Turbine Design and Analysis System (TDAAS) developed by John Clark of the Air Force Research Laboratory. TDAAS integrates several government-funded design utilities including airfoil and grid generation capability with a Reynolds-Averaged Navier-Stokes flow solver into a single, menu-driven, Matlab-based system. Transition modeling is achieved with the recently developed model of Praisner and Clark, and this study validates the use of the model for design purposes outside of the Pratt & Whitney (P&W) design system where they were created. Turbulence modeling is achieved with the Baldwin and Lomax zero-equation model. The experimental validation consists of testing the front-loaded L2F along with a previously designed, mid-loaded blade (L1M) in a linear turbine cascade in a low-speed wind tunnel over a range of Reynolds numbers at 3.3% freestream turbulence. Hot-wire anemometry and pressure measurements elucidate these comparisons, while a shear and stress sensitive film (S3F) also helps describe the flow in areas of interest. S3F can provide all 3 components of stress on a surface in a single measurement, and these tests extend the operational envelope of the (open full item for complete abstract)

Committee: Mitch Wolff (Advisor) Subjects: