Doctor of Philosophy (Ph.D.), University of Dayton, 2024, Engineering

With the increasing interest in electric vertical takeoff and landing air vehicles and small-scale Unmanned Air Vehicles, many novel design concepts favor the fixed-pitch-propeller as the primary propulsion system due to its simplicity and reliability. This expands the application scenario of the fixed-pitch propeller from axial forward flight to edgewise flight conditions. The current study investigated the changes in its performance when operating at higher incidence angle conditions as well as the proximity effects of the propellers in these conditions. It is hypothesized that the propeller performance under various conditions and proximities can be reasonably predicted by modeling the changes in the inflow angle of the propeller. This hypothesis was tested using three major steps. First, a relationship between inflow angle, propeller inclination angle, and advance ratio was established using a series of experimental investigations. Second, this relationship was used to predict the performance of two propellers in tandem configuration with various horizontal and vertical offset distances. Third, the same model was used to predict the ceiling effect of the propeller at different incidence angles and advance ratios. All experiments were conducted at the University of Dayton Low-Speed Wind Tunnel (UD-LSWT) Laboratory under its open jet configuration. Force-based experiments, flow visualization as well as phase-locked Particle Image Velocimetry (PIV) experiments were conducted for all investigations. The changes in propeller performance at various flight conditions were quantified and several normalization methods were successfully employed indicating the predictability of various propeller forces and moments. A novel propeller axial thrust prediction model was proposed considering the propeller performance as a summation of propeller-like components and wing-like component, with an overall error of less than 8.3%. Flow visualization and PIV results confirmed the (open full item for complete abstract)

Committee: Sidaard Gunasekaran (Committee Chair); Michael OL (Committee Member); Markus Rumpfkeil (Committee Member); Aaron Altman (Committee Member) Subjects: Aerospace Engineering

Master of Science (M.S.), University of Dayton, 2023, Aerospace Engineering

There has been a recent surge in the need for unmanned aerial vehicles (UAVs), drones, and air taxis for a variety of commercial, entertainment, and military applications. New aircraft designs put forth by companies have shown to feature multiple lift producing surfaces and rotors acting in proximity to each other. These configuration choices are primarily informed by the “compactness” requirement in the design. For this reason, configurational choices are being considered that would otherwise not receive attention. Multi-wing configurations or distributed lift systems become a compelling choice in conceptual design of future UAVs and private air vehicles (PAVs) that complements the vertical takeoff and landing capabilities of the design. For multi-wing configurations to be considered in the early conceptual design process, the reliability of traditional lower order aerodynamic methods in predicting these aerodynamic effects must be determined. However, the nature of a highly distributed lift configuration, with 10 or more lifting surfaces in close proximity, does not lend itself to rapid or accurate viscous numerical solution. Moreover, highly distributed lift configurations drive individual lifting surface Reynolds numbers into a range where viscous interactions could have a profound effect on aerodynamic performance. As such, the degree of dependence of wing-wing interactions due to viscous effects could be determined in a first iteration through a reductionist approach. Focusing specifically on the three-dimensional viscous interactions and the aerodynamic forces on the upstream and downstream wings allows for a direct determination of the importance and isolated contribution of these effects. Proximity effects due to wing-wing interactions were experimentally quantified as a function of gap and stagger across a wide range of different relative angles of attack (decalage). The proximity effects and the zone of influence at different gap and stagger locations wer (open full item for complete abstract)

Committee: Sidaard Gunasekaran (Committee Chair); Aaron Altman (Committee Member); Michael Mongin (Committee Member); Markus Rumpfkeil (Committee Member) Subjects: Aerospace Engineering; Engineering; Mechanical Engineering

Master of Science, The Ohio State University, 2019, Aero/Astro Engineering

Active flow control (AFC) in the form of a wall normal slot was investigated on a NACA 643-618 laminar wing model. The wing model has a leading-edge sweep of (Λ = 30°) and tests were performed using a chordwise Reynolds number of 100,000 with a specific focus on the stall characteristics and changes in performance of an AFC slot with spanwise location. The study included comparing a passive boundary layer fence (BLF) and an AFC slot at the same spanwise locations: 0.60z/b, 0.70z/b, and 0.80z/b. Changing the location of the passive BLF resulted in increases in the maximum lift coefficient (CLMax) over the baseline ranging from 10.20-19.30%, with higher gains seen for fences closer to the root. The BLF at 0.60z/b experienced an unstable longitudinal static stability derivative (CMα) at an angle 13° higher than the baseline. Moving the fence outboard to 0.80z/b resulted in delaying this unstable behavior by an additional α=6°. An AFC slot was found to improve upon aspects of the BLF performance at all spanwise locations tested for a Cμ=10.33%. The slot was found to improve CLMax by up to 23.4% at the lowest spanwise location tested (0.60z/b) and this decreased to a 10.6% benefit at 0.80z/b. For the AFC slot, maximum lift performance increased monotonically as more momentum was introduced into the system. In all cases, moving the slot further outboard increased the stall angle. At all spanwise locations, the AFC slot outperformed the BLF in terms of delaying stall and an unstable CMα. Fluorescent tufts were used to visualize the surface flow for the baseline and AFC at all spanwise locations. The results corroborated the load cell findings and helped to visualize separation and spanwise flow at key angles of attack such as stall for the baseline wing. At higher angles of attack, evidence of the AFC slot could clearly be seen in the attached, streamwise flow directly outboard of the fence location. Evidence of a fence and tip vortices were also present for the (open full item for complete abstract)

Committee: Jeffrey Bons (Advisor); James Gregory (Committee Member) Subjects: Aerospace Engineering

Master of Science in Mechanical Engineering (MSME), Wright State University, 2018, Mechanical Engineering

High-lift low-pressure turbine blades produce significant losses at the junction with the endwall. The losses are caused by several complex three-dimensional vortical flow structures, which interact with the blade suction surface boundary layer. This study investigates the unsteady characteristics of these endwall flow structures on a highly loaded research profile and the adjacent endwall using surface-mounted hot-film sensors. Experiments were conducted in a low-speed linear cascade wind tunnel. The front-loaded blade profile was subjected to three different inlet conditions, consisting of two turbulence levels, and three incoming boundary layer thicknesses. Multiple surface-mounted hot-film sensors were installed throughout the passage. This thesis progressed in three stages of research. The first verified that the hot-film sensors could be used to detect flow structures in the cascade. The second used the results from installed hot-films to examine the unsteady characteristics of vortices formed near the leading edge and the propagation of the passage vortex across the passage where it interacts with a corner separation along the suction surface. Simultaneous measurements from the hot-film sensors were analyzed for frequency spectra and time lag in order to provide new insight into the endwall flow dynamics. Finally, signatures from the hot-films were linked to specific flow phenomena through concurrent flow visualization. At each stage of the investigation, results were compared to the results of a numerical simulation.

Committee: Mitch Wolff Ph.D. (Advisor); Rolf Sondergaard Ph.D., P.E. (Committee Member); Christopher Marks Ph.D. (Committee Member) Subjects: Aerospace Engineering; Engineering; Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2018, Aeronautical and Astronautical Engineering

The effect of passive and active boundary-layer fences (BLF) on a NACA 643-618 laminar wing (aspect ratio = 4.3) at a chordwise Reynolds number of 100,000 with sweep (lambda = 30°) is evaluated. The application of a passive BLF at z/b = 0.7 is responsible for an increase in the maximum lift coefficient (CL max) of 14.3%, a higher stall angle of attack (alpha) by 10°, and a delay in alpha by 16° where an unstable longitudinal static stability derivative (CMalpha) first occurs. The application of an active flow control (AFC) wall-normal steady blowing slot at z/b = 0.7 is responsible for an increase in CL max of 12.8%, a higher stall alpha by 17°, and a delay in alpha of 23° where an unstable CMalpha first occurs. Stereo-PIV results reveal that both configurations (passive BLF and AFC slot) create two vortices (a fence vortex and a tip vortex) which along with the physical fence itself are responsible for restoring lift outboard of the fence/slot, resulting in beneficial performance gains observed at higher alpha. Surface flow visualization via fluorescent tufts corroborates these findings. Duplicating (and even improving upon) the effects of passive flow control through active flow control allows for significant performance benefits at higher alpha (with AFC turned on), while avoiding the drag penalties of a passive fence by turning AFC off at lower a where control is unnecessary. Computational simulations of similar test configurations are performed match well with experimental results, further enhancing confidence of findings and showing promise for future predictive tools with respect to this form of active flow control as applied to a swept-wing.

Committee: Jeffrey Bons (Advisor); Mohammad Samimy (Committee Member); James Gregory (Committee Member) Subjects: Aerospace Engineering

Master of Science in Mechanical Engineering (MSME), Wright State University, 2016, Mechanical Engineering

Improvements in turbine design methods have resulted in the development of blade profiles with both high lift and good Reynolds lapse characteristics. An increase in aerodynamic loading of blades in the low pressure turbine section of aircraft gas turbine engines has the potential to reduce engine weight or increase power extraction. Increased blade loading means larger pressure gradients and increased secondary losses near the endwall. Prior work has emphasized the importance of reducing these losses if highly loaded blades are to be utilized. The present study analyzes the secondary flow field of the front-loaded low-pressure turbine blade designated L2F with and without blade profile contouring at the junction of the blade and endwall. The current work explores the loss production mechanisms inside the low pressure turbine cascade. Stereoscopic particle image velocimetry data, total pressure loss data and oil flow visualization are used to describe the secondary flow field. The flow is analyzed in terms of total pressure loss, vorticity, Q-Criterion, Reynolds' stresses, turbulence intensity and turbulence production. The flow description is then expanded upon using an Implicit Large Eddy Simulation of the flow field. The RANS momentum equations contain terms with static pressure derivatives. With some manipulation these equations can be rearranged to form an equation for the change in total pressure along a streamline as a function of velocity only. After simplifying for the flow field in question the equation can be interpreted as the total pressure transport along a streamline. A comparison of the total pressure transport calculated from the velocity components and the total pressure loss is presented and discussed. Peak values of total pressure transport overlap peak values of total pressure loss through and downstream of the passage suggesting that total pressure transport is a useful tool for localizing and predicting loss origins and loss development using (open full item for complete abstract)

Committee: Mitch Wolff Ph.D. (Advisor); Rolf Sondergaard Ph.D. (Committee Member); Rory Roberts Ph.D. (Committee Member) Subjects: Aerospace Engineering; Engineering

Master of Science in Mechanical Engineering, Cleveland State University, 2013, Fenn College of Engineering

The purpose of this thesis is to document the impact of incidence angle and Reynolds number variations on the 3-D flow field and midspan loss and turning of a 2-D section of a variable-speed power-turbine (VSPT) rotor blade. Aerodynamic measurements were obtained in a transonic linear cascade at NASA Glenn Research Center in Cleveland, OH. Steady-state data were obtained for ten incidence angles ranging from +15.8&00B0; to -51.0&00B0;. At each angle, data were acquired at five flow conditions with the exit Reynolds number (based on axial chord) varying over an order-of-magnitude from 2.12 &00D7; 10^5 to 2.12 &00D7; 10^6. Data were obtained at the design exit Mach number of 0.72 and at a reduced exit Mach number of 0.35 as required to achieve the lowest Reynolds number. Midspan total-pressure and exit flow angle data were acquired using a five-hole pitch/yaw probe surveyed on a plane located 7.0 percent axial-chord downstream of the blade trailing edge plane. The survey spanned three blade passages. Additionally, three-dimensional half-span flow fields were examined with additional probe survey data acquired at 26 span locations for two key incidence angles of +5.8&00B0; and -36.7&00B0;. Survey data near the endwall were acquired with a three-hole boundary-layer probe. The data were integrated to determine average exit total-pressure and flow angle as functions of incidence and flow conditions. The data set also includes blade static pressures measured on four spanwise planes and endwall static pressures.

Committee: Mounir Ibrahim PhD (Committee Chair); Miron Kaufman PhD (Committee Member); Ralph Volino PhD (Committee Member) Subjects: Aerospace Engineering; Mechanical Engineering