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

Master of Science, The Ohio State University, 2022, Aerospace Engineering

A review of recent publications regarding Martian rotorcraft aerodynamics and NASA's proposed design of a future Mars Helicopters was performed. Rotorcraft flight on Mars is a difficult feat to achieve because of the unique flight condition the vehicle is governed by: compressible, low Reynolds number flow (Re). Airfoil performance expeditiously drops once crossing into the low Reynolds number flow domain (i.e. Re < 10^5). Moreover, modeling airfoil performance at low Reynolds number for Mars rotor applications is complex to assess given the presence of Mach effects. There are few tools available to estimate performance of rotor systems in the Mars atmosphere, thus, a reduced order modeling method for Martian flight vehicle design is proposed. Tuning of a blade element momentum theory (BEMT) model will aid in providing performance estimates for this unique environment, which will be validated with experiments. The work presented in this thesis addresses numerical, computational, and experimental resources that were used to assess the aforementioned flow condition. BEMT is an inexpensive predictive modeling tool for estimating rotorcraft performance and was the primary analysis tool used in this study. BEMT relies on the equating of lifting momentum theory and circulation theory, and most importantly on high-fidelity 2-D airfoil performance look up tables. BEMT modeling for terrestrial applications has been well established, including many suggested corrections to the model for yielding better agreement between experimental and numerically estimated rotor performance. However, no BEMT correction has been suggested for compressible, low Reynolds number flow that governs the Martian rotocraft flight condition. Addressing the knowledge gap, along with the desire to rely on BEMT's relatively quick and modular analysis capability thus led to the research effort described herein. Although a proposed correction to BEMT for the aforementioned flow condition is not within (open full item for complete abstract)

Committee: Jeffrey Bons (Advisor); Matthew McCrink (Committee Member); Clifford Whitfield (Committee Member) Subjects: Aerospace Engineering

Master of Science, The Ohio State University, 2018, Aero/Astro Engineering

Small-scale rotors exhibit degraded aerodynamic efficiency, which has been linked to non-ideal losses within their wake. Many small unmanned aircraft systems (UAS) are powered by such rotors, and are currently at the forefront of aerospace research for a multitude of innovative applications. As such, a comprehensive understanding of their operational capabilities is critical for implementation in the field. A great deal of attention has been given to characterize the performance of large-scale rotor models. However, similar studies for small-scale, low Reynolds number (Re) applications has received relatively little attention. This work seeks to gather insight into the behavior of the rotor wake structures as a function of Re, relate this to performance capabilities and the corresponding far-field acoustic signature. Two-component particle image velocimetry (PIV), performance, and acoustic measurements were performed using three small-scale, NACA 0012 rotors operated over a range of low-Reynolds number conditions. Rotor geometry and operational speed (Ω) were varied to obtain the desired Re variation. Spanwise PIV has demonstrated an absence of tip vortex formation as the operational thrust coefficient (CT) is increased, suggesting the presence of outboard tip stalling. Phase-locked, chordwise PIV has confirmed this hypothesis, showing the development of flow separation and a highly turbulent downstream wake. Thrust and torque measurements show degraded rotor performance at the onset of these conditions, especially at low Re. A vortex identification scheme was used to locate downstream tip vortices and characterize their size, swirl velocity, and aperiodic wandering behavior for different operational conditions. When observed at constant wake age, the wandering motion of the vortices behaved independently of vortex Reynolds number (Rev) scaling. The normalized standard deviation of the tip vortex wander was found to match well with historically observed t (open full item for complete abstract)

Committee: James Gregory Ph.D (Advisor); Jeffrey Bons Ph.D (Committee Member); Matthew McCrink Ph.D (Committee Member) Subjects: Aerospace Engineering

Doctor of Philosophy, The Ohio State University, 2015, Mechanical Engineering

Flow control experiments were performed on a NACA 0015 airfoil in fully-reversed condition, which is anticipated to occur on the retreating blade side of advanced helicopters such as slowed-rotor compound rotorcraft. Control was achieved using nanosecond dielectric barrier discharge (NS-DBD) plasma actuators. The Reynolds number based on a chord length of 203 mm was fixed at 5.0 · 105, corresponding to a freestream velocity of ~38 m/s. Two angles of attack were considered: α = 0° and 15°, each of which is relevant to a particular implementation of slowed-rotor technology. At α = 0°, the flow resembles that of a flow behind a cylinder. A von Karman vortex street formed in the wake where alternating vortex shedding occurred at a Strouhal number of 0.12. Excitation was performed using an NS-DBD on one side of the airfoil, with plasma formation just upstream of the separation line. However, there was no discernible influence upon the baseline behavior. At α = 15°, fully separated flow on the suction side extended well beyond the airfoil with naturally shed vortices at a Strouhal number of 0.19. Plasma actuation was evaluated at both the aerodynamic leading-edge (ALE) and aerodynamic trailing-edge (ATE) of the airfoil. The flow responded to the plasma actuation at the ALE by generating organized coherent structures in the shear layer over the separated region. Moderate excitation around the natural shedding Strouhal number had the most significant effects: synchronizing the shedding from the ALE and ATE, creating moderately sized structures that convected far downstream, greatly reducing the separation area, increasing lift, and decreasing drag. Excitation at much higher Strouhal numbers resulted in the flow returning to its natural shedding state, but with less coherent structures that diffused in the wake. This reduced the separation area and significantly reduced drag. Plasma actuation at the ATE caused a reduction in the magnitude of the fundamental and harmon (open full item for complete abstract)

Committee: Mo Samimy (Advisor); Igor Adamovich (Committee Member); Datta Gaitonde (Committee Member); James Gregory (Committee Member) Subjects: Aerospace Engineering; Fluid Dynamics; Mechanical Engineering

Master of Science, University of Toledo, 2014, Mechanical Engineering

Helicopters and other Vertical Take-Off or Landing (VTOL) vehicles exhibit an interesting combination of structural dynamic and aerodynamic phenomena which together drive the rotor performance. The combination of factors involved make simulating the rotor a challenging and multidisciplinary effort, and one which is still an active area of interest in the industry because of the money and time it could save during design. Modern tools allow the prediction of rotorcraft physics from first principles. Analysis of the rotor system with this level of accuracy provides the understanding necessary to improve its performance. There has historically been a divide between the comprehensive codes which perform aeroelastic rotor simulations using simplified aerodynamic models, and the very computationally intensive Navier-Stokes Computational Fluid Dynamics (CFD) solvers. As computer resources become more available, efforts have been made to replace the simplified aerodynamics of the comprehensive codes with the more accurate results from a CFD code. The objective of this work is to perform aeroelastic rotorcraft analysis using first-principles simulations for both fluids and structural predictions using tools available at the University of Toledo. Two separate codes are coupled together in both loose coupling (data exchange on a periodic interval) and tight coupling (data exchange each time step) schemes. To allow the coupling to be carried out in a reliable and efficient way, a Fluid-Structure Interaction code was developed which automatically performs primary functions of loose and tight coupling procedures. Flow phenomena such as transonics, dynamic stall, locally reversed flow on a blade, and Blade-Vortex Interaction (BVI) were simulated in this work. Results of the analysis show aerodynamic load improvement due to the inclusion of the CFD-based airloads in the structural dynamics analysis of the Computational Structural Dynamics (CSD) code. Improvements came (open full item for complete abstract)

Committee: Chunhua Sheng Ph.D. (Advisor); Abdeh Afjeh Ph.D. (Committee Member); Ray Hixon Ph.D. (Committee Member); Glenn Lipscomb Ph.D. (Committee Member) Subjects: Aerospace Engineering; Fluid Dynamics; Mechanical Engineering