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

MS, University of Cincinnati, 2016, Engineering and Applied Science: Aerospace Engineering

In an aircraft engine at high altitude, the low-pressure turbine (LPT) section can experience low-Reynolds number (Re) flows making the turbine blades susceptible to large separation losses. These losses are detrimental to the performance of the turbine and lead to a roadblock for “higher-lift” blade designs. Accurate prediction of the separation characteristics and an understanding of mitigation techniques are of the utmost importance. The current study conducts simulations of flow control techniques for the Air Force Research Laboratory (AFRL) L2A turbine blade at low-Re of 10,000 based on inlet velocity and blade axial chord. This blade was selected for its “high-lift” characteristics coupled with massive separation on the blade at low-Re which provides an excellent test blade for flow control techniques. Flow control techniques involved various configurations of vortex generator jets (VGJs) using momentum injection (i.e. jet blowing). All computations were executed on dual-topology, multi-block, structured meshes and incorporated the use of a parallel computing platform using the message passing interface (MPI) communications. A high-order implicit large eddy simulation (ILES) approach was used in the simulations allowing for a seamless transition between laminar, transitional, and turbulent flow without changing flow solver parameters. A validation study was conducted involving an AFRL L1A turbine blade which showed good agreement with experimental trends for cases which controlled separation in the experiments. The same cases showed good agreement between different grid sizes. The differences between experimental and numerical results are largely attributed to differences in the setup. That is, the simulation did not include freestream turbulence or wind-tunnel wall effects. The flow control study conducted for the L2A blade showed a small degree of separation control for jets placed just downstream (DS) of the separation point. A limited study was cond (open full item for complete abstract)

Committee: Kirti Ghia Ph.D. (Committee Chair); Rolf Sondergaard Ph.D. (Committee Member); Shaaban Abdallah Ph.D. (Committee Member); Urmila Ghia Ph.D. (Committee Member) Subjects: Aerospace Materials

Master of Science (M.S.), University of Dayton, 2020, Aerospace Engineering

Ice accretion is a primary operational flight hazard for which all FAA certified aircraft are evaluated. Due to the geometric limitation of icing research tunnels and the required icing studies performed prior to flight tests, a recommended scaling method by Anderson and Tsao is utilized to adapt icing tunnel parameters (such as the flow temperature, the test section flow velocity, the water droplet median volume diameter (MVD), the liquid water content (LWC), and the ice accretion time, τ, etc.), along with model scaling to ensure the ice accretion collected is representative of the full-scale ice formation. Previous results have indicated good geometric agreement between the ice accretions formed on a full-scale model and the ice accretions on a scaled model, using the recommended scaling method under Title 14 of the Code of Federal Regulations (CFR), Part 25, Appendix C envelope. However, with the addition of the Appendix O envelope, which includes a large range of Supercooled Large Drop (SLD) conditions, the scaling method needed to be revised. SLD conditions refer to large median volume diameter (MVD) droplet conditions ranging from 50μm to greater than 500μm in the Appendix O envelope and generate larger frontal ice shape variation along with larger ice accretion further aft on a model. Prior work by Anderson and Tsao evaluating the use of the ice shape scaling method for a limited range of SLD conditions, up to 190μm, was based on geometric similitude of the frontal ice shape between the full-scale and scale collected ice accretions within allowable tolerances. The geometries of the full-scale and scale model collected ice accretions show significantly greater geometric variation under SLD conditions than Appendix C conditions, especially in the feather region, the ice accretions aft of the main formation on the leading edge. This brings into question the scaling methods ability to preserve the aerodynamics associated with the full-scale ice shape including (open full item for complete abstract)

Committee: Sidaard Gunasekaran (Advisor); Joshua Heyne (Committee Member); Markus Rumpfkeil (Committee Member); Jenching Tsao (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

MS, University of Cincinnati, 2017, Engineering and Applied Science: Aerospace Engineering

CFD analysis of turbulent twin-impinging round jets was performed to establish the growth profile and velocity characteristics of resultant jet. To ensure that a high degree of confidence can be assigned to the planned multi-jet impingement simulations, a single axisymmetric jet was first numerically resolved and compared to published jet experiments results. This required the definition of inlet boundary condition of the jet to be accurately documented. To that end, a turbulent flow exiting a long circular pipe was first modelled and analyzed to ensure that the inlet boundary condition to a single axisymmetric jet was in good agreement with the experiments. Once, the development length based on mean velocity was calculated, the pipe flow at a Reynolds number of 7,500 was analyzed and compared with in house and published experimental data. It was observed that the solution using the SST turbulence model performs better than the solution obtained using the Realizable k-e model in the pipe domain. Once the analysis was completed, velocity and turbulence components at the outlet of the pipe were extracted and used as input for the single jet flow simulations. Single axi-symmetric round jet flow was analyzed using computational techniques and validated with experimental results to establish the suitable turbulence model for simulation of low Reynolds number jets exiting from fully developed pipe. It was observed that although all the turbulence models studied could closely predict the mean velocity field, they were not able to accurately predict the turbulence intensity distributions. From the models studied, it was concluded that SST k-? model was the best turbulence model for simulating low Reynolds number jet flow exiting from fully developed pipe. Based on the insight gained from single jet analysis, CFD analysis on turbulent impinging jets was performed. Multiple Reynolds numbers and impingement angles were considered for the study to gain better understanding (open full item for complete abstract)

Committee: Peter Disimile Ph.D. (Committee Chair); Shaaban Abdallah Ph.D. (Committee Member); Milind Jog Ph.D. (Committee Member) Subjects: Aerospace Materials

Doctor of Philosophy (PhD), Wright State University, 2013, Engineering PhD

Vortex structures and vortical formation in flapping flight are directly related to the force production. To analyze the connection between vortex structures and aerodynamic performance of flapping flight, we have developed highly efficient algorithms for large-scale flow simulations with moving and deforming bodies. To further understand the underlying mechanisms of force generation caused by the coherent structures of the vortex formation, a new analysis method has been developed to measure the influence of Proper Orthogonal Decomposition (POD) modes on aerodynamic forces. It is challenging to finish three-dimensional Direct Numerical Simulations (DNS) of insect flight in a limited amount of time. In the current work, the Modified Strongly Implicit Procedure (MSIP) has been implemented into an existing Computational Fluid Dynamics (CFD) solver, as a smoother for the multigrid method to solve the pressure equation and an iterative method to solve the momentum equation. The new solver is capable of performing a 17-million-mesh simulation within 10 days on a single core of an Intel i5-3570 chip at 3.4GHz, nearly 10 times faster than the traditional Line-SOR solver. Based on this numerical tool, the free flight of a dragonfly for eight-and-a-half wing beats is studied in detail. The results show that the dragonfly has experienced two flight stages during the flight. In a maneuver stage, wing-wake interaction generated by the fore- and hindwings attenuates the total force by 8% (peak value). In contrast, in an escape stage, the fore- and hindwings collaborate to generate force which is 8% larger than when they flap separately. Especially, the peak force on the forewing is significantly increased by 42% in a downstroke and this enhancement is known to associate with a distorted trailing edge vortex, as demonstrated by a theoretical model based on wake survey methods. The movement of the trailing edge vortex is a response to the motion of the hindwing. When the fore- (open full item for complete abstract)

Committee: Haibo Dong Ph.D. (Advisor); George Huang Ph.D. (Committee Member); Joseph Shang Ph.D. (Committee Member); Keke Chen Ph.D. (Committee Member); Aaron Altman Ph.D. (Committee Member) Subjects: Aerospace Engineering; Engineering; Fluid Dynamics

Master of Science in Engineering (MSEgr), Wright State University, 2012, Mechanical Engineering

Today's unmanned aerial vehicles are being utilized by numerous groups around the world for various missions. Most of the smaller vehicles that have been developed use commercially-off-the-shelf parts, and little information about the performance characteristics of the propulsion systems is available in the archival literature. In light of this, the aim of the present research was to determine the performance of various small-scale propellers in the 4.0 to 6.0 inch diameter range driven by an electric motor. An experimental test stand was designed and constructed in which the propeller/electric motor was mounted in a wind tunnel for both static and dynamic testing. Both static and dynamic results from the present experiment were compared to those from previous studies. For static testing, the coefficient of thrust, the coefficient of propeller power, and the overall efficiency, defined as the ratio of the propeller output power to the electrical input power, were plotted versus the propeller rotational speed. For dynamic testing, the rotational speed of the propeller was held constant at regular intervals while the freestream airspeed was increased from zero to the windmill state. The coefficient of thrust, the coefficient of power, the propeller efficiency and the overall efficiency were plotted versus the advance ratio for various rotational speeds. The thrust and torque were found to increase with rotational speed, propeller pitch and diameter, and decrease with airspeed. Using the present data and data from the archival and non-archival sources, it was found that the coefficient of thrust increases with propeller diameter for square propellers where D = P. The coefficient of thrust for a family of propellers (same manufacturer and application) was found to have a good correlation from static conditions to the windmill state. While the propeller efficiency was well correlated for this family of propellers, the goodness of fit parameter was improved by modifying t (open full item for complete abstract)

Committee: Scott K. Thomas PhD (Committee Chair); Haibo Dong PhD (Committee Member); Zifeng Yang PhD (Committee Member); Mitch Wolff PhD (Committee Member) Subjects: Aerospace Engineering; Engineering; Mechanical Engineering

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

Master of Science (M.S.), University of Dayton, 2008, Aerospace Engineering

Reynolds number, Strouhal number, and formation number are insufficient to quantify the flow properties of a flapping wing system. These parameters do not take enough information from the input variables into account. As part of the current study, the velocity profile and angle of attack were varied during a single pure plunge flapping stroke using an infinite aspect ratio flat plate. Although the velocity profile was either a constant velocity or quarter-sine velocity, the average Reynolds number was held constant at 3000. Strong differences in the flow structure, both qualitatively and quantitatively, were obtained. A new metric is proposed that is able to take these differences in the input variables into account. This metric utilizes the theory of maximum work potential and statistical regressions of the experimental data in order to obtain a model of the experimental parameter space. With this model, estimates of the desired outputs can be made given values for the inputs.The main portion of this study focuses on the differences in flow structure, using qualitative and quantitative techniques, due to finite aspect ratio and flapping about a hinge point. Data at various spanwise and chordwise locations were taken in order to analyze the leading edge, trailing edge, and tip vortices. A small study was also conducted on the effects of changing Reynolds number. It was found that for the infinite aspect ratio plate, using a quarter-sine velocity profile, instead of a constant velocity profile, enhances the production of circulation. Operating at a slight angle of attack (85° instead of 90°) also enhances circulation production; however, operating at a large angle of attack (60° instead of 90°) has the opposite effect due to pinch-off of both the leading and trailing edge vortices. Hinging the wing at the root and using a finite aspect ratio causes the constant velocity profile to produce higher values of circulation than the quarter-sine velocity profile. This trend (open full item for complete abstract)

Committee: Aaron Altman PhD (Advisor); Michael Ol PhD (Committee Member); Raymond Kolonay PhD (Committee Member) Subjects: Fluid Dynamics