Master of Science, The Ohio State University, 2020, Mechanical Engineering

In order to keep turbine blade surface temperature below melting point in gas turbine engines, internal passages in blades must be used to route cooler air through the blade. Design optimization of cooling passages necessitates an understanding of heat transfer patterns to minimize cooling mass flow. This project compares two approximations used to determine the heat transfer rate inside cooling channels in both computational and experimental investigations. The two approximations used in this project are constant surface temperature and transient heating. In an operating engine, the accuracy of both these conditions are not guaranteed. During steady state operation, the blade can cycle through many different flow paths which will impart different temperatures across the surface, and at no time will a blade be under completely uniform temperature except for the starting cycle. However, to make measurements of heat transfer easier, the two assumptions mentioned beforehand are utilized extensively. The constant surface temperature method uses a heater attached to the back of a thin copper plate to hold the surface temperature at a constant value in air flow. In the transient full-field method, thermochromic liquid crystals, which change colors with temperature, are applied to flat plate and turbulated geometries to capture the change in wall temperature during heating and cooling processes. Heat transfer rates are then derived from the transient temperature data using a semi-infinite solid model. The constant temperature approach is better established than the transient method and produces significantly higher Nusselt numbers, but the transient method provides better spatial resolution. A numerical conjugate heat transfer model is used to further investigate the discrepancy between the methods. The experimental geometry is replicated for both methods to gain an understanding of the fluid dynamics in each setup and how they differ.

Committee: Randall Mathison Ph.D (Advisor); Michael Dunn Ph.D (Committee Member) Subjects: Aerospace Engineering; Mechanical Engineering

Master of Sciences, Case Western Reserve University, 2017, Geological Sciences

With many current and upcoming space missions exploring C-type asteroids, there is a need for understanding the physical properties of asteroid surface material. Adhesion forces (here including cohesion) are a key component of strength in small asteroids. Asteroid models are highly dependent on values for adhesion, but without in-situ or laboratory measurements on appropriate materials, values are assumed or derived. We conducted a series of experiments with NASA Glenn Research Center's “Adhesion Rig” - a custom instrument with a torsion balance in ultrahigh vacuum - to produce the first measurements of adhesion in asteroid-derived materials (CM2 meteorites). Five individual minerals were also tested to evaluate plausible terrestrial analogs for regolith and to understand the relevance of mineralogical variation observed among C-type asteroids. An average adhesion force of 89 µN was measured for CM2s; similar to previous estimates. None of the minerals tested were similar enough to be considered viable analogs.

Committee: Ralph Harvey (Advisor); Steven Hauck (Committee Member); Zhicheng Jing (Committee Member) Subjects: Geological; Geology; Mineralogy

Doctor of Philosophy, The Ohio State University, 2016, Mechanical Engineering

An experiment was performed at The Ohio State University Gas Turbine Laboratory for a film-cooled high-pressure turbine stage operating at design-corrected conditions, with variable rotor and aft purge cooling flow rates. Several distinct experimental programs are combined into one experiment and their results are presented. Pressure and temperature measurements in the internal cooling passages that feed the airfoil film cooling are used as boundary conditions in a model that calculates cooling flow rates and blowing ratio out of each individual film cooling hole. The cooling holes on the suction side choke at even the lowest levels of film cooling, ejecting more than twice the coolant as the holes on the pressure side. However, the blowing ratios are very close due to the freestream massflux on the suction side also being almost twice as great. The highest local blowing ratios actually occur close to the airfoil stagnation point as a result of the low freestream massflux conditions. The choking of suction side cooling holes also results in the majority of any additional coolant added to the blade flowing out through the leading edge and pressure side rows. A second focus of this dissertation is the heat transfer on the rotor airfoil, which features uncooled blades and blades with three different shapes of film cooling hole: cylindrical, diffusing fan shape, and a new advanced shape. Shaped cooling holes have previously shown immense promise on simpler geometries, but experimental results for a rotating turbine have not previously been published in the open literature. Significant improvement from the uncooled case is observed for all shapes of cooling holes, but the improvement from the round to more advanced shapes is seen to be relatively minor. The reduction in relative effectiveness is likely due to the engine-representative secondary flow field interfering with the cooling flow mechanics in the freestream, and may also be caused by shocks and other compr (open full item for complete abstract)

Committee: Randall Mathison (Advisor); Michael Dunn (Committee Member); Sandip Mazumder (Committee Member); Jeffrey Bons (Committee Member) Subjects: Aerospace Engineering; Engineering; Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2014, Mechanical Engineering

Three-passage serpentines with aspect ratios of 1:1, 1:2, and 1:6 were numerically studied using computational fluid dynamics and heat transfer. A CFD modeling methodology was systematically developed that balanced accurately resolving the flow physics with minimizing the computational cost, targeting industrial preliminary design requirements. The method was benchmarked against two published data sets consisting of turbulators on the leading and trailing walls in skewed 45 deg; to the flow offset parallel configuration with a fixed rib pitch to height ratio of 10 and a rib height to hydraulic diameter of 0.1 to 0.058, utilizing Reynolds numbers of 25,000 and 50,000 and rotation number ranging from 0 and 0.25. Predictions were completed to study the effects of changing aspect ratio between 1:1, 1:2, and 1:6 and changing rotation numbers from 0 to 0.3. The 1:6 aspect ratio predictions varied from the lower aspect ratios. Differences included flow recirculation along the leading wall of the first passage for rotation numbers greater than or equal to 0.2 and high Nusselt numbers immediately downstream of the turn for the wall opposite the Coriolis force direction. Overall enhancement values for the test section showed the aspect ratio has a greater influence on Nusselt numbers than rotation.

Committee: Michael Dunn Ph.D (Advisor); Jen-Ping Chen Ph.D (Committee Member); Randall Mathison Ph.D (Committee Member); Mohammad Samimy Ph.D (Committee Member); Jeffrey Rambo Ph.D (Committee Member) Subjects: Mechanical Engineering

Master of Sciences (Engineering), Case Western Reserve University, 2014, EMC - Mechanical Engineering

A macroscopic model of flow in a redox flow battery is developed. The model is a layered system comprised of a single passage of a serpentine flow channel and a parallel underlying porous electrode (or porous layer). As the fluid moves away from the entrance of the flow channel, two distinct fully developed flow regime evolve in the channel and the underlying porous layer, respectively. The effects of the inlet volumetric flow rates, permeability of the porous layer, thickness of the flow channel and thickness of the porous layer on the nature of the mass flow in the porous layer are investigated. The results show that, for a Reynolds number of 91.5 with the ideal plug flow inlet condition, the average filtration velocity decreases by a factor of about two as the number of carbon fiber paper layers is increased from 1 to 7. Significantly, reactant flow convection is found to estimate a corresponding maximum current density 403mA cm-2 and 742mA cm-2, which compares favorably with experiments of ~400mA cm-2 and ~750mA cm-2, for a single layer and three layers of the carbon fiber paper.

Committee: Iwan Alexander (Advisor); Robert Savinell (Advisor); Joseph Prahl (Committee Member); Donald Feke (Committee Member) Subjects: Aerospace Engineering; Chemical Engineering; Energy; Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2010, Mechanical Engineering

This work aims at developing linear mathematical models of single-mesh spur and helical gears mounted on compliant parallel shafts, and single span of a serpentine belt with pulleys also mounted on parallel compliant shafts. Both the geared shaft models are hybrid discrete-continuous ones where the gears modeled as rigid disks along with the mesh spring form the discrete elements while the elastic shafts having transverse as well as torsional flexibility constitute the continuous elements. The non-dimensional governing equations along with the natural boundary conditions are developed using the Hamilton's principle. The governing equations of the flexural and torsional shafts vibrations and the equations of motion of the disks are written in an extended operator form to prove the self-adjointness of the system. The assumed modes method is used to discretize the system equations where the matching conditions are incorporated with the use of Lagrange multipliers. Orthonormal global basis functions for flexure and torsion are chosen from separate families forming complete sets. The sensitivities of the natural frequencies of different modes to mesh stiffness, torsional and flexural rigidities of the shafts, and lengths of the shafts are examined and the results are correlated with the modal energy distributions. Excitation in the form of the loaded static transmission error at the gear mesh is identified and converted to the discretized form and the response for the same is calculated. Torsional spring at the gear mesh in the helical gear-shaft model accounts for the energy stored due to the relative tilting of the gears. The rotation speed is high and therefore, the gyroscopic effect is non-negligible. Hamilton's principle is used to obtain the non-dimensional governing equations and the equations of motion of the disks. Excitation in the form of the loaded static transmission error at the gear mesh is incorporated in the equations of motion. The extended operator fo (open full item for complete abstract)

Committee: Prof. Rama Yedavalli PhD (Advisor); Prof. Daniel Mendelsohn PhD (Advisor); Prof. Ahmet Kahraman PhD (Committee Member); Prof. Gary Kinzel PhD (Committee Member) Subjects: Engineering

Doctor of Philosophy, The Ohio State University, 2006, Mechanical Engineering

Serpentine belts are widely used for efficient power transmission in automobiles and heavy vehicles, but they suffer noise and wear problems that have their roots in system vibration. The primary goal of this work is to develop mathematical models for serpentine drives with nonlinear elements and implement vibration analysis to understand certain nonlinear dynamic behaviors and provide guidance for practical design. Nonlinear one-way clutches integrated with accessory pulleys are effective devices to decouple the motions of an accessory and its pulley during disengagements and mitigate the rotational pulley vibration problems. A mathematical model of a one-way clutch in belt-pulley systems is established, where a wrap-spring type of clutch is modeled as a nonlinear spring with discontinuous stiffness. Analysis of steady state and transient vibrations exhibits the mechanisms behind one-way clutches' effectiveness, and identifies where the one-way clutch works most effectively to reduce vibration and noise. The method of multiple scales is employed to approximate the steady-state periodic solutions. This study evaluates the validity of the perturbation method for such strong nonlinearity through comparison of analytical and numerical solutions. A one-way clutch that functions based on the relative velocity of the driven pulley and its accessory is common in applications. This type of one-way clutch is included in a hybrid continuum-discrete model incorporating span vibration and pulley rotation. The engagement/disengagement status transitions lead to a piece-wise linear system with alternate locked clutch and disengaged clutch configurations. The dynamic response and dynamic tension fluctuations are examined for varying system parameters. A tensioning system, consisting of a rigid arm pivoting around a fixed point and an idler pulley rotating at the free end of the arm, is typically used in belt drives to maintain belt tension as operating conditions change. Dry frict (open full item for complete abstract)

Committee: Robert Parker (Advisor) Subjects: Engineering, Mechanical

Doctor of Philosophy, The Ohio State University, 2004, Mechanical Engineering

Belt vibration and slip are primary concerns in the design of serpentine belt drives. Belt-pulley coupling is essential for the analysis. This work investigates issues to advance the understanding of belt-pulley mechanics. Closed-form eigensolution approximations for an axially moving beam with small bending stiffness are given. This model is the first order approximation for the transverse vibration of each span in a serpentine belt drive. Perturbation techniques for algebraic equations and the phase closure principle are used. The eigensolutions are interpreted in terms of propagating waves. For a complete serpentine belt drive, a hybrid continuous-discrete model is built. Incorporation of belt bending stiffness introduces linear belt-pulley coupling. This model can explain the transverse span vibrations caused by crankshaft pulley fluctuations at low engine idle speeds where other coupling mechanisms do not. For the steady state analysis, a novel transformation of the governing equations to a standard ODE form for general-purpose BVP solvers leads to numerically exact steady solutions. A closed-form singular perturbation solution is developed for the small bending stiffness case. A coupling indicator based on the steady state is defined to quantify the undesirable belt-pulley coupling. A spatial discretization is developed to find the free vibration eigensolutions. In contrast to prior formulations, this discretization is numerically robust and free of missing/false natural frequency concerns. New dynamic properties induced by bending stiffness are characterized. Dynamic response calculations using the discretized model follow naturally. The effects of major design variables are investigated. This provides knowledge to help optimize structural design, especially to reduce large belt transverse vibration. Finally, to better predict the belt-pulley contact interactions applicable to serpentine belt drives an improved model is established for the steady state mechan (open full item for complete abstract)

Committee: Robert Parker (Advisor) Subjects: Engineering, Mechanical