Doctor of Philosophy, The Ohio State University, 2024, Aerospace Engineering

Fluid-Structure Interactions (FSI) are a quintessential multi-disciplinary challenge, where the flowfield is influenced by the structure, and structural deformation is induced by the flow pressure. Computational and experimental research thrusts often seek to answer specific problems for specific configurations, offering observational answers to relatively complex problems. While there is a large body of work on FSI as a whole, the specific coupling mechanisms between the fluid and structural surface in the context of turbulent boundary layers (TBLs) in supersonic flows is an under-explored area of study. This dissertation details progress addressing this gap through cooperative consideration of high-fidelity simulations, classical semi-empirical models, analysis of the governing equations, and data-driven models. Large-Eddy Simulations (LES) of TBLs with static deformations are compared against classical semi-empirical models to characterize applicability to statically deformed surfaces for predicting loads transmitted from the boundary layer to the structure. Additionally, analysis of the governing equations, in conjunction with data-driven modeling, is used to extract a coherent link between structural deformation and the onset of local flow separations. Finally, a parametric study is carried out using Reynolds-Average Navier-Stokes (RANS) and Kriging surrogates to assess the impact of statically deformed surfaces on a downstream ramp. LES indicates that for a variety of deformations sized on the order of the incoming boundary layer, localized flow separation can develop. This leads to important flow modifications that are not readily captured with low-fidelity or semi-empirical models. Motivated by this, a first-order link between local flow separation and structural deformation parameters is established using the Momentum Integral Equation (MIE) combined with data-driven analysis. The curvature of the surface is identified as the dominant structural param (open full item for complete abstract)

Committee: Jack McNamara (Advisor); Datta Gaitonde (Advisor); Scott Peltier (Committee Member); Jen-Ping Chen (Committee Member); Lian Duan (Committee Member) Subjects: Aerospace Engineering

Doctor of Philosophy, The Ohio State University, 2022, Aerospace Engineering

Understanding the physics of the pressure fluctuations induced by high-speed turbulent boundary layers (TBLs) is of major practical importance. The fluctuating pressure on aerodynamic surfaces of flight vehicles determines the vibrational loading of the vehicles and often leads to damaging effects as fatigue and flutter. The freestream pressure fluctuations radiated from the tunnel-wall TBLs are responsible for the genesis of freestream acoustic noise in conventional (i.e., noisy) supersonic and hypersonic wind tunnels. In this manuscript, wall and freestream pressure fluctuations induced by high-speed TBLs were characterized by direct numerical simulations (DNS). The DNS database covered a broad range of flow conditions (Mach number of $M_\infty = 2.5-14$, wall-to-recovery temperature ratio of $T_w/T_r = 0.18-1.0$, Reynolds number of $Re_\tau=450-1172$) and geometric configurations (flat plate, sharp circular cone, two dimensional channel, realistic wind-tunnel nozzle). The DNS overcame multiple experimental difficulties and provided access to wall and freestream pressure statistics that were difficulty to obtain otherwise, including the root-mean-square fluctuations and higher order moments (skewness and flatness) , probability density function , two-point correlation, convection speed, and coherence function. The study yielded useful insights into the physics of the boundary-layer-induced pressure field and provided critical assessment to reduced-order models such as the Corcos theory for modeling the wall pressure and the eddy-Mach-wave radiation theory for predicting the freestream acoustic pressure.

Committee: Lian Duan (Advisor); Datta Gaitonde (Committee Member); Jack McNamara (Committee Member); Mei Zhuang (Committee Member) Subjects: Aerospace Engineering

Doctor of Philosophy, Case Western Reserve University, 2022, EMC - Aerospace Engineering

A series of experiments were performed at Mach 2.5 in a circular test section in an effort to characterize an impinging/reflected shock wave turbulent boundary layer interaction generated by a cone, and provide benchmark quality datasets for CFD validation without the pitfalls inherent in rectangular configurations. Three different cone angles were used in the experiments to study unseparated and separated interaction. Three dimensional interactions were also created by offsetting the cone from the test section centerline. The experiments included surface flow visualization, static wall and pitot pressure measurements, and normal hot-wire measurements. The hot-wire measurements were used to calculate mean mass fluxes and total temperatures, turbulence intensities, and a mass flux signal. A series of calculations were also performed, ranging from simple inviscid one-dimensional numerical methods to more complex three-dimensional RANS CFD were performed in an effort to show the gaps between these techniques and experimental data. Surface flow visualization and static pressure showed that the spatial extent of the shock wave turbulent boundary layer interaction increased with increasing cone angle. The maximum static pressure was found to also increase with increasing cone angle, and to vary with circumferential angle. In the asymmetric configurations, the maximum pressure was found when the shock generator was closest to the test section centerline. The probability density functions near the wall in the interaction region were found to be bimodal for the separated cases. Evidence of reflected shock unsteadiness was also seen as bimodal distributions in the probability density functions. The power spectral densities showed increased low frequency contributions in the separated regions, with a peak frequency one order of magnitude lower than the incoming intermittent boundary layer turbulence frequency. Downstream of the interaction, the reflected shock wave co (open full item for complete abstract)

Committee: Paul Barnhart (Advisor); Yasuhiro Kamotani (Committee Member); David Davis (Committee Member); Kenneth Loparo (Committee Member); Brian Maxwell (Committee Member) Subjects: Aerospace Engineering

Doctor of Philosophy, The Ohio State University, 2019, Aero/Astro Engineering

Recent experimental and computational investigations have provided a comprehensive phenomenological description of unsteadiness in nominally two-dimensional (2-D), spanwise homogeneous shock-wave/turbulent-boundary-layer interactions (STBLIs), including both the impinging-shock and compression-ramp configurations. However, a complete mechanistic description of unsteadiness from an objective dynamical systems perspective has been lacking. Furthermore, the STBLIs encountered in many aerospace applications are fundamentally three-dimensional (3-D), in which the separation structure and topology are profoundly different from those exhibited by 2-D interactions, rendering many of the conclusions derived for the latter inapplicable. This dissertation addresses the main knowledge gaps and advances the understanding of STBLI unsteadiness by providing: (1) an objective mechanistic description of unsteadiness in 2-D interactions, (2) a phenomenological description of unsteadiness in nominally 3-D interactions (swept interactions that are inherently not spanwise homogeneous), including the sharp-fin and swept-compression-ramp configurations, (3) an objective mechanistic description of unsteadiness in these 3-D interactions, and (4) a phenomenological description of unsteadiness in a representative compound 3-D interaction (a double-fin inlet/isolator configuration). The approach employs high-fidelity large-eddy simulations of various 2-D and 3-D STBLIs in the high-supersonic (Mach 2-4) speed regime. Simulation accuracy is ensured through extensive comparison with experimental data obtained from concurrent experimental campaigns at partner institutions. The phenomenological description of unsteadiness is then compiled from various analyses of the resulting, spatiotemporally varying, turbulent flow. These include spectra of the unsteady fluctuations, band-isolated fluctuation dynamics obtained through temporal filtering, reduced-order representations, correlations, and other (open full item for complete abstract)

Committee: Datta Gaitonde PhD (Advisor); Mohammad Samimy PhD (Committee Member); Jen-Ping Chen PhD (Committee Member) Subjects: Aerospace Engineering

Master of Science, University of Akron, 2018, Mechanical Engineering

This study numerically investigates the laterally heated vertical cylinder and the length scale associated with this reactor. For natural convection the important dimensionless characteristic is the Rayleigh number, which predicts the flow regime as laminar, transitional, or turbulent. The Rayleigh number is useful as a design tool for scaling a reactor. Up to this point the associated length scale has been assumed as various definitions of length and diameter and has not yet been thoroughly investigated. The current assumed definitions for the length scale: height, diameter, and volume to lateral surface area, are directly studied in a multi-dimensional (2D and 3D) numerical parametric study involving these length scales and aspect ratio (height/diameter). Other important characteristics such as the ratio of heating to cooling and thickness of the divider (insulator) between heating and cooling are also studied. The study begins with turbulent transient 2D axisymmetric simulations and proceeds to turbulent transient 3D simulations then compares the 3D and 2D simulations. Finally, 2D and 3D laminar simulations are investigated. Presented are the results of the fluid flow speeds, thermal environments, flow patterns, boundary layer thickness, boundary layer velocity, and normal probability density functions which provide a unique way of studying how the Rayleigh number is influenced by variables. The numerical simulations are examined for spatial step, time step, and relative convergence by a mesh study, time step study, and thermal analysis, respectively. The turbulence model used (k-ω SST) is based on recent published studies. All simulations were conducted with the commercially available software ANSYS FLUENT. Findings are discussed when they prove significant, and aid in developing a fundamental understanding of the physics occurring inside this reactor setup. The results indicate that the current the length scales assumed for this reactor are incorrec (open full item for complete abstract)

Committee: Braun Minel J (Advisor); Nicholas Garafolo G (Committee Member); Scott Sawyer (Committee Member); Abhilash Chandy J (Other) Subjects: Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 1979, Graduate School

Committee: Not Provided (Other) Subjects: Engineering

Doctor of Philosophy, The Ohio State University, 1976, Graduate School

Committee: Not Provided (Other) Subjects: Engineering

Doctor of Philosophy, The Ohio State University, 1976, Graduate School

Committee: Not Provided (Other) Subjects: Engineering

Doctor of Philosophy, Case Western Reserve University, 1992, Mechanical Engineering

A numerical investigation of the interaction of an incident oblique shock wave with a turbulent duct flow is presented. The investigation consisted of solving the three dimensional, unsteady, compressible, mass averaged Navier-Stokes equations. An implicit finite volume, lower-upper time marching code (RPLUS) has been employed and modified. A three dimensional Baldwin-Lomax turbulence model has been programmed in conjunction with the code. Computed results are obtained at Mach number 2.9 for a turning angle of 12.99 degrees and Reynolds number based on duct width of 1.36 × 107. Under various inlet conditions, the results clearly depict the flow characteristics including the shock structure, the separated flow region, the wall pressure distribution and the skin friction distribution. The findings provide a physical understanding of the three dimensional vortex structure of the flow in a duct in which a shock wave interacts with a turbulent boundary layer. The results show that the ratio of the boundary layer thickness to the duct width is the critical parameter in determining the separation structure. The computational results also show that the corner vortices and center separation structures are closely related. However, the non-uniformities and secondary flows in the approach boundary layer do not change the separation structure qualitatively.

Committee: Isaac Greber (Advisor) Subjects: Engineering, Aerospace

Doctor of Philosophy, Case Western Reserve University, 1991, Aerospace Engineering

An investigation of the structure and development of streamwise vortices embedded in a turbulent boundary layer was conducted in the test facility CW-22 at NASA Lewis Research Center. The vortices were generated by a single spanwise row of rectangular vortex generator blades. A single embedded vortex was examined, as well as arrays of embedded counter-rotating vortices produced by equally spaced vortex generators. Measurements of the secondary velocity field in the crossplane provided the basis for characterization of vortex structure. Vortex structure was characterized by four descriptors. The center of each vortex core was located at the spanwise and normal position of peak streamwise vorticity. Vortex concentration was characterized by the magnitude of the peak streamwise vorticity, and the vortex strength by its circulation. Measurements of the secondary velocity field were conducted at two crossplane locations to examine the streamwise development of the vortex arrays. Large initial spacings of the vortex generators produced pairs of strong vortices which tended to move away from the wall region while smaller spacings produced tight arrays of weak vortices close to the wall. The crossplane structure of embedded vortices is observed to be very s imilar to that exhibited by the two dimensional Oseen vortex with matching descriptors. Quantitative comparisons are established. A model of vortex interaction and development is constructed using the experimental results. The model is based on the structure of the Oseen vortex. Vortex trajectories are successfully modelled by including the convective effects of neighbors, and images to represent the wall. The streamwise decay of circulation is successfully modelled for the single vortex, and for large initial spacings, by accounting for the effects of wall friction. An additional mechanism associated with the turbulent stress field in the near vicinity of the vortex cores is postulated to explain the large losses in cir (open full item for complete abstract)

Committee: Isaac Greber (Advisor) Subjects: