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Riley, Zachary BryceInteraction Between Aerothermally Compliant Structures and Boundary-Layer Transition in Hypersonic Flow
Doctor of Philosophy, The Ohio State University, 2016, Aero/Astro Engineering
The use of thin-gauge, light-weight structures in combination with the severe aero-thermodynamic loading makes reusable hypersonic cruise vehicles prone to fluid-thermal-structural interactions. These interactions result in surface perturbations in the form of temperature changes and deformations that alter the stability and eventual transition of the boundary layer. The state of the boundary layer has a significant effect on the aerothermodynamic loads acting on a hypersonic vehicle. The inherent relationship between boundary-layer stability, aerothermodynamic loading, and surface conditions make the interaction between the structural response and boundary-layer transition an important area of study in high-speed flows. The goal of this dissertation is to examine the interaction between boundary layer transition and the response of aerothermally compliant structures. This is carried out by first examining the uncoupled problems of: (1) structural deformation and temperature changes altering boundary-layer stability and (2) the boundary layer state affecting structural response. For the former, the stability of boundary layers developing over geometries that typify the response of surface panels subject to combined aerodynamic and thermal loading is numerically assessed using linear stability theory and the linear parabolized stability equations. Numerous parameters are examined including: deformation direction, deformation location, multiple deformations in series, structural boundary condition, surface temperature, the combined effect of Mach number and altitude, and deformation mode shape. The deformation-induced pressure gradient alters the boundary-layer thickness, which changes the frequency of the most-unstable disturbance. In regions of small boundary-layer growth, the disturbance frequency modulation resulting from a single or multiple panels deformed into the flowfield is found to improve boundary-layer stability and potentially delay transition. For the latter, transitional boundary-layer aerothermodynamic load models are developed and incorporated into a fundamental aerothermoelastic code to examine the impact of transition onset location, transition length and transitional overshoot in heat flux and fluctuating pressure on the response of panels. Results indicate that transitional fluid loading can produce larger thermal gradients, greater peak temperatures, earlier flutter onset, and increased strain energy accumulation as compared to a panel under turbulent loading. Sudden transition, with overshoot in heat flux and fluctuating pressure, occurring near the leading edge of the panel provides the most conservative estimate for determining the life of the structure. Finally, the coupled interaction between boundary-layer transition and structural response is examined by enhancing the aerothermoelastic solver to allow for time-varying transition prediction as a function of the panel deformation and surface temperature. A kriging surrogate is developed to reduce the online computational expense associated with transition prediction within an aerothermoelastic simulation. For the configurations examined in this study, panel deformation has a more dominant effect on boundary-layer stability than surface temperature. Allowing for movement of the transition onset location results in characteristically different panel deformations due to spatial variation in the thermal bending moment. The response of the clamped panel is more sensitive to the transition onset location than the simply-supported panel.

Committee:

Jack McNamara (Advisor); Jeffrey Bons (Committee Member); Datta Gaitonde (Committee Member); Sandip Mazumder (Committee Member); Benjamin Smarslok (Committee Member); S. Michael Spottswood (Committee Member)

Subjects:

Aerospace Engineering

Keywords:

hypersonic; boundary-layer stability; boundary-layer transition; aerothermoelastic; parabolized stability equations; surrogate modeling; kriging

Sohn, Ki-HyeonExperimental study of boundary layer transition with elevated freestream turbulence on a heated flat plate
Doctor of Philosophy, Case Western Reserve University, 1991, Mechanical Engineering
A detailed investigation to document momentum and thermal development of boundary layers undergoing natural transition on a heated flat plate was performed. Experimental results of both overall and conditionally sampled characteristics of laminar, transitional and low Reynolds number turbulent boundary layers are presented. Measurements were acquired in a low-speed, closed-loop wind tunnel with a freestream velocity of 100 ft/s and zero pressure gradient over a range of freestream turbulence intensities (TI) from 0.4% to 6%. The distributions of skin friction, heat transfer rate and Reynolds shear stress were all consistent with previously published data. Reynolds analogy factors for Reθ < 2300 were found to be well predicted by laminar and turbulent correlations which accounted for an unheated starting length. The measured laminar value of Reynolds analogy factor was as much as 53% higher than Pr-2/3. A small dependence of turbulent results on TI was observed. Conditional sampling performed in the transitional boundary layer indicated the existence of a near-wall drop in intermittency, pronounced at certain low intermittencies, which is consistent with the cross-sectional shape of turbulent spots observed by others. Non-turbulent intervals were obse rved to possess large magnitudes of near-wall unsteadiness and turbulent intervals had peak values as much as 50% higher than were measured at fully turbulent stations. Non-turbulent and turbulent profiles in transitional boundary layers cannot be simply treated as Blasius and fully turbulent profiles, respectively. The boundary layer spectra indicate predicted selective amplification of T-S waves for TI ~ 0.4%. However, for TI ~ 0.8% and 1.1%, T-S wave are localized very near the wall and do not play a dominant role in the transition process

Committee:

Eli Reshotko (Advisor)

Subjects:

Engineering, Mechanical

Keywords:

Boundary layer transition; Heated flat plate

Balla, Joseph V.Pressure-Sensitive Paint for Detection of Boundary Layer Transition
Master of Science, The Ohio State University, 2012, Aero/Astro Engineering
A polymer/ceramic pressure-sensitive paint (PSP) system was evaluated to detect the laminar -turbulent transition location. A preliminary investigation was completed at the Wright-Patterson Air Force Base Trisonic Gasdynamics facility on a flat plate designed specifically for this test. Reynolds number (3.6 — 8.9x106 /m) and Mach number (0.4 — 0.8) sweeps were completed for various angles of attack (-2° — -8°). PSP results were obtained using either a biluminophore or platinum porphyrin (PtTFPP) on a polymer/ceramic basecoat. Pressure fluctuation levels measured by Kulite pressure transducers were ~ 400 Pa for a frequency bandwidth of 0 – 50 kHz. Significant power was seen in the sub-10 kHz range, but any variation in fluctuations due to Mach or Reynolds number was seen in the 25—50 kHz range. Due to low signal levels the PSP response was recorded at <3 kHz. Due to the nature of the closed-loop tunnel, the model had reached thermal equilibrium prior to images being recorded, and the transition location could not be evaluated using the temperature channel of the biluminophore PSP. The laminar-turbulent transition location was detected using PC-PtTFPP PSP on a NASA HSNLF(1)-0213 airfoil at Mach 0.28 free-stream, chord Reynolds number of 1.8 million, and -6° angle of attack in the OSU 6” x 22” transonic wind tunnel. Thermal imaging was used for verification of the laminar-turbulent transition location. After evaluation of the PSP results and comparison with Kulite results, it was concluded that the PSP was not sensitive enough to pressure to detect transition using the surface pressure fluctuations, and that the laminar-turbulent transition location was seen by the PSP as a result of its temperature sensitivity.

Committee:

James Gregory (Advisor); Jeffrey Bons (Committee Member)

Subjects:

Aerospace Engineering

Keywords:

Pressure-sensitive paint; boundary-layer; transition