Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 111 for “"Unsteadiness"”.
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Unsteadiness in shock-wave/boundary layer interactions
… for better understanding of the low-frequency unsteadiness observed in shock<br/>wave/turbulent boundary layer interactions has been driving research in this area for<br/>several decades. This work investigates the interaction between an impinging oblique<br/>shock and a supersonic turbulent …
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Post-stall hysteresis and flow field unsteadiness on an NACA 0012 airfoil
… study was conducted to understand flow field unsteadiness associated with static stall hysteresis on an NACA 0012 airfoil at Rec = 1.0 × 10^6. Unsteady pressure measurements were acquired to evaluate the performance of the airfoil, and a hysteresis loop was identified in the vicinity of the …
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Effects Of Transport Properties And Flame Unsteadiness On Nitrogen Oxides Emissions From Laminar Hydrogen Jet Diffusion Flames
… determine how the fuel Lewis number and the flow unsteadiness play a combined role in maximum flame temperature and affect NOx emission from jet diffusion flame. The fuel Lewis number is varied by increasing/decreasing the mole fraction of diluents in the fuel stream. Therefore, maximum flame …
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An analytical and numerical study of the second-order effects of unsteadiness on the performance of turbomachines
Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1992.
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Characterization of Onset and Transition to Instability in Supersonic Retropropulsion
… (SRP) to understand the characteristics of shock unsteadiness and the parameters that determine transition to unsteady regimes. Data collected in the NASA Unitary Wind Tunnel were studied to determine instability characteristics in shocks as angle of attack, Mach number, and nozzle configuration …
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Active and Passive Flow Control over the Flight Deck of Small Naval Vessels
… that the use of porous surfaces decreases the unsteadiness of the flow field. Further improvements are found by injecting air through these porous surfaces, causing a reduction in unsteadiness in the landing region of 6.6% at 0 degrees wind-over-deck (WOD) and 8.3% at 20 degrees WOD. Other …
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Time-resolved heat flux measurements of the turbulent junction vortex system
… between the surface heat flux and the velocity unsteadiness. The study of this three-dimensional vortex system through time-resolved heat flux measurements is unique; as far as the author is aware, no previously published work has demonstrated the correlation between flow unsteadiness and its …
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High Fidelity Simulation of Loss Mechanisms in Compressors
… As a result, previously unexplored effects of unsteadiness can be simulated and their impact on loss understood. The work undertaken in this thesis aims to establish a framework for accurate loss predictions using scale-resolving simulations and inform the field with regards to the effects of …
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Unsteady modes in the flowfield about an airfoil with a leading-edge horn-ice shape
… array measurements. The maximum amount of unsteadiness in the iced-airfoil flowfield was observed to increase with increasing angle of attack. For a fixed angle of attack prior to stall, a change in the feature height of the simulated ice shape led to a change in the distribution of …
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Impeller-diffuser interaction in centrifugal compressors
… impeller tip leakage flow . In particular, the unsteadiness due to the upstream potential effect of the diffuser vanes led to larger viscous losses associated with the impeller tip leakage flow. The consequent changes at the impeller exit with increasing interaction were identified as reduced …
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An experimental study of unsteady separation in a two-dimensional flow
… is strongly correlated to two factors: flow unsteadiness and flow ejection from the wall. The balance of the characteristic length and time scales of unsteadiness and ejection determines whether the separating structure is moving or is fixed.
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Scaling of impeller response to impeller-diffuser interactions in centrifugal compressors
… to relate the level of impeller passage unsteadiness to the level of performance change due to interaction, which are shown to be important. The ratio of the unsteady amplitude, of blade leakage velocity or blade loading, to the time average value appears to be a parameter capable of …
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Unsteady adjoint analysis for output sensitivity and mesh adaptation
… problems exhibiting small-scale output unsteadiness when solved with time-inaccurate iterative solvers. It is demonstrated that unconverged steady flow calculations, even with small output unsteadiness, can lead to significant variability in the estimated output sensitivity due to the …
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Loss mechanisms in a highly loaded transonic axial turbine stage
… higher value. Loss arising from flow unsteadiness contributes an additional loss of about 1/6 of that in steady flow approximation; 3/4 of the flow unsteadiness induced loss occurs in the downstream vane where the flow is threaded with propagating shocks from the upstream blade and …
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The Effect of Blade Row Interaction on Rotor Film Cooling
… main-stream boundary conditions. The effect of unsteadiness is set by non-linearity in the hole response. Unsteadiness reduces film effectiveness by up to 31% with cylindrical holes at a low momentum flux ratio, because the response to perturbations is non-linear. Cylindrical holes at a high …
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Turbine tip clearance loss mechanisms
… downstream transition duct geometry, and unsteadiness due to an upstream nozzle guide vane. Tip leakage loss changes due to three-dimensional blade stacking (bowing or reverse bowing) are verified to be associated with changes in the magnitude of blade tip loading, which create differences …
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The Dynamic Character of the Flow Over a 3.5 Caliber Tangent-Ogive Cylinder in Steady and Maneuvering States at High Incidence
… slender forebodies - whether due to the natural unsteadiness or forced maneuvering - is not well-understood. This body of work documents three experimental investigations into the unsteadiness of the flow over a 3.5 caliber tangent-ogive cylinder at high angles of incidence. The goal of the …
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Impact of unsteady secondary air flow interaction with main flow on loss generation in axial turbines
… assess the role of vane-rotor stage induced flow unsteadiness on loss generation from purge flow interacting with main flow. Computational models of varying physical and geometry complexity that range from simple bladeless annulus configurations to vane-rotor stage configurations were used for …
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Characterization of unsteady loading due to impeller-diffuser interaction in centrifugal compressors
… for predicting the absolute magnitude of loading unsteadiness. Errors of up to 14% exist between absolute values of flow quantities. Evidence suggests that the k - e turbulence model used is inappropriate for centrifugal compressor flow and is the significant source of these errors. The unsteady …
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Turbulence Modeling and Simulation of Unsteady Transitional Boundary Layers and Wakes with Application to Wind Turbine Aerodynamics
… of a circular cylinder for generating coherent unsteadiness and a downstream airfoil in the cylinder wake. The cylinder flow is subcritical, with a Reynolds number of 64,000 based upon the cylinder diameter. The quantitative dynamics of vortex shedding and Reynolds stresses in the cylinder near …
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