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 25 for “"laminar separation"”.
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Low Reynolds Number Laminar Separation Bubble Control Using a Backward Facing Step
<p>The problem of a laminar separation bubble on the upper surface of a 9.5% thick airfoil operated at low Reynolds number (R<sub>N</sub> = 380,000) was investigated experimentally.</p> <p>An unmodified LRN-010 airfoil and a modified LRN-010 airfoil with a backward facing step on its upper surface …
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The development of kinetic models and simulation methods to study molecular fluctuations, modal response, shock-laminar separation bubble instabilities
Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2022-11-11 without embargo terms
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The effect of free stream disturbances and control surface deflections on the performance of the Wortmann airfoil at low Reynolds numbers
… data, and flow-visualization studies. The laminar separation bubble which frequently occurs on the upper surface of the wing is found to dominate its performance and gives rise to a hysteresis loop for lift and drag. Changes in airfoil performance due to positive flap or control surface …
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Aspect ratio effects on wings at low Reynolds numbers
… wingtips have a rather restricted effect on the laminar separation bubble. The disappearance of the bubble extends only for a small distance inboard from the tips. The size of the hysteresis loop and the Reynolds number at which hysteresis starts was found to be influenced by the aspect ratio. …
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Effects of Free Stream Turbulence on Compressor Cascade Performance
… cascade angles where transition exists within a laminar separation bubble, increasing free-stream turbulence suppressed the extent of the laminar separation bubble and led to an earlier turbulent reattachment.
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Shock oscillation mechanisms of highly separated transitional shock-wave/boundary-layer interactions
… inlet of the turbofan engine. Consequently, a laminar boundary layer persists on the suction side of the transonic fan during cruise. Additionally, the trend in compressor design is higher blade loading, leading to larger separations. These conditions combined induce a shock oscillation with …
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Numerical Simulation of Vortex Generating Jets in Zero and Adverse Pressure Gradients
… pressure gradient was applied, inducing a laminar separation zone on the plate. A pulsed angled jet induced strong spanwise vortices in the separated shear layer which appear to weaken the separation zone and allow the bulk jet fluid to flush the remaining low-momentum fluid out of the …
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Numerical studies of the flow around an airfoil at low Reynolds number
… and linear stability analysis. The behaviour of laminar separation bubbles formed on a NACA-0012 airfoil at Rec = 5 £ 104 and incidence 5± is investigated. Initially volume forcing is introduced in order to promote transition to turbulence. After obtaining sufficient data from this forced case, …
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Separation and wakes over three-dimensional bodies
The laminar flow over a prolate spheroid was investigated via flow visualization and Laser-Doppler Velocimetry. Experiments were conducted in a water tunnel and the flow was visualized with dyes. The measurement of three-dimensional boundary layers required a special design of the laser optics. …
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Unsteady flow physics of airfoil dynamic stall
… dynamic stall process. A spatially-contracting laminar separation bubble was also identified near the airfoil leading edge from the characteristic pressure plateau in the surface pressure distribution. The dominant frequencies associated with the laminar separation bubble were extracted using a …
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The hemisphere-cylinder at an angle of attack
… were focused mainly on the development of the laminar separation bubble as a function of angle of attack, the conditions under which open and closed separation exist and the interaction between the separation bubble and the leeward vortices. A digital processing method was developed to convert …
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High-order implicit large-eddy simulation for transitional aerodynamics flows
… for natural transition to turbulence through a laminar separation bubble. In short, this thesis aims to demonstrate the potential of high-order ILES for simulating transitional aerodynamic flows. This will be illustrated through numerical results and supported by theoretical considerations.
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Aerodynamic and Acoustic Modeling for eVTOL Rotor Noise Prediction
… low-Reynolds-number flow physics, including laminar-turbulent transition and laminar separation bubble behavior.</p> <p>Predicted acoustic spectra were validated against experimental measurements obtained in the Virginia Tech Stability Wind Tunnel. Results demonstrate that turbulence model …
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Boundary layer transition in simulated turbine blade flow
… algorithm was developed to discriminate between laminar and turbulent flow. This was used to conditionally sample the signal in the transition region and hence provide mean laminar and turbulent velocity profiles in the transition region. It also provided a measurement of the intermittency. …
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Aerodynamic characterization of a Griffith-type transonic, laminar-flow airfoil
… airfoil to evaluate the effectiveness of its laminar flow qualities and boundary-layer flow-control characteristics in the transonic regime. Airfoil surface and wake pressure data were acquired to characterize the aerodynamic performance across a range of α = -2˚ to 2˚ and M = 0.3 to 0.7. In …
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Investigation of transition to turbulence at low Reynolds numbers using Implicit Large Eddy Simulations with a Discontinuous Galerkin method
The present work predicts the formation of laminar separation bubbles at low Reynolds numbers and the related transition to turbulence. In addition to being one of the first Implicit Large Eddy Simulation studies using a high-order Discontinuous Galerkin method, unique attention is given to the …
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Aerodynamic Response of a Two-Dimensional Cambered Wing at Low Reynolds Numbers in Steady-State Onset Turbulence
… effects of low Reynolds numbers and consequent laminar separation. In order to improve the design of UAVs for their operating conditions, it is important to understand how a low Reynolds number aerofoil responds to turbulent flows. Furthermore, it is unclear whether camber alters this response. …
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Bio-Inspired Axial Fan Design, 3D Printing Fabrication and Characterization for Noise and Flow Performance Optimization
… beamforming measurements, reveal the role of laminar separation bubbles and trip location in controlling boundary-layer development and acoustic scattering. Finally, the developed noise-control strategies are integrated at the system level, where their combined effects on rotor aerodynamic and …
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Aerodynamic and Aeroacoustic Analysis of Low Reynolds Number Propellers Using Higher-Order RANS Transition Turbulence Modeling
… complex boundary layer phenomena like laminar separation, flow transition and reattachment. These effects are known to greatly alter the flow at and near the rotor wall, influencing its aerodynamic performance as well as the noise generated. Capturing these effects in our computational …
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Towards a silent fan: an investigation of low-speed fan aeroacoustics
… boundary layers that are thicker and liable to laminar separation. Surface treatments such as boundary layer trips could be used to prevent such separation and potentially reduce noise. Based on the thesis findings, further tests, simulations and possible design modifications are suggested to …
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