Other Mechanical Engineering Commons^™

Scaling Investigations Of Wall-Bounded Turbulent Flow, Nikolay Gustenyov

Theses and Dissertations--Mechanical and Aerospace Engineering

This dissertation investigates the scaling behavior, structural organization, and modeling of turbulence in wall-bounded flows across a wide range of Reynolds numbers and surface conditions. Through high-resolution experimental studies in zero-pressure- gradient turbulent boundary layers and pipe flows (2000 < Reτ < 38 200), the wall- dependence of turbulent length scales is examined with a focus on both small-scale dissipative motions and large-scale structures. When external intermittency is properly accounted for, dissipative motions are shown to obey inner scaling even in outer- scaled regions, while large-scale motions exhibit outer scaling behavior deep into the inner region. These findings are consistent across internal (pipe) and external (boundary layer) flows and are reflected in distinct features of the longitudinal wavenumber spectrum.

The dissertation also explores the development of a turbulent boundary layer transitioning from a smooth solid wall to a liquid surface. An internal boundary layer forms in response to stochastic surface waves, resulting in increased turbulence intensity and displaced momentum relative to solid-wall cases. Near the liquid surface, turbulence generation aligns with wavenumbers corresponding to the surface waves, introducing distinct small-scale …

High-Altitude Balloon-Launched Uncrewed Aircraft System Measurements Of Atmospheric Turbulence And Qualitative Comparison With Infrasound Microphone Response, Anisa Haghighi

Theses and Dissertations--Mechanical and Aerospace Engineering

This study explores the use of a balloon-launched uncrewed aircraft system (UAS) to measure atmospheric turbulence in the troposphere and lower stratosphere using both wind velocity measurements and infrasonic acoustic energy. The UAS, a glider configured for autonomous descent along a predefined trajectory, had on board, in situ sensors to capture thermodynamic and kinematic atmospheric parameters. Additionally, it carried an infrasonic microphone to evaluate its potential for remotely detecting clear-air turbulence by capturing infrasonic waves. The system’s performance was assessed over the course of three test flights conducted in New Mexico, USA, in 2021. The descent enabled high-resolution profiling, with …

Influence Of Swirl And Turbulence In The Particle Removal Using Fog In A Pipe Flow, Nisarg T. Patel

All Theses

Fog-and-tube scrubbers are employed to remove harmful ultrafine aerosols, such as Diesel particulate matter (DPM), from an airflow. The underlying principle of this removal process involves enlarging the aerosol particles by coagulating them with fog drops, which are subsequently eliminated through inertial impaction onto the tube wall. Previous research conducted by Tabor et al. (2021) demonstrated an increase in scavenging of ultrafine DPM particles, ranging from 11.5 nm to 154 nm, by as large as 45% over the no fog case. This finding is crucial in addressing the challenges associated with conventional filtration methods for capturing ultrafine particles.

The present …

Utilization Of Uncrewed Aircraft Systems Towards Investigating The Structure Of The Atmospheric Surface Layer, Loiy Al-Ghussain

Theses and Dissertations--Mechanical and Aerospace Engineering

This study presents two approaches to investigate the surface-layer structure during the morning transition using uncrewed aircraft systems. The first approach employs three uncrewed aircraft systems- each equipped with a single multi-hole probe- simultaneously measuring horizontal transects were partnered with a fourth measuring vertical profiles during two consecutive mornings as part of the 2017 Collaboration Leading Operational Unmanned Aerial System Development for Meteorology and Atmospheric Physics (CLOUDMAP) measurement campaign near Stillwater, Oklahoma, U.S.A. Data were analyzed to extract time-dependent single-point statistics of kinematic and thermodynamic variables from the uncrewed aircraft systems. In addition, an approach is presented by which multi-point …

Quantification Of Reynolds Shear Stress Wave-Phase Dependence In Fixed-Bottom Offshore Wind Turbine Via Quadrant Analysis, Cerrina Mouchref

University Honors Theses

As the need for a reliable renewable energy supply is increasing, many have looked to offshore wind because they hold more potential for power production than onshore wind. Interests in expanding offshore wind energy has brought along many challenges when it comes to understanding the complex dynamics experienced offshore, including the relationship between the wind-turbine generated wakes and ocean waves. This experimental study characterizes the relationship between Reynolds shear stress and the phase of surface waves above the air-sea interface in the wind-turbine wake region. The experimental setup combines a wave tank, wind tunnel, and a fixed-bottom wind turbine. Particle …

On The Improvements Of Boundary-Layer Representation For High Resolution Weather Forecasting In Costal-Urban Environments, David Melecio-Vazquez

Dissertations and Theses

As large urban centers around the world become more densely populated, the global conversion from natural to man-made land surfaces will only increase. These land-use changes affect the urban surface energy budget which in turn changes the structure of the planetary boundary layer (PBL) above. With current high-performance computing systems, meteorological and built environment information can be better utilized to quantify the anthropogenic effects of these modifications. Although these systems have improved forecasting near-surface weather conditions, a comprehensive approach to represent urban impacts on the PBL is still limited. Improved PBL representation can lead to better weather and climate forecasts, …

A Numerical And Experimental Study Of Lid Driven Square Cavity Flow For Laminar And Turbulent Cases, Abdullah Bin Naeem

LSU New Orleans Theses and Dissertations

Experimental and numerical studies are performed on steady and unsteady lid-driven cavity flow for laminar flow regime. In the experiments, a PIV and an LDA were employed to measure the global and local velocities, respectively inside a cavity of AR 1.0. The velocity vector plots and streamline plots which represent unsteady circulation patterns are obtained using the PIV. The steady local velocities measured with LDA are then used to calibrate the PIV measurements. The numerical study is performed using a commercial CFD solver. For turbulent flow simulation RANS equations with K-Epsilon closure model were used. From the PIV calibration study, …

Determining The Severity Of Obstructive Sleep Apnea (Osa) By Using Numerical Analysis, Ming Lok Ang

Student Works (2020-2029)

Computational technologies and biomechanical theories have been applied to study upper airway mechanics in obstructive sleep apnea (OSA). In this study, the patient is selected from ENT Department, UMMC, diagnosed with mild to severe OSA. In addition, the patient underwent maxillomandibular advancement (MMA) surgical treatment. Therefore, 3-dimensional modeling software will be used to model the upper airway, based on patient specific geometrical characteristics obtained from medical imaging and computed tomography (CT). Hence, providing an accurate assessment of airflow characteristics. Computational fluid dynamics (CFD) analysis will be combined with upper airway geometries obtained before and after surgical to determine the effects …

Development Of An Unmanned Aerial Vehicle For Atmospheric Turbulence Measurement, Brandon M. Witte

Theses and Dissertations--Mechanical and Aerospace Engineering

An unmanned aerial vehicle was developed to study turbulence in the atmospheric boundary layer. The development of the aircraft, BLUECAT5, and instrumentation package culminated in a series of flight experiments conducted in two different locations near Stillwater, Oklahoma, USA. The flight experiments employed the use of two of the unmanned aerial vehicles flying simultaneously, each containing a five-hole pressure probe as part of a turbulence-measuring instrumentation package. A total of 18 flights were completed with the objective to measure atmospheric properties at five altitudes between 20 and 120 meters. Multiple flights were flown over two days in which the effects …

Microphone-Based Pressure Diagnostics For Boundary Layer Transition, Spencer Everett Lillywhite

Master's Theses

An experimental investigation of the use low-cost microphones for unsteady total pressure measurement to detect transition from laminar to turbulent boundary layer flow has been conducted. Two small electret condenser microphones, the Knowles FG-23629 and the FG-23742, were used to measure the pressure fluctuations and considered for possible integration with an autonomous boundary layer measurement system. Procedures to determine the microphones’ maximum sound pressure levels and frequency response using an acoustic source provided by a speaker and a reference microphone. These studies showed that both microphones possess a very flat frequency response and that the max SPL of the FG-23629 …