Aerodynamics and Fluid Mechanics Commons^™

Effect Of Morphology And An Upstream Tall Building On A Street Canyon Flow, Haoran Du

Electronic Thesis and Dissertation Repository

The effects of the morphological model and the existence of an upstream tall building on the turbulent street canyon flow and the overlying boundary layer are investigated in a wind tunnel, using Stereoscopic Particle Image Velocimetry (S-PIV) measurements. The velocity variances, Reynolds shear stress, and turbulent kinetic energy are found to be larger than in a similar idealized street canyon model. Increasing building height results in a decrease in vertical mass fluxes across the opening of the canyon, at least in the canyon portion directly downstream of the building. The interaction between the large-scale structures in the overlying boundary layer …

Flow Characterization Over Biomimetic Fish Scale Arrays, Isaac Nr Clapp Mr.

Electronic Thesis and Dissertation Repository

The contributions of drag to energy consumption in the transportation sector are significant and often unavoidable. Biomimetic surfaces are promising as passive drag reduction mechanisms. Among them, fish scale arrays are beneficial in the laminar and transitional flow regimes but lack fundamental understanding. This research addressed this need and investigated the underlying flow mechanisms over fish scale arrays. Experimental measurements revealed the presence of flow recirculation, streamwise velocity streaks, spanwise velocity fluctuations, and wall normal vorticity streaks, all of which play a role in the near wall flow behaviour. Numerical simulations revealed the superior friction drag reduction capabilities of the …

Carbon Nanotube-Based Microscale Capacitive Flow Sensors, Nathaniel Holmes

Electronic Thesis and Dissertation Repository

Micro-scale flow sensors present several advantages over traditional flow sensing
methods, including minimal flow disruption, high spatial resolution, and low unit
cost. Many existing micro-scale thermal and piezo flow sensors struggle with temperature drift and require complicated fabrication processes. This thesis details
the development of a 60 μm by 60 μm by 50 μm drag-based capacitive flow sensor
constructed from vertically aligned carbon nanotube forests. The construction
of a thermal chemical vapour deposition system for sensor synthesis is also de-
tailed. Manual manipulation of the sensor with an atomic force microscope probe
was found to produce a full scale signal …

A Computational Fluid Dynamics-Based Surrogate Wind Turbine Blade Aerodynamic Model For Hybrid Simulation, Eric Lalonde

Electronic Thesis and Dissertation Repository

Hybrid simulation (HS) is a promising technique for studying wind turbines due to the presence of scaling errors in wind tunnel testing. However, HS of wind-loaded structures is limited by the current practice of using lower-accuracy, "pre-calculated" aerodynamic loads, which uncouple the aerodynamic loading from the structural response. This thesis presents six stand-alone studies that collectively build towards a novel HS framework that employs a computational fluid dynamics (CFD) based surrogate model to generate higher-accuracy aerodynamic loads within the HS loop. An experimentally-validated residential wind turbine model equipped with an external damping system was used to illustrate the proposed framework. …

Complicating Factors In Hydraulic Jumps: The Effects Of Earth's Rotation, Muveno Pascoal Elias Mucaza

Electronic Thesis and Dissertation Repository

Hydraulic jumps at the interface of stratified rotating fluids are studied. The flow is de- fined with continuous density and velocity profiles, with the velocity in each layer changing (upstream shear). The study is conducted in jumps defined by an imposed velocity transition, and jumps developing over a topography.

The numerical simulations conducted showed the qualitative structure of the flow changing in the cross-width direction, as well as the size and amount of turbulence of the jumps. Mixing in these jumps was shown to increase towards the side of the domain where the jumps were larger and more turbulent. The …

Implication Of City Growth On Wind-Induced Loads For Cladding And Structural Design, Hadil M. Abdallah

Electronic Thesis and Dissertation Repository

As cities grow, the urban topology changes in density resulting in continuous variations in wind flow. The interaction of flow with this changing surrounding environment drives the aerodynamics to become more complex and varying, subjecting the building to significant changes in wind-induced-loads both on structural and non-structural elements. In this study, a series of boundary layer wind tunnel tests are conducted to investigate the impact of city growth on cladding and structural loading by using a typical tall building adopted from the Commonwealth Advisory Aeronautical Council (CAARC) building model. The city growth is represented by five different generic surrounding configurations, …

Simulation Of Operational Extreme Wind Conditions For Horizontal Axis Wind Turbines Based On Iec Standard, Kamran Shirzadeh Ajirlo

Electronic Thesis and Dissertation Repository

The possibility of simulating deterministic extreme operational conditions for horizontal axis wind turbines based on the IEC 61400-1 standard in the WindEEE Dome at Western University was investigated. WindEEE has 60 fans (a matrix of 4 by 15 with 0.8m diameter each) on one of the walls to generate straight and sheared flows. These fans were controlled by their power set-points and by their adjustable Inlet Guiding Vanes (IGV) to generate the Extreme Operational Gust (EOG), positive and negative Extreme Vertical Shear (EVS), and Extreme Horizontal Shear (EHS) cases as per IEC 61400-1 standard to be further applied for testing …

Joint Wind And Ice Effects On Transmission Lines In Mountainous Terrain, Daniel Davalos Arriaga

Electronic Thesis and Dissertation Repository

Atmospheric icing on mountainous terrain can produce catastrophic damages to transmission lines when incoming particles impinge and accrete on the cable surface of the system. The first challenge in wind-ice loading is determining joint statistics of wind and ice accretion on transmission lines. This study analyzes the weather characteristics for a specific site of study using 15 years of historical data to use as inputs for ice accretion modeling. The joint wind and ice hazard is characterized by simulating 500 years of icing events from the fitted probability distributions of ice accretion and wind on ice velocities. The second challenge …

Characterization For Spray Droplet Behaviour In Afterburner-Like Flow Conditions, Matthew D. Mahaffy

Electronic Thesis and Dissertation Repository

Fuel injection processes can contribute to combustion instability in highly energetic combustion systems. In gas turbine engine afterburners, jet-in-crossflow (JIX) injection is used. Part one of the thesis study investigates the interaction between spray droplets and turbulent flow properties of a JIX. Jet-in-counterflow (JIC) configuration was also investigated. Part two of the investigation examined the behaviour of JIX droplets around a bluff body. Droplet size and flow turbulence was characterized simultaneously using particle image velocimetry and image processing techniques. Turbulence and droplet size were correlated, particularly at momentum flux ratios ≥ 60. High speed imaging was used to identify droplet …

Modal Analysis And Analytical Modeling Of Tornado-Like Vortices, Mohammad Karami

Electronic Thesis and Dissertation Repository

Regardless of the type of vortex chamber, many tornado simulators generate flows that reveal similar flow patterns and a general agreement on the variations of the flow structures with swirl ratio (the ratio of tangential velocity to radial velocity) was achieved. However, very little is known about the underlying physics of the flow, mostly of the fluctuating one, as the previous studies have mainly focused on qualitative flow visualization and the quantitative description of the mean flow.

Herein, coherent structures in tornado-like vortices are extracted using modal decomposition techniques. Modal analysis helps us to better understand the complex vortex dynamics …

Transient Analysis Of Full Scale And Experimental Downburst Flows, Junayed Chowdhury

Electronic Thesis and Dissertation Repository

Downbursts are highly transient natural phenomena which produce strong downdrafts evolving from a cumulonimbus cloud They induce an outburst of damaging winds on or near to the ground causing an immense damage to the ground mounted structures and aircrafts. This study investigates the transient nature of downbursts using wind speed records from full scale downburst events employing an objective methodology. This method can detect the abrupt change points in a downburst time series based on statistical parameters such as mean, standard deviation and linear trend. In addition to the analysis of the full scale downburst events, several large scale experimental …

The Spanwise Structure Of The Roof-Level Turbulence In A Street Canyon Flow, Tomek Jaroslawski

Electronic Thesis and Dissertation Repository

In the present work, for the first time, the spanwise organization of turbulent flow along an urban street canyon subjected to wind normal to the street axis using a boundary layer wind tunnel is systematically investigated.The effect of upstream roughness and canyon width on the turbulence in a street canyon flow is presented. Measurements in a horizontal plane were conducted at near roof-level of a street canyon using Stereoscopic Particle Image Velocimetry. Three upstream roughness arrays and two canyon width (W) to height (h) aspect ratios (AR = W / h = 1 and 3) were …

On The Reduction Of The Driving Force In Shear-Driven Flows, Sakib Shadman

Electronic Thesis and Dissertation Repository

In shear-driven flows, an external driving force is needed to maintain the relative movement of horizontal plates. This thesis presents a systematic analysis on using spatially periodic heating and grooved surfaces to control this force. It is found that the use of periodic heating creates a buoyancy-driven effect that always reduces this force. The use of proper heating may even lead to the complete elimination of this force. It is further found that the use of isothermal grooved surfaces always enhances flow resistance, resulting in an increase of this force. When grooves and heating are applied together, their interaction induces …

A Numerical Investigation Of Human Cough Jet Development And Droplet Dispersion, Ran Bi

Electronic Thesis and Dissertation Repository

As part of the Western Cold and Flu aerosol (WeCoF) studies, the present study provides Computational Fluid Dynamics (CFD) modelling of human cough flow. The cough flow is characterized in two different aspects, the flow field and the droplets. In the study of the flow field of coughing, various dynamic characteristics, including the velocity variation, streamwise penetration and power spectral density, are examined. CFD simulations using two different approaches, the unsteady Reynolds Averaged Navier-Stokes (URANS) and the large eddy simulation (LES), are performed for comparison purposes. The numerical results are validated by the experimental data obtained from the measurements by …

Assessment Of Dynamic Effect Of Transmission Line Conductor Longitudinal Reaction Due To Downburst Loading, Ibrahim Ibrahim

Electronic Thesis and Dissertation Repository

Due to the locality and non-stationary nature of downburst wind loading events, their effect on the structural response of transmission line structures is of special nature that differs from conventional atmospheric boundary layer wind loading. Acknowledging such difference, the current thesis aims to quantify the dynamic effect associated with downburst loading on transmission line systems. To achieve that, several steps had to be realized, including experimentally verifying the numerical model used for analysis using wind field that was generated using computational fluid dynamics. The verified model was extended from model scale to full scale, where the wind field used for …

Estimation Of Turbulence Effects On Wind-Induced Suctions On The Roof Of A Low-Rise Building, Chieh-Hsun Wu

Electronic Thesis and Dissertation Repository

The effects of turbulence in the atmospheric boundary layer (ABL) on surface pressures of a typical low-rise building roof are investigated in this thesis. A 1/50 geometrically-scaled model of the Texas Tech University Wind Engineering Field Research Lab (WERFL) building model is used for pressure measurements in wind tunnel experiments. ABL wind turbulence intensities ranging from about 10% to 30%, and length scales ranging from 6 to 12 times of the building height (H) are generated. The effects of ABL turbulence on the mean roof pressures within the separated flow are explained from the time-averaged Navier-Stokes equations. The pressure fields …

Numerical Simulation Of Air Flow In Aeroengine Compressors, Shady Mohamed Mohamed Ali

Electronic Thesis and Dissertation Repository

The performance of an aeroengine is influenced by the performance of the compressor system. A typical compressor consists of multistage axial compressors followed by a centrifugal stage. Here, a high-speed centrifugal and an axial stage are investigated in terms of turbulence modelling, flow blockage and rotor-stator (R-S) gap using the commercial software ANSYS CFX. The curvature corrected Shear stress transport (SST-CC) model of Smirnov and Menter is investigated for the first time in a high-speed centrifugal stage in terms of curvature and rotation effects. The SST-CC predictions are compared with the standard SST, Speziale, Sarkar, and Gatski Reynolds stress model …

Foundation Effects Of Trees Under Wind Loads, Padmavathi Venkata Sagi

Electronic Thesis and Dissertation Repository

Winching tests were conducted on a mature 24-year-old Norway spruce tree. The tree was instrumented with strain gauges along the root structure and tilt sensors along the tree stem and was winched to failure. Tracked tree-root system response to failure load and the material properties of the tree-root-soil system were used to examine the applicability of simple engineering principles to tree stability analysis. Tree stability was studied using the principles of Winkler foundation model for the first time. In order to study the very complex windthrow phenomenon, a novel experimental technique was used. Tree saplings with complete structural root systems …

Numerical Investigation Of Full Scale Thunderstorm Downbursts: A Parametric Study And Comparison To Meteorological Model, Christopher Oreskovic

Electronic Thesis and Dissertation Repository

A series of Large Eddy Simulations using an atmospheric meteorological cloud model have been used to investigate the important geometric and thermal parameters that influence a thunderstorm downburst outflow, as it pertains specifically to the idealized cooling source model. A separate set of Large Eddy Simulations make use of the same idealized cooling source model, in a realistic atmospheric base state using real field sounding data, in an attempt to make a quantifiable comparison to a downburst from a full cloud simulation. Randomness has been added to the cooling source forcing function to mimic the thermal variation in a real …

Wind And Thermal Effects On Ground Mounted Photovoltaic (Pv) Panels, Chowdhury Mohammad Jubayer

Electronic Thesis and Dissertation Repository

A combination of Computational Fluid Dynamics (CFD) simulations and wind tunnel experiments are carried out to investigate the effects of wind on the aerodynamic loading and heat transfer of a ground mounted stand-alone photovoltaic (PV) panel with tilt angle of 25^o in open country atmospheric boundary layer. Several azimuthal wind directions are considered: Southern 0^o, Southwest 45^o, Northwest 135^o and Northern 180^o. Three dimensional Reynolds-Averaged Navier-Stokes (RANS) approaches with an unsteady solver using Shear Stress Transport (SST) k-ω turbulence closure are employed for the CFD simulations, whereas Particle Image Velocimetry (PIV) and …

Response Of Transmission Line Conductors Under Downburst Wind, Haitham Aboshosha

Electronic Thesis and Dissertation Repository

Electricity is transmitted by Transmission Lines (TLs) from the source of production to the distribution system and then to the end consumers. Failure of a TL can lead to significant economic losses and to negative social consequences resulting from the interruption of power. High Intensity Winds (HIW), in the form of downbursts and tornadoes, are believed to be responsible for more than 80% of the weather-related failure of TLs around the world. The studies reported in this thesis are part of an ongoing extensive research program at Western University focusing on the response of TLs under HIW. Previous investigations conducted …

Physical Simulation Of Tornado-Like Vortices, Maryam Refan

Electronic Thesis and Dissertation Repository

Scaling ratios of simulations are essential to research the effect of tornadic winds on buildings and structures, in both experimental and numerical studies. In order to determine the proper scaling, access to wind fields of simulated and full-scale tornadoes is needed. For the first time here Doppler radar tornado velocity fields are analyzed and compared to experimental tornado-like vortices data in order to establish the scaling necessary to simulate tornadoes in a physical laboratory setting.

A prototype three-dimensional wind testing chamber capable of simulating tornadoes, named Model WindEEE Dome (MWD), was designed and built. Tornado-like vortices were simulated and investigated …

Experimental Investigation Of Wind Effect On Solar Panels, Ayodeji Abiola-Ogedengbe

Electronic Thesis and Dissertation Repository

Photovoltaic Solar Panels for electricity generation are outdoor low-rise structures that are vulnerable to damage by the wind. The existing building codes do not contain information about the impact of the wind on these structures and hence do not provide comprehensive guidelines to mitigate such impact. The present study is a contribution to the ongoing efforts to codify the wind loading on solar panels. In this study, experimental investigations were conducted on the scaled model of a ground-mounted solar panel structure whose surface is geometrically similar to an inclined flat plate and mounted on three-legged support. The panel comprises of …

Near-Wake Flow Dynamics Of A Horizontal Axis Wind Turbine, Pooyan Hashemi Tari

Electronic Thesis and Dissertation Repository

Experiments have been conducted in a large wind tunnel set-up in order to study the flow structures within the near-wake region of a horizontal axis wind turbine. Particle Image Velocimetry (PIV) has been employed to quantify the mean and turbulent components of the flow field. The measurements have been performed in multiple adjacent horizontal planes in order to cover the area behind the rotor in a large radial interval, at several locations downstream of the rotor. The measurements were phase-locked in order to facilitate the re-construction of the three-dimensional flow field. Acquiring uniform particle distribution in the measurement planes as …

The Near Wake Of A European Starling, Adam J. Kirchhefer

Electronic Thesis and Dissertation Repository

The wake of a freely flying European starling (Sturnus vulgaris) was measured using high speed, time-resolved, particle image velocimetry, simultaneously with high speed cameras which imaged the bird. These measurements have been used to generate vector maps in the near wake that can be associated with the bird’s location and wing configuration. A kinematic analysis has been performed on select sequences of measurements to characterize the motion of the bird, as well as provide a point of comparison between the bird of the present study and other birds or flapping wings. Time series of measurements have been expressed …

Numerical Investigation Of Highly Curved Turbulent Flows In Centrifugal Compressors And In A Simplified Geometry, Kevin J. Elliott

Electronic Thesis and Dissertation Repository

Curvature effects are investigated in terms of a recently developed curvature corrected turbulence model in turbomachinery applications. Two centrifugal compressor stages and a curved geometry modelled after a centrifugal impeller are simulated using the curvature corrected SST (SST-CC) turbulence model. This work improves the understanding of how the SST-CC model predicts curvature effects. An analysis of the SST-CC production multiplier in both centrifugal cases reveals that the model is appropriately accounting for curvature effects, showing increased production near concave surfaces and decreased production near convex surfaces. This correlates well with the simplified geometry results and demonstrates that the simplified geometry …

Experimental And Numerical Study Of Flow Structures Associated With Low Aspect Ratio Elliptical Cavities, Taravat Khadivi

Electronic Thesis and Dissertation Repository

The flow regimes associated with a 2:1 aspect ratio, elliptical planform cavity in a turbulent flat plate boundary layer have been systematically examined for various depth/width ratios (0.1 to 1.0) and yaw angles (0° to 90°), using a combination of wind tunnel experiments (involving Particle Image Velocimetry and helium bubble visualization) and Computational Fluid Dynamics (CFD) simulations (employing three- dimensional steady calculations with the Reynolds Stress model turbulence closure). Satisfactory agreement has been found between the results using the two methods, indicating that the steady numerical simulations can be a cost-effective tool to predict the mean flow features.

The flow …

Vortex Shedding From Elongated Bluff Bodies, Zachary J. Taylor

Electronic Thesis and Dissertation Repository

As the spans of suspension bridges increase, the structures become inherently flexible. The flexibility of these structures, combined with the wind and particular aerodynamics, can lead to significant motions. From the collapse due to flutter of the Tacoma Narrows Bridge to the case of vortex-induced vibrations (VIV) of the Storebælt Bridge, it is evident that a better understanding of the aerodynamics of these geometries is necessary. The work herein is motivated by these two problems and is presented in two parts.

In the first part, the focus is on the physical mechanisms of vortex shedding. It is shown that the …