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This thesis involves the experimental testing of a bluff body with a blunt base to evaluate the effectiveness of end-plate tabs in reducing drag. The bluff body is fitted with interchangeable end plates; one plate is flush with the rest of the exterior and the other plate has small tabs protruding perpendicularly into the flow. The body is tested in the Cal Poly 3ft x 4ft low speed wind tunnel. Testing is conducted in three phases. The first phase was the hot-wire measurement of streamwise velocity of the near wake behind the bluff body. An IFA300 thermal anemometry system with a hot-wire probe placed behind the model measures the wake velocity fluctuations. The power spectral density on the model without tabs shows large spikes at Strouhal numbers of 0.266, 0.300, and 0.287 at corresponding Re = 41,400, 82,800, 124,200 where vortex shedding occurs. The model with tabs shows no such peaks in power and therefore has attenuated vortex generation in the wake flow at that location. The second phase of testing was pressure testing the model through the use of pressure ports on the exterior of the bluff body. A Scanivalve pressure transducer measured multiple ports almost simultaneously through tubing that was connected to the model internally and routed through the model’s strut mount and outside of the wind tunnel. This pressure testing shows that the model with tabs is able to achieve up to 36% increase in Cp at Reh = 41,400 on the base region of the bluff body and no negative pressure spikes that occur as a result of vortex shedding. The last phase of testing is the measurement of total drag on the model through a sting balance mount. This testing shows that the drag on the model is reduced by 14% at Re = 41,400. However it also shows that as velocity increased, the drag reduction is reduced and ultimately negated at Re = 124,200 with no drag loss at all. The addition of tabs as a passive flow control device did eliminate vortex shedding and alter the base pressure of the bluff body. This particular model however showed no reduction in total drag on the model at high Reynolds numbers higher than 124,000. Further study is necessary to isolate the exact geometry and flow velocities that should be able to produce more favorable drag results for a bluff body with this type of passive flow control device.

An experimental wind tunnel study on the dynamic response of a 300 m tall guyed telecommunication mast under various wind loads was undertaken at the Boundary Layer Wind Tunnel Laboratory (BLWTL) in the University of Western Ontario, London, Canada. Although the dynamic response of guyed masts subjected to turbulent wind loads has been routinely analyzed using a number of numerical models, typically in the frequency domain, limited experimental verification of the dynamic analysis results has been performed. Full-scale measurements, where available, have proven to be difficult to correlate with analytical models due to the tremendous uncertainty inherent in field measurements. As a result, the need for systematic validation of existing analytical models remains.<p>In this investigation, a representative 300 m tall guyed telecommunication mast has been designed and modeled to an appropriate scale. Based on Canadian Standard CSA S37-01, and an empirical study on 41 existing guyed masts, the 300 m tall guyed mast was designed using wind load conforming to representative Canadian climate data obtained from National Building Code of Canada (NBCC 1995). Appropriate properties for the dynamically scaled full aeroelastic model were derived from the 300 m tall prototype guyed mast, which was intended to represent a realistic guyed mast for broadcasting applications in Canada.<p>The wind tunnel test of the guyed mast model was carried out in both open country and over water exposures, simulating medium and low turbulence flow conditions, respectively. Dynamic response characteristics measured during the wind tunnel tests have been analysed and summarized, including dynamic displacements, bending moments, response spectra and peak factors, as well as natural frequencies, mode shapes and structural damping. Comparisons have been made with predictions obtained from an existing frequency domain analysis model. <p>The wind tunnel test results show that good agreement was generally achieved between the frequency domain analytical model and the wind tunnel model with respect to both the magnitude and distribution of the monitored responses. It was found that measured dynamic bending moments were distributed in a fairly uniform manner over the mast height, and that mean (static) bending moments exhibit large variations, along with near-zero response zones at points of contraflexure. It was also found that nonlinear damping effects, associated with vibrations of the highly slackened leeward guys on the upper levels of the mast, may be beneficial in reducing dynamic mast displacements. <p>The spectrum studies indicated that lowest modes were dominated by large guy movements at top guy level and small mast movements, the middle modes were characterized by coupled effects between the guyed cables and mast, meanwhile the highest modes involved significant mast movements with little guy vibration. It is evident that the top of the mast displacement are dominated by the first and second modes.

An experimental wind tunnel study on the dynamic response of a 300 m tall guyed telecommunication mast under various wind loads was undertaken at the Boundary Layer Wind Tunnel Laboratory (BLWTL) in the University of Western Ontario, London, Canada. Although the dynamic response of guyed masts subjected to turbulent wind loads has been routinely analyzed using a number of numerical models, typically in the frequency domain, limited experimental verification of the dynamic analysis results has been performed. Full-scale measurements, where available, have proven to be difficult to correlate with analytical models due to the tremendous uncertainty inherent in field measurements. As a result, the need for systematic validation of existing analytical models remains.<p>In this investigation, a representative 300 m tall guyed telecommunication mast has been designed and modeled to an appropriate scale. Based on Canadian Standard CSA S37-01, and an empirical study on 41 existing guyed masts, the 300 m tall guyed mast was designed using wind load conforming to representative Canadian climate data obtained from National Building Code of Canada (NBCC 1995). Appropriate properties for the dynamically scaled full aeroelastic model were derived from the 300 m tall prototype guyed mast, which was intended to represent a realistic guyed mast for broadcasting applications in Canada.<p>The wind tunnel test of the guyed mast model was carried out in both open country and over water exposures, simulating medium and low turbulence flow conditions, respectively. Dynamic response characteristics measured during the wind tunnel tests have been analysed and summarized, including dynamic displacements, bending moments, response spectra and peak factors, as well as natural frequencies, mode shapes and structural damping. Comparisons have been made with predictions obtained from an existing frequency domain analysis model. <p>The wind tunnel test results show that good agreement was generally achieved between the frequency domain analytical model and the wind tunnel model with respect to both the magnitude and distribution of the monitored responses. It was found that measured dynamic bending moments were distributed in a fairly uniform manner over the mast height, and that mean (static) bending moments exhibit large variations, along with near-zero response zones at points of contraflexure. It was also found that nonlinear damping effects, associated with vibrations of the highly slackened leeward guys on the upper levels of the mast, may be beneficial in reducing dynamic mast displacements. <p>The spectrum studies indicated that lowest modes were dominated by large guy movements at top guy level and small mast movements, the middle modes were characterized by coupled effects between the guyed cables and mast, meanwhile the highest modes involved significant mast movements with little guy vibration. It is evident that the top of the mast displacement are dominated by the first and second modes.

Designing wind driven cross ventilation for a building is challenging due to the dynamic characteristics of wind. While numerous studies have studied various aspects of cross ventilation, few have had an opportunity to examine the topic with a holistic approach utilizing multiple research techniques. Thus, this dissertation combined three different investigation methods: wind tunnel analysis, full scale experiments and computational fluid dynamics (CFD) to examine the physics of wind driven cross ventilation. Following the systematic approaches of the three methods, this study first conducted full scale measurements of wind properties, façade pressures, air flow rates through small window openings, and tracer gas concentrations in a multi-zone test house. Secondly, a scaled model of the test house was studied in a boundary layer wind tunnel (BLWT) for its façade pressures and ventilation rate under various wind incident angles. Finally, a CFD model of the test house was simulated under various constraints to determine the factors which affect indoor air distribution during wind driven cross ventilation events. The full scale experimental results showed a strong correlation between the cross ventilation rate and the wind velocity component normal to the inlet openings. This correlation suggested that the cross ventilation flow rate could be estimated from wind conditions alone. A closer examination of the wind characteristics also revealed that the cyclical pattern of changing wind direction could be impacted by obstructions which are kilometers upwind, suggesting that distant landscapes could have an impact on cross ventilation flows. The combination of CFD and full scale measurements also showed that local heat sources can generate significant buoyancy driven flow and affect indoor mixing during wind-driven cross ventilation scenarios. Experimentally validated parametric CFD analyses demonstrated the effect of interior heat loads in driving internal airflow, and suggest that a small source (35W/m2) can increase the indoor mixing from less than 1 ACH to 8 ACH between indoor spaces. Finally, the wind tunnel and CFD coupled analysis was found to predict the cross ventilation flow which was also validated against the full scaled measurements. The prediction, which may only be applicable to similar building types with small openings, showed significant agreement that such method has potential as an innovative design tool for natural ventilation in buildings. / text

An experimental study of active control of fully separated flow over a symmetrical circular-arc airfoil at high angles of attack was performed. The experiments were carried out in a low-speed, open circuit wind tunnel. Angles of attack from 10 to 40 degrees were tested. Low-power input, unsteady excitation was applied to the leading or trailing edge shear layers. The actuation was provided by the periodic oscillation of a 4-percent-chord flap placed on the suction side of the airfoil and facing the sharp edge. Vortex-shedding frequencies were measured and harmonic combinations selected as the applied actuator frequencies. Pressure measurements over the airfoil show that the control increased the normal force coefficient by up to 70%. This supports the idea of vortex capture in the time-averaged sense, enhancing the lift on the airfoil by managing the shear layer roll up. The results indicate the viability of the control of large-scale flow fields by exploiting the natural amplification of disturbances triggered by small-scale actuators. The application of flow control on sharp-edged aircraft wings could lead to improved maneuverability, innovative flight control and weight reduction. These can be achieved by inexpensive, low-power, rugged actuators. / Master of Science

With a look towards the future, which involves a push towards utilizing renewable energy sources and cementing energy independence for future generations, the design of more efficient aircraft and novel energy systems is of utmost importance. This dissertation looks at leveraging some of the benefits offered by inflatable wings for use in tethered kite-like systems towards the goal of designing a High Altitude Aerial Platform (HAAP). Uses of such a system include Airborne Wind Energy Systems (AWES), among others. The key bene- fit offered by such wings is their lightweight construction and durability, but challenges to aerodynamic performance arise out of their flexible nature and non-standard airfoil profile. Studying the aerodynamic behavior of such wings forms the critical focus of this research. This effort primarily encompasses an experimental investigation of two swept, tethered, inflatable wings conducted in the Virginia Tech Stability Wind Tunnel, and numerical CFD computations of these wings. The experiment was conducted in the modular wall configuration of the anechoic test section at speeds ranging from 15 − 32.5 m/s for three different tether attachment configurations and wings constructed out of two different fabric materials. Along with static aeroelastic deformation data using a 3D photogrammetry system, aerodynamic measurements were taken in the form of Pitot and static pressure measurements in the wake of the wing, force and moment measurements at the base of the mount, and tension measurements at the tether attachment locations. This provides a data set for validating static aeroelastic modeling approaches for such a system and highlights the dramatic effect of the variability in test configuration on the wing's aerodynamics. In addition to the wind tunnel tests, 3D steady RANS CFD computations of the rigid 3D scanned inflatable wing geometry were conducted in the wind tunnel environment for these configurations to validate the CFD modeling approach and highlight the level of detail necessary to accurately characterize the wing aerodynamic performance. Static aeroelastic deformation data from the 3D photogrammetry system, at a speed of 27.5 m/s, were also used to deform the 3D scanned inflatable wing geometry, and RANS CFD computations of this deformed inflatable wing were conducted at a wind tunnel speed of 27.5 m/s. Several turbulence models were investigated and comparisons were made with the wind tunnel test data. Good agreement was found with experimental data for the forces and moments and wake Pitot pressure coefficient contours. Comparisons were also made with the rigid wing CFD computations at the same tunnel speed of 27.5 m/s to illustrate the effect of static aeroelastic deformations on the aerodynamic performance, wake Pitot pressure coefficient contours and wing-tip vortex structures, of these flexible inflated wings. In effect, this research utilizes the synergy be- tween wind tunnel experiments and numerical CFD computations to study the flow behavior over inflatable wings and provide a comprehensive verification and validation approach for modeling such complex systems. / Doctor of Philosophy / With a look towards the future, which involves a push towards utilizing renewable energy sources and cementing energy independence for future generations, the design of more efficient aircraft and novel energy systems is of utmost importance. This dissertation looks at leveraging some of the benefits offered by inflatable wings for use in tethered kite-like systems towards the goal of designing a High Altitude Aerial Platform (HAAP). Uses of such a system include Airborne Wind Energy Systems (AWES), among others. The key benefit offered by such wings is their lightweight construction and durability, but challenges to aerodynamic performance arise out of their flexible nature and non-standard airfoil profile. Studying the aerodynamic behavior of such wings forms the critical focus of this research. This effort primarily encompasses an experimental investigation of two swept, tethered, inflatable wings conducted in the Virginia Tech Stability Wind Tunnel, and computer simulations of the aerodynamic flow over these wings. The experiment was conducted in the modular wall configuration of the anechoic test section at speeds ranging from 15 − 32.5 m/s for three different tether attachment configurations and wings constructed out of two different fabric materials. Along with measurements of the wing deformations using a 3D photogrammetry system, aerodynamic measurements were taken in the form of pressure measurements in the wake of the wing, force and moment measurements at the base of the mount, and tension measurements at the tether attachment locations. This provides a data set for validating static aeroelastic modeling approaches for such a system and highlights the dramatic effect of the variability in test configuration on the wing's aerodynamics. In addition to the wind tunnel tests, detailed computer simulations of the scanned inflatable wing geometry were conducted in the wind tunnel environment for these configurations to validate the computational modeling approach and highlight the level of detail necessary to accurately characterize the wing aerodynamic performance. The wing deformation data from the 3D photogrammetry system, at a speed of 27.5 m/s, were also used to deform the scanned inflatable wing geometry, and computer simulations of this deformed inflatable wing geometry were conducted at a wind tunnel speed of 27.5 m/s. Good agreement was found between the experimental and computational forces and moments and wake Pitot pressure coefficient contours. Comparisons were also made with the undeformed wing computations at the same tunnel speed of 27.5 m/s to illustrate the effect of wing flexibility on the aerodynamic performance. In effect, this research utilizes the synergy between wind tunnel experiments and numerical CFD computations to study the flow behavior over inflatable wings and provide a comprehensive verification and validation approach for modeling such complex systems.

Sufficient heat dissipation is crucial to the effective operation of friction based braking systems. Such cooling is generally provided by ensuring a sufficient supply of cooling air to the heated components, hence the aerodynamics in the region of the brake components is extremely important. The objective of the research was to develop an understanding of how aerodynamics could be used to improve the cooling of automotive disc brakes. Two separate sets of wind tunnel experiments were developed. Tests were performed on a vented disc (rotor) to measure the internal flow through the vents on a rotating vented disc under various conditions, including an isolated disc in still air, the disc in still air with the wheel on, the disc in moving air with the wheel on, and an on-road simulation using a ¼ car. On vehicle tests were also performed in a wind tunnel using a purpose built brake test rig. These tests measured the thermal performance of different brake discs under various operating parameters; including constant load braking, and cooling from high temperature under various speeds, wheels and disc types. It was found that airflow through vented rotors was significantly reduced during simulated on-road driving, compared to when measured in isolation, but not particularly affected by the vehicles speed. In the situations tested, vented discs offered a 40+% improvement in cooling over an equivalent sized solid rotors. However the research indicates that the greatest benefit of vented rotors over solid will be in vehicles where air entering the wheel cavity is limited, such as low drag vehicles. It was also found that the most significant improvements in brake thermal performance could be achieved by maximising the airflow into the region of the brake components; including increasing the open area of the wheel, and increasing the vehicle velocity. Other improvements can be achieved by using a wheel material with good conductive capability, and increasing the mass of the disc. Evidence of vortex shedding was also discovered in the airflow at the exit of an internal vented rotor, any reduction in this flow disturbance should lead to increased airflow with associated improvements in thermal performance.

Methods for structural design, control, and testing offlexible aircraft structures are considered. Focus is onnonconventional aircraft con- figurations and control concepts.The interaction between analysis and testing is a central topicand all studies include validation testing and comparisonbetween computational and experimental results. The first part of the thesis is concerned with the designand testing of an aeroelastic wind-tunnel model representing aBlended Wing Body (BWB) aircraft. The investigations show thata somewhat simplified wind-tunnel model design concept isuseful and efficient for the type of investigations considered.Also, the studies indicate that well established numericaltools are capable of predicting the aeroelastic behavior of theBWB aircraft with reasonable accuracy. Accurate prediction ofthe control surface aerodynamics is however found to bedifficult. A new aerodynamic boundary element method for aeroelastictimedomain simulations and its experimental validation arepresented. The properties of the method are compared totraditional methods as well as to experimental results. Thestudy indicates that the method is capable of efficient andaccurate aeroelastic simulations. Next, a method for tailoring a structure with respect to itsaeroelastic behavior is presented. The method is based onnumerical optimization techniques and developed for efficientdesign of aeroelastic wind-tunnel models with prescribed staticand dynamic aeroelastic properties. Experimental validationshows that the design method is useful in practice and that itprovides a more efficient handling of the dynamic aeroelasticproperties compared to previous methods. Finally, the use of multiple control surfaces andaeroelastic effects for efficient roll maneuvering isconsidered. The idea is to design a controller that takesadvantage of the elasticity of the structure for performancebenefits. By use of optimization methods in combination with afairly simple control system, good maneuvering performance isobtained with minimal control effort. Validation testing usinga flexible wind-tunnel model and a real-time control systemshows that the control strategy is successful in practice.Keywords: aeroelasticity, active aeroelastic structures,aeroelastic tailoring, control, structural optimization,wind-tunnel testing. / QC 20120320