Wind-tunnel measurements are an important step during the windturbinedesign process. The goal of wind-tunnel tests is to estimate theoperational performance of the wind turbine, for example by measuringthe power and thrust coecients. Depending on the sizes of both thewind turbine and the test section, the eect of blockage can be substantial.Correction schemes for the power and thrust coecients havebeen proposed in the literature, but for high blockage and highly loadedrotors these correction schemes become less accurate.A new method is proposed here to calculate the eect a cylindricalwind-tunnel test section has on the performance of the wind turbine.The wind turbine is modeled with a simplied vortex model. Usingvortices of constant circulation to model the wake vortices, the performancecharacteristics are estimated. The test section is modeled witha panel method, adapted for this specic situation. It uses irrotationalaxisymmetric source panels to enforce the solid-wall boundary condition.Combining both models in an iterative scheme allows for thesimulation of the eect of the presence of the test-section walls on windturbines performace.Based on the proposed wind-tunnel model, a more general empirical correlationscheme is proposed to estimate the performance characteristicsof a wind turbine operating under unconned conditions by correctingthe performance measured in the conned wind-tunnel conguration.The proposed correction scheme performs better than the existing correctionschemes, including cases with high blockage and highly loadedrotors.

This volume covers the phases from design to manufacturing of a wind tunnel testsupport structure for a conceptual blended wingbodyUAV designed by KTH GreenRaven Project students. The innovative aircraft design demonstrates sustainabilitywithin aviation by utilizing a hybrid electricfuelcell propulsion system. The windtunnel test to be conducted at Bristol University will produce data to evaluate theaerodynamic properties of the model for design verification. The wind tunnel modelis a smallscaled1.5mspanmodel supported by struts that change the pitch andyaw angles during testing. An external force balance provided by Bristol Universitymeasures the loads and moments experienced by the model. The main requirementsfor the structure are to withstand the aerodynamic loads imposed by the model andto change the model’s orientation while maintaining wind speed during the test. Themaximum aerodynamic loads were provided in a matrix, the largest of which was usedas the load condition for the support equating to a 512N lift at 14◦ AOA. Trade studieswere conducted to determine the mechanisms to satisfy the requirements while stayingwithin budget. The chosen design for the support structure includes a circular baseplate constrained by a locking ring with positioning pins to change the yaw angle. Themain strut is mounted at the the center of the circular base plate. A hinge bracketat the top of the strut interfaces with another hinge bracket within the model viaa clevis pin. An electric linear actuator mounted downstream of the main strut isused to vary the pitch angle, with the center of rotation at the clevis pin. Once thedesign was finalized, finite element analysis was done to verify the structural stabilityof the design. The FEA results were compared to EulerBernoulliapproximations fordeflection. Manufacturing of the components was outsourcedwhile assembly andprogramming of the actuator was done inhouse. / Det här examensarbetet är en del av ett projekt som omfattar processen från designtill tillverkning av en vindstunnelstödstruktur för en konceptuell UAV av typenflygande vinge, designad av KTH Green Raven Projectstudenter.Den innovativaflygplanskonstruktionen visar hållbarhet inom flygindustrin genom att användahybridbränsleceller som framdrivningssystem. Vindtunneltest som genomförs vidBristol University kommer att producera data för att utvärdera de aerodynamiskaegenskaperna hos modellen för verifiering av designen. Vindtunnelmodellen är ennedskalad modell på 1,5 m som stöds av stag som ändrar anfallsochgirvinklarnaunder testningen. En extern mätsond från Bristol University mäter de krafter ochmoment som modellen utsätts för. De viktigaste kraven för konstruktionen är attmotstå de aerodynamiska lasterna som modellen påför och att ändra modellensorientering samtidigt som vindhastigheten bibehålls under testet. De maximalaaerodynamiska belastningarna tillhandahölls i en matris; varav den största användessom lastfall för stödet motsvarande en 512N lyftkraft vid 14◦ anfallsvinkel. Jämförandestudier genomfördes för att bestämma mekanismerna för att uppfylla kraven samtidigtsom de låg inom budgeten. Den valda konstruktionen för stödkonstruktionenbestår av en cirkulär basplatta som fixeras med hjälp av en låsring, och som harpositioneringsstift för att ändra girvinkeln. En huvudstång är monterad i mitten avbasplattan upp till ett gångjärnsfäste i modellen. Bakom detta sitter ett linjärt ställdonsom dras ut och skjuts ihop för att ändra modellens attityd med rotationscentrum viddet övre fästet på huvudstaget. När designen slutfördes gjordes en finit elementanalysför att verifiera dess strukturella stabilitet. FEAresultatenjämfördes med EulerBernoulliuppskattningarför utböjning. Tillverkningen av komponenterna överlätstill extern part, medan monteringen och programmeringen av ställdonet gjordesinternt.

This study investigates the wake shading effect in wind farms, focusing on turbine spacing, horizontal rotor tilt (yaw angle), wind speed, and power production. With the global population increasing, the demand for energy continues to rise, emphasizing the importance of renewable energy sources like wind power. In wind farms, where multiple turbines operate together, the wake effect resulting from one turbine's influence on wind flow for others significantly impacts their power production. This research is focused around Jädraås Wind Power Park in Sweden, using a scaled model of a section of this park in a controlled environment to conduct a detailed analysis. Utilizing both experimental setups in a wind tunnel and numerical simulations for visualization, the study explores the dynamics of wake interactions among turbines and proposes to mitigate their adverse effects.Through the experiments conducted in the wind tunnel, the results demonstrate significant wakeinduced power losses at downstream turbines. The yaw adjustment mechanism of the upstream turbine is used so as to see how it has affected the power output of downstream turbine. The results also indicate significant reductions in power production as a function of turbine spacing. Specifically, the maximum reduction in power output, influenced by the presence of two upstream turbines, occurred at closer spacings between them: a decrease of 66% at 2.08D (2.08 Rotor Diameters between the downstream and the nearest upstream turbine) and 45% at 4.15D. Conversely, at broader spacings of 7.29D and 8.3D, the reductions were more moderate, a decrease of 28% and 18%, respectively. These findings underscore the critical influence of spatial arrangement on the wake-induced power losses within wind farms.Through an investigation of two purposely positioned upstream and downstream turbines at 4D meter of spacing, the optimal yaw angle for maximum combined power generation has been predicted using sinusoidal fitting, the results indicated that at yaw angle range of ±11° of theupstream turbine rotor, a maximum combined power output has been observed. Hence, a sophisticated optimization mechanism should be employed in an operating wind farm so as tolower wake effects.

Computational Fluid Dynamics (CFD) can play an important role in building design. For all aspects and stages of building design, CFD can be used to provide more accurate and rapid predictions of building performance with regard to air flow, pressure, temperature, and similar parameters. Generally, the process involved in conducting CFD analyses is relatively complex and requires a good understanding of how best to utilize computational numerical methods. Moreover, the level of skill required to perform an accurate CFD analysis remains a challenge for many professionals particularly architects. In addition, the user needs to input a number of different items of information and parameters into the CFD program in order to obtain a successful and credible solution. This research seeks to improve the general understanding of how CFD can best be used as a design assistance tool. While there have been a number of quantitative studies suggesting CFD may be a useful tool for building related airflow assessment, few researchers have explored the more qualitative aspects of CFD, in particular developing a better understanding of the procedures required for the proper application of CFD to whole building analysis. This study therefore adopted a combined qualitative and quantitative methodology, with the researcher immersing himself into a case study approach and defining several lessons-learned that are documented and shared. This research will assist practicing architects and architecture students to better understand the application of CFD to building analysis and design. / Ph. D.

The coastal population is growing, putting extra stress on coastal sediments and protection features, such as beach dunes. Moreover, global warming will increase the frequency of storms, and coastal dunes and other defense infrastructure will be subjected to increased erosion and scouring, endangering the people they are meant to protect. Understanding soil dynamics and fluid interaction is crucial to predict the effects of sand erosion. In particular, the study of wind erosion of sands in coastal dunes is essential due to the protective role these earthen structures have during storm events. One of the challenges about predicting wind erosion in coastal dunes is its extended spatial scale and the associated economic and logistics costs of sampling and characterizing the sediments. Because of this, in-situ testing for sediment characterization is essential. In particular, the usage of free-fall penetrometers (FFP) is appealing due to their portability and robustness. The sediment properties obtained with this type of testing can later be used to assess wind erosion susceptibility by determining, for example, the wind velocity to initiate the erosion process. FFP testing involves dropping an instrumented probe that impacts the soil and measures the kinematics or kinetics during the penetration process. For example, deceleration measurements are used to compute an equivalent quasi-static failure, which is not in line with the dynamic process characteristic of FFP testing. This preassumed failure mechanism is used to back-calculate the sand's geomechanical properties. However, soil behavior is highly complex under rapid loading, and incorporating this behavior into FFP sediment characterization models is challenging. Advanced numerical modeling can improve the understanding of the physics behind FFP testing. This thesis presents various advancements in numerical modeling and erosion models to bridge FFP in-situ testing with predicting the initiation of wind erosion of sands. First, improvements oriented to the Material Point Method (MPM) for modeling in-situ FFP testing are proposed. The numerical results show that the simulation of FFP deployment in sands is affected by strain localization and highlight the importance of considering constitutive models sensitive to different loading rates. Because of the importance of rate effects in soil behavior, the second aspect of this thesis proposes a novel consistency framework. Two constitutive models are adapted to study strain-rate sensitive non-cohesive materials: i) a strain-softening Mohr-Coulomb, and ii) a NorSand model. In addition to increased strength, the proposed framework captures increased dilatation, an early peak deviatoric stress, and relaxation. Finally, a novel sand erosion model is derived using a continuum approximation and limit equilibrium analysis. The erosion law considers geotechnical parameters, the effects of slope, and moisture suction, in a combined manner. The proposed model is theoretically consistent with existing expressions in the literature. It covers a wide range of environmental and geometrical conditions and helps to reconcile the results from FFP testing with the prediction of the initiation of wind erosion. The model was validated in a wind tunnel and is demonstrated to be a viable alternative for predicting sand erosion initiation. This thesis opens up new research prospects, such as improving the soil characterization models or the direct prediction of sand erosion using rapid, reliable, and efficient in-situ testing methods. / Doctor of Philosophy / With global warming and climate change, it is expected that the frequency and intensity of storms will increase. This increment will put extra stress on coastal sediments such as beach sand and coastal dunes, making them prone to erosion. Coastal dunes lose their ability to withstand storms as they erode, potentially making coastal flooding more frequent. In light of this, all stakeholders involved in the protection against coastal disasters must have the tools to predict, prepare for, and mitigate for situations like the ones stated above. An essential aspect of the prediction component is dependent on a successful sediment characterization, for example, determining how much wind the sand can withstand before it erodes. Free-fall penetrometers (FFP) are devices designed to conduct the characterization mentioned above. However, the procedures used to perform this characterization are mainly based on empirical or semi-empirical expressions. Computer models, capable of simulating the physics behind FFP testing, can bring more insight into the process of interaction between FFP devices, sands, and water and can be the basis to improve the characterization methods. The latter results can be utilized for instance to predict wind erosion, including several properties of the sand, such as its mineralogy and shape. This study contributes to developing the computer simulations of FFP deployment and the wind erosion prediction models. Eventually, these developments can help engineers and coastal managers to anticipate and prepare for more frequent coastal hazards.

This work reports the experimental and numerical study of the thermal management of Li-ion battery packs under the context of electric vehicle (EV) or hybrid EV (HEV) applications. Li-ion batteries have been extensively demonstrated as an important power source for EVs or HEVs. However, thermal management is a critical challenge for their widespread deployment, due to their highly dynamic operation and the wide range of environments under which they operate. To address these challenges, this work developed several experimental platforms to study adaptive thermal management strategies. Parallel to the experimental effort, multi-disciplinary models integrating heat transfer, fluid mechanics, and electro-thermal dynamics have been developed and validated, including detailed CFD models and lumped parameter models. The major contributions are twofold. First, this work developed actively controlled strategies and experimentally demonstrated their effectiveness on a practical sized battery pack and dynamic thermal loads. The results show that these strategies effectively reduced both the parasitic energy consumption and the temperature non-uniformity while maintaining the maximum temperature rise in the pack. Second, this work established a new two dimensional lumped parameter thermal model to overcome the limitations of existing thermal models and extend their applicable range. This new model provides accurate surface and core temperatures simulations comparable to detailed CFD models with a fraction of the computational cost. / Ph. D.

Unsteady aerodynamic modeling is indispensable in the design process of rotary air vehicles, flapping flight and agile unmanned aerial vehicles. Undesirable vibrations can cause high-frequency variations in motion variables whose effects cannot be well predicted using quasi-steady aerodynamics. Furthermore, one may exploit the lift enhancement that can be generated through an unsteady motion for optimum design of flapping vehicles. Additionally, undesirable phenomena like the flutter of fixed wings and ensuing limit cycle oscillations can be exploited for harvesting energy. In this dissertation, we focus on modeling the unsteady nonlinear aerodynamic response and present various applications where unsteady aerodynamics are very relevant. The dissertation starts with experiments for measuring unsteady loads on an NACA-0012 airfoil undergoing a plunging motion under various operating conditions. We supplement these measurements with flow visualization to obtain better insight into phenomena causing enhanced lift. For the model, we present the frequency response function for the airfoil at various angles of attack. Experiments were performed at reduced frequencies between 0.1 and 0.95 and angles of attack up to 65 degrees. Then, we formulate an optimization problem to unify the transfer function coefficients for each regime independently to obtain one model that represents the global dynamics. An optimization-based finite-dimensional (fourth-order) approximation for the frequency responses is developed. Converting these models to state-space form and writing the entries of the matrices as polynomials in the mean angle of attack, a unified unsteady model was developed. In the second set of experiments, we measured the unsteady plunging forces on the same airfoil at zero forward velocity. The aim is to investigate variations of the added forces associated with the oscillation frequency of the wing section for various angles of attack. Data of the measured forces are presented and compared with predicted forces from potential flow approximations. The results show a significant departure from those estimates, especially at high frequencies indicating that viscous effects play a major role in determining these forces. In the second part of this dissertation, we consider different applications where unsteady loads and nonlinear effects play an important role. We perform a multi-objective aerodynamic optimization problem of the wing kinematics and planform shape of a Pterosaur replica ornithopter. The objective functions included minimization of the required cycle-averaged aerodynamic power and maximization of the propulsive efficiency. The results show that there is an optimum kinematic parameter as well as planform shape to fulfill the two objectives. Furthermore, the effects of preset angle of attack, wind speed and load resistance on the levels of harvested power from a composite beam bonded with the piezoelectric patch are determined experimentally. The results point to a complex relation between the aerodynamic loading and its impact on the static deflection and amplitudes of the limit cycle oscillations as well as the level of power harvested. This is followed by testing of a centimeter scale micro wind turbine that has been proposed to power small devices and to work as a micro energy harvester. The experimental measurements are compared to predicted values from a numerical model. The methods developed in this dissertation provide a systematic approach to identifying unsteady aerodynamic models from numerical or experimental data that may work within different regimes. The resulting reduced-order models are expressed in a state-space form, and they are, therefore, both simple and efficient. These models are low-dimensional linear systems of ordinary differential equations so that they are compatible with modern flight dynamic models. The specific form of the obtained added force model, which defines the added forces as a function of plunging velocity and drag forces, guarantees that the resulting model is accurate over a range of high frequencies. Moreover, presented applications give a sense of the broad range of application of unsteady aerodynamics. / Ph. D.

Transition is an important phenomenon in large scale, commercial, wind tunnel testing at low speeds because it is an excellent indicator of an airfoil performance. It is difficult to estimate transition through numerical techniques because of the complex nature of viscous flow. Therefore experimental techniques can be essential. Over the transition region the rate of heat transfer shows significant increases which can be detected using infrared thermography. This technique has been used predominantly at high speeds, on small models made of insulated materials, and for short test runs. Large scale testing has not been widely undertaken because the high sensitivity of transition to external factors makes it difficult to detect. The present study records the process undertaken to develop, implement and validate a transition detection system for continual use in the Virginia Tech Stability Wind Tunnel: a low speed, commercial wind tunnel where large, aluminium models are tested. The final system developed comprises of two high resolution FLIR A655sc infrared cameras; four 63.5-mm diameter circular windows; aluminium models covered in 0.8-mm silicone rubber insulation and a top layer of ConTact© paper; and a series of 25.4-mm wide rubber silicone fiberglass insulated heaters mounted inside the model and controlled externally by experimenters. This system produces images or videos of the model and the associated transition location, which is later extracted through image processing methods to give a final transition location in percentage chord. The system was validated using two DU96-W-180 airfoils of different chord lengths in the Virginia Tech Stability Wind Tunnel, each tested two months apart. The system proved to be robust and efficient, while not affecting the airfoil performance or any other system in use in the wind tunnel. Transition results produced by the system were compared to measurements obtained from pressure data and stethoscope tests as well as the numerical predictions of XFOIL. The transition results from all four methods showed excellent agreement with each other for the two models, for at least two Reynolds numbers and for several angles of attack on both suction and pressure side of the model. The agreement of data obtained under such different conditions and at different times suggests that the infrared thermography system efficiently and accurately detects transition for large aluminium models at low speeds. / Master of Science

This study is undertaken to characterize the aerodynamic behavior of Kevlar-wall test sections and specifically those containing two-dimensional, lifting models. The performance of the Kevlar-wall test section can be evaluated against the standard of the hard-wall test section, which in the case of the Stability Wind Tunnel (SWT) at Virginia Tech can be alternately installed or replaced by the Kevlar-wall test section. As a first step towards the evaluation of the Kevlar-wall test section aerodynamics, a validation of the hard-wall test section at the SWT is performed, in part by comparing data from NACA 0012 airfoil sections tested at the SWT with those tested at several other reliable facilities. The hard-wall test section showing good merit, back-to-back tests with three different airfoils are carried out in the SWT's hard-wall and Kevlar-wall test sections. Kevlar-wall data is corrected for wall interference with a panel method simulation that simulates the unique boundary conditions of Kevlar-wall test sections including the Kevlar porosity, wall deflection, and presence of the anechoic chambers on either side of the walls. Novel measurements of the boundary conditions are made during the Kevlar-wall tests to validate the panel method simulation. Finally, sensitivity studies on the input parameters of the panel method simulation are conducted. The work included in this study encompasses a wide range of issues related to Kevlar-wall as well as hard-wall tunnels and brings to light many details of the performance of such test sections. / Master of Science

Two experiments were conducted to investigate Adaptive Noise Cancelling and Cepstrum echo removal post-processing techniques on acoustic data from a linear microphone array in an anechoic chamber. A point source speaker driven with white noise was used as the primary signal. The first experiment included a background speaker to provide interference noise at three different Signal-to-Noise Ratios to simulate noise propagating down a wind tunnel circuit. The second experiment contained only the primary source and the wedges were removed from the floor to simulate reflections found in a wind tunnel environment. The techniques were applicable to both signal microphone and array analysis. The Adaptive Noise Cancellation proved successful in its task of removing the background noise from the microphone signals at SNRs as low as -20 dB. The recovered signals were then used for array processing. A simulation reflection case was analyzed with the Cepstral technique. Accurate removal of the reflection effects was achieved in recovering both magnitude and phase of the direct signal. Experimental data resulted in Cepstral features that caused errors in phase accuracy. A simple phase correction procedure was proposed for this data, but in general it appears that the Cepstral technique is and would be not well suited for all experimental data. / Master of Science