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Development of surface preparation procedure recommendations for wind turbine blade field repairs
(Montana State University - Bozeman, College of Engineering, 2022) Lusty, Ariel Francis; Chairperson, Graduate Committee: Douglas S. Cairns
Wind turbine blades necessitate reliable field repairs. However, the effects of current wind turbine field repair surface preparation techniques were not well- documented. Poorly informed surface preparation procedures lead to poor quality repairs, so surface preparation procedure recommendations for wind turbine blade field repairs were developed. The effectiveness of current surface preparation techniques, the effects of contaminants, and alternative techniques were evaluated. Current surface preparation techniques involve using solvent wiping to remove contamination. Results indicated that solvent wiping does not significantly affect bond strengths, but solvents can gel resin surfaces. Measuring the changes in bond strengths due to contamination from composite dust and hydraulic oil with time indicated that contamination diffusion effects along bond lines were negligible, but that composite dust and hydraulic oil diminished bond strengths. Contaminants should thus be removed from bond line surfaces prior to repairs. The goal of considering alternative techniques was to increase and equalize the surface energy of repair surfaces using plasma or sizing. There were significant drops in contact angles on composite surfaces treated with plasma, so plasma treatments should continue to be considered for composite surface preparation methods. To examine sizing effects, sizing was applied to scarfed surfaces and specimens were tested in tension. Applying sizing to tapered surfaces prior to scarf repairs did not affect scarf tension ultimate stress values, failure modes, or failure surface elemental composition. In addition, there was a stiffness reduction in the scarfed specimens compared to unscarfed specimens, indicating that the scarf tension repair did not fully restore the composite plate's original properties. Scarf tension experiments were simulated using finite element analysis and results had good agreement between the experiments and the model. The surface preparation recommendation is to test whichever surface preparation methods and adhesive-substrate combinations are used for a repair prior to implementation in the field. Implementing testing of surface preparation methods with adhesive-substrate combinations into surface preparation procedures will decrease lifetime costs and increase energy production for wind turbines, which will ultimately reduce reliance on fossil fuels for societal energy needs.
Controlling the area expansion of a backwards centrifugal fan blade passage using the principles of a diffuser and computational fluid dynamics
(Montana State University - Bozeman, College of Engineering, 2021) Michalson, Adam Jeffrey; Chairperson, Graduate Committee: Erick Johnson
Centrifugal Fans are widespread in today's modern built environment. While a few variations of these fans exist, backward centrifugal fans are an efficient economical option capable of producing the pressure and airflow required for many modern building systems. Even though fans have become necessary piece of building engineering to facilitate occupant health and comfort, fan design almost exclusively relies on approximations to equations that have not changed since the 1950s and can consume, on average, 15% of a building's electrical consumption. Additionally, the approximations made support the ease and low cost of manufacturability. The traditional centrifugal fan design is made from stamped metal parts creating a fan blade sandwich with the blades held between an inlet shroud and a backplate. This rectangular blade passage is where the fluid flows through and picks up tangential acceleration. However, since the 1950s, nearly all advancements in fan design have been through incremental changes that are made by individual companies, and these resulting designs and performance data remain proprietary. This research revisits the foundations of centrifugal fan design with more modern tools and utilizes the concept of the diffuser to strictly control the expansion of the blade passage to improve centrifugal fan efficiency. Computational fluid dynamics was used to evaluate the performance of the new design against a traditionally manufactured fan. Combining the diffuser concept with an elliptical profile for the blade passage better controls the uniformity of the velocity field and pressure gradients through the passageway, while also reducing turbulence. Simulations of the new design against the traditional approach to fan design show an increase of nearly 10% in total efficiency.
Reduced-order aeroelastic modeling of a torsionally compliant UAV rotor blade
(Montana State University - Bozeman, College of Engineering, 2021) Marks, Montana William; Chairperson, Graduate Committee: Mark Jankauski
Small-scale quadrotor helicopters, or quadcopters, have increased in popularity significantly in the past decade. These unmanned aerial vehicles (UAVs) have a wide range of applications - from aerial photography and cinematography to agriculture. Increasing flight time and payload capacity are of the utmost importance when designing these systems, and reducing vehicle weight is the simplest method for improving these performance metrics. However, lighter components and structures are often more flexible and may deform during operation. This is especially the case for flexible UAV blade rotor behavior during flight. Modeling rotor blade deformations is non-trivial due to the coupling between the structure and the surrounding flow, which is called Fluid-Structure Interaction (FSI). Several methods exist for FSI modeling where the most common involves integrating Finite Element and Computational Fluid Dynamics solvers. However, these higher-fidelity models are computationally expensive and are not ideal for parametric studies that consider variable rotor geometry, material properties or other physical characteristics. This research develops low-order modeling techniques that can be leveraged by UAV rotor designers. Here, a reduced-order FSI model of a small-scale UAV rotor blade is developed using Lagrangian mechanics paired with a blade element model. The rotor blade is discretized into rectangular elements along the span. Each blade element is constrained to uni-axial rotation about the span-wise axis and is treated as a torsional stiffness element. The quasi-static equilibrium state of the structure due to aerodynamic forces at user-defined operational conditions is then determined. The model presented is capable of producing a converged solution in as little as 0.016 seconds, as opposed to higher-order FSI models, which can take up to several orders of magnitude longer to solve. It is determined that the deflection of a flexible blade can reduce the total aerodynamic lift from 18-25% when compared to a rigid blade with the same initial geometry. It is shown that the model allows a user to tailor the initial pre-twist of the flexible rotor blade such that losses in lift are reduced to 0.68-5.7%.
The design and testing of an axial condenser fan
(Montana State University - Bozeman, College of Engineering, 2021) Kirk, David Michael; Chairperson, Graduate Committee: Kevin Amende
Axial or propeller fans are a subset of turbomachinery whose application is prevalent in everyday life. In the case of heating, ventilation, air conditioning, and refrigeration (HVAC&R), fans can be a large source of inefficient energy consumption due to their physical operating nature. With the global push for more efficient systems, components of HVAC&R equipment such as fans have become a focal point for researchers in academia and industry alike. Technological improvements in research equipment such as computational fluid dynamics (CFD) and additive manufacturing play a large role in achieving these improved efficiencies. The goal of this research is to improve the efficiency of an axial fan intended for cooling a micro-channel heat exchanger that is used in rooftop condenser units. A higher efficiency retrofit fan was iteratively designed using a commercial CFD software package, Star CCM+, which constitutes much of the research conducted in this project. The iterative models show that significant efficiency gains can be achieved through incremental alterations of classical fan blade geometry elements such as pitch, camber, skew, cross section loft path, chord length, thickness, etc. A physical model of the fan design thought to be the optimal choice for experimental analysis was 3D printed and tested using an AMCA Standard 210 setup. Upon analysis of the physical test results, several discrepancies between simulated and actual results were discovered, highlighting the importance of CFD model validation in the design process. Despite the efficiency gains and advancements in user-friendly packaged software, the simulation underpredicted the power demand and incorrectly depicted the fan's performance at critical operating points showing that improper usage of these experts' tools can inadvertently lead to developed solutions with significant error. While the designed fan achieves an improved peak static efficiency and volumetric flow rate of 53.9% and 4334 CFM respectively, it ultimately did not meet the operating parameters of the specific unit it was designed for and further improvements to the CFD model are needed.
Combining acoustic emission and guided ultrasonic waves for global property prediction and structural health monitoring of glass fiber composites
(Montana State University - Bozeman, College of Engineering, 2018) Murdy, Paul; Chairperson, Graduate Committee: David A. Miller
Since the turn of the century, wind turbines have been rapidly growing in size and are projected to continue growing as the technology develops. These increases in size have led to increased failure rates of the glass fiber composite turbine blades. Because of this, it is of utmost importance to understand failure mechanisms in glass fiber composites and investigate new approaches to predicting failures. This has led to advancements in structural health monitoring of large composites structures by applying sophisticated sensing technologies, in attempts to evaluate material damage states and predict structural failures before they occur. This research has taken a novel approach to apply multiple ultrasonic monitoring techniques, in the form of acoustic emission and guided ultrasonic waves, simultaneously to the mechanical testing of glass fiber reinforced composite laminates. Testing of the composite laminates was conducted in the form of increasing load-unload-reload static tension tests and tension-tension fatigue tests, to measure modulus degradation of the laminates while applying the monitoring techniques. Acoustic emission was used to detect damage events that occurred within laminates in real-time and guided ultrasonic waves were applied periodically to the laminates to observe changes in wave propagation and relate back to damage severity within the laminates. Furthermore, the acoustic emission and guided ultrasonic wave datasets were combined and used to train multivariate regression models to predict modulus degradation of the laminates tested, with no prior knowledge of the laminates' loading histories. Overall, the predictive models were able to make good predictions and showed the potential for combining multiple monitoring techniques into singular systems and statistical predictive models. This research has shown that the combination of the two measurement techniques can be implemented for more accurate and reliable monitoring of large composite structures than the techniques used individually, with minimal additional hardware. Ultimately, this research has paved the way for a new form of smart structural health monitoring, with superior predictive capabilities, which will benefit the renewable energy through reducing maintenance and repair costs and mitigating the risk of wind turbine blade failures.
Experimentation and finite element analysis of repairs on composite laminates and sandwich beam structures
(Montana State University - Bozeman, College of Engineering, 2018) Ibitoye, Oluwafemi Ayodele; Chairperson, Graduate Committee: Douglas S. Cairns
Composites like other engineering materials suffer damage due to mishandling, manufacturing defects and under design. Once they are damaged, an available option may be to restore them to working condition. This work investigated the characteristics of repairs done on wind turbine grade fiber reinforced composite laminates and sandwich beams. Two layups ([0] 2 and [45/-45/0/-45/45]) were investigated with varied forms of repair (infusion bonded, adhesive bonded, infusion with overply) conducted on them. Repaired laminate specimens and repaired sandwich beams were subjected to static tensile loads and four-point flexure respectively. Three-dimensional finite element models augmented with cohesive traction separation relationship were used to analyze bond behavior and compare with experimental observation. Strain data was collected using the process of digital image correlation. Results showed that repairs certainly reduced the stress concentration around regions of damage up to certain strain levels. Similarity in debond behavior was also observed between laminates and sandwich beams of similar ply orientation. Differences were noted in the debond behavior of the two different layups ([0] 2 and [45/-45/0/-45/45]) that were repaired and tested. The observations provided conclusions that could help improve the repair effectiveness of composites.
Evaluation of pitch control techniques for a cross-flow water turbine
(Montana State University - Bozeman, College of Engineering, 2017) Gauthier, Timothy Andrew; Chairperson, Graduate Committee: Erick Johnson
Cross-flow water turbines are complex devices that have yet to see large-scale implementation relative to conventional horizontal-axis wind turbines. While wind energy was the primary target of past investigations, water energy follows most of the same dynamic principles. However, water currents tend to be much more stable than their wind current counterparts, and many water currents exist in channels that favor the compact shape of the cross-flow turbine. These advantages have rejuvenated interest in cross-flow turbine design for marine energy generation. Computational models give engineers the ability to accurately estimate what designs work best to avoid costly field maintenance and downtime. Specifically, computational fluid dynamics uses the Navier-Stokes equations, a set of differential equations that describe the pressure and velocity fields in a fluid domain. The Reynold-Averaged Navier-Stokes turbulence model described in this work examines how controlling the pitch of water turbine blades can improve system performance and reliability. Pitch means that the blade noses up or down about the chord line which runs from leading edge to trailing edge relative to the inflow. Pitch control was originally developed for helicopter blades and is commonly used by conventional wind turbines, but pitch control for water turbines is a relatively new research area. Initial results suggest significant incremental gain in power output with pitch control up to 149%, as compared to a no-pitch case, based on a to-scale representation of the cross-flow water turbine in the Fluids and Computations Laboratory at Montana State University. Simultaneous reliability gain is observed as the force transmitted by the water to the blades is reduced by 135%; this may allow for lower cost turbine structures and streamlined hydrofoil design. Additionally, turbine wake profile visualization and blade pressure coefficient curves describe the viscous interaction both quantitatively and qualitatively. Cross-flow water turbines have the potential to become a significant worldwide energy source, with performance optimization studies such as these a necessary prerequisite.
Influence of fabric architecture on damage progression as evidenced by acoustic emission
(Montana State University - Bozeman, College of Engineering, 2016) Lolatte, Austin James; Chairperson, Graduate Committee: David A. Miller
Fabric reinforced polymer matrix composites are integral structural materials used in wind turbine blades. Wind turbines are expected to increase in size and utilization as global focus turns toward power generation utilizing renewable sources. How these materials change properties due to damage accumulated are important to the future of wind energy. They feature damage mechanisms that are unique from any other engineering material. These factors are now driving innovation for design and manufacturing of the blades. This has led to investigation in characterizing the mechanical behavior of the composites. These composites were manufactured using unidirectional and biaxial fiber layups from three fabrics composed of an epoxy matrix and glass fibers. The effect of the architecture of the fibers on damage progression was determined with acoustic emission sensors that were attached linearly to capture elastic waves emitted by damage mechanisms inside the samples during testing. The critical data extracted from the elastic waveforms include the peak frequency and absolute energy released by the samples and how they are associated with the strength of the samples. A static loading scenario was determined to be the optimal testing method. The use of AE measurements proved to be an invaluable tool to determine how the damage progression of composite materials lead to failure for some, while not being accurate for others. Results found that simple architecture differences for the same fibers have drastic effects on damage progression. However, the energy measurements proved to be imperfect with current technology and application; improvement will be necessary for AE instruments to be a viable tool for energy measurement in the future. AE provides a unique analysis that can identify and characterize damage related to fabric composition. The frequency content provides a consistent method of identifying damage mechanisms between varying materials. Optimal architecture and layup can be determined with the help of AE. Correlating acoustic energy to actual energy dissipated still has potential as a valuable tool if improvement in sensor technology can be achieved. Ultimately, a foundation for correlating mechanical properties of the materials and damage progression to fabric architecture and layup using AE tools was created.
Exploring the effects of fiber angle and stacking sequence on the static strength and acoustic emission signature of epoxy-fiberglass composites in marine environments
(Montana State University - Bozeman, College of Engineering, 2017) Nunemaker, Jake Douglas; Chairperson, Graduate Committee: David A. Miller
Marine Hydro-Kinetic (MHK) devices encompass promising new technologies designed to harness energy from ocean currents and tides. However, there are unique challenges to successful implementation of MHK devices. Material selection and characterization are crucial steps in the design process as the marine environment can be extremely detrimental to many materials systems. Epoxy-fiberglass composites, the premier material in wind turbine blades are being studied for use in MHK due to desirable price and durability. Preliminary research has shown a significant drop in ultimate strength due to moisture absorption in unidirectional laminates. This research extends these studies by exploring these effects on balanced and unbalanced off-axis fiber angles for a common epoxy-fiberglass material system. Ply by ply analysis is completed to explore the efficacy of a strength reduction prediction method for off-axis laminates. It also extends the study to include acoustic emission analysis to further investigate the material degradation at a micromechanical level. Partial saturation strength reduction in symmetric laminates is also studied.
Investigation of the effect of in-plane fiber waviness in composite materials through multiple scales of testing and finite element modeling
(Montana State University - Bozeman, College of Engineering, 2015) Lerman, Michael William; Chairperson, Graduate Committee: Douglas S. Cairns
Defects in materials can reduce strengths and lifetimes of manufactured parts. The number of possible defects increase with the complexity inherent in composite materials. The wind industry uses composite wind turbine blades in which the manufacturing process induces a number of defects. In order for the wind industry to continue sustainable expansion, the effects of defects must be better understood. In-plane (IP) fiber waviness is the focus of this work. The three main parts of this work include testing on the coupon level, modeling on the coupon level, and testing of beams in four-point bending (with and without defects). The coupon level testing includes partial IP waves, similar to those in manufactured parts, rather than full width IP waves. This allows investigation into complex interactions and varying failure mechanisms caused by the fiber misalignment gradient. Partial waves are also modeled to both validate testing as well as to increase robustness of a previously developed progressive damage modeling method. Lastly, a sandwich beam test specimen for testing in 4-point bending is developed to investigate the effects of fiber waviness in both tension and compression when loaded in flexure.

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