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This Thesis describes a technique for collecting, moulding and testing naturally occurring ice accretions. Faithful reproductions of the ice shapes were cast in silicone rubber from which wind tunnel models were made. They were tested using a specifically designed wind tunnel rig which measured the aerodynamic lift, drag and pitching moment of the models. From the aerodynamic data the gradients of lift, drag and pitching moment of each ice shape were calculated. The aerodynamic data were consequently used in a two-dimensional two degree of freedom theoretical aerodynamic model which included aerodynamic lift, drag, moment, ice eccentricity, conductor wake effects and the mechanical properties of the conductor. Wind tunnel tests were carried out on a specifically designed wind tunnel dynamic rig. Instabilities of the coupled vertical/torsional galloping were established. Regions of instability were also predicted using a two-dimensional theoretical conductor model. The initial theoretical analysis formed the basis upon which a more sophisticated three-dimensional finite element aeroelastic model was developed. The effects of ice and wind on the natural frequencies and the stability of the conductor were investigated. The use of galloping control devices, the pendulum detuners was also examined. Results showed that the pendulums had a stabilising effect in controlling the vertical/torsional frequency ratio of twin bundles. The vibration characteristics and the stability of quad bundles were investigated using finite elements. In this case, the pendulums shifted the torsional frequencies of the bundle to higher values close to the corresponding vertical frequencies, thus enhancing coupling and having an adverse effect on stability. Finally, limitations in the performance of the pendulum detuners were predicted.

Wind farms are nowadays more often constructed in alpine terrain than earlier due to theprofitable wind resource as well as, often, less conflicting interests than in more denselypopulated areas. The cold climate poses a relatively new challenge to the wind power industrysince icing of the wind turbine blades and sensors may induce losses in production, increasethe wear and tear of the components, leading to a shortening of structural life time as well as itdecreases the availability and hence reducing the economical profitability for the owner.This study focuses on modelling of ice accretion on a vertically mounted cylinder,dimensioned to correspond to an IceMonitor, and comparing the results with measured iceload on a similar instrument during the winter of 2009/2010. The modelling is carried outwith both a statistical approach using multiple linear regression and a physical approach usingmodel for ice accretion. Ice load was also modelled for the period 1989-2009 using the ERAinterimre-analysis data set in order to compare the winter 09/10 with a longer referenceseries. Modelled ice loads for four winters between 2005 and 2009 were compared withproduction data to investigate a possible connection between ice load and production losses.The results showed that the statistical approach was unable in its current form toreproduce and predict measured ice loads and the method was deemed unsuitable. Thephysical model shows more promising results, although with problems in modelling rapid iceaccretion and ice shedding events.No clear connection between measured production losses and modelled ice loads wasfound when analyzing available data. Uncertainties in input data correction as well asimportance of ice density are possible sources of error.Due to confidentiality of some of the data, the measurement sites used in this thesis aredenoted site A, site B and site C.

An aircraft may experience inlight ice accretion and corresponding reductions in performance and control when the vehicle encounters clouds of super-cooled water droplets. In order to study anti-icing coatings, the EADS-IW Surface Engineering Group is building a refrigerated wind tunnel. Several variations of droplet delivery systems were explored to determine the most effective way to introduce mono-dispersed droplets into the wind tunnel. To investigate this flow, timeurate, unsteady viscous flow simulations were performed using the Loci/CHEM flow solver with a multi-scale hybrid RANS/LES turbulence model. A Lagrangian droplet model was employed to simulate the movement of water droplets in the wind tunnel. It was determined that the droplet delivery system required pressure relief to properly orient the flow inside the droplet delivery tube. Additionally, a streamlined drop tube cross-section was demonstrated to reduce turbulence in the wake and decrease the variability in droplet trajectories in the test section.

Researchers have been developing techniques to predict inlight icing in order to determine aircraft behavior under different icing conditions. A key component of the techniques is the mesh generation strategy. Automated meshing facilitates numerical simulation of ice accretion on realistic aircraft configurations by deforming the surface and volume meshes in response to the evolving ice shape. The objective of this research is to validate an ice accretion strategy for wings, using a previously developed meshing strategy. The intent is to investigate the effect of varying numerical parameters, on the predicted ice shape. Using this framework, results are simulated for rime and glaze ice accretions on a rectangular planform wing with a constant GLC-305 airfoil section. The number of time steps is shown to have a significant effect on the ice shape, depending on the icing time and conditions. Decreasing the height smoothing parameters generally improves the ice shape accuracy.

This study proposes a method to enhance the anti-icing capabilities of superhydrophobic surfaces by utilizing vibration to further reduce contact time of an impacting droplet in addition to keeping the droplet in the Cassie-Baxter regime, where surface adhesion is lower than the opposing Wenzel regime. We tested this with two methods: by investigating the effects of vibration normal to the plane of a superhydrophobic surface being impacted by water droplets in a room temperature environment, with the surface horizontal in a room temperature environment and tiled in a subzero degree environment. The amplitude and frequency of the vibration were varied in our experiments. Our results show that the mean contact time of a 10µL droplet consistently decreased linearly as the vibration frequency increased, though the standard deviations drastically increased. The ice accretion in the second phase of the testing also had significant variance, which obfuscated any reliable trend from the introduction of vibration.

No description available.

Wind turbines often operate under cold weather conditions where icing may occur. Icing causes the blade sections to stall prematurely reducing the power production at a given wind speed. The unsteady aerodynamic loads associated with icing can accelerate blade structural fatigue and creates safety concerns. In this work, the combined blade element-momentum theory is used to compute the air loads on the baseline rotor blades, prior to icing. At each blade section, a Lagrangian particle trajectory model is used to model the water droplet trajectories and their impact on the blade surface. An extended Messinger model is next used to solve the conservation of mass, momentum, and energy equations in the boundary layer over the surface, and to determine ice accretion rate. Finally, the aerodynamic characteristics of the iced blade sections are estimated using XFOIL, which initiate the next iteration step for the computation of air loads via combined blade element theory. The procedure repeats until a desired exposure time is achieved. The performance degradation is then predicted, based on the aerodynamic characteristics of the final iced blades. The 2-D ice shapes obtained are compared against experimental data at several representative atmospheric conditions with acceptable agreement. The performance of a generic experimental wind turbine rotor exposed to icing climate is simulated to obtain the power loss and identify the critical locations on the blade. The results suggest the outboard of the blade is more prone to ice accumulation causing considerable loss of lift at these sections. Also, the blades operating at a higher pitch are expected to accumulate more ice. The loss in power ranges from 10% to 50% of the rated power for different pitch settings under the same operating conditions.

Wind turbines are becoming a more common sight and a more important part in the power grid. The benefits are mainly that wind energy is a renewable energy source and a single wind turbine can produce enough electricity to cover several households’ annual electricity need and not producing carbon dioxide as a rest product. Drawbacks are fluctuation in wind speed, which makes it difficult to regulate. The turbines need to be placed far from cities which cause losses in transmission in the national power grid.  In cold areas with long winters there is a risk of high energy losses due to iced blades. If there is ice accretion on the wind turbine blades it can cause a production loss and in extension economical losses by not selling the electricity. Finding those events is of high interest and there are methods to prevent and remove ice. However, there are occasions when there is ice on the blades, but no sensors signal this, and the production loss is a fact. There is a presumed production loss of 5-25 % annually due to icing on wind turbines in Sweden, depending on where the site is located. There is no general method for detecting ice in the industry but there are several methods available developed by different parties.  In this master’s thesis, a software has been developed in cooperation with Siemens Gamesa Renewable Energy to identify production losses on wind turbines due to icing using historical SCADA data. The software filters the raw data to construct a reference curve, to which data during cold weather is compared. It was found that low temperature causes ice losses, and the risk of an ice loss increases as temperature decreases. The annual losses at investigated wind farms were 4-10 % of the expected annual production. / Vindkraftverk blir en allt vanligare syn och en viktigare del i kraftnätet. Fördelarna är framförallt att det är en förnybar energykälla, det blir inga koldioxidutsläpp när vindkraftverken har installerats och ett vindkraftverk kan täcka flera hushålls årliga elbehov. Nackdelar är att vinden inte går att kontrollera och elproduktionen inte är garanterad eller konstant. Vindkraftverk placeras långt ifrån tätorter, vilket leder till förluster under distribution.  I kalla regioner med långa vintrar uppstår en risk för energiförluster på grund av nedisade turbinblad. Om det finns ispåbyggnad på turbinbladen kan det orsaka produktionsförluster och följaktligen en ekonomisk förlust. Det är av stort intresse i att upptäcka dessa och det finns flera metoder för att förbygga is och även avisning. Det antas vara produktionsförluster på 5-25 % årligen på grund av is i Sverige, beroende på vindparkens placering. Det finns ingen generell metod för att upptäcka is inom industrin, men det finns flera metoder utvecklade av olika parter.  I det här examensarbetet har en mjukvara utvecklats i samarbete med Siemens Gamesa Renewable Energy för att upptäcka produktionsförluster hos vindkraftverk orsakade av nedisade turbinblad genom att använda SCADA-data. Mjukvaran filtrerar rådata för att beräkna en referenskurva, mot vilken data för kallt väder kan jämföras. Den visar att det finns korrelation mellan låg temperatur och produktionsförluster samt att risken för produktionsförlust ökar då temperaturen sjunker. De årliga produktionsförlusterna hos de undersökta vindparkerna var 4-10 % av den förväntade årliga produktionen.

Atmospheric icing presents serious challenges to the development of wind power of the wind energy industry in cold regions. The potential detrimental impact on the safe operation of wind turbines and the energy harvest hasn't been fully understood and requires further investigation. This thesis presents the research on icing profiles under different weather conditions and their impact on natural frequency, fatigue life, and lift and drag of the wind turbine blade. The research aims to develop a further understanding of the effect of atmospheric ice accretion on the structural integrity and aerodynamic performance of wind turbine blades through numerical and aerodynamic investigations to address the challenges facing the industry. A 5-MW NREL (National Renewable Energy Laboratory) wind turbine blade was selected for this study, due to availability of required geometric design parameters and experimental data for verification. The turbine rotor and its three blades were modelled and numerically simulated with commercial finite element software ANSYS. Three icing scenarios were chosen according to the ISO Standard and the corresponding icing profiles were developed to investigate their influence on vibrational behaviours of the wind turbine blade and rotor under different weather conditions. Icing loads were applied on the leading edge of the blade and natural frequency results were compared between clean and iced blades. It was found that harsh icing weather drove the natural frequency down to the near resonance limit, which could lead to significant issue on structural integrity of the wind turbine. The effect of atmospheric ice accretion with additional load due to varying wind speeds on the fatigue life of the wind turbine blade has been investigated. Significant reduction of fatigue life was found due to the increase of the von Mises stresses. Finally, computational fluid dynamics (CFD) analysis was carried out to investigate the effect of atmospheric ice accretion on the aerodynamic performance of typical 1-MW and 5-MW wind turbine blades. Results of the drag and lift coefficients and power production under different icing scenarios were obtained for five angles of attack. Compared with the results of the clean aerofoil profile, remarkable reduction in the power generation was observed due to the accreted ice at various aerofoil sections in the spanwise direction of the blade, demonstrating the detrimental impact of atmospheric icing on energy harvest for the wind energy industry.