Rotorcraft vehicles are highly sensitive to ice accretion. When ice forms on helicopter rotor blades, performance degradation ensues due to a loss of lift and rise in drag. The presence of ice increases torque, power required, and leads to rotor vibrations. Due to these undesirable changes in the vehicle's performance, the FAA requires intensive certification to determine the helicopter’s airworthiness in icing conditions. Since flight tests and icing tunnel tests are very expensive and cannot simulate all conditions required for certification, it is becoming necessary to use computational solvers to model ice growth and subsequent performance degradation. Currently, most solvers use the strip theory approach for 3D shapes. However, rotor blades can experience significant span-wise flow from separation or centrifugal forces. The goal of this work is to investigate the influence of span-wise flow on ice accretion. The classical strip theory approach is compared to a curved surface streamline based approach to assess the relative differences in ice formation.

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Core engine icing has been recognized to affect a wide variety of engines since the 1990's. This previously unrecognized form of icing occurs in flights through high altitude convective regions and vicinity of thunderstorms. Engine icing events involve power loss or damage associated to the engine core, namely instabilities such as compressor surge, stall, engine rollback and even combustor flameout events. The effects on compressor performance are significant in understanding the response of the engine to atmospheric ice ingestion. A one-dimensional axisymmetric flow model is used to simulate the continuous phase through the compressor. The steady state operation of dry air is validated with an industrial database. By changing an exit throttle, the point where the dry compressor mass flow rate slowly starts to drop, is predicted. The stage that is the first to locally collapse, causing the remaining stages and eventually the complete compressor failure, is determined. The continuous flow model is then coupled with a Lagrangian model for the discrete phase in a framework that conserves mass, momentum and energy. From numerical simulations of the coupled, continuous-discrete phase flow model, it is observed that a rematching of the stages across the compressor occurs with increasing ice flow rates to accommodate loss of energy to the ice flow. The migration of the operating point towards the stall point at the rear stage eventually causes the compressor to stall. The onset of stall is characterized by initial oscillations followed by a rapid decay of pressures of the last stage with the instability traveling quickly towards the front of the compressor. Effectively, a reduction in the compressor stall margin is observed as the ice flow rate increases. Further, the relevance of factors such as blockage due to discrete particles and break/splash semi-empirical models in the icing physics, are analyzed through parametric studies. Conclusions are drawn that underscore the influence of the assumptions and models in prediction of the flow behavior in the presence of ice ingestion. Smaller ice crystal diameters have a greater influence on the gas flow dynamics in terms of a higher reduction in surge margin. The break empirical model for ice crystals and splash model for the droplets that are used to calculate the secondary particle size upon impact with rotor blades have a significant influence on the gas flow predictions.

Icings, also known as aufeis, are groundwater fed sheet-layered ice bodies that normally forms in local depression or more often in low angled, shallow river beds. Understanding their distribution in the Mackenzie Valley corridor (N.W.T.) and adjacent Yukon (618,430 km2) provided important insights to groundwater discharge and recharge. This study aimed at; i) creating the first extensive map of icings in Northwestern Canada, using over 500 late-winter scene Landsat 5 and 7; and ii) assessing hydrographic parameters (streamflow, baseflow and winter contribution) and terrain factors (slope, permafrost, geology) on icing distribution at the watershed level. Results show that; 1) icings are likely to develop close to geological faults on carbonate foothills and mountainous terrain, where continuous permafrost is present and on slopes of less than 5 degrees; 2) in the continuous permafrost zone, the cumulative surface area of icings, winter discharge and winter contribution to total annual discharge have significant positive relations with watershed extents. Icings located at the southern boundary of continuous permafrost are more sensitive to degrading permafrost and the predicted increase in groundwater discharge which may lead to a later icing accretion and earlier ablation during the year.

An aircraft will encounter freezing rain, snow, and ice during ground operation and flight. In cold conditions, ice may form on th einlet and internal stators and rotors of the gas turbine engine. When ice accumulates on blades (and/or stators), the aerodynamic characteristics of the blades change due to the altered size, shape, and roughness. This change causes the blade to no longer operate at its design point and decreases compressor performance. Therefore, characterization of the aerodynamic performance is required to define the associated losses due to the effects of supercooled liquid water ingestion. This characterization can be accomplished through analysis and test. This research developed an analysis method to calculate the aerodynamic changes on a blade due to ice accumulation and the associated degradation in performance.

Detaljerad information om vindförhållandena på en site är en nödvändighet för att göra beräkningar av lönsamhet i ett vindkraftsprojekt. Mätningarna behöver vara kontinuerliga och så korrekta som möjligt. Därtill bör de göras under minst ett års tid eftersom vindförhållandena på en plats är säsongsberoende. Under vintertid och framför allt på högre latituder eller altituder, kan mätutrustning påverkas av nedisning. En nedisad anemometer kan ge databortfall eller felaktiga mätningar. Identifiering av felaktiga data är en viktig del av analyseringsarbetet eftersom risken annars är att vindförhållandena på platsen underskattas. Då instrumentet är helt fastfruset kan en enklare analys av data göras genom att titta på standardavvikelsen av vindhastigheten. Svårigheten i detektionen är vid lätt till måttlig nedisning då vindstyrkan, och även standardavvikelsen, kan se normal ut trots att felaktiga värden redovisats. I detta arbete analyseras 1 Hz data från skålkorsanemometer för att söka ett matematiskt sätt att avgöra om lätt till måttlig nedisning påverkat instrumentet under mätperioden. I ett experiment har olika typer av nedisning simulerats på skålkorsanemometrar. Därefter har vindhastighetsfördelningen för en ”nedisad” anemometer kunnat jämföras med fördelningen uppmätt med en anemometer som varit opåverkad under samma mätperiod. I denna jämförelse har visats att trots en differens i medelvind-hastighet på upp till 15 % under mätperioden syns ingen, för detektion av nedisning, användbar skillnad i någon av de statistiska parametrar som jämförts i arbetet. Förutom analys av mätdata från egna experiment har även data från Suorva samt från en höghöjdsmast i Norrland analyserats. För analys av mätdata från masten i Norrland har ett en algoritm utarbetats för automatisk detektion av tidpunkter med instrumentell nedisning. Isdetektionen baseras på antaganden om standardavvikelse av vindhastighet och vindriktning, förändring av vindriktning samt en regression mellan vindhastigheten på två höjder. / Detailed information about the wind conditions on a site is a necessity for calculations of profitability from a wind power project. Hence the continuity and the correctitude of the measurements are crucial when making the site evaluations. Due to the season dependence of the wind conditions the measurements also needs to be done for at least a whole year. During wintertime and particularly on higher altitudes and/or latitudes the instruments may be affected by icing. An iced up anemometer often underestimates the wind speed and severe icing can lead to instrument breakage and loss of data. Identification of inaccurate measurements is of great importance in the analysis of the site’s energy potential. The difficulty in detecting light to moderate icing lies in that the wind speed and the standard deviation of the wind may seem normal, although the anemometer is underestimating the wind speed due to icing. In this thesis 1 Hz data from cup anemometers are analysed in search for a mathematical way to determine whether the instrument has been affected by icing during the measurement. An experiment has been performed simulating different types of icing on anemometers. The wind velocity distribution of an “iced up” anemometer has been compared to the wind velocity distribution of an unaffected anemometer for the same measuring period. Also the turbulence intensity and the change of mean wind velocity between observations have been evaluated. The comparison of these statistical variables between the instruments has showed that none of them are applicable for detection of icing. In addition to analysing data from the experiment a pre-study on the subject has been made analysing measurements with possible icing from the Suorva valley. Also, the results from the experiment have been compared to results from a conventional measuring mast placed in the northern part of Sweden. For the analysis of the mast data an algorithm for detection of icing during measurements has been implemented. This automatic detection of icing is based on assumptions about the standard deviation of wind speed, the standard deviation of the wind direction, the change of wind direction and regression between wind velocities of two heights.

This dissertation presents a methodology to simulate the dispersion of water droplets in the air flow typical of an Icing Tunnel. It is based on the understanding the physical parameters that influence the uniformity and the distribution of cloud of droplets in the airflow and to connect them with analytical parameters which may be used to describe the dispersion process. Specifically it investigates the main geometrical and physical parameters contributing to the droplets dispersion at different tunnel operative conditions, finding a consistent numerical approach to reproduce the local droplets dynamic, quantifying the possible limits of commercial CFD methods, pulling out the empirical parameters/constant needing to simulate properly the local conditions and validating the results with calibrated experiment. An overview of the turbulence and multiphase flow theories, considered relevant to the Icing Tunnel environment, is presented as well as basic concepts and terminology of particle dispersion. Taylor’s theory of particle dispersion has been taken as starting point to explain further historical development of discrete phase dispersion. Common methods incorporated in commercial CFD software are explained and relative shortcomings underlined. The local aerodynamic condition within tunnel, which are required to perform the calculation with the Lagrangian particle equation of motions, are generated numerically using different turbulent models and are compared to the historical K-ε model. Verification of the calculation is performed with grid independency studies. Stochastic Separated Flow methods are applied to compute the particle trajectories. The Discrete Random Walk, as described in the literature, has been used to perform particle dispersion analysis. Numerical settings in the code are related to the characteristics of the local turbulent condition such as turbulence intensity and length scales. Cont/d.

Thesis (M.App.Sc.) - Carleton University, 2001. / Includes bibliographical references (p. 80-83). Also available in electronic format on the Internet.