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Turbomachinery operating on aircraft are often exposed to dusty or sandy environments during typical service. Engines on commercial and military flights operating in desert regions such as the Middle East or even Phoenix, Arizona can become severely damaged by ingesting dirt, grit, sand, and dust. Due to the high speeds, pressures, and temperatures, ingested particles can inflict erosion upon the blades, stators, and other components within the operating turbomachinery. Left unchecked, this erosion can lead to an increase in surge and stall probability while also contributing to higher service frequency and maintenance cost. Historically, particle-induced erosion is thoroughly documented and has been studied extensively; however, the underlying physics that govern the particle-surface interactions present in turbomachinery have remained elusive. The work described in this dissertation aims to describe a novel experimental technique used to measure and quantify particle-surface interactions characteristic of those present in turbomachinery. Specifically, the technique captures fully time-resolved trajectories of microparticles rebounding off a flat surface. It has been developed to measure the coefficient of restitution for particles of various material composition and shape incident on various surface materials at differing speeds and angles of incidence. The coefficient of restitution is a kinetic energy conservation metric that characterizes the amount of kinetic energy lost by particle during impact with a static surface and can be related to erosion extent and erosion mode. Many key findings were made during the experimental campaign that focused on particle bounce. It is shown that measuring fully-time resolved trajectories of bouncing particles leads to the highest quality coefficient of restitution data. Specifically, obtaining fully-time resolved trajectories allows for the stochasticity present in particle bounce to be measured and for the uncertainty in the coefficient of restitution to be fully characterized. It is shown that particle shape is not only the key driver that contributes to the stochasticity present in particle rebound, but also an important factor for determining the amount of plastic deformation that occurs on the flat surface. These findings are underscored in a novel coefficient of restitution model that accounts for the jagged particle shape present on typical particles and the plastic deformation of the surface material. This novel model also provides an analytical prediction of some of the stochasticity, or spread, present in coefficient of restitution measurements caused by particle shape. The modeled particle bounce and surface deformation is compared with experimental results. It is demonstrated that the new model accurately captures the slope of normal coefficient of restitution vs. normal velocity while surface deformation measurements can be used as an auxiliary validation for particle bounce models. In addition to measuring the coefficient of restitution for particle bounce, a novel measurement technique has also been developed to directly measure particle breakage. Along with the breakage probability of a particle, both the number and speed of the fragments for each broken breakage are measured. As expected, the breakage probability generally scales with normal velocity. It is shown that the average rebounding angle distribution for broken fragments is identical to that of bouncing particles for identical impact conditions. Moreover, average fragment velocities were shown to be about the same as that of bouncing particles. Finally, it is demonstrated that automated breakage detection allows for a significantly higher number of breakage events to be measured. This allows for the accuracy of the breakage probability measurement to be directly estimated with an uncertainty estimate. Raw results from the experimental study along with the novel coefficient of restitution model can be used to develop models for erosion in turbomachinery. Specifically, the coefficient of restitution is typically implemented in computational fluid dynamics (CFD) simulations to predict particle paths and induced erosion in turbomachinery. Currently, CFD simulation results do not agree with real-world erosion findings. This implies that the underlying physics governing erosion are not fully understood. Higher accuracy models, such as the one developed in this dissertation, coupled with empirical data can be leveraged to increase the accuracy of CFD simulations to predict erosion. In the long term, if erosion can be predicted, new engine designs can be developed that will be erosion resistant. These engines may feature new geometry to aid in expelling particles from an engine along with different materials that may be more erosion resistant. / Doctor of Philosophy / Erosion induced by particle ingestion has plagued aircraft since their inception. During operation within dusty environments, sand, dirt, and grit can be ingested into operating turbomachinery such as turbofan engines, turboshaft engines, and turbojet engines. High relative speeds between the rotating turbomachinery and particles coupled with high temperatures and pressures results in deformation and erosion of critical engine surfaces. Left unchecked, erosion of the engine can lead to significant safety concerns as engine failure can occur. Additionally, eroded engines require increased maintenance and servicing costs. While the effects of erosion have been extensively studied over the past few decades, the underlying physics that govern the erosion process have remained elusive. This work aims to elucidate some of the underlying physics that govern particle-surface interactions within turbomachinery. A novel experimental technique used to characterize particle bounce and particle breakage has been developed. Specifically, microparticles characteristic of those often ingested into engines are accelerated towards a flat surface made of materials often used in turbomachinery. A high-speed camera is used to image particle trajectories before and after impact and kinetic energy loss of each particle is measured. These measurements are used to compute the coefficient of restitution, which is a parameter that can be directly related to erosion location, extent, and mode. Additionally, the technique is also capable of detecting particle breakage and characterizing the number and speed of resulting fragments from the breakage event. The coefficient of restitution measurements are leveraged to draw key insights relating to irregular particle shape and deformation of the surface. These insights are then used to develop a novel coefficient of restitution and surface deformation model. This novel model accounts for the jagged particle shape characteristic of particles often ingested into turbomachinery. Moreover, the model also accounts for the stochasticity in coefficient of restitution measurement results induced by the jagged geometry. These contributions to the understanding of particle-surface interactions can significantly aid the development of erosion resistant designs for aircraft engines.

Jet engines often operate under dirty conditions where large amounts of particulate matter can be ingested, especially, sand, ash and dirt. Particulate matter in different engine components can lead to degradation in performance. The objective of this dissertation is to investigate sand transport and deposition in the internal cooling passages of turbine blades. A simplified rectangular geometry is simulated to mimic the flow field, heat transfer and particle transport in a two pass internal cooling geometry. Two major challenges are identified while trying to simulate particle deposition. First, no reliable particle-wall collision model is available to calculate energy losses during a particle wall interaction. Second, available deposition models for particle deposition do not take into consideration all the impact parameters like impact velocity, impact angle, and particle temperature. These challenges led to the development of particle wall collision and deposition models in the current study. First a preliminary simulation is carried out to investigate sand transport and impingement patterns in the two pass geometry by using an idealized elastic collision model with the walls of the duct without any deposition. Wall Modeled Large Eddy Simulations (WMLES) are carried to calculate the flow field and a Lagrangian approach is used for particle transport. The outcome of these simulations was to get a qualitative comparison with experimental visualizations of the impingement patterns in the two pass geometry. The results showed good agreement with experimental distributions and identified surfaces most prone to deposition in the two pass geometry. The initial study is followed by the development of a particle-wall collision model based on elastic-plastic deformation and adhesion forces by building on available theories of deformation and adhesion for a spherical contact with a flat surface. The model calculates deformation losses and adhesion losses from particle-wall material properties and impact parameters and is broadly applicable to spherical particles undergoing oblique impact with a rigid wall. The model is shown to successfully predict the general trends observed in experiments. To address the issue of predicting deposition, an improved physical model based on the critical viscosity approach and energy losses during particle-wall collisions is developed to predict the sand deposition at high temperatures in gas turbine components. The model calculates a sticking or deposition probability based on the energy lost during particle collision and the proximity of the particle temperature to the softening temperature. For validation purposes, the deposition of sand particles is computed for particle laden jet impingement on a coupon and compared with experiments conducted at Virginia Tech. Large Eddy Simulations are used to calculate the flow field and heat transfer and particle dynamics is modeled using a Lagrangian approach. The results showed good agreement with the experiments for the range of jet temperatures investigated. Finally the two pass geometry is revisited with the developed particle-wall collision and deposition model. Sand transport and deposition is investigated in a two pass internal cooling geometry at realistic engine conditions. LES calculations are carried out for bulk Reynolds number of 25,000 to calculate flow and temperature field. Three different wall temperature boundary conditions of 950 oC, 1000 oC and 1050 oC are considered. Particle sizes in the range 5-25 microns are considered, with a mean particle diameter of 6 microns. Calculated impingement and deposition patterns are discussed for different exposed surfaces in the two pass geometry. It is evident from this study that at high temperatures, heavy deposition occurs in the bend region and in the region immediately downstream of the bend. The models and tools developed in this study have a wide range of applicability in assessing erosion and deposition in gas turbine components. / Ph. D.

Recently, powders of the size d (0.1 μm < d < 10 μm) have been referred to ultrafine particles. The particle shape considered is assumed to be a sphere of the diameter d. The handling of powders is of great importance for processing of pharmaceuticals, cement, chemicals and other products. Most of these technological processes involve powder compaction, storage, transportation, mixing, etc, therefore, understanding of the fundamentals of particles interaction behaviour is very essential in the design of machines and equipment as well as in powder technology, cleaning of environment and other areas. The dynamic behaviour of particulate systems is very complicated due to the complex interactions between individual particles and their interaction with the surroundings. Understanding the underlying mechanisms can be effectively achieved via particle scale research. The problem of a normal contact may be resolved in a number of ways. In spite of huge progress in experimental techniques, direct lab tests with individual particles are still rather time-consuming and expensive. The interaction of particles as solid bodies is actually a classical problem of contact mechanics. In the case of ultrafine particles, the reduction of the particle size shifts the contact zones into the nanoscale or subnanoscale. Thus, steadily increasing contribution of adhesion has to be considered in the development of the physically correct constitutive models and numerical tools. Consequently, it may... [to full text] / Ultrasmulkios dalelės yra šiuolaikinės chemijos, farmacijos, maisto ir kitų pramonės šakų produktų sudėtinė dalis. Tiriant pramoninius technologinius procesus, neišvengiamai reikalingos teorinės žinios apie ultrasmulkių dalelių elgseną. Išsamus supratimas įmanomas tik atlikus įvairius tyrimus. Pastaruoju metu milteliai, klasifikuojami kaip ultrasmulkios (0,1 < d < 10 μm) dalelės, imti plačiai naudoti pramoniniuose procesuose, todėl suprasti ultrasmulkių dalelių elgsenos fundamentalumą miltelių technologijoje yra labai svarbu. Ultrasmulki dalelė yra itin maža, todėl su ja atlikti fizinį eksperimentą, kuris reikalauja specialios įrangos bei žinių, labai sunku. Tokiu atveju dažniausiai naudojamas skaitinis eksperimentas, kurį galima atlikti virtualiai. Skaitinio eksperimento metu yra tiriamos dinaminės ultrasmulkios dalelės savybės bei sprendžiamas dinaminis uždavinys. Taikant skaitinius modelius bei dalelės judėjimą aprašančias jėgų lygtis, naudojami sąveikos modeliai, apimantys adhezinę, klampią, tamprią bei tampriai plastinę sąveikas. Mikroskopinis adhezinės sąveikos modeliavimas – aktualus mechanikos mokslo uždavinys. Taikant sąveikos modelius, svarbu pritaikyti ir diskrečiųjų elementų metodą, kadangi, norint aprašyti dalelių elgseną, visų pirma reikia su-vokti ir aprašyti dalelės modelį. Dalelės elgsenos skaitiniam modeliavimui siūlomi teoriniai modeliai leidžia tirti dalelės sąveiką su dalele ar tampria puserdve bei sąveikos dinamiką. Šie modeliai galėtų būti pritaikyti... [toliau žr. visą tekstą]

In this thesis, the ribbed ducts of the internal cooling passage in turbine blading are investigated to demonstrate the effects of high speed rotation. Rotation coupled with high temperature operating conditions alters the mean flow, turbulence, and heat transfer augmentation due to Coriolis and centrifugal buoyancy forces that arises from density stratification in the domain. Gas turbine engines operate in particle laden environments (sand, volcanic ash), and particulate matter ingested by the engine can make their way into the blade internal cooling passages over thousands of operating hours. These particulates can deposit on the walls of these cooling passages and degrade performance of the turbine blade. Large-Eddy Simulations (LES) with temperature dependent properties is used for turbulent flow and heat transfer in the ribbed cooling passages and Lagrangian tracking is used to calculate the particle trajectories together with a wall deposition model. The conditions used are Re=100,000, Rotation number, Ro = 0.0 and 0.2, and centrifugal Buoyancy parameters of Bo=0, 0.5, and 1.0. First, the independent effects of Coriolis and centrifugal buoyancy forces are investigated, with a focus on the additional augmentation obtained in heat transfer with the addition of centrifugal buoyancy. Coriolis forces are known to augment heat transfer at the trailing wall and attenuate the same at the leading wall. Phenomenological arguments stated that centrifugal buoyancy augments the effects of Coriolis forces in outward flow in the first pass while opposing the effect of Coriolis forces during inward flow in the second pass. In this study, it was found that in the first pass, centrifugal buoyancy had a greater effect in augmenting heat transfer at the trailing wall than in attenuating heat transfer at the leading wall. On the contrary, it aided heat transfer in the second half of the first pass at the leading wall by energizing the flow near the wall. Also, contrary to phenomenological arguments, inclusion of centrifugal buoyancy augmented heat transfer over Coriolis forces alone on both the leading and trailing walls of the second pass. Sand ingestion is then investigated, by injecting 200,000 particles in the size range of 0.5-175μm with 65% of the particles below 10 μm. Three duct wall temperatures are investigated, 950, 1000 and 1050 °C with an inlet temperature of flow and particles at 527 °C . The impingement, deposition levels, and impact characteristics are recorded as the particles move through the domain. It was found that the Coriolis force greatly increases deposition. This was made prevalent in the first pass, as 84% of the deposits in the domain occurred in the first pass for the rotating case, whereas only 27% of deposits occurred in the first pass for the stationary case with the majority of deposits occurring in the bend region. This was due to an increased interaction with the trailing wall in the rotating case whereas particles in the stationary case were allowed to remain in the mean flow and gain momentum, making rebounding from a wall during collision more likely than deposition. In contrast, the variation of wall temperatures caused little to no change in deposition levels. This was concluded to be a result of the high Reynolds number used in the flow. At high Reynolds numbers, the particles have a short residence times in the internal cooling circuit not allowing the flow and particles to heat up to the wall temperature. Overall, 87% of the injected particles deposited in the rotating duct whereas 58% deposited in the stationary duct. / Master of Science

Diploma thesis describes design and function verification of device for filling tap hole of electric arc furnace with tap hole diameter from 190 mm to 250 mm. The theses includes drive design calculation of chute swinging movement and bearing calculations. Another part of the thesis deals with verification of device functions which it is completed with process description of creating DEM simulation in program YADE. The thesis also includes basic experiments for determination angle of internal friction, angle of repose, coefficient of restitution and angle of material friction on a steel surface. Drawing documentation of selected assemblies is part of the thesis.