Heat removal in high pressure turbine seal segments

An important parameter for turbomachinery designers is “clearance control”, because the clearances between interfaces must be set to optimum values to maximize power output, operational life and efficiency. Leakage of hot gas result- ing from excessive clearance, can lead to flow instabilities, components overheat- ing, lower cycle efficiency and a dramatic increase in specific fuel consumption (SFC). Seal segments are used to reduce blade tip leakage, maintain coolant air flow and the stability of rotor-dynamic systems, helping to maximize blade perfor- mance. Seal segments in the High-Pressure Turbine (HPT) stages are one of the hottest components as they face the hot gases coming from the combustion chamber with temperatures which can reach 1700 0 C and which makes them sub- ject to oxidation, erosion, and creep. Thus, seal segments need to be protected. They are currently cooled using jet impingement techniques, passing cooling air (supplied by the high-pressure stage of the compressor) through channels to di- rectly impinge on the hot surfaces. The focus of this research was to improve the jet impingement cooling of the seal segments in HPTs by investigating methods that provide more effective heat removal. The role played by configurations of ribs (surface roughness using be- spoke turbulators), custom-made seal-segments, and surface features such as contouring, both in isolation and combination, were investigated using numerical methods. A set of 174 simulations were carried including the use of uniform and non-uniform roughness elements with different shapes and heights. Firstly, three different uniform roughness elements were tested, a square cross-sectional continuous rib, a hemi-spherical pin-fin and a cubical pin-fin for three jet impingement angles of α=90°, 60° and 45°. Each roughness element was also tested for six different heights (e) between 0.25 mm and 1.5 mm in increments of 0.25 mm. Results are presented in the form of average Nusselt number within and beyond the stagnation region. Secondly, the effect of using a roughness element with a square cross section in the shape of a circle, on the average Nu was investigated for four different radial locations (R), three jet angles (α) and six rib heights (e). Finally, the roughness element used was continuous, of square cross-sec- tion, in the shape of tear drops and reversed tear drops. This meant the rib did not act as a total barrier to flow in either the uphill or downhill direction

Etude et développement de micro-oscillateurs fluidiques pour le refroidissement de systèmes électroniques embarqués

Dans le domaine aéronautique, les contraintes sur le refroidissement sont multiples. L'efficacité d'un système de refroidissement ne se résume plus au simple taux de chaleur dissipée, mais englobe d'autres facteurs comme la compacité, le poids, la robustesse, le coût de maintenance ainsi que la durabilité. Une conception du système de refroidissement qui intègre ces aspects pourrait diminuer les coûts de fonctionnement, notamment la consommation de kérosène, et donc réduire l'impact environnemental du vol. La multiplication de systèmes embarqués dans l'aéronautique amène des contraintes supplémentaires pour leur refroidissement. Dans ce contexte, les actionneurs fluidiques présentent un fort potentiel. Ces travaux portent plus précisément, sur l'utilisation de jets pulsés produits par des oscillateurs fluidiques pour refroidir une surface chauffée. Plusieurs travaux sur les jets d'impact ont montré qu'il était possible d'améliorer la dissipation thermique en introduisant des pulsations dans l'écoulement. Il manque cependant un consensus dans la littérature autour de l'ensemble des conditions opératoires propices à l'amélioration des performances. D'où la nécessité de mener une étude sur l'écoulement produit par ces dispositifs fluidiques et le refroidissement qui en résulte. En amont de cela, il est nécessaire de se pencher sur l'effet de certains paramètres liés à la géométrie du l'oscillateur sur son mode de fonctionnement, en commençant par la caractérisation de l'écoulement pulsé produit par l'oscillateur. AK cette fin, un prototype d'oscillateur est réalisé en fabrication additive puis caractérisé via une reconstruction spatiale 2D et 3D du champ de vitesse à l'aide d'un seul fil-chaud et d'une sonde de pression placée au niveau des canaux de retours. Cette méthode de mesure nous permet de mettre en évidence des structures cohérentes et suivre leur évolution. En marge de cette étude, un réseau de neurones artificiels profond, ayant des fonctions d'activations sinusoïdales atypiques, est utilisé pour créer une représentation implicite du champ de vitesse. L'oscillateur ainsi caractérisé a alors été utilisé pour refroidir une plaque en verre chauffé. Des tests sont pratiqués sur des jets stationnaires et des jets pulsés de même débit massique moyen. Une amélioration considérable des performances est observée pour des faibles distances d'impact et des hautes fréquences de pulsation. Des simulations numériques sont ensuite réalisées en utilisant des méthodes statistiques en un point (dites RANS) et des modèles hybrides LES/RANS. En vue de concevoir un système de refroidissement compact et capable de cibler des composants de tailles submillimétriques, des versions micrométriques de ces mêmes oscillateurs ont été conçues et fabriquées ainsi qu'une instrumentation électronique à même de les caractériser. Rares sont les études menées sur les microjets d'impact alors qu'aucune étude n'a pu être recensée à ce jour sur les microjets d'impact pulsés ni sur les micro-oscillateurs fluidiques gazeux. Le défi est donc double : de montrer que les micro-oscillateurs à gaz peuvent fonctionner à cette échelle et de les utiliser pour refroidir des composants dissipateurs de chaleur. À cela vient s'ajouter un problème non moins ambitieux, celui d'instrumenter l'oscillateur ainsi que la surface d'impact chauffée. Étant donné que la fréquence d'oscillation à cette échelle-là se mesure en kilohertz et que les fluctuations de température sont relativement faibles, des capteurs thermiques à base de couches de polysilicium fortement dopé ont donc été produits. Bien que leur haute sensibilité thermique ait été déjà démontrée, il est question ici d'améliorer leur temps de réponse. Pour ce faire, les capteurs ont été partiellement désolidarisés du substrat en silicium. Cette amélioration de la dynamique du capteur a été obtenue au prix d'une structure fragilisée qu'il a fallu prendre en compte dans les étapes technologiques suivantes.Thermal management in the aerospace industry is subject to a number of constraints. The suitability of a cooling system does not only depend on the heat flux that it can evacuate, but also includes such aspects as compactness, weight, sturdiness, cost of maintenance and durability. Taking these factors into consideration contributes to reducing fuel consumption, thus reducing the carbon footprint of the airplane. With this in mind, fluidic actuators were developed for electronics cooling applications on-board airplanes. In other words, the aim is to cool heated surfaces using the periodic unsteady flow produced by no-moving-parts fluidic oscillators. Previous studies had shown the possibility of enhancing jet impingement heat transfer by introducing a periodic perturbation in the flow. Nevertheless, the exact experimental conditions that lead to this improvement remain somewhat inconsistent across different studies. For this reason, this study tackles both the flow features of the pulsed impinging jet as well as their effects on heat transfer. In preparation, the oscillator is characterized by assessing its response to changes in design parameters and experimental conditions. This was followed by a two- and three-dimensional reconstructions of the velocity field outside the device using a hot-wire and a pressure transducer mounted onto one of the feedback loops. Using this technique, it was possible to deduce certain flow characteristics as well as detect and track the evolution of large coherent vortices produced by the pulsed jet. The data from these exhaustive measurements was then used to train a deep neural network that uses sinusoidal activation functions. The result is an implicit representation of the flow that could be useful to designers when the oscillator is only part of a larger system. The oscillators were then used to cool a heated plate whose temperature was measured using an infrared camera. Both steady and pulsed jets were studied for a large range of frequencies, impact distances and flow rates. Remarkable enhancement was observed for small impact distances and high frequencies. Simulations where then performed using both RANS and hybrid LES/RANS approaches. In the second part of this work, a miniaturized version of the oscillator was produced that can efficiently target small electronic components. Impinging microjets have rarely been studied, while little to no works could be found on pulsed microjets of air or no-moving-parts microfluidic oscillators. The goal of the present study is then twofold, to prove that functional microfluidic oscillators with air as working fluid can be produced and that they can efficiently cool a heated surface. From an experimental standpoint, this requires proper instrumentation capable of acquiring measurements at the spatial and temporal scales of the system. For this end, high-sensitivity thermal sensors were implemented inside the microfluidic device as well as on the heated target surface. The current iteration of these sensing elements involves partially suspending them over the substrate on which they were built in order to reduce their thermal inertia. The carefully suspended structures were shown to withstand the subsequent fabrication steps despite undergoing high temperatures and pressures

Heat Transfer Mechanism In Particle-Laden Turbulent Shearless Flows

Particle-laden turbulent flows are one of the complex flow regimes involved in a wide range of environmental, industrial, biomedical and aeronautical applications. Recently the interest has included also the interaction between scalars and particles, and the complex scenario which arises from the interaction of particle finite inertia, temperature transport, and momentum and heat feedback of particles on the flow leads to a multi-scale and multi-physics phenomenon which is not yet fully understood. The present work aims to investigate the fluid-particle thermal interaction in turbulent mixing under one-way and two-way coupling regimes. A recent novel numerical framework has been used to investigate the impact of suspended sub-Kolmogorov inertial particles on heat transfer within the mixing layer which develops at the interface of two regions with different temperature in an isotropic turbulent flow. Temperature has been considered a passive scalar, advected by the solenoidal velocity field, and subject to the particle thermal feedback in the two-way regime. A self-similar stage always develops where all single-point statistics of the carrier fluid and the suspended particles collapse when properly re-scaled. We quantify the effect of particle inertial, parametrized through the Stokes and thermal Stokes numbers, on the heat transfer through the Nusselt number, defined as the ratio of the heat transfer to the thermal diffusion. A scale analysis will be presented. We show how the modulation of fluid temperature gradients due to the statistical alignments of the particle velocity and the local carrier flow temperature gradient field, impacts the overall heat transfer in the two-way coupling regime

Aeronautical engineering: A continuing bibliography with indexes (supplement 256)

This bibliography lists 426 reports, articles, and other documents introduced into the NASA scientific and technical information system in August 1990. Subject coverage includes: design, construction and testing of aircraft and aircraft engines; aircraft components, equipment and systems; ground support systems; and theoretical and applied aspects of aerodynamics and general fluid dynamics

Thirteenth Workshop for Computational Fluid Dynamic Applications in Rocket Propulsion and Launch Vehicle Technology

This conference publication includes various abstracts and presentations given at the 13th Workshop for Computational Fluid Dynamic Applications in Rocket Propulsion and Launch Vehicle Technology held at the George C. Marshall Space Flight Center April 25-27 1995. The purpose of the workshop was to discuss experimental and computational fluid dynamic activities in rocket propulsion and launch vehicles. The workshop was an open meeting for government, industry, and academia. A broad number of topics were discussed including computational fluid dynamic methodology, liquid and solid rocket propulsion, turbomachinery, combustion, heat transfer, and grid generation

The 2nd International Conference on Advances in Mechanical Engineering

The Second International Conference on Advances in Mechanical Engineering, ICAME-22, was held on 25th August, 2022 at the Mechanical Engineering Department of Capital University of Science and Technology. All articles underwent a rigorous single-blind peer review process. ICAME-22 accepted papers in the disciplines of experimental and computational fluid dynamics, thermodynamics, heat Ttransfer, machine and mechanisms, design, solid mechanics, manufacturing, production and industrial engineering, engineering management, technology management, renewable energy, environmental engineering, bioengineering, materials, failure analysis, and related fields

Engineering Fluid Dynamics 2019-2020

This book contains the successful submissions to a Special Issue of Energies entitled “Engineering Fluid Dynamics 2019–2020”. The topic of engineering fluid dynamics includes both experimental and computational studies. Of special interest were submissions from the fields of mechanical, chemical, marine, safety, and energy engineering. We welcomed original research articles and review articles. After one-and-a-half years, 59 papers were submitted and 31 were accepted for publication. The average processing time was about 41 days. The authors had the following geographical distribution: China (15); Korea (7); Japan (3); Norway (2); Sweden (2); Vietnam (2); Australia (1); Denmark (1); Germany (1); Mexico (1); Poland (1); Saudi Arabia (1); USA (1); Serbia (1). Papers covered a wide range of topics including analysis of free-surface waves, bridge girders, gear boxes, hills, radiation heat transfer, spillways, turbulent flames, pipe flow, open channels, jets, combustion chambers, welding, sprinkler, slug flow, turbines, thermoelectric power generation, airfoils, bed formation, fires in tunnels, shell-and-tube heat exchangers, and pumps

Glossary of terms and table of conversion factors used in design of chemical propulsion systems

The glossary presented is based entirely on terms used in the monographs on Chemical Propulsion. Significant terms relating to material properties and to material fabrication are presented. The terms are arranged in alphabetical order, with multiple word terms appearing in the normal sequence of usage; for example, ablative cooling appears as such, not as cooling, ablative, and lip seal appears as such, not as seal, lip. Conversion Factors for converting U.S. customary units to the International System of Units are presented in alphabetical order of the physical quantity (e.g., density, heat flux, specific impulse) involved

Aeronautical engineering: A special bibliography with indexes, supplement 41, February 1974

This special bibliography lists 514 reports, articles, and other documents introduced into the NASA scientific and technical information system in January 1974

An Experimental Investigation Into The Effects Of High Free-Stream Turbulence On Full Coverage Shaped Hole Film Cooling In An Accelerating Boundary Layer

The purpose of this study is to experimentally investigate the effects of high free stream turbulence on shaped hole film cooling and heat transfer in an accelerating boundary layer. Film cooling is one of most widely used techniques in cooling high pressure turbine blades and endwalls, whether they are land based power turbines or those used for aircraft propulsion. In the section immediately after the combustor, there is very high turbulence and acceleration, and adequate cooling must be implemented to ensure that components do not prematurely fail. This study is able to apply high turbulence intensities to a test section whose acceleration profile yields a favorable pressure gradient and allows us to see the real world effects on shaped hole film cooling effectiveness and heat transfer from high turbulence intensities. The experimentation was conducted in the University of North Dakota large scale low velocity wind tunnel facility. A total of six well documented turbulence intensities ranging from 0.7% to 13.7% were implemented on a large cylindrical test surface at Reynolds numbers of 250,000 and 500,000 and four blowing ratios. The low Reynolds number setup used blowing ratios of M = 0.55, 0.97, 1.35, and 1.89, while only the lowest two blowing ratios were tested at the high Reynolds number. The six turbulence intensities were achieved using a low turbulence (LT) nozzle (Tu = 0.7%), the LT nozzle with a small grid at two locations (Tu = 3.5% and 7.8%), the LT nozzle with a large grid (Tu = 8.1%), and a mock aero combustor with and without a decay spool (Tu = 9.3% and 13.7%). The shaped holes leading edge insert was designed to provide full coverage with two staggered rows of holes with 8º lateral expansion. Both rows of holes are introduced to the surface at 30º. Data showed turbulence to be detrimental to shaped hole film cooling effectiveness in all cases, and to increase heat transfer as the early onset of transition was amplified. The low Reynolds number showed improved film cooling effectiveness over the high Reynolds number due to a longer transition region and slower boundary layer growth. Comparisons of shaped hole film cooling to previous slot film cooling data show the slot to have similar performance in the latter half of the test surface. However, heat transfer and adiabatic effectiveness were much higher in near region due to the slot’s superior coverage. IR camera measurements of shaped hole film cooling show the coolant coverage of the surface at the two low blowing ratios, giving a better perspective on the behavior of the coolant jets after ejection. These data should be useful for comparison in future studies