Academic literature on the topic 'Low pressure part'

This paper describes an investigation into the behavior of the pressure surface separation at midspan in a linear cascade. It is found that the pressure surface separation can be a significant contributor to the profile loss of a thin, solid, low-pressure turbine blade that is typical of current engine designs. Numerical predictions are first used to study the inviscid behavior of the blade. These show a strong incidence dependence around the leading edge of the profile. Experiments then show clearly that all characteristics of the pressure surface separation are controlled primarily by the incidence. It is also shown that the effects of wake passing, freestream turbulence and Reynolds number are of secondary importance. A simple two-part model of the pressure surface flow is then proposed. This model suggests that the pressure surface separation is highly dissipative through the action of its strong turbulent shear. As the incidence is reduced, the increasing blockage of the pressure surface separation then raises the velocity in the separated shear layer to levels at which the separation can create significant loss.

Low-pressure steam turbine parts are generally exposed to lowest steam parameters only and it could seem that they should not be susceptible to permanent deformation. However, this assumption is incorrect and permanent changes in geometry become visible in low-pressure turbine casings when they are disassembled after the first time in operation. The driving mechanism of the plastic deformation of the low-pressure casings is mainly the non-uniform temperature field. This paper deals with results obtained from a numerical FEM simulation of a steam turbine low pressure part, which includes elastic-plastic behavior of the material, and results measured under the real conditions.

This paper describes a study of the interaction between the pressure surface separation and the secondary flow on low-pressure turbine blades. It is found that this interaction can significantly affect the strength of the secondary flow and the loss that it creates. Experimental and numerical techniques are used to study the secondary flow in a family of four low-pressure turbine blades in linear cascade. These blades are typical of current designs, share the same suction surface and pitch, but have differing pressure surfaces. A mechanism for the interaction between the pressure surface separation and the secondary flow is proposed and is used to explain the variations in the secondary flows of the four blades. This mechanism is based on simple dynamical secondary flow concepts and is similar to the aft-loading argument commonly used in modern turbine design.

AbstractThe effects of scale and aeration on violent breaking wave impacts with trapped and entrained air are investigated both analytically and numerically. By dimensional analysis we show that the impact pressures for Froude scaled conditions prior to the impact depend on the scale and aeration level. The Bagnold–Mitsuyasu scaling law for the compression of an air pocket by a piston of incompressible water is rederived and generalised to 3D air pockets of arbitrary shape. Numerical results for wall pressure, force and impulse are then presented for a flip-through impact, a low-aeration impact and a high-aeration impact, for nine scales and five levels of initial aeration. Two of these impact types trap a pocket of air at the wall. Among the findings of the paper is that for fixed initial aeration, impact pressures from the flip-through impact broadly follow Froude scaling. This is also the case for the two impact types with trapped air pockets for impact pressures below 318 kPa, while impact pressures above this value broadly follow the Bagnold–Mitsuyasu scaling law with full-scale pressures greater than those predicted by the Froude law. For all impact types, the effect of aeration is found to reduce the maximum impact pressure, maximum force and impulse. Good agreement with the asymptotic model of Peregrine & Thais (J. Fluid Mech., vol. 325, 1996, pp. 377–397) is found for the flip-through impact pressure and a fair agreement is found for the low- and high-aeration impacts. Based on the numerical results, a modified scaling curve that combines Froude scaling and the Bagnold–Mitsuyasu law is suggested. The practical implications of the findings are discussed and attention is drawn to the limitations of physical model tests.

A method for increasing the peak output of steam power plants through use of a low-pressure feedwater storage system is presented. The generalized availability analysis involves only the low-pressure turbine, low-pressure feedwater heaters, and the storage system. With daily cycling and storage charging at near base load conditions, the turnaround efficiency of the energy storage system was found to approach 100 percent. Storage system turnaround efficiency is decreased when the energy is stored during plant part-load operation.

Diploma thesis named Steam turbine in the combi cycle deals with design of low pressure part of three-body turbine and it’s lateral outlet throat to the air condenser. Before the design itself, the thermal schema of entire turbine is calculated. Than follows the detail draft, the strength calculations are included as well. Turbine has any technological consumption of steam or any regenerativ consumption. Turbine will be suplly to Panama. The thesis includes following drawings: cut of flowing part, design of outlet throat and fixing of inner body in outer body of low pressure part. The diploma thesis is created for Doosan Škoda Power company.

Thesis focuses on a detailed technical description of all important parts of secondary circuit in Dukovany power plant and its connection to other systems of power plant. In thesis are analyzed significant adjustments which have been made during the entire operation of power plant including in particular the actions associated with project called Utilization of project reserves of units EDU. In the main part of the thesis were carried out calculations of the power plant's power for states before and after the modernization and there is also analyzed the impact of individual changes on the whole power plant. These changes are with the entire secondary circuit drawn in the T-s diagram.

This master thesis was carried out at Scania CV AB, and was proposed in order to explore the possibilities to modernize the present test rig for low pressure parts in the fuel systems in trucks. The rig at the present is hard to maneuver and it is also problematic to do accurate measurements, thus maintain decent repeatability when testing a series of parts. It is also almost impossible to regulate flow and pressure. By integrating a computer for the controlling of the rig and logging of data many of the problems can be solved. During the time of the thesis a conceptual plan, hardware suggestions and complete software was designed to meet today’s requirements for the testing of low pressure parts. Models of flow and pressure have also been made in order to prove what control strategy is the best one to use. The software has been implemented and tested for flow control and is shown to work satisfactory.

La carencia de servicios básicos como agua potable, para zonas como Cajamarquilla, es un problema social que se debe solucionar. Ante esta situación existen proyectos para dotar de servicios de agua a la zona, que por la geografía que presentan se utilizarán reservorios apoyados en los cerros aledaños. El procedimiento de diseño de un reservorio circular de concreto para la zona, servirá como guía para futuros proyectos. Siendo el objetivo de la investigación proponer criterios y un método adecuado para diseñar la estructura de un reservorio de concreto armado que cumplan con los parámetros de la propuesta de norma E030 2014 para la zona de Cajamarquilla, dada la poca información que existe de estos a pesar de ser de uso muy común en nuestro país. El tipo de la investigación es cualitativo, correlacional y de diseño experimental puro, con el fin de obtener resultados certeros para el diseño de reservorio. Finalmente, el método a usar es el que propone la norma del ACI 350-06, basándose en masas impulsivas y convectivas, del modelo de Housner, para el análisis estático mientras que para análisis el dinámico se utilizó el software Sap2000, por el método de elementos finitos y aplicando el espectro de diseño de la norma ACI 350 adecuándose a la norma peruana, como también para el diseño estructural de los elementos del tanque. La distorsión hallada es de 0.001 y que las cortantes basales estáticas y dinámicas son similares estando en un rango de 90%, por lo que se cumplen con los parámetros de la nueva propuesta de norma E030 2014. The lack of basic services such as water, to areas like Cajamarquilla, is a social problem to be solve. In this situation there are plans to provide water services to the area, by geography reservoirs that have supported in the surrounding hills are used. The process of designing a concrete circular reservoir area will serve as a guide for future projects. As the aim of the research propose criteria and an appropriate method to design the structure of a reinforced concrete reservoir that meet the parameters of the proposed rule for the 2014 E030 Cajamarquilla area, given the little information that exists in spite of these It is very commonly used in our country. The type of research is qualitative, pure correlational and experimental design, in order to obtain accurate results reservoir design. Finally, the method used is the standard proposed by the ACI 350-06, based on impulsive and convective mass Housner model for static analysis while for the Sap2000 dynamic analysis software used by the method of and applying the finite element design spectrum ACI 350 standard adapting to the Peruvian standard, as well as for the structural design of the elements of the tank. The distortion founded that the cutting 0.001y static and dynamic baseline are like being in a range of 90%, so that meet the parameters of the new E030 2014 proposed rule.

The Treaty of Rome assigns overriding importance to price stability in the firm belief that maintaining stable prices on a sustained basis is a crucial pre-condition for increasing economic welfare and the growth potential of an economy. Price stability is given formal expression in the Stability and Growth Pact, which confines the budgetary freedom of Member States within precisely defined parameters. The European Union takes the view that by helping to create a favourable economic environment, sound monetary policy should secure the broad objectives of the Community laid down in Article 3. One of these objectives is the promotion of social justice and protection. The thesis focuses on an aspect of social protection: the provision of old age security. The realisation that current pension schemes in many Member States will not be fiscally sustainable has forced their governments to start the process of legislative reform. The challenge is to design pension systems that do not place too heavy a burden on members of working age, while still offering an adequate level of benefit to retired members. Pension system reform has often proved a particularly difficult and awkward political undertaking. The thesis argues that Member States with ageing populations will find it increasingly difficult to maintain high standards of social provision and still comply with the obligations of the Pact. It is contended that continuing demographic imbalance will be a constant impediment to the required maintenance of budgetary balance. Countries have implemented changes, such as increases in statutory retirement age, and reductions in replacement rate, so as to avoid further increasing the contribution burden borne by the diminishing proportion of workers. The thesis concludes that public pension design modifications, whether parametric, such as raising the retirement age, or systemic, such as the introduction of a funded component, will only alleviate and not solve the problem. The only answer is an increased number of younger workers, and that requires birth-rates to move towards replacement level.

Um modelo computacional autoconsistente para a cinética da descarga em um plasma frio, fracamente ionizado, do tipo produzido em tubos de descarga, foi desenvolvido. Ele foi utilizado para investigar a dinâmica das várias propriedades do plasma, tais como temperaturas, densidades e fluxos das espécies que o compõe. Em particular, o modelo desenvolvido considera explicitamente a composição do plasma contendo várias espécies em vários estados de excitação eletrônica. Pode-se determinar a dinâmica das populações envolvidas nas transições laser do átomo de cobre, num modelo autoconsistente para lasers operando em altas taxas de repetição (-5KHz). O modelo mais completo construido considera cinco níveis para o gás tampão (Ne) e nove níveis para o átomo de cobre. O laser de cobre apresenta duas transições, uma no verde e outra no amarelo (5106 A e 5782 A), ambas terminando em estados metaestáveis de longa duração ( -270 J.LS), no átomo livre. No caso mais geral foram considerados trinta processos para determinar a dinâmica do plasma. O tratamento considera, primeiramente, somente a variação temporal e foi utilizado para estudar o plasma formado por três combinações diferentes de espécies: o gás de He puro; a mistura de He:Cu e por último a mistura Ne:Cu, correntemente utillizada em lasers a vapor de cobre. A evolução temporal da temperatura de elétrons, temperatura dos átomos e densidades das espécies, em particular a das espécies excitadas nos niveis de transição laser, pode ser determinada e os resultados comparados com resultados experimentais e de simulação reportados na literatura, mostrando boa concordância no comportamento geral. Verificou-se neste modelo que o principal mecanismo de desexcitação do nível metaestável inferior da transição laser são as colisões superelásticas e não a desativação via interação com as paredes (difusão). Após este primeiro tratamento o modelo passou a considerar também a dependência radial do plasma numa simetria cilíndrica (modelo radial). Neste caso, o efeito de penetração do campo elétrico é explicitamente considerado e o modelo pode ser aplicado tanto a tubos de pequeno como de grande diâmetro, uma vez que o diâmetro é uma grandeza fundamental para a obtenção de lasers de alta potência. Demonstrou-se que esse efeito produz uma distribuição de população dos níveis envolvidos nas duas transições laser (verde e amarela) do cobre, temporalmente distintas e crescentes da borda para o centro, o que concorda com resultados da literatura. Assim, o pulso do laser irá se iniciar com a emissão verde na borda do tubo, conforme predições de nosso modelo. Determinou-se também que existe um limite máximo para o comprimento do tubo do laser, decorrente da existência de uma janela temporal de ganho (-100 ns).
A self-consistent computational model was developed to describe the electrical discharge in a cold plasma, weakly ionized, of the kind usually produced in discharge tubes. The various properties of the species of the plasma as temperature of the electrons, its densities and fluxes could then be obtained. In particular, the model explicitly considers the plasma containing different species in different state of electronic excitation. From these quantities, one can determine the dynamics of the populations involved in the copper atomic laser transition, in a self-consistent model for lasers operation in high repetition rates (-5KHz). The most complete model developed takes into account five level for the buffer gas and nine levels for the copper atom. The copper laser shows two transitions, one in the green and other in the yellow, (5106 Å e 5782 Å), both ending in metaestable states of long duration (~270 µs), in the free atom. In the most complete case studied, thirty processes were considered in the calculations of the plasma dynamics. The formalism first considers solely the temporal dependence and it was used to study the plasma formed by three species: pure He; He and Cu; and Ne and Cu, the last one been currently used in copper vapor lasers. The time dependent populations of the electrons temperature, atoms temperature and densities, in particular the excited levels involved in the laser transitions, could be determined and the results were compared with experimental and simulated results of literature, showing a general good agreement. It was verified, in this model, that the main deexcitation mechanism of the lower metastable laser level is superelastic collisions and not deexcitation via interactions with the walls (diffusion). Therefore, the model was extended to take into account the radial dependence of the plasma in a cylindrical symmetry (radial model). In this case, the skin penetration effect of the electrical field was explicitly considered and the model can then be applied to either small and large diameters, as the diameter is a fundamental parameter for obtaining high power lasers. It is shown that this effect produces a temporally distinct population distribution in the levels of the laser transitions (yellow and green) of the copper atoms, that start in the border and goes to the center, in agreement with the literature. Therefore, the laser pulse starts with the green emission in the border, according to the prediction of our model. It was also found that there is a limit for the maximum length of the laser tube due to the existence of a time window for the positive gain of the laser (~100 ns).

The mechanism by which loss of serum proteins into the urine causes expansion of extracellular fluid volume and oedema has become clearer. A key initiating abnormality is avid sodium retention by the kidney, leading to increased whole-body sodium and increased extracellular fluid volume. This appears to be driven primarily by overactivation of the amiloride-sensitive epithelial sodium channel (ENaC) in the collecting duct, activated proteolytically through abnormal filtration of plasminogen, and its activation to plasmin in the nephron. Conventional explanations for nephrotic oedema focused on low colloid osmotic pressure as a consequence of loss of serum proteins, leading to egress of extracellular fluid from the intravascular compartment. It was hypothesized that this led to underfilling of the circulation and a drive to sodium retention. While low osmotic pressure may play a part in the clinical picture of nephrotic syndrome, a variety of observations suggest that underfilling is not a common feature except in the most severe nephrotic syndrome. Furthermore the gradient in colloid osmotic pressure between serum and interstitium tends to be preserved in nephrotic syndrome. The distribution of excess extracellular fluid is markedly different in patients with nephrotic syndrome from that seen in patients who have reduced glomerular filtration rate as the cause of sodium retention. This is not fully understood but hypotheses centre on capillary permeability and colloid osmotic pressure effects.

A large part of the chapter is dedicated to the story of one of the biggest frauds in science. It is the story of Hendrik Schön and his fantastic discoveries in the field of molecular electronics, and how wrong and manipulated papers ended up getting published in the scientific journals Science and Nature. This provides a stimulus to think about the rules of modern science and how it puts high pressure on young researchers to obtain wonderful results. The last part of the chapter deals with the actual dimensions of fraud in science (still low but growing) and with the dimension of other phenomena such as general cases of misconduct.

Acute brain injury can precipitate a hypertensive response, which for the most part is the result of stress-induced, increased sympathetic activity. Acute stroke with hypertension may not be a response but more often a prior, untreated hypertension or a patient with no access to medication. This hypertensive response may wane quickly, and aggressive treatment of these temporary surges in blood pressure could have unwanted consequences. Important characteristics of most antihypertensive drugs used in the neurosciences intensive care unit are cost, having a rapid onset with a short duration of action, and having a low incidence of adverse side effects. Many of the antiarrhythmic drugs also have antihypertensive effects, so these drug classes are best combined in one chapter. This chapter discusses blood pressure targets, the most appropriate antihypertensive medications to use for acute management, and clinically relevant cardiac arrhythmias and their treatment.

On 28 February 2014, Russian forces moved out of their base on the Black Sea into Crimea, triggering a crisis with Ukraine that quickly spread to Eastern Ukraine. Russia has attempted to justify its actions in Ukraine. On close analysis, no argument is adequate to avoid the charge of aggression, which is any serious violation of United Nations Charter Article 2(4). Article 2(4) is no mere treaty rule. It is jus cogens, a peremptory norm, meaning it is durable, impervious to modification. Facts on the ground in Ukraine may remain unchanged without sufficient international pressure. Regardless, Russia’s presence will remain unlawful.

This chapter discusses the types of disputes which commonly arise in relation to energy and infrastructure construction projects. In terms of physical subject matter — that is, what is being built — this encompasses a wide range of structures, both onshore and offshore. The chapter describes the types of energy and infrastructure construction projects covered here. Moreover, it shows that, despite the variety of problems which can arise in disputes, there are common pressure points in projects which give rise to similar issues. Therefore, the chapter identifies some of the standard form contracts which are used (often in an adapted form) in these types of projects. Next, the chapter considers — from an English law perspective — some of the types of clauses which commonly feature in energy and infrastructure construction contracts.

This chapter provides a working definition of transnational corruption, including its history and the elements that constitute the ‘corruption equation’. It then takes a closer look at contemporary corruption by considering two extremes: that of developing States with kleptocratic rulers, and mature industrial democracies. It concludes that in a global environment of contractual uncertainty, corporate actors are under considerable pressure to maintain the economic viability of present and future projects, and ‘the persistence of experienced operators’ in those industries is necessary to produce reasonable returns. In many cases, to help compensate for such uncertainty, corruption is used as a tool to ensure certainty in two areas that may adversely affect their investment: political uncertainty and economic uncertainty.

The importance of managing legal risk effectively has increased following the recent financial crisis. As the modern regulatory regime for financial markets (global and domestic) continues to evolve, legal risk management techniques must evolve with it. The pressure to attach more importance to ethics and culture within financial institutions will also have an effect on how lawyers do their job. Rightly or wrongly, the responsibility for checking that proper governance principles are observed is bound to fall on their shoulders to some extent. This chapter discusses the role of lawyers and the legal department in legal risk management, opinions and similar documents, document retention, and clarity of lawyer roles.

This chapter examines the recognition and enforcement of arbitral awards. It discusses the carrying out, or performance, of awards, so as to place recognition and enforcement in their proper context. In arbitration, if the losing party fails to carry out an award, the winning party needs to take steps to enforce performance of it. Two steps may be taken. The first is to exert some form of pressure, commercial or otherwise, in order to show the losing party that it is in its interests to perform the award voluntarily. The second is to invoke the powers of the state to obtain a charge over the losing party’s assets or in other ways to compel performance of the award. Pressure may also be exerted through adverse publicity. This method is adopted by trade associations and has the effect of discouraging other traders in the market from dealing with the defaulting party.

Surgical resection of supratentorial brain tumors presents a unique set of challenges to the anesthesiologist. While symptoms from these lesions vary in presentation, increased intracranial pressure (ICP) is frequently part of the constellation and an important piece of anesthetic management. Along with maintenance of ICP, the goals of induction, maintenance, and emergence from these resections are to maintain cerebral blood flow (CBF) and cerebral metabolic rate and optimize neuroprotection. There is no single technique that is agreed upon in literature to encompass these goals, however a combination of IV anesthetics with low-dose volatile agents (0.5 MAC) is common in practice. Management of ICP is the hallmark of these cases since increased ICP may lead to ischemia, poor surgical visualization, and catastrophic herniation.

AbstractInteragency collaboration is increasingly prevalent in welfare contexts due to the current pressure for integrating different professional domains around desired effects on citizens’ life and well-being. In the context of prison service this is equally important, due to the complexity in the constellation of actors that come into contact with a citizen before, during and after imprisonment. Drawing on a combination of neo-institutional theory (DiMaggio & Powell in The New Institutionalism in Organizational Analysis. University of Chicago Press, Chicago, IL, 1991) and sensemaking theory (Weick in Sensemaking in Organizations. Sage, Thousand Oaks, CA, 1995), we investigate an example of how “the Norwegian import model” enables actors to make sense of their work in a way that enables a practice of “living with” contradictions. Based on empirical data produced as part of the COLAB project, this chapter analyses the interagency collaboration of staff and management in a Norwegian low-security prison where professionals target the inmates’ education, health care, sports & leisure, faith and social services. The chapter identifies some key local practices, which underpin the collaboration across sectors and professions. These three practices are narrative practices, practices related to tools and documents, and shared meetings.

AbstractThe structural properties of cast aluminum parts are strongly affected by the solidification in the production process. The solidification dynamics determines the Secondary Dendrite Arm Spacing (SDAS), directly affecting the structural strength of the alloy. Simulation techniques enable the integrated design of chassis parts and their production equipment. However, in order to effectively predict the SDAS formation, the simulation models need to be investigated and calibrated. The present research investigates the SDAS formation models and identifies a robust relation to be used in Design by Simulation phases for AlSi7Mg0.3 parts.

AbstractThe control of the administration by administrative courts follows very particular rules. Two elements of the German system stand out: first, the intensive type of control which makes the scope for independent administrative decision-making an exception. Second, the quite strict restrictions on locus standi. The development of administrative law by the courts and its application by the administration are an elementary part of the German legalistic tradition. The courts of audit at all levels of government also play an independent role. They can control the proper as well as the efficient use of funds from the respective budgets. While there is no enforcement mechanism, the publication of the findings certainly leads to pressure to comply.

The pulmonary circulation is a low-resistance, low-pressure, high-flow system because its primary function is to oxygenate blood. For that reason, pulmonary circulation is different from systemic circulation. Because resistance is lower in pulmonary circulation, pressures across the pulmonary vascular bed also are substantially lower. An efficient system includes inherently low resistance. This allows the entire cardiac output to flow through without high-pressure areas, thereby diminishing the danger of rupturing thin gas-exchange surfaces. One other consequence of low resistance is that the pulmonary circulation is unusually susceptible to the effects of gravity. No substantial part of the cerebral circulation collapses in the head-up position because it is held open by the rigid cranium and the architecture of the venous sinuses. Pulmonary circulation is different. There is less ‘stenting open’ of pulmonary capillaries, and they are therefore more likely to partially or fully collapse when transmural pressure becomes negative.

The last two decades have seen an exponential growth in the fields of electronic communication and information technology. Not surprisingly, ICT devices have become an integral part of our daily life. As demands for the development of more compact and versatile devices arise, there is mounting pressure on the designers to efficiently use the available resources. The new age ICT has become a matter of serious concern for the environment due to increased power consumption by the devices, the backbone infrastructure and eventual electronic waste disposal. This chapter describes techniques to reduce power consumption in ICT by reducing power at the very basal level of usage, which is the hardware. Careful architecture and design in hardware that keeps the principles of carbon reduction in mind can not only increase the efficiency of the device but also help in making it a green device. The primary focus of the chapter is to reduce the power utilized in the computation part of the device. The chapter also provides a background to other studies being carried out to reduce power consumed by the device as a whole.

This paper describes an investigation into the behaviour of the pressure surface separation at midspan in a linear cascade. It is found that the pressure surface separation can be a significant contributor to the profile loss of a thin, solid, low pressure turbine blade that is typical of current engine designs. Numerical predictions are first used to study the inviscid behaviour of the blade. These show a strong incidence dependence around the leading edge of the profile. Experiments then show clearly that all characteristics of the pressure surface separation are controlled primarily by the incidence. It is also shown that the effects of wake passing, freestream turbulence and Reynolds number are of secondary importance. A simple two-part model of the pressure surface flow is then proposed. This model suggests that the pressure surface separation is highly dissipative through the action of its strong turbulent shear. As the incidence is reduced, the increasing blockage of the pressure surface separation then raises the velocity in the separated shear layer to levels at which the separation can create significant loss.

Modern low pressure turbines (LPT) feature high pressure ratios and moderate Mach and Reynolds numbers, increasing the possibility of laminar boundary-layer separation on the blades. Upstream disturbances including background turbulence and incoming wakes have a profound effect on the behavior of separation bubbles and the type/location of laminar-turbulent transition and therefore need to be considered in LPT design. URANS are often found inadequate to resolve the complex wake dynamics and impact of these environmental parameters on the boundary layers and may not drive the design to the best aerodynamic efficiency. LES can partly improve the accuracy, but has difficulties in predicting boundary layer transition and capturing the delay of laminar separation with varying inlet turbulence levels. Direct Numerical Simulation (DNS) is able to overcome these limitations but has to date been considered too computationally expensive. Here a novel compressible DNS code is presented and validated, promising to make DNS practical for LPT studies. Also, the sensitivity of wake loss coefficient with respect to freestream turbulence levels below 1% is discussed.

This paper describes a study of the interaction between the pressure surface separation and the secondary flow on low pressure turbine blades. It is found that this interaction can significantly affect the strength of the secondary flow and the loss that it creates. Experimental and numerical techniques are used to study the secondary flow in a family of four low pressure turbine blades in linear cascade. These blades are typical of current designs, share the same suction surface and pitch, but have differing pressure surfaces. A mechanism for the interaction between the pressure surface separation and the secondary flow is proposed and is used to explain the variations in the secondary flows of the four blades. This mechanism is based on simple dynamical secondary flow concepts and is similar to the aft-loading argument commonly used in modern turbine design.

Bolted joints are the most common type of fastener in army vehicles and play a very important role in maintaining the structural integrity of combat vehicles. In combat, these vehicles may be subjected to various kinds of shock loading, such as initiated by a mine blast, projectile impact, or frontal crash. This study analyzes the transient behavior of structures with bolted joints subjected to impact or shock loads using experimental methods and Finite Element Analysis (FEA). Factors such as damping that affect the bolted joint structures for shock loading are studied. Only a limited amount of published literature describes the proper method for analyzing transient shock propagation across bolted connections for high-impact loading. The initial case study focused on a simple cantilever beam with a bolted lap joint subjected to relatively low levels of impact force. The second case study used a flat plate bolted to a hat-section. These simple configurations are representative of structures found in many military ground vehicles that can be subjected to transient impact and blast loads. These structures were subjected to low-impact loading (non-destructive) using impact hammers and high-impact loading (destructive) using an air gun. The responses were measured using accelerometers. LS-DYNA FE solver was used to simulate the shock propagation in the bolted structures. For all the bolted structures, the modal analysis was performed both experimentally and numerically. The results are in excellent agreement for the lower modes and exhibit a small deviation in the higher modes. Secondly, the time history responses of experimental and FE analysis are compared. This is a two-part paper. In this first paper, a simplified bolted connection (bolted cantilever beam) is used for studying the low-impact shock propagation.

This two-part paper presents a detailed experimental investigation of the laminar separation and transition phenomena on the suction surface of a high-lift low-pressure (LP) turbine airfoil, PakB. The first part describes the influence of Reynolds number, freestream turbulence intensity and turbulence length scale on the PakB airfoil under steady inflow conditions. The present measurements are distinctive in that a closely-spaced array of hot-film sensors has allowed a very detailed examination to be made of both the steady and unsteady behaviour of the suction surface boundary layer. In addition, this paper presents a technique for interpreting the transition process in steady, and periodically unsteady, separated flows based on dynamic and statistical properties of the hot-film measurements. Measurements were made at Reynolds number varying from 25,000 to 150,000 and for freestream turbulence intensities of 0.4%, 2% and 4%. Two separate grids were used to generate turbulence intensity of 4% with integral length scales of about 10% and 40% of the airfoil axial chord length. The first is comparable with the turbulence length scales expected in the engine and the second is considerably larger. While the higher levels of freestream turbulence intensity promoted earlier transition and a shorter separation bubble, the varying turbulence length scale did not have a noticeable effect on the transition process. The size of the separation bubble increased with decreasing Reynolds number, and under low freestream turbulence levels the bubble failed to reattach at low Reynolds numbers. As expected, the losses increased with the length of the separation bubble on the suction side of the airfoil, and increased significantly when the bubble failed to reattach.

The relative motion of rotor and stator blade rows causes periodically unsteady flows that influence the performance of airfoils through their effects on the boundary layer development. Part 1 of this two-part paper described the influence of Reynolds number, freestream turbulence intensity and turbulence length scales on a low-pressure (LP) high-lift turbine airfoil, PakB, under steady inlet flow conditions. The aerodynamic behaviour of the same airfoil under the influence of incoming wakes is presented in Part 2. The unsteady effects of wakes from a single upstream blade-row were measured in a low-speed linear cascade facility at Reynolds numbers of 25000, 50000 and 100000 and at two freestream turbulence intensity levels of 0.4% and 4%. In addition, eight reduced frequencies between 0.53 and 3.2, at three flow coefficients of 0.5, 0.7 and 1.0 were examined. The complex wake-induced transition, flow separation and reattachment on the suction surface boundary layer was determined from an array of closely-spaced surface hot-film sensors. The wake-induced transition caused the separated boundary layer to reattach to the suction surface at all conditions examined. The time-varying profile losses were measured downstream of the trailing edge. Profile losses increase with decreasing Reynolds number and the influence of increased freestream turbulence intensity is only evident in between wake-passing events at low reduced frequencies. At higher values of reduced frequency, the losses increase slightly and for the cases examined here, losses were slightly larger at lower flow coefficients than the higher flow coefficients. An optimum wake-passing frequency was observed at which the profile losses were a minimum.

The numerical simulation of the flow past a circular cylinder forced to oscillate transversely to the incident stream is presented here for a fixed Reynolds number equal to 100. The 2D Navier-Stokes equations are solved with a classical Finite Volume Method with an industrial CFD code which has been coupled with a user subroutine to obtain an explicit staggered procedure providing the cylinder displacement. A preliminary work is conducted in order to check the computation of the wake characteristics for Reynolds numbers smaller than 150. The Strouhal frequency fS, the lift and drag coefficients CL and CD are thus controlled among other parameters. The simulations are then performed with forced oscillations f0 for different frequency rations F = f0/fS in [0.50–1.50] and an amplitude A varying between 0.25 and 1.25. The wake characteristics are analysed using the time series of the fluctuating aerodynamic coefficients and their FFT. The frequency content is then linked to the shape of the phase portrait and to the vortex shedding mode. By choosing interesting couples (A,F), different vortex shedding modes have been observed, which are similar to those of the Williamson-Roshko map.

1.1 Macroeconomic summary Economic recovery has consistently outperformed the technical staff’s expectations following a steep decline in activity in the second quarter of 2020. At the same time, total and core inflation rates have fallen and remain at low levels, suggesting that a significant element of the reactivation of Colombia’s economy has been related to recovery in potential GDP. This would support the technical staff’s diagnosis of weak aggregate demand and ample excess capacity. The most recently available data on 2020 growth suggests a contraction in economic activity of 6.8%, lower than estimates from January’s Monetary Policy Report (-7.2%). High-frequency indicators suggest that economic performance was significantly more dynamic than expected in January, despite mobility restrictions and quarantine measures. This has also come amid declines in total and core inflation, the latter of which was below January projections if controlling for certain relative price changes. This suggests that the unexpected strength of recent growth contains elements of demand, and that excess capacity, while significant, could be lower than previously estimated. Nevertheless, uncertainty over the measurement of excess capacity continues to be unusually high and marked both by variations in the way different economic sectors and spending components have been affected by the pandemic, and by uneven price behavior. The size of excess capacity, and in particular the evolution of the pandemic in forthcoming quarters, constitute substantial risks to the macroeconomic forecast presented in this report. Despite the unexpected strength of the recovery, the technical staff continues to project ample excess capacity that is expected to remain on the forecast horizon, alongside core inflation that will likely remain below the target. Domestic demand remains below 2019 levels amid unusually significant uncertainty over the size of excess capacity in the economy. High national unemployment (14.6% for February 2021) reflects a loose labor market, while observed total and core inflation continue to be below 2%. Inflationary pressures from the exchange rate are expected to continue to be low, with relatively little pass-through on inflation. This would be compatible with a negative output gap. Excess productive capacity and the expectation of core inflation below the 3% target on the forecast horizon provide a basis for an expansive monetary policy posture. The technical staff’s assessment of certain shocks and their expected effects on the economy, as well as the presence of several sources of uncertainty and related assumptions about their potential macroeconomic impacts, remain a feature of this report. The coronavirus pandemic, in particular, continues to affect the public health environment, and the reopening of Colombia’s economy remains incomplete. The technical staff’s assessment is that the COVID-19 shock has affected both aggregate demand and supply, but that the impact on demand has been deeper and more persistent. Given this persistence, the central forecast accounts for a gradual tightening of the output gap in the absence of new waves of contagion, and as vaccination campaigns progress. The central forecast continues to include an expected increase of total and core inflation rates in the second quarter of 2021, alongside the lapse of the temporary price relief measures put in place in 2020. Additional COVID-19 outbreaks (of uncertain duration and intensity) represent a significant risk factor that could affect these projections. Additionally, the forecast continues to include an upward trend in sovereign risk premiums, reflected by higher levels of public debt that in the wake of the pandemic are likely to persist on the forecast horizon, even in the context of a fiscal adjustment. At the same time, the projection accounts for the shortterm effects on private domestic demand from a fiscal adjustment along the lines of the one currently being proposed by the national government. This would be compatible with a gradual recovery of private domestic demand in 2022. The size and characteristics of the fiscal adjustment that is ultimately implemented, as well as the corresponding market response, represent another source of forecast uncertainty. Newly available information offers evidence of the potential for significant changes to the macroeconomic scenario, though without altering the general diagnosis described above. The most recent data on inflation, growth, fiscal policy, and international financial conditions suggests a more dynamic economy than previously expected. However, a third wave of the pandemic has delayed the re-opening of Colombia’s economy and brought with it a deceleration in economic activity. Detailed descriptions of these considerations and subsequent changes to the macroeconomic forecast are presented below. The expected annual decline in GDP (-0.3%) in the first quarter of 2021 appears to have been less pronounced than projected in January (-4.8%). Partial closures in January to address a second wave of COVID-19 appear to have had a less significant negative impact on the economy than previously estimated. This is reflected in figures related to mobility, energy demand, industry and retail sales, foreign trade, commercial transactions from selected banks, and the national statistics agency’s (DANE) economic tracking indicator (ISE). Output is now expected to have declined annually in the first quarter by 0.3%. Private consumption likely continued to recover, registering levels somewhat above those from the previous year, while public consumption likely increased significantly. While a recovery in investment in both housing and in other buildings and structures is expected, overall investment levels in this case likely continued to be low, and gross fixed capital formation is expected to continue to show significant annual declines. Imports likely recovered to again outpace exports, though both are expected to register significant annual declines. Economic activity that outpaced projections, an increase in oil prices and other export products, and an expected increase in public spending this year account for the upward revision to the 2021 growth forecast (from 4.6% with a range between 2% and 6% in January, to 6.0% with a range between 3% and 7% in April). As a result, the output gap is expected to be smaller and to tighten more rapidly than projected in the previous report, though it is still expected to remain in negative territory on the forecast horizon. Wide forecast intervals reflect the fact that the future evolution of the COVID-19 pandemic remains a significant source of uncertainty on these projections. The delay in the recovery of economic activity as a result of the resurgence of COVID-19 in the first quarter appears to have been less significant than projected in the January report. The central forecast scenario expects this improved performance to continue in 2021 alongside increased consumer and business confidence. Low real interest rates and an active credit supply would also support this dynamic, and the overall conditions would be expected to spur a recovery in consumption and investment. Increased growth in public spending and public works based on the national government’s spending plan (Plan Financiero del Gobierno) are other factors to consider. Additionally, an expected recovery in global demand and higher projected prices for oil and coffee would further contribute to improved external revenues and would favor investment, in particular in the oil sector. Given the above, the technical staff’s 2021 growth forecast has been revised upward from 4.6% in January (range from 2% to 6%) to 6.0% in April (range from 3% to 7%). These projections account for the potential for the third wave of COVID-19 to have a larger and more persistent effect on the economy than the previous wave, while also supposing that there will not be any additional significant waves of the pandemic and that mobility restrictions will be relaxed as a result. Economic growth in 2022 is expected to be 3%, with a range between 1% and 5%. This figure would be lower than projected in the January report (3.6% with a range between 2% and 6%), due to a higher base of comparison given the upward revision to expected GDP in 2021. This forecast also takes into account the likely effects on private demand of a fiscal adjustment of the size currently being proposed by the national government, and which would come into effect in 2022. Excess in productive capacity is now expected to be lower than estimated in January but continues to be significant and affected by high levels of uncertainty, as reflected in the wide forecast intervals. The possibility of new waves of the virus (of uncertain intensity and duration) represents a significant downward risk to projected GDP growth, and is signaled by the lower limits of the ranges provided in this report. Inflation (1.51%) and inflation excluding food and regulated items (0.94%) declined in March compared to December, continuing below the 3% target. The decline in inflation in this period was below projections, explained in large part by unanticipated increases in the costs of certain foods (3.92%) and regulated items (1.52%). An increase in international food and shipping prices, increased foreign demand for beef, and specific upward pressures on perishable food supplies appear to explain a lower-than-expected deceleration in the consumer price index (CPI) for foods. An unexpected increase in regulated items prices came amid unanticipated increases in international fuel prices, on some utilities rates, and for regulated education prices. The decline in annual inflation excluding food and regulated items between December and March was in line with projections from January, though this included downward pressure from a significant reduction in telecommunications rates due to the imminent entry of a new operator. When controlling for the effects of this relative price change, inflation excluding food and regulated items exceeds levels forecast in the previous report. Within this indicator of core inflation, the CPI for goods (1.05%) accelerated due to a reversion of the effects of the VAT-free day in November, which was largely accounted for in February, and possibly by the transmission of a recent depreciation of the peso on domestic prices for certain items (electric and household appliances). For their part, services prices decelerated and showed the lowest rate of annual growth (0.89%) among the large consumer baskets in the CPI. Within the services basket, the annual change in rental prices continued to decline, while those services that continue to experience the most significant restrictions on returning to normal operations (tourism, cinemas, nightlife, etc.) continued to register significant price declines. As previously mentioned, telephone rates also fell significantly due to increased competition in the market. Total inflation is expected to continue to be affected by ample excesses in productive capacity for the remainder of 2021 and 2022, though less so than projected in January. As a result, convergence to the inflation target is now expected to be somewhat faster than estimated in the previous report, assuming the absence of significant additional outbreaks of COVID-19. The technical staff’s year-end inflation projections for 2021 and 2022 have increased, suggesting figures around 3% due largely to variation in food and regulated items prices. The projection for inflation excluding food and regulated items also increased, but remains below 3%. Price relief measures on indirect taxes implemented in 2020 are expected to lapse in the second quarter of 2021, generating a one-off effect on prices and temporarily affecting inflation excluding food and regulated items. However, indexation to low levels of past inflation, weak demand, and ample excess productive capacity are expected to keep core inflation below the target, near 2.3% at the end of 2021 (previously 2.1%). The reversion in 2021 of the effects of some price relief measures on utility rates from 2020 should lead to an increase in the CPI for regulated items in the second half of this year. Annual price changes are now expected to be higher than estimated in the January report due to an increased expected path for fuel prices and unanticipated increases in regulated education prices. The projection for the CPI for foods has increased compared to the previous report, taking into account certain factors that were not anticipated in January (a less favorable agricultural cycle, increased pressure from international prices, and transport costs). Given the above, year-end annual inflation for 2021 and 2022 is now expected to be 3% and 2.8%, respectively, which would be above projections from January (2.3% and 2,7%). For its part, expected inflation based on analyst surveys suggests year-end inflation in 2021 and 2022 of 2.8% and 3.1%, respectively. There remains significant uncertainty surrounding the inflation forecasts included in this report due to several factors: 1) the evolution of the pandemic; 2) the difficulty in evaluating the size and persistence of excess productive capacity; 3) the timing and manner in which price relief measures will lapse; and 4) the future behavior of food prices. Projected 2021 growth in foreign demand (4.4% to 5.2%) and the supposed average oil price (USD 53 to USD 61 per Brent benchmark barrel) were both revised upward. An increase in long-term international interest rates has been reflected in a depreciation of the peso and could result in relatively tighter external financial conditions for emerging market economies, including Colombia. Average growth among Colombia’s trade partners was greater than expected in the fourth quarter of 2020. This, together with a sizable fiscal stimulus approved in the United States and the onset of a massive global vaccination campaign, largely explains the projected increase in foreign demand growth in 2021. The resilience of the goods market in the face of global crisis and an expected normalization in international trade are additional factors. These considerations and the expected continuation of a gradual reduction of mobility restrictions abroad suggest that Colombia’s trade partners could grow on average by 5.2% in 2021 and around 3.4% in 2022. The improved prospects for global economic growth have led to an increase in current and expected oil prices. Production interruptions due to a heavy winter, reduced inventories, and increased supply restrictions instituted by producing countries have also contributed to the increase. Meanwhile, market forecasts and recent Federal Reserve pronouncements suggest that the benchmark interest rate in the U.S. will remain stable for the next two years. Nevertheless, a significant increase in public spending in the country has fostered expectations for greater growth and inflation, as well as increased uncertainty over the moment in which a normalization of monetary policy might begin. This has been reflected in an increase in long-term interest rates. In this context, emerging market economies in the region, including Colombia, have registered increases in sovereign risk premiums and long-term domestic interest rates, and a depreciation of local currencies against the dollar. Recent outbreaks of COVID-19 in several of these economies; limits on vaccine supply and the slow pace of immunization campaigns in some countries; a significant increase in public debt; and tensions between the United States and China, among other factors, all add to a high level of uncertainty surrounding interest rate spreads, external financing conditions, and the future performance of risk premiums. The impact that this environment could have on the exchange rate and on domestic financing conditions represent risks to the macroeconomic and monetary policy forecasts. Domestic financial conditions continue to favor recovery in economic activity. The transmission of reductions to the policy interest rate on credit rates has been significant. The banking portfolio continues to recover amid circumstances that have affected both the supply and demand for loans, and in which some credit risks have materialized. Preferential and ordinary commercial interest rates have fallen to a similar degree as the benchmark interest rate. As is generally the case, this transmission has come at a slower pace for consumer credit rates, and has been further delayed in the case of mortgage rates. Commercial credit levels stabilized above pre-pandemic levels in March, following an increase resulting from significant liquidity requirements for businesses in the second quarter of 2020. The consumer credit portfolio continued to recover and has now surpassed February 2020 levels, though overall growth in the portfolio remains low. At the same time, portfolio projections and default indicators have increased, and credit establishment earnings have come down. Despite this, credit disbursements continue to recover and solvency indicators remain well above regulatory minimums. 1.2 Monetary policy decision In its meetings in March and April the BDBR left the benchmark interest rate unchanged at 1.75%.

Macroeconomic Summary Overall inflation (1.61%) and core inflation (excluding food and regulated items) (1.11%) both declined beyond the technical staff’s expectations in the fourth quarter of 2020. Year-end 2021 forecasts for both indicators were revised downward to 2.3% and 2.1%, respectively. Market inflation expectations also fell over this period and suggested inflation below the 3% target through the end of this year, rising to the target in 2022. Downward pressure on inflation was more significant in the fourth quarter than previously projected, indicating weak demand. Annual deceleration among the main groups of the consumer price index (CPI) was generalized and, except for foods, was greater than projected in the October report. The CPI for goods (excluding foods and regulated items) and the CPI for regulated items were subject to the largest decelerations and forecasting discrepancies. In the first case, this was due in part to a greater-than-expected effect on prices from the government’s “VAT-fee day” amid weak demand, and from the extension of some price relief measures. For regulated items, the deceleration was caused in part by unanticipated declines in some utility prices. Annual change in the CPI for services continued to decline as a result of the performance of those services that were not subject to price relief measures, in particular. Although some of the overall decline in inflation is expected to be temporary and reverse course in the second quarter of 2021, various sources of downward pressure on inflation have become more acute and will likely remain into next year. These include ample excesses in capacity, as suggested by the continued and greater-than-expected deceleration in core inflation indicators and in the CPI for services excluding price relief measures. This dynamic is also suggested by the minimal transmission of accumulated depreciation of the peso on domestic prices. Although excess capacity should fall in 2021, the decline will likely be slower than projected in the October report amid additional restrictions on mobility due to a recent acceleration of growth in COVID-19 cases. An additional factor is that low inflation registered at the end of 2020 will likely be reflected in low price adjustments on certain indexed services with significant weight in the CPI, including real estate rentals and some utilities. These factors should keep inflation below the target and lower than estimates from the previous report on the forecast horizon. Inflation is expected to continue to decline to levels near 1% in March, later increasing to 2.3% at the end of 2021 and 2.7% at year-end 2022 (Graph 1.1). According to the Bank’s most recent survey, market analysts expect inflation of 2.7% and 3.1% in December 2021 and 2022, respectively. Expected inflation derived from government bonds was 2% for year-end 2021, while expected inflation based on bonds one year forward from that date (FBEI 1-1 2022) was 3.2%.

From this edition, the Financial Stability Report will have fewer pages with some changes in its structure. The purpose of this change is to present the most relevant facts of the financial system and their implications on the financial stability. This allows displaying the analysis more concisely and clearly, as it will focus on describing the evolution of the variables that have the greatest impact on the performance of the financial system, for estimating then the effect of a possible materialization of these risks on the financial health of the institutions. The changing dynamics of the risks faced by the financial system implies that the content of the Report adopts this new structure; therefore, some analyses and series that were regularly included will not necessarily be in each issue. However, the statistical annex that accompanies the publication of the Report will continue to present the series that were traditionally included, regardless of whether or not they are part of the content of the Report. In this way we expect to contribute in a more comprehensive way to the study and analysis of the stability of the Colombian financial system. Executive Summary During the first half of 2015, the main advanced economies showed a slow recovery on their growth, while emerging economies continued with their slowdown trend. Domestic demand in the United States allowed for stabilization on its average growth for the first half of the year, while other developed economies such as the United Kingdom, the euro zone, and Japan showed a more gradual recovery. On the other hand, the Chinese economy exhibited the lowest growth rate in five years, which has resulted in lower global dynamism. This has led to a fall in prices of the main export goods of some Latin American economies, especially oil, whose price has also responded to a larger global supply. The decrease in the terms of trade of the Latin American economies has had an impact on national income, domestic demand, and growth. This scenario has been reflected in increases in sovereign risk spreads, devaluations of stock indices, and depreciation of the exchange rates of most countries in the region. For Colombia, the fall in oil prices has also led to a decline in the terms of trade, resulting in pressure on the dynamics of national income. Additionally, the lower demand for exports helped to widen the current account deficit. This affected the prospects and economic growth of the country during the first half of 2015. This economic context could have an impact on the payment capacity of debtors and on the valuation of investments, affecting the soundness of the financial system. However, the results of the analysis featured in this edition of the Report show that, facing an adverse scenario, the vulnerability of the financial system in terms of solvency and liquidity is low. The analysis of the current situation of credit institutions (CI) shows that growth of the gross loan portfolio remained relatively stable, as well as the loan portfolio quality indicators, except for microcredit, which showed a decrease in these indicators. Regarding liabilities, traditional sources of funding have lost market share versus non-traditional ones (bonds, money market operations and in the interbank market), but still represent more than 70%. Moreover, the solvency indicator remained relatively stable. As for non-banking financial institutions (NBFI), the slowdown observed during the first six months of 2015 in the real annual growth of the assets total, both in the proprietary and third party position, stands out. The analysis of the main debtors of the financial system shows that indebtedness of the private corporate sector has increased in the last year, mostly driven by an increase in the debt balance with domestic and foreign financial institutions. However, the increase in this latter source of funding has been influenced by the depreciation of the Colombian peso vis-à-vis the US dollar since mid-2014. The financial indicators reflected a favorable behavior with respect to the historical average, except for the profitability indicators; although they were below the average, they have shown improvement in the last year. By economic sector, it is noted that the firms focused on farming, mining and transportation activities recorded the highest levels of risk perception by credit institutions, and the largest increases in default levels with respect to those observed in December 2014. Meanwhile, households have shown an increase in the financial burden, mainly due to growth in the consumer loan portfolio, in which the modalities of credit card, payroll deductible loan, revolving and vehicle loan are those that have reported greater increases in risk indicators. On the side of investments that could be affected by the devaluation in the portfolio of credit institutions and non-banking financial institutions (NBFI), the largest share of public debt securities, variable-yield securities and domestic private debt securities is highlighted. The value of these portfolios fell between February and August 2015, driven by the devaluation in the market of these investments throughout the year. Furthermore, the analysis of the liquidity risk indicator (LRI) shows that all intermediaries showed adequate levels and exhibit a stable behavior. Likewise, the fragility analysis of the financial system associated with the increase in the use of non-traditional funding sources does not evidence a greater exposure to liquidity risk. Stress tests assess the impact of the possible joint materialization of credit and market risks, and reveal that neither the aggregate solvency indicator, nor the liquidity risk indicator (LRI) of the system would be below the established legal limits. The entities that result more individually affected have a low share in the total assets of the credit institutions; therefore, a risk to the financial system as a whole is not observed. José Darío Uribe Governor