Flow Instability Effects Related to Purge through a Gas Turbine Chute Seal

This paper investigates flow instabilities inside the cavity formed between the stator and rotor disks of a high-speed turbine rig. The cavity rim seal is of chute seal design. The influence of flow coefficient on the sealing effectiveness at constant purge flow rate through the wheel-space is determined. The effectiveness at different radial positions over a range of purge flow conditions and flow coefficients is also studied. Unsteady pressure measurements have identified the frequency of instabilities that form within the rim seal, phenomena which have been observed in other studies. Frequencies of these disturbances, and their correlation in the circumferential direction have determined the strength and speed of rotation of the instabilities within the cavity. Large scale unsteady rotational structures have been identified, which show similarity to previous studies. These disturbances have been found to be weakly dependent on the purge flow and flow coefficients, although an increased purge reduced both the intensity and speed of rotation of the instabilities. Additionally, certain uncorrelated disturbances have been found to be inconsistent (discontinuous) with pitchwise variation.QC 20220503</p

Pembuatan Company Profile DS Computer

Perkembangan dunia teknologi yang semakin maju membuat komputer menjadi alat yang sangat umum dan dibutuhkan oleh masyarakat dalam kegiatan sehari - hari. Hal ini menyebabkan permintaan masyarakat akan komputer meningkat. Oleh karena itu banyak bermunculan toko komputer dan menyebabkan persaingan dagang diantara mereka. Untuk mengatasinya diperlukan media promosi yang tepat, salah satunya adalah Company Profile. Company Profile adalah media promosi yang berisi informasi tentang perusahaan serta produk dari perusahaan tersebut, dan juga dapat di fungsikan untuk mengenalkan perusahaan kepada masyarakat, jika masyarakat mengenal perusahaan kita maka minat beli dari masyarakat pun akan meningkat. Oleh karena itu dibuatlah DS Computer Company Profile ini. Di dalam Company Profile ini terdapat sejarah singkat mengenai toko DS Computer dan juga review dari beberapa produk yang ditawarkan

Experimental investigation and modeling of a reciprocating piston expander for waste heat recovery from a truck engine

Waste heat recovery using an (organic) Rankine cycle has the capacity to significantly increase the efficiency of heavy-duty engines and thereby reduce fuel consumption and CO2 emissions. This paper evaluates a reciprocating piston expander used in a Rankine cycle for truck waste heat recovery by quantifying its performance on the basis of experimental results and simulations. The experimental results were obtained using a setup consisting of a 12.8 L heavy-duty Diesel engine connected to a Rankine cycle with water and are used to calibrate a semi-empirical expander model. At an engine power between 75 and 151 kW, this system recovered between 0.1 and 3 kW, resulting in an expander filling factor between 0.5 and 2.5, and a shaft isentropic effectiveness between 0.05 and 0.5. The calibrated model indicated that the heat loss (16%), mechanical loss (6–25%), pressure drop (13–42%), and leakage (25–75%) all contributed significantly to the expander performance loss. A simulation study with acetone, cyclopentane, ethanol, methanol, and R1233zd(E), showed that a change of working fluid significantly impacts the expander performance, with the filling factor varying between 0.5 and 2.2 and the effectiveness between 0.01 and 0.5, depending on the working fluid, expander speed, and pressure ratio. The results of the optimization of the built-in volume ratio and inlet valve timing during a typical long haul driving cycle showed that acetone and R1233zd(E) provided the highest available power around 3 kW absolute, or 2.2% relative to the engine. The main contributions of this paper are the presentation of experimental results of an engine coupled to a Rankine cycle, and the quantification of performance losses and the effect of working fluid variation using an adapted semi-empirical expander model, which allows for a selection of the working fluid and geometrical modifications giving optimal performance during a long haul driving cycle

Numerical Characterization of Entropy Noise With a Density Based Solver

In this work, dbnsTurbFoam, a new coupled density based solver, written in the framework of foam-extend, is considered. The solver is first assessed on two canonical compressible flow scenarios, namely the Sod’s shock tube and the ONERA S8 transonic channel. Results are compared with analytical formulations and experiments, respectively. 2-D Unsteady Reynolds Averaged Navier-Stokes simulations and 3-D Large Eddy Simulations of the flow within the passages of a geometrically simplified High Pressure Turbine Nozzle Guide Vane are then performed. Results are compared against experimental data in order to justify the geometrical simplifications made. Finally, the case of a sinusoidal temperature forcing at the inlet is considered in order to study the phenomenon of indirect combustion noise. Notably, the impact of the forcing on the vortex shedding dynamics and on the losses is discussed

Flow Instabilities in Gas Turbine Chute Seals

The ingress of hot annulus gas into stator-rotor cavities is an important topic to engine designers. Rim-seals reduce the pressurised purge required to protect highly-stressed components. This paper describes an experimental and computational study of flow through a turbine chute seal. The computations – which include a 360º domain - were undertaken using DLR TRACE’s time-marching solver. The experiments used a low Reynolds number turbine rig operating with an engine-representative flow structure. The simulations provide an excellent prediction of cavity pressure and swirl, and good overall agreement of sealing effectiveness when compared to experiment. Computation of flow within the chute seal showed strong shear gradients which influence the pressure distribution and secondary-flow field near the blade leading edge. High levels of shear across the rim-seal promote the formation of large-scale structures at the wheel-space periphery; the number and speed of which were measured experimentally and captured, qualitatively and quantitatively, by computations. A comparison of computational domains ranging from 30º to 360º indicate that steady features of the flow are largely unaffected by sector size. However, differences in large-scale flow structures were pronounced with a 60º sector and suggest that modelling an even number of blades in small sector simulations should be avoided. <br/

Global Vascular Guidelines on the Management of Chronic Limb-Threatening Ischemia

Chronic limb-threatening ischemia (CLTI)is associated with mortality, amputation, and impaired quality of life. These Global Vascular Guidelines (GVG)are focused on definition, evaluation, and management of CLTI with the goals of improving evidence-based care and highlighting critical research needs. The term CLTI is preferred over critical limb ischemia, as the latter implies threshold values of impaired perfusion rather than a continuum. CLTI is a clinical syndrome defined by the presence of peripheral artery disease (PAD)in combination with rest pain, gangrene, or a lower limb ulceration >2 weeks duration. Venous, traumatic, embolic, and nonatherosclerotic etiologies are excluded. All patients with suspected CLTI should be referred urgently to a vascular specialist. Accurately staging the severity of limb threat is fundamental, and the Society for Vascular Surgery Threatened Limb Classification system, based on grading of Wounds, Ischemia, and foot Infection (WIfI)is endorsed. Objective hemodynamic testing, including toe pressures as the preferred measure, is required to assess CLTI. Evidence-based revascularization (EBR)hinges on three independent axes: Patient risk, Limb severity, and ANatomic complexity (PLAN). Average-risk and high-risk patients are defined by estimated procedural and 2-year all-cause mortality. The GVG proposes a new Global Anatomic Staging System (GLASS), which involves defining a preferred target artery path (TAP)and then estimating limb-based patency (LBP), resulting in three stages of complexity for intervention. The optimal revascularization strategy is also influenced by the availability of autogenous vein for open bypass surgery. Recommendations for EBR are based on best available data, pending level 1 evidence from ongoing trials. Vein bypass may be preferred for average-risk patients with advanced limb threat and high complexity disease, while those with less complex anatomy, intermediate severity limb threat, or high patient risk may be favored for endovascular intervention. All patients with CLTI should be afforded best medical therapy including the use of antithrombotic, lipid-lowering, antihypertensive, and glycemic control agents, as well as counseling on smoking cessation, diet, exercise, and preventive foot care. Following EBR, long-term limb surveillance is advised. The effectiveness of nonrevascularization therapies (eg, spinal stimulation, pneumatic compression, prostanoids, and hyperbaric oxygen)has not been established. Regenerative medicine approaches (eg, cell, gene therapies)for CLTI should be restricted to rigorously conducted randomizsed clinical trials. The GVG promotes standardization of study designs and end points for clinical trials in CLTI. The importance of multidisciplinary teams and centers of excellence for amputation prevention is stressed as a key health system initiative. © 2019 Society for Vascular Surgery and European Society for Vascular Surger

Palestinian Freelance Journalists - self-censorship, customers and role in society

Title: Palestinian freelance journalists - self-censorship, customers and role in society Number of pages: 67 Authors: Linnea Fridh and Jens Wingren Mentor: Gabriella Sandstig Course: Bachelor thesis, Journalism studies Period: Spring 2015 University: Faculty of Journalism, Media and Communication (JMG) University of Gothenburg Purpose/ Aim: The aim of the study is to map and analyse the working conditions, possibilities and limitations of Palestinian freelance journalists.. Main results: By analysing the answers of our respondents we have concluded that the main possibility with the working conditions of Palestinian freelance journalists is their flexibility. As long as they are financially safe (for example from working another job) they can be more straightforward and uncompromising in their journalism. Freelance journalists are however limited by the financial scarcity of the Palestinian media that don’t pay them enough and offer lacking support. Feeling excluded from the union is also something that specifically affects the freelance journalists and might make them feel more vulnerable. There is therefore a slight paradox inherent in the situation of the Palestinian freelancer: they have the opportunity to do good and critical journalism, but only if they can support themselves financially in some other way. Another finding of this study is that freelance journalists may alter their implications of professional ideals such as objectivity and neutrality when they work with foreign news desks. Working with this kind of customers also provides a way of expressing oneself with less fear of repercussions from differing factors in Palestinian society that might want to silence dissent

Experimental Investigation of Performance, Flow Interactions and Rotor Forcing in Axial Partial Admission Turbines

The thesis comprises a collection of four papers with preceding summary and supplementary appendices. The core investigation solely is of experimental nature although reference and comparisons with numerical models will be addressed. The first admission stage in an industrial steam turbine is referred to as the control stage if partial admission is applied. In order to achieve high part load efficiency and a high control stage output it is routinely applied in industrial steam turbines used in combined heat and power plants which frequently operate at part load. The inlet flow is individually throttled into separate annular arcs leading to the first stator row. Furthermore, partial admission is sometimes used in small-scale turbine stages to avoid short vanes/blades in order to reduce the impact from the tip leakage and endwall losses. There are three main aspects regarding partial admission turbines that need to be addressed. Firstly, there are specific aerodynamic losses: pumping-, emptying- and filling losses attributed to the partial admission stage. Secondly, if it is a multistage turbine, the downstream stages experience non-periodic flow around the periphery and circumferential pressure gradients and flow angle variations that produce additional mixing losses. Thirdly, the aeromechanical condition is different compared to full admission turbines and the forcing on downstream components is also circumferentially non-periodic with transient load changes. Although general explanations for partial admission losses exist in open literature, details and loss mechanisms have not been addressed in the same extent as for other sources of losses in full admission turbines. Generally applicable loss correlations are still lacking. High cycle fatigue due to unforeseen excitation frequencies or due to under estimated force magnitudes, or a combination of both causes control stage breakdowns. The main objectives of this thesis are to experimentally explore and determine performance and losses for a wide range of partial admission configurations. And, to perform a forced response analysis from experimental data for the axial test turbine presented herein in order to establish the forced response environment and identify particularities important for the design of control stages. Performance measurements concerning the efficiency trends and principal circumferential and axial pressure distortions demonstrate the applicability of the partial admission setup employed in the test turbine. Findings reveal that the reaction degree around the circumference varies considerably and large flow angle deviations downstream of the first rotor are present, not only in conjunction to the sector ends but stretching far into the admission sector. Furthermore, it is found that the flow capacity coefficient increases with reduced admission degree and the filling process locally generates large rotor incidence variation associated with high loss. Moreover, the off design conditions and efficiency deficit of downstream stages are evaluated and shown to be important when considering the overall turbine efficiency. By going from one to two arcs at 52.4% admission nearly a 10% reduction in the second stage partial admission loss, at design operating point was deduced from measurements. Ensemble averaged results from rotating unsteady pressure measurements indicate roughly a doubling of the normalized relative dynamic pressure at rotor emptying compared to an undisturbed part of the admission jet for 76.2% admission. Forced response analysis reveals that a large number of low engine order force impulses are added or highly amplified due to partial admission because of the blockage, pumping, loading and unloading processes. For the test turbine investigated herein it is entirely a combination of number of rotor blades and low engine order excitations that cause forced response vibrations. One possible design approach in order to change the force spectrum is to alter the relationship between admitted and non-admitted arc lengths.Denna sammanläggningsavhandling består av fyra artiklar och föregås av en sammanfattning med kompletterande bilagor. Kärnan av undersökningen är experimentell även om referenser och jämförelser med numeriska modeller förekommer där så bedöms lämpligt. Det första steget i en industriell ångturbin kallas reglersteg om partialpådrag tillämpas. Det används rutinmässigt i kraftvärmeanläggningar som ofta körs vid dellaster för att åstadkomma en hög dellastverkningsgrad och hög stegeffekt. Inloppsflödet delas in separata och individuellt strypreglerade pådragsbågar som leder till det första munstycksgittret. Ibland används partialpådrag i små turbiner för att undvika korta blad och på så sätt minska takläckage och ändväggsförlusternas inflytande på den totala förlusten. Det finns i huvudsak tre aerodynamiska/aeromekaniska egenheter som bör beaktas. Först det första är det speciella aerodynamiska förluster associerade till partialpådrag eller reglersteget: ventilations-, tömnings och fyllningsförluster. För det andra, om det är en flerstegsturbin påverkas också nedströms steg negativt av det asymmetriska flödet runt omkretsen som innefattar stora tryckvariationer och flödesvinkelvariationer. För det tredje är den aeromekaniska situationen speciell jämfört med ett fullpådraget steg. För partialpådrag existerar dynamiska krafter med snabba laständringar vid in och utpassering i pådragsbågen. Även om det existerar generella förklaringar i den öppna litteraturen angående förluster så har inte förlustmekanismerna utretts i samma omfattning jämfört med fullpådrag. Ingen generell förlustkorrelation finns. Utmattning på grund oförutsedda excitationsfrekvenser, underskattade kraftamplituder eller en kombination av båda orsakar reglerstegshaveri för ångturbinintressenter. De huvudsakliga målsättningarna med denna studie är att experimentellt utforska och bestämma prestanda och förluster för ett stort antal partialpådragskonfigurationer. Samt att genomföra en vibrationsanalys (relaterat till aerodynamiska kraftimpulser) utifrån mätdata från provturbinen avhandlad häri. Detta för att kartlägga de aeromekaniska förutsättningarna och om möjligt identifiera egenheter viktiga för konstruktion av reglersteg. Prestandamätningar rörande verkningsgradstrender och generella strömningsvariationer runt omkretsen bekräftar resultat från den öppna litteraturen och därmed demonstrerar dugligheten av den partialpådragskonfiguration som används i luftprovturbinen. Dessutom visar resultaten bland annat att reaktionsgraden varierar kraftigt runt omkretsen med stora variationer i rotorns utloppsvinkel inte enbart i anslutning till sektorändar utan långt in i pådragssektorn. Flödeskapacitetskoefficienten eller turbinkonstanten ökar med minskat pådrag och fyllningsprocessen genererar stora variationer i rotorns inloppsvinkel förknippade med höga förluster. Det är viktigt att beakta dellastförutsättningarna och verkningsgradsminskningen för nedströms steg. Genom att använda två pådragsbågar istället för en för ett givet pådrag av 52,4% minskar partialpådragsförlusterna för nedströmssteget med nästan 10 % vid designpunkten, härlett från mätningar. Samlade medelvärden från roterande instationära mätningar visar på en fördubbling av det relativa dynamiska trycket vid rotortömning jämfört med en opåverkad del av pådragsbågen. Vibrationsanalys (relaterat till aerodynamiska kraftimpulser) av mätdata avslöjar att partialpådrag orsakar en stor mängd kraftimpulser med låga varvtalsmultiplar, främst från ventilationen och påavlastningsprocesserna. För provturbinen så är det helt och hållet kombinationer mellan antalet rotorblad och dessa kraftimpulser som orsakar strömningspåverkade vibrationer. Ett möjligt tillvägagångssätt konstruktionsmässigt för att ändra kraftspektrumet är att ändra längförhållandet mellan pådragen och blockerad del.QC 2012010

A Hands-On Student Lab for the Relation Between Unsteady Aerodynamics and Structural Dynamics

A small plate is excited with sound from a portable speaker. Strain gauges and a fast data acquisition unit are used to measure the variations in surface strain on the plate. This is the setup of a new student laboratory to combine theory and practice within unsteady aerodynamics and structural dynamics. To clearly visualize and offer important hands-on lessons for graduate students in a master’s program in aeromechanics, a lab facility has been put together for the participants to study the interaction between unsteady aerodynamics and structural dynamics. The facility was run the first time with students during spring this year, with successful results both in terms of measurements and learning outcomes.QC 20180625</p

On the use of methane in rocket nozzle cooling channels : Bench scale trials

A combination of conjugate heat transfer calculations and experiments in a dedicated test rig at Royal Institute of Technology (KTH), Sweden are performed in order to characterize methane’s impact on the nozzle cooling channels in terms of heat transfer, coking and pressure loss. The design procedure includes development of a numerical conjugate heat transfer model as well as inert trials, not only in order to validate model but more importantly to gain experience in order to reduce uncertainties in the final design. In the final design, the methane can be pre-heated to 655 K at pressure levels between 10 to 160 bars and enters the final heater that simulates the heat load from the flame-side with electric cartridges heating a well-insulated copper block. The heat flux is between 1 to 7 MW/m2 for cooling channel flows representative to a full-scale nozzle of an upper stage engine.MERiT - MEthane in Rocket nozzle cooling channels - conjugate heat Transfer measurement