The general trend of efficiency increase, weight and noise reduction has derived in the design of more slender, loaded, and 3D shaped blades. This has a significant impact on the stability of fan, and low pressure turbine blades, which are more prone to aeroelastic phenomena such as flutter. The flutter phenomenon is a self-excited, self-sustained unstable vibration produced by the interaction of flow and structure. These working conditions will induce either blade overload, or High Cycle Fatigue (HCF) produced by Limited Cycle Oscillation (LCO). The main objectives of the present work are on the investigation of the aeroelastic properties of a high-lift low-pressure in the light of the local flow features present in such profiles, in nominal and extreme off-design conditions both in high and low subsonic Mach number, for three dif-ferent rigid body modes. In addition, the validity of the linearity assump-tion of the influence coefficient technique has also been investigated, in order to expand the understanding of the physical limits of this assumption. This work has been designed as experimental investigation in the influence coefficient domain focused on a high-lift low-pressure turbine designed by ITP within the framework of the European FP7 project FU-TURE. These experiments have been carried out in the Aeroelastic test rig (AETR), at KTH Stockholm, which consist of an instrumented annular sector cascade with a single oscillating blade. The results acquired have been supported by numerical results provided by a non-propietary commercial software package (ANSYS CFX). The results suggest that the typical three-dimensional effects associated secondary flow features and tip leakage flows have a significant influence on the aeroelastic performance and the cascade stability. However the major influence appears as a consequence of the separation surface on the pressure side which appears at extreme off-design operating conditions. The contribution to stability of this local feature depend on the oscillation mode showing for the axial and torsion mode a neutral stability contribution, which is directly associated with the geometrical properties of the cascade. However, on the circumferential mode this separation surface has a stabilizing effect much more independent of the blade geometry. The study of the linearity assumption of the influence coefficient domain has revealed, that an apparent linear relation between the integrated unsteady response and the vibrational amplitude, does not necessary imply that the local unsteady response is linear with respect to the oscillation amplitude. The results also suggest that the validity of the linearity as-sumption is more sensitive to high oscillation amplitudes at high Mach conditions. / <p>QC 20140609</p>

<p dir="ltr">Investigating clearance flows and blockage generation in axial compressors represents a longstanding area of research for enhancing aerodynamic performance and operational stability in turbomachinery. With advancements in computational fluid dynamics (CFD), opportunities to explore these phenomena have expanded, allowing a deeper understanding of the turbomachine's inherently complex and highly unsteady flow fields. This work delves into these topics, focusing on the Purdue 3-Stage (P3S) compressor, an engine-representative, multistage, high-speed compressor.</p><p dir="ltr">The primary objective of this research is to compare the performance and stability characteristics of two distinct stator configurations: a shrouded baseline configuration and a cantilevered stator configuration. This comparison reveals the impacts of clearance flows and blockage generation on compressor operation. Through a series of experimental investigations, this study aims to identify the differences in performance and stability traits between these configurations and the flow structures responsible.</p><p dir="ltr">Experimental characterization has a central role in this study, involving the analysis of leakage flow structures, corner separations, wake structures, and resulting endwall blockage generation. This research seeks to provide detailed insights into the flow phenomena within the compressor by utilizing detailed measurement techniques, such as circumferential interrogation of the flow field using 7-element Kiel-head rakes. Pressure deficits associated with leakage flows, corner separations, and wakes are quantified to assess their impact on compressor performance.</p><p dir="ltr">In conjunction with experimental investigations, this work outlines the development and validation of the supporting high-fidelity CFD models. These models, employing scale-adaptive turbulence model simulations, aim to simulate the flow field within the compressor with accuracy and reliability. Validation of these models against experimental data ensures their fidelity in capturing the complex flow phenomena observed experimentally. Furthermore, a detailed exploration of convergence aspects, including iterative convergence, grid convergence, and periodic-unsteady signals, lays the foundations for building confidence in the model predictions.</p><p dir="ltr">The computational models complement experimental findings, allowing for a comprehensive flow field analysis focusing on endwall flow structures. Visualization of vortex core and three-dimensional blockage regions provides valuable insights into the flow physics governing compressor performance. Moreover, the comparative nature of computational simulations facilitates systematic exploration of geometric changes and their effects on compressor operation. This study leverages complementary methodologies of experimental measurements and high-fidelity computational models to advance the understanding of clearance flows and blockage generation in axial compressors.</p><p dir="ltr">The experimental analysis concludes that the cantilevered configuration achieves better performance and stability than the shrouded stator configuration. However, this conclusion is not apparent when the machine is considered holistically. The cantilevered stages show significant performance improvements, with increases in total pressure ratio of up to 1% and an increase in isentropic efficiency of as much as 2%. However, the common Stage 3 shrouded Stator 3 shows a corresponding deficit of as much as 2% loss in efficiency relative to the fully shrouded stator configuration baseline. These contrasting benefits in the cantilevered stator compressor show that Stage 3 seems to cancel the overall benefits gained by the cantilevered stator. Similar studies have been done on low-speed multistage compressors, but this shows the value of the study in a high-speed research compressor with appreciable stagewise temperature and density increase.</p>

The first bypass turbofan engines came into operation in the early 1970s. The need for reductions in the fuel consumption affected aircraft noise positively through reductions in the jet noise. Over the past decades, the bypass ratio of turbofan engines has continuously increased and, as a result, aircraft engine noise has decreased to a level comparable to the noise originated from the turbulent flow around the airframe for take-off and landing conditions. Although aircraft have become quieter, the number of individuals affected by the aviation growth is likely to increase. Airframe noise has been currently identified as the ultimate aircraft noise barrier and many efforts devoted to its reductions have focused specifically on landing gears and high-lift devices, which are the most relevant noise contributors. Some devices have been designed to reduce flap noise, however, not all of them have been successfully tested in a detailed large-scale flap model due to their difficult implementation in real flap side-edges. This research investigates the relationship between the parameters of a large-scale flap model at 1.50×106 Reynolds number and the physics responsible for flap side-edge noise generation, one of the most dominant sources of the airframe noise. Experimental tests were conducted in a wind-tunnel and flow-field measurements were taken by a multi-hole pitot probe and an aerodynamic balance and complemented by phased microphone array techniques towards a deeper understanding of flap side-edge noise sources and their correlations to unsteady vorticity fluctuations. Conventional beamforming and CLEAN-SC and DAMAS deconvolution methodologies provided far-field acoustic spectra estimations and noise source mapping. The model used for the tests consists of an unswept isolated flap element with representative tip details present in conventional medium-range transport aircraft. The instrumentation includes 106 steady pressure taps distributed chord-wise and span-wise and a sand trip tape to transition the laminar boundary layer. Different side-edge devices were assessed towards airframe noise reductions. A perforated side-edge treatment was also applied to the flap side-edge. Results of aerodynamic and aeroacoustic tests conducted in the LAE-1 closed circuit wind tunnel with a closed test section at the São Carlos School of Engineering - University of São Paulo (EESC-USP) at up to 40 m/s flow speeds provided specific information on the aeroacoustic and aerodynamic characterization of the dominant acoustic source mechanisms of the flap model. / Os primeiros motores turbofan com razão de desvio entraram em operação no início dos anos 70. A necessidade de reduções no consumo de combustível afetou positivamente o ruído das aeronaves através de reduções no ruído do jato. Nas últimas décadas, a razão de desvio de motores turbofan aumentou continuamente e, como resultado, o ruído do motor da aeronave diminuiu para um nível comparável ao ruído originado do fluxo turbulento ao redor do airframe para as condições de decolagem e pouso. Embora as aeronaves tenham-se tornado mais silenciosas, é provável que o número de indivíduos afetados pelo crescimento da aviação aumente. Atualmente, o ruído de airframe tem sido identificado como a barreira máxima de ruído para aeronaves e muitos esforços dedicados à sua redução se concentraram especificamente no trem de pouso e dispositivos de alta sustentação, que são os contribuidores de ruído mais relevantes. Alguns dispositivos foram projetados para reduzir o ruído do flap, no entanto, nem todos deles foram testados com sucesso em um modelo detalhado de flap de grande escala, devido a sua difícil implementação nas bordas laterais do flap real. Esta pesquisa investiga a relação entre os parâmetros de um modelo de flap de grande escala com número de Reynolds de 1.50 × 106 e a física responsável pela geração de ruído na borda lateral do flap, uma das fontes mais dominantes do ruido de airframe. Testes experimentais foram realizados em um túnel de vento e as medidas do escoamento foram tomadas por uma sonda pitot de múltiplos furos e uma balança aerodinâmica e complementadas por técnicas de antenas de microfones para um entendimento mais profundo das fontes de ruído da ponta do flap e suas correlações com flutuações instáveis de vorticidade. O beamforming convencional e as metodologias de deconvolução CLEAN-SC e DAMAS forneceram estimativas de espectros acústicos de campo distante e mapeamento de fontes de ruído. O modelo usado para os testes consiste em um elemento de flap isolado, sem enflechamento, com detalhes de ponta representativos presentes em aeronaves convencionais de transporte de médio alcance. A instrumentação inclui 106 tomadas de pressão estacionárias distribuídas na corda e na envergadura e um trip de fita de areia para fazer a transição da camada limite laminar. Diferentes dispositivos de borda lateral foram avaliados em relação às reduções de ruído de airframe. Um tratamento perfurado de borda lateral também foi aplicado à borda lateral do flap. Os resultados dos testes aerodinâmicos e aeroacústicos realizados no túnel de vento de circuito fechado LAE-1, com seção de provas fechada na Escola de Engenharia de São Carlos - Universidade de São Paulo (EESC-USP) com velocidade de fluxo de até 40 m/s forneceram informações específicas sobre a caracterização aeroacústica e aerodinâmica dos mecanismos dominantes de fonte acústica do modelo de flap.

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Wind propulsion is a traditional way to propel ships over the oceans. In the recent development towards more sustainable shipping, sailing is considered in the industry again with high momentum. For a modern merchant ship, the aerodynamic forces generated on the particular rigging are unusual. Tailored research and experiments are required to understand their influence on the ship’s sailing behaviour. This work concerns the aerodynamic interactions on a model-sized car carrier with four 360° rotatable, symmetric, rigid wings aligned along the centreline on deck. Differential pressures on the wings are measured to capture the generated normal forces. In a comprehensive post-processing, data recorded in systematic experiments at two apparent wind angles were evaluated. A comparison for the different wing positions on board the model shows stronger interactions in upwind sailing conditions than when reaching. The two-dimensional data prove a significant influence of the hull in the normal force profiles over the wing span. The results of this work indicate that the aerodynamic conditions while sailing have to be attentively considered for efficient wing trimming. / Under en lång tid användes främst vindkraft för framdrivningen av fartyg. Det är först på senare år att seglingskonceptet har fått ett nytt uppsving inom marinindustrin med tanke på dess hållbarhet. För fraktfartyg är de aerodynamiska krafterna vid segling ovanliga. Därför behövs särskild forskning och experimentella metoder för att förstå hur de påverkar fartygens seglingsbeteende. I detta arbete undersöks aerodynamiska interaktioner på en modell av ett biltransportfartyg med fyra symmetriska, 360° roterbara vingsegel på däck längs midskeppslinjen. I systematiska experiment på två kurser mot vinden mättes differenstryck över vingprofilen för att undersöka de genererade normalkrafterna. En jämförelse av data från de fyra olika vingpositionerna och båda kurserna mot vinden visar att de aerodynamiska interaktionerna är starkare på kryss än vid halvvind. De upmätta profilerna av tvådimensionella normalkraftkoefficienter över vingspannet visar på betydande aerodynamiska interaktioner med fartygets skrov. Resultaten av detta arbete visar hur viktigt det är med en grundlig undersökning av strömningsförhållandena för en effektiv segeltrim.