Academic literature on the topic 'Inter-Turbine duct'

Aggressive inter-turbine duct, which has ultra-high bypass ratio and ultra-short axial length, is widely applied in the modern turbofan engine because it can reduce engine weight and improve low-pressure rotor dynamic characteristics. However, the aggressive inter-turbine duct that has swirling flow, wake, shock, and tip clearance leakage flow of upstream high-pressure turbine, and even has structs in its flow channel, is liable to separate, especially in high-altitude low Reynolds number (Re) condition. In addition, its downstream low-pressure turbine is on the edge of separation too. In this paper, an integrated aggressive inter-turbine duct embedded with wide-chord low-pressure turbine nozzle is adopted to eliminate the aggressive inter-turbine duct's end-wall separation. Since there are many studies on suppressing the blade suction surface's separation by upstream wake, in this study inherent wake is utilized to suppress the boundary layer separation on low-pressure turbine nozzle's suction surface in the integrated aggressive inter-turbine duct. The paper studies the unsteady flow mechanisms of the integrated aggressive inter-turbine duct (especially the separation and transition mechanisms of low-pressure turbine nozzle's suction surface boundary layer) by the computatioinal simulation method.

The paper presents the total pressure experimental measurements carried out at the Romanian Research and Development Institute for Gas Turbines COMOTI in order to determine the total pressure losses in the Inter - Turbine Duct of a two spools gas turbine, as a function of the gas turbine operating regime (mass flow rate) and rotational speed. The Inter - Turbine Duct experimental assembly has been designed, manufactured and tested at COMOTI. The total pressures were measured as a function of the pre-swirling angle, which simulates the influence of the high pressure turbine rotational speed located upstream of the Inter turbine duct in the real gas turbine, as well as for three operational regimes, without the pre-swirlers modules. The results indicate that the total pressure loss along the Inter - Turbine Duct is of maximum 0.9 %. The lowest overall total pressure loss occurs at 0o pre-swirling angle, around 0.8%, while along the ITD struts, the lowest pressure loss is obtained for a 15o pre-swirling, below 0.1%. The influence of the operating regime on the total pressure loss was found to be linearly, the pressure loss increasing with the reduced mass flow rate, between 1% and 1.9% overall, and between about 0.1% and 0.4 % along the struts.

Inter-turbine diffusers are becoming of increasing importance to the aero gas turbine designer to diffuse the flow between the HP (high-pressure) or IP (intermediate-pressure) turbine and the LP (low-pressure) turbine. Diffusing the flow upstream of the LP turbine and raising the mean passage radius increases stage efficiency. These inter-turbine diffusers, which have high curvature, S-shaped geometry and low-energy wakes created by the upstream turbine, together give rise to secondary flows, making the flow fully three-dimensional. Using both experimental measurements and CFD (computational fluid dynamics) predictions, this paper demonstrates how the secondary flow behaviour is controlled by both the duct diffusion rate and upstream wake intensity.

Aggressive inter-turbine duct (AITD) which has ultra-short axial length and ultra-large area ratio is widely applied in the modern turbofan engine to meet the demand of higher efficiency and better low pressure rotor dynamic characteristics. However, the adverse stream-wise pressure gradient in this duct is enhanced, and there are complicate upstream and downstream flow conditions. The flow field of the AITD and its downstream low pressure turbine is seriously deteriorated and prone to separate, especially in high-altitude cruise state. The integrated AITD which integrates the AITD with strut had been proved to can restrain the traditional AITD's three-dimensional flow separation. Besides, periodic wake can suppress the downstream blade suction surface's flow separation by “calmed region” effect according to former studies. The AITD of this research taken from a real engine utilizes integrated design and inherent upstream wake to suppress the flow separation of the AITD's end wall and low pressure turbine nozzle's suction surface correspondingly. In this article, the computational simulation method is used to quantify the impact of turbulence intensity ( T u) on the integrated AITD's unsteady flow characteristics, especially the separation and transition mechanism of low pressure turbine nozzle's suction surface boundary layer. Research shows that the impact of T u on the integrated AITD's flow property depends on the balance of T u's dual effect.

The composition of the time-resolved surface pressure field around a high-pressure rotor blade caused by the presence of neighboring blade rows is investigated, with the individual effects of wake, shock and potential field interaction being determined. Two test geometries are considered: first, a high-pressure turbine stage coupled with a swan-necked diffuser exit duct; secondly, the same high-pressure stage but with a vane located in the downstream duct. Both tests were conducted at engine-representative Mach and Reynolds numbers, and experimental data was acquired using fast-response pressure transducers mounted on the mid-height streamline of the HP rotor blades. The results are compared to time-resolved computational predictions of the flowfield in order to aid interpretation of experimental results and to determine the accuracy with which the computation predicts blade interaction. The paper is split into two parts: the first investigating the effect of the upstream vane on the unsteady pressure field around the rotor (vane-rotor interaction), and the second investigating the effect of the downstream vane on the unsteady pressure field around the rotor (rotor-vane interaction). The paper shows that at typical design operating conditions shock interaction from the upstream blade row is an order of magnitude greater than wake interaction and that with the design vane-rotor inter-blade gap the presence of the rotor causes a periodic increase in the strength of the vane trailing edge shock. The presence of the potential field of the downstream vane is found to affect significantly the rotor pressure field downstream of the Mach one surface within each rotor passage.

Abstract Civil aviation has instilled new perceptions of a smaller world, creating new opportunities for trade, exchange of cultures and travelling for leisure. However, it also brought with it an unforeseen impact on the environment. Aviation currently contributes to about 3·5% of the global warming attributed from human activities. With the forecasted rate of growth, this is expected to rise to about 15% over the next 50 years. Although it is projected that the annual improvements in aircraft fuel efficiency are of the order of 1-2%, it is suggested that the current gas turbine design is fully exploited and further improvements are difficult to achieve. A new generation of aero engine core concepts that can operate at higher thermal efficiencies and lower emissions is required. One possibility of achieving higher core efficiencies is through the use of an inter-cooled (IC) core at high overall pressure ratios (OPR). The concept engine, expected to enter into service around 2020, will make use of a conventional heat exchanger (HEX) for the intercooler. This paper seeks to introduce a heat pipe heat exchanger (HPHEX) as an alternative design of the intercooler. The proposed HPHEX design takes advantage of the convenience of the geometry of miniature heat pipes to provide a reduction in pressure losses and weight when compared to conventional HEX. The HPHEX will be made of a number of stages, each stage being made of a large number of miniature heat pipes in radial configuration, that will extend from the inter-compressor duct to the bypass split, thus eliminating any ducting to and from the intercooler. This design offers up to 32% reduction in hot pressure losses, 34% reduction in cold pressure losses and over 41% reduction in weight.

La réduction de consommation de carburant dans l'aéronautique est devenue un des principaux axes de recherche, afin de réduire l'empreinte environnementale de l'aviation, mais aussi pour réduire le coût d'exploitation des aéronefs. Les motoristes, outre l'étude des technologies de rupture, travaillent aussi à l'optimisation incrémentale des turbomachines afin d'en augmenter le rendement, en réduire le poids et en faciliter l'intégration.Les turbines sont à la fois les composants les plus lourds du moteur, et ceux dont leur rendement impacte le plus la consommation spécifique. Le lien entre la turbine haute pression et la turbine basse pression est assuré par le canal inter-turbine, étudié dans le cadre de cette thèse.Depuis une vingtaine d'années, les chercheurs et les industriels essaient d'optimiser ce composant, afin de le rendre plus compact et plus performant sur le plan aérodynamique. Ce processus d'optimisation est contraint par deux principales difficultés. Premièrement, la méconnaissance de l'écoulement en sortie de turbine haute pression, qui ne permet pas de quantifier exactement les non-homogénéités de l'écoulement en entrée. Deuxièmement, la forme globalement divergente des parois qui amplifient ces non-homogénéités d'entrée, en augmentant les pertes par mélange.Les études menées visent à quantifier les erreurs sur la prédiction des performances du canal inter-turbine par simulations numériques, induites par une mauvaise modélisation des pertes par mélange.Dans un premier temps, une configuration industrielle d'un banc d'essais est analysée, afin de démonter l'impact d'une mauvaise description des non-homogénéités de l'écoulement (appelés distorsions) sur les performances du canal inter-turbine. De nombreuses simulations numériques RANS stationnaires et instationnaires ont été effectuées pour répondre à cette question, et comparées sur la base des mesures. Les pertes par mélange calculées démontrent une forte dépendance des différents mécanismes à la distorsion elle-même, et à l'état de la turbulence en entrée. Ainsi, une compréhension plus complète du mécanisme d'interaction entre distorsion et turbulence s'avère nécessaire pour la bonne conception du composant. Or ce sont deux caractéristiques de l'écoulement qui sont mal connues en sortie de turbine haute pression, du fait de la difficulté à mesurer dans de tels environnements.Une fois les mécanismes de base identifiés, deux simplifications de la géométrie seront proposées, afin d'étudier séparément les effets de la divergence des parois externes (diffusion) et de la déviation de l'aubage, sur les pertes par mélange.Concernant la diffusion, l'évolution d'un sillage dans un divergent a été étudié sur un cas académique pour mieux comprendre et quantifier le mélange dans un tel environnement. Les simulations mettent en évidence le lien entre les pertes et la turbulence injectée en entrée. Une simulation de type LES permet de mieux comprendre ce phénomène d'interaction, et de vérifier la validité de l'approche RANS à deux équations pour laquelle un comportement anistrope de la turbulence est hors de portée.Concernant l'influence de la déviation, l'évolution des pertes par mélange, qui diminuent ou augmentent avec celle-ci, est un débat ouvert depuis les années '50 en environnement turbine. Jusqu'à maintenant, la communauté scientifique a essayé de répondre à cette question au travers d'analyses complexes et résolues en temps de turbines conventionnelles. L'originalité et la simplicité de l'approche proposée dans ce mémoire se base sur une comparaison de deux géométries de turbines co- et contra-rotatives, avec la capacité d'étudier le sillage dans son propre repère de génération, sans l'utilisation de post-traitements complexes.Enfin, les résultats et les connaissances acquises sur les configurations simplifiées seront appliquées à la géométrie industrielle, et donneront lieu à des recommandations de dimensionnement du canal inter-turbine
Reducing fuel consumption in aeronautics is one of the main areas of research, in order to reduce the environmental footprint of aviation, but also to reduce aircraft operational cost. In addition to studying disruptive technologies, engine manufacturers are also working on the incremental optimisation of turbomachinery to increase efficiency, reduce weight and facilitate integration.Turbines are both the heaviest engine components and those whose efficiency has the greatest impact on specific fuel consumption. The link between the high-pressure and the low-pressure turbine is provided by the inter-turbine duct, studied in this thesis.During the last twenty years, academics and companies have been trying to optimise this component, in order to make it shorter and more aerodynamically efficient. This optimisation process is constrained by two main difficulties. Firstly, the lack of knowledge of the high-pressure turbine outlet flow, which prevent accuracy on non-homogeneities (distortion) of the inlet flow quantification. Secondly, divergent shape of the walls amplifies these inlet distortions, increasing the mixing losses.The studies carried out aim at error quantification on the prediction of the inter-turbine duct performances by numerical simulations, induced by an improper modelling of mixing losses.In a first step, an industrial configuration of a test bench is analysed, in order to demonstrate the impact of an incorrect description of the flow distortions on the performances of the inter-turbine duct. Several steady and unsteady RANS numerical simulations have been performed to answer this question, and compared to experiments. The calculated mixing losses show a strong dependence of the different mechanisms on the distortion itself, and on the inlet turbulence. Thus, a more complete understanding of the interaction mechanism between distortion and turbulence is necessary for the proper design of the component. However, these are two flow characteristics that are poorly known at high-pressure turbine outlet, due to measuring difficulties in such environments.Once the main mechanism has been identified, two simplifications of the geometry will be proposed, in order to study separately the effects of the divergence of the external walls (diffusion) and of the deflection of the blade, on the mixing losses.Concerning diffusion, the evolution of a wake in a divergent has been studied on an academic case to better understand and quantify the mixing in such environments. The simulations highlight the link between losses and inlet turbulence. A LES simulation allows a better understanding of this interaction phenomenon, and to verify the validity of the two-equation models used in RANS approach, for which anisotropic turbulence behaviour is not modelled.Concerning the influence of the deviation, the evolution of the mixing losses, which decrease or increase with the deviation, has been an open debate since the 1950s in turbine environments. Until now, the scientific community has tried to answer this question through complex and time-resolved analyses of conventional turbines. The originality and simplicity of the approach proposed in this work is based on a comparison of two co- and contra-rotating turbine geometries, studing the wake in its own generation frame, without using complex post-processing.Finally, the results and knowledge gained from the simplified configurations will be applied to the industrial geometry, and will result in recommendations for the sizing of the inter-turbine channel

Inter-turbine diffusers or swan neck ducts (SND's) provide flow continuity between the H.P. and L.P. turbine, which with diffusing of the flow allow; greater stage efficiencies to be achieved as a consequence of reducing both the stage loading and flow coefficient of the L.P. turbine. This thesis presents an experimental and computational investigation into the local flow development and overall performance of two different severity diffusing annular sshaped ducts, with the same overall diffusion ratio of 1.5, in order to validate the CFD code M.E.F.P. The first less severe diffusing duct was used to investigate the effects of inlet swirl on the duct performance. It was found that at an optimum swirl angle of 15 degrees, the duct total pressure loss coefficient was approximately half the value at 0 or 30 degrees swirl. The second more severely diffusing duct had simple symmetrical aerofoil struts added, which simulated struts required in real inter-turbine diffusers to support inner shafts and supply vital engine services. The total pressure loss developed by the 30% shorter duct was 15% greater that of the longer duct, and when struts were added to the second duct the loss almost doubled. These increases were attributed to gradually worsening casing surface flow separations which also acted to reduce the overall static pressure recovery of the ducts as their losses increased. The computational investigations were made on the more severe duct with and without struts. The code, Moore's Elliptic Flow Solver (M.E.F.P) which used a mixing length model, predicted flow separation in the strutted duct case albeit in slightly the wrong position, however, it failed to predict any secondary flow for the unstrutted case and hence correlated worse with the measured results. This was also true of the results predicted by a version of Dawes BTOB3D.

The inter-turbine transition duct (ITD) between the high-pressure (HP) and low-pressure (LP) turbines of a gas turbine has the potential for significant length reduction and therefore engine weight reduction and/or aerodynamic performance improvement. This potential arises because very little is understood of the flow behavior in the duct in relation to the hub and casing shapes, and the flow entering the duct (e.g., swirl angle, turbulence intensity, periodic unsteadiness and blade tip vortices from upstream HP turbine blade rows). Moreover, it is unclear how well CFD is able to predict the complex flow-field in these ducts. This paper presents the results of a detailed experimental and computational study of an ITD, which is representative of a modern engine design. The experiments were conducted in a low-speed annular test rig where the effects of inlet free-stream turbulence intensities and swirl angle were investigated. Numerical studies were performed using commercial CFD software. The capability of different turbulence models, including the B-L, S-A, k-ε and SST models, have been explored. The predicted results are compared with the experimental data. Both experimental and numerical results are analyzed in detail to investigate the flow development both inside the ITD and along the end-walls.

Modern direct-drive turbofan engines typically have the fan turbine designed at significantly higher diameter than the gas producer turbine. Furthermore, the gas turbine industry is being pushed to shorten engine length with the goal of reducing weight. This results in a need to design very aggressive inter-turbine-ducts (ITD’s) that have high endwall slopes. The gas turbine design cycle typically begins with conceptual design where many engine configuration iterations are made. During conceptual design, there usually is little firm geometric definition or time for detailed CFD studies on aggressive ITD’s. This can cause a large amount of risk to the engine development schedule and cost if the space allocated for the ITD during conceptual design is found to be insufficient later in the design cycle. Therefore, simple analytical tools for accurately assessing the risk of an ITD in conceptual design are important. The gas turbine industry is familiar with the Sovran and Klomp annular diffuser performance chart [1] as a conceptual design tool for assessing ITD’s. However, its applicability to modern gas turbine ducts with high endwall slope is limited. The location of the maximum pressure recovery for a given length, the Cp* line, considers only two geometric parameters: area ratio and normalized length. The chart makes no distinction of risk of flow separation regarding the level of slope or the pitch-wise turning in the duct. However, intuition would suggest that a high slope duct would have more risk of separation than an equivalent area ratio duct with low slope. Similarly, a duct that turns the flow from axial to radial would be expected to be riskier than a pure axial duct. To help assess the interaction of duct slope and pitch-wise turning with area ratio and length, an analytical Design of Experiments (DOE) was run using approximately sixty different duct configurations. The DOE was carried out using 3D, steady CFD analysis. The results of the DOE are presented with insights provided into how the Cp* line may shift as a function of duct slope. Of particular interest is that slope by itself does not work particularly well as a risk indicator. However, a combination of new area ratio-length and slope-length parameters was found to segregate ducts between separated and non-separated cases.

The present work, a continuation of a series of investigations on the aerodynamics of aggressive inter-turbine ducts (ITD), is aimed at providing detailed understanding of the flow physics and loss mechanisms in four different ITD geometries. A systematic experimental and computational study was carried out for varying duct mean rise angles and outlet-to-inlet area ratio while keeping the duct length-to-inlet height ratio, Reynolds number and inlet swirl constant in all four geometries. The flow structures within the ITDs were found to be dominated by the counter-rotating vortices and boundary layer separation in both the casing and hub regions. The duct mean rise angle determined the severity of adverse pressure gradient in the casing’s first bend whereas the duct area ratio mainly governed the second bend’s static pressure rise. The combination of upstream wake flow and the first bend’s adverse pressure gradient caused the boundary layer to separate and intensify the strength of counter-rotating vortices. At high mean rise angle, the separation became stronger at the casing’s first bend and moved farther upstream. At high area ratios, a 2-D separation appeared on the casing. Pressure loss penalties increased significantly with increasing duct mean rise angle and area ratio.

To reduce the harmful effects of aviation on the environment, aircraft gas turbine manufacturers continue to focus on producing engines with lower specific fuel consumption and weight. To address the engine weight challenges, R&D efforts continue to center around extending aerodynamic design limits, thus enabling reduced airfoil/stage count, reducing engine length or some combination thereof. The inter-turbine transition duct (ITD), located between the high-pressure (HP) and low-pressure (LP) turbines, is one of the components for which potentially significant weight reduction can be achieved through aggressive aerodynamic designs. Such ducts could have larger HP-to-LP radial offset and/or shorter length resulting in Aggressive Inter-Turbine Ducts (AITD). This paper presents a geometry optimization process to design AITD with minimum total pressure losses. Geometry optimizations were performed using the built-in optimization process in NUMECA Fine/Turbo 8.7. To evaluate the optimization process, one baseline ITD geometry was first generated with the same inlet and outlet coordinates as an existing ITD. The performance of the optimized ITD was studied numerically in comparison with the existing ITD. After the evaluation study, a second ITD geometry with more aggressive parameters, equivalent to increasing mean rising angle by 25% was optimized. Based on the studies of those two optimized geometries, a generic design rule of ITD with mild parameters was developed and the third ITD geometry with increased 20% area ratio (AR) was designed. The performance of designed ITDs was investigated numerically and the results are discussed in the paper.

This paper presents the experimental investigation of the flow in an aggressive inter-turbine duct (AITD). The goal is to improve the understanding of the flow mechanisms within the AITD and of the underlying physics of low-profile vortex generators (LPVGs). The flow structures in the AITD are dominated by counter-rotating vortices and boundary layer separations in both the casing and hub regions. At the first bend of the AITD, the casing boundary layer separates in a 3D mode because of the upstream wakes; this is followed by a massive 2D boundary layer separation. Due to the effect of the radial pressure gradient at the first bend, the streamwise vorticity generated by the casing 3D separation stays close to the casing endwall, and later mixes with the casing counter-rotating vortices formed at the second bend. By using LPVGs with different configurations installed on the casing, the casing boundary layer separation is significantly reduced. The streamwise vortices generated by the LPVGs have the potential to generate another pair of counter-rotating vortices at the AITD second bend, which help to delay/prevent the boundary layer separation. Therefore, the total pressure loss in the AITD was significantly reduced.

Abstract In recent years, lot of turbine research is focused on the study and optimization of inter-turbine ducts, an aero-engine component for which the design is becoming more challenging due to the turbofan architecture evolution. Starting from the early design phase, the knowledge of the component performance and outlet flow pattern is crucial in the design of the low pressure turbine. To improve prediction, multi-row unsteady simulations are deployed. Unfortunately, some questions arise in the use of these simulations, among others the knowledge of the turbulent boundary conditions and the contribution of the unsteady simulations to the flow solution. In this paper steady and time resolved RANS simulations of a turning inter-turbine duct are investigated. Particularly, two questions are addressed. The first one is the influence of the turbulent quantities boundary conditions in the case of a k–ω Wilcox turbulence model in the flow field solution. The second one is the contribution of the unsteadiness to the mean flow prediction. It will be shown that the mean flow depends on inlet turbulence only if the turbulence length scale is relatively high; otherwise the flow field is almost turbulence-invariant. For the unsteady simulations, unsteadiness modifies the mean flow solution only with low inlet turbulence.

Inter-turbine diffusers which provide flow continuity between the H.P. and L.P. turbines, are increasingly important within modern aero gas turbines, as the fan and hence L.P. turbine diameters increase with thrust. These gas turbines rely on struts within the inter-turbine diffuser to serve both as load bearing supports for inner spools and as passages to supply the engine with vital services such as cooling air and lubrication oil. Experimental measurements have been made on a representative test rig in order to investigate the affect of a ring of struts on both the local and general flow phenomena as well as investigating their effect on overall duct performance. More realistic flow conditions are made available by the use of inlet wakes representative of those created by an upstream turbine row. Measurements include static pressures on the strut and duct surfaces along with velocity and total pressure measurements at various axial locations. From these results calculations of total pressure loss have been made. The experimental results presented in this paper have been used to validate C.F.D. flow predictions on the duct with and without struts. The computational results included, capture the main physical features of the flow but clear limitations are observed and are discussed in this paper.

Annular S-shaped intermediate turbine ducts are used in modern multi-spool jet engines to connect the high pressure turbine with the low-pressure turbine. The trend towards engines with larger by-pass ratios requires the future intermediate turbine ducts to be shorter and have larger radial off-set. This paper deals with the design and performance evaluation of a state-of-the-art annular S-shaped intermediate turbine duct. The details of the design of the intermediate turbine duct are presented together with static pressure measurements and oil film flow visualization along the endwalls, and area traverses at the inlet and outlet planes using a 5-hole probe. The measurements were done for three operating points of the turbine. From the flow visualization no separation could be detected at design point conditions, but for off-design conditions regions of separation were detected on the guide vanes located within the inter-turbine duct. The pressure loss coefficient was shown to be comparable for the two cases with lowest swirl angle, but the design point showed a slightly lower pressure loss. For the case with the largest flow angle the pressure loss coefficient was clearly larger than for the other two cases, which can be associated with the separation found on the guide vanes.

The inter-turbine transition duct (ITD) of a gas turbine engine has significant potential for engine weight reduction and/or aerodynamic performance improvement. This potential arises because very little is understood of the flow behavior in the duct in relation to the hub and casing shapes and the flow entering the duct (e.g., swirl angle, turbulence intensity, periodic unsteadiness and blade tip vortices from upstream HP turbine blade rows). In this study, the flow development in an ITD with different inlet swirl distributions was investigated experimentally and numerically. The current paper, which is the first part of a two-part paper, presents the investigations of the influences of the casing swirl variations on the flow physics in the ITD. The results show a fair agreement between the predicted and experimental data. The radial pressure gradient at the first bend of ITD drives the low momentum hub boundary layer and wake flow radially, which results in a pair of hub counter-rotating vortices. Furthermore, the radially moving low momentum wake flow feeds into the casing region and causes 3D casing boundary layer. At the second bend, the reversed radial pressure gradient together with the 3D casing boundary layer generates a pair of casing counter-rotating vortices. Due to the local adverse pressure gradient, 3D boundary layer separation occurs on both the casing and hub at the second bend and the exit of the ITD, respectively. The casing 3D separation enhances the 3D features of the casing boundary layer as well as the existing casing counter-rotating vortices. With increasing casing swirl angle, the casing 3D boundary layer separation is delayed and the casing counter-rotating vortices are weakened. On the other hand, although the hub swirls are kept constant, the hub counter-rotating vortices get stronger with the increasing inlet swirl gradient. The total pressure coefficients within the ITD are significantly redistributed by the casing and hub counter-rotating vortices.