Intermediate Turbine Duct Research Articles

Unsteady Investigation of Intermediate Turbine Ducts Under the Influence of Purge Flows

Abstract The aerodynamic flow field at the outlet of a high-pressure turbine (HPT) stage in a modern turbofan engine is highly unsteady and strongly influenced by periodic fluctuations from the HPT rotor, also interacting with the HPT stationary vanes. Downstream of the last HPT stage, the flow enters the intermediate turbine duct (ITD), where new unsteady components are generated, due to the interaction between the incoming flow and the struts supporting the ITD. This paper illustrates the differences between the unsteady flow behavior in two state-of-the-art ITD configurations for turbofan engines: the turbine center frame and the turbine vane frame. The experimental results discussed in this work are obtained in the Transonic Test Turbine Facility, situated at Graz University of Technology, Austria. To achieve engine-representative operating conditions at the ITD inlet and outlet sections, the tested setups include not only the duct, but also the last HPT stage and the first low-pressure turbine stage row. Additionally, the test rig features a secondary air supply system, capable of feeding purge air to every stator–rotor cavity in the test vehicle. Unsteady measurement data at the inlet and outlet of the two duct configurations are acquired with fast-response aerodynamic pressure probes, for two purge flow conditions. Azimuthal mode decomposition is applied to phase-averaged data at selected radial positions, to isolate and quantify the contribution of different interaction modes to the overall unsteady flow field.

Experimental and Numerical Investigation of a Turbine Vane Frame with Splitters at Different Operating Points

A turbine vane frame is a special type of intermediate turbine duct, and is one option to improve the efficiency and reduce the length and weight of an aero-engine. However, due to its geometry, it features a complex flow field, and therefore in-depth aerodynamic investigations are necessary. Especially for aviation, every component needs to function reliably during all operating points. To perform this study at the Institute for Thermal Turbomachinery at the Graz University of Technology, the Subsonic Test Turbine Facility for Aerodynamic, Aeroacoustic and Aeroelastic Investigations was equipped with a turbine vane frame and a low-pressure turbine located downstream. Measurements were taken with aerodynamic five-hole probes for three operating points, and were compared with steady-state and transient simulations as well as analytic solutions for the pressure drop in the TVF. Finally, the most important loss mechanisms are described.

Data-driven estimation of entropy production by large scale motions in an intermediate turbine duct

In modern gas turbines, the physics of three-dimensional inflow for aggressive intermediate turbine ducts are strongly associated with large-scale coherent motions, which contribute to the production of irreversible aerodynamic and thermodynamic energy losses. To address this problem, an extended data-driven approach for estimating the irreversible losses through viscosity dissipation and heat transfer in turbulent flows is proposed. An aggressive intermediate turbine duct connected to a high-pressure turbine is numerically investigated using the detached-eddy simulation framework. The influence of tip leakage vortices and rotor wakes on the aerodynamics in the duct is assessed through quadruple proper orthogonal decomposition analysis. The entropy production rate corresponding to the coherent structures is then identified, and the irreversible losses in the duct subject to unsteady flow motions are quantitatively evaluated. The results indicate that the coherent structures in the intermediate turbine duct are strongly associated with the upstream conditions, including the tip leakage flow and rotor wakes. Direct viscous dissipation accounts for the majority of the irreversible losses, with coherent perturbed dissipation contributing to 7.25% and 5.54% of the total for tip gap sizes of 1.5% and 3.5% span, respectively. The streamwise development of coherent perturbations is restricted compared with that in the mean structure, and the stochastic part contributes little to the viscous dissipation. The proposed method provides a systematic procedure for estimating the irreversible energy losses in unsteady turbulent flow, and highlights the significance of unsteady aero-thermodynamics in the design of turbomachinery.

Aerodynamics and Sealing Performance of the Downstream Hub Rim Seal in a High-Pressure Turbine Stage

The purpose of the paper is to characterize the aerodynamic behavior of a rotor-downstream hub cavity rim seal in a high-pressure turbine (HPT) stage. The experimental data are acquired in the Transonic Test Turbine Facility at the Graz University of Technology: the test setup includes two engine-representative turbine stages (the last HPT stage and first LPT stage), with the intermediate turbine duct in between. All stator-rotor cavities are supplied with purge flows by a secondary air system, which simulates the bleeding air from the compressor stages of the real engine. The HPT downstream hub cavity is provided with wall taps and pitot tubes at different radial and circumferential locations, which allows the performance of steady pressure and seed gas concentration measurements for different purge mass flows and HPT vanes clocking positions. Moreover, miniaturized pressure transducers are adopted to evaluate the unsteady pressure distribution, and an oil flow visualization is performed to retrieve additional information on the wheel space structures. The annulus pressure asymmetry depends on the HPT vane clocking, but this is shown to have negligible impact on the minimum purge mass flow required to seal the cavity. However, the hub pressure profile drives the distribution of the cavity egress in the turbine channel. The unsteady pressure field is dominated by blade-synchronous oscillations. No non-synchronous components with comparable intensity are detected.

Influence of Upstream Sweeping Wake Number on the Unsteady Flow Mechanism in an Integrated Aggressive Intermediate Turbine Duct

This paper focuses on the dynamic internal flow in the integrated aggressive intermediate turbine duct (AITD) with different HPT wake numbers, using CFX Solver with dynamic Reynolds-averaged Navier–Stokes equations (RANS), the shear stress transmission κ-ω turbulence model (SST) and the γ-θ transition model. The HPT wakes are simulated using sweeping rods, with the number of rods ranging from 14 to 56 and a reduced frequency of 1.07. The increasing wake number reduces the radial pressure gradient in the integrated AITD, and then decelerates the radial migration and dissipation of wake vortices, so that some residual wakes can reach the integrated low-pressure turbine guide vane (LPT-GV) to enhance the suppression of flow separation to a certain extent. On the other hand, the increase in wake number can also weaken the skewness and stretching of the wake, thereby increasing the duration of flow separation suppression. When there are too many wakes, the mixing between adjacent wakes accelerates the dispersion of wake vortices, leading to increased total pressure loss and an enhanced turbulence intensity. This enhanced turbulence intensity promotes bypass transition on the suction surface of the LPT-GV in advance, thereby completely eliminating flow separation on the LPT-GV in the entire spatiotemporal domain, which is beneficial for reducing separation loss, but also increasing turbulent viscous loss. When N ≤ 28, the gross loss of the integrated AITD studied in this paper reaches a minimum value (around 0.22), as the benefits brought by the wake suppression of flow separation can offset the wake dissipation loss and the turbulent viscous loss caused by the wake-induced transition. Considering that wake loss is inherently present, using sweeping wakes to inhibit the flow separation on the integrated LPT-GV can bring certain aerodynamic benefits when the wake number is less than 28.

Improved prediction of coherent structure in an intermediate turbine duct

Modeling the unsteady flow in an intermediate turbine duct in an aero-engine is highly challenging partly owing to the complex physics subjected to unsteady vortical flow upstream. In this paper, the high-fidelity detached eddy simulations of an aggressive intermediate turbine duct are performed and validated against published data. The dominating coherent flow motions are then captured with sparsity-promoting dynamics mode decomposition under different tip gap sizes and rotating speeds of the rotor blade. Furthermore, a novel low-order spectrum reconstruction method based on selected flow modes and Gaussian fitting is proposed for fast prediction of the instantaneous flowfield in the intermediate turbine duct. The sources of error are discussed and a potential approach to improve the prediction accuracy is proposed. It reveals that the proposed method achieves accurate and generalized performance in reconstructing and predicting flow fields with periodic features for a small cost of calculation time. The maximum root mean squared error in the scenario of tip gap size and rotating speed variation is below 5.96 and 8.41, respectively. The error analysis shows that the variation of flow modes under different inflow conditions and nonlinearity of interacting flow structure accounts for the major part of prediction error. By applying a Proper orthogonal decomposition (POD) interpolation on the flow modes, the maximum root mean squared error in the scenario of tip gap size and rotating speed variation can drop to 4.76 and 2.69 without breaking the physical meaning of the representative modes. The novelty of the present work lies at the proposed prediction method combining DMDSP and POD-interpolation, of which the majority of the physical information are maintained and the prediction accuracy is improved. It may provide a promising approach for turbomachinery design, flow prediction, and investigating underlying mechanisms with low data requirements.

The Effects of Hub Profile on the Aerodynamics of Integrated Intermediate Turbine Ducts

Abstract The integration design of the intermediate turbine ducts (ITDs) with the first row of the low-pressure turbine vane can significantly reduce the length of the turbine section, thus reducing the weight and drag of the aero-engine. This paper investigates the effects of the hub profile on the aerodynamic performance of integrated ITDs (IITDs). The flow features and loss mechanism of four IITDs are studied by experimental, numerical, and theoretical methods. In the baseline case, an open corner separation occurs near the hub-suction surface corner, which results in a significant loss. The loss is broken down into the parts generated by the mean vortex and turbulence theoretically. The open corner separation causes significant turbulence loss. To reduce the size of the separation zone, the positive radial/spanwise pressure gradient near hub is increased by moving the hub profile near the vane rear part slightly downward. As a result, a small closed corner separation with three-dimensional topology occurs instead of the open corner separation in the baseline case. The corner shape factor is defined to quantitatively describe the closed corner separation. When the hub profile moves further downward, the loss due to the corner separation reduces, but the loss generated in the vane passage away from hub increases mainly due to the mixing as the low-momentum flow near the hub transports toward the mid span. The change of the overall loss is subject to the combination of the two effects, and should be balanced during the design process.

The Interaction of Main Stream Flow and Cavity Flows in Turbine Center Frames and Turbine Vane Frames

Abstract This paper focuses on the interaction between the last high-pressure turbine (HPT) stage purge flows and the intermediate turbine duct (ITD) in modern turbofan engines. Two state-of-the-art ITD concepts are analyzed in this work: the turbine center frame (TCF), which is supported by symmetric aerodynamic strut fairings and generally adopted in conventional dual-spool engines; the turbine vane frame (TVF), which features turning struts and splitters and is typical of geared turbofan engines. The measurement campaigns for both setups are carried out in the transonic test turbine facility (TTTF) at Graz University of Technology. The test vehicles consist of an HPT stage, the ITD (TCF or TVF), and the first low-pressure turbine (LPT) vane or blade row. The same HPT stage is used for both ducts, to enable consistent, engine-representative inlet conditions between the two solutions. All the HPT stator–rotor cavities are supplied with purge flows by a secondary air system, with independent mass flow and temperature control for each purge line. Five-hole probe data are acquired at the inlet and outlet sections of the ITDs, to characterize the aerodynamic flow field entering and leaving the duct. In addition to the pneumatic probe tests, seed gas concentration measurements are performed in the same planes, to track down the cavity air in the mainstream and investigate its postegress behavior. Finally, detailed post-test computational fluid dynamics (CFD) results are presented to get additional insight into the flow phenomena developing through the strut passage.

Loss evaluation and aerodynamics investigation of an aggressive intermediate turbine duct under off-design conditions

To maximize the performance of the intermediate turbine duct (ITD) under off-design conditions, the loss generation in a one-half stage turbine was quantified using entropy generation and the global entropy generation rate. The numerical results solved by the unsteady Reynolds-averaged Navier–Strokes equations were first verified. Then, the aerodynamic losses within the high-pressure turbine stage were evaluated by efficiency loss under nine operating conditions composed of three rotor speeds and three rotor tip gaps. Finally, the disturbance modes caused by the upstream wake were captured by the dynamic mode decomposition method. Different from the influence of tip gaps, losses of the high-pressure turbine and the ITD are due to the swirl angle display an opposite trend. Under the influence of the interaction between the tip leakage flow and the shroud flow of the ITD, the viscous dissipation and turbulent dissipation increase with a larger tip gap owing to the dominant counter-rotating vortices and secondary flow occurring near the upstream of the ITD shroud. In addition, a large gap seems to enlarge the swirl component of the inflow angle, especially over 80% passage height, leading to greater dissipation losses in these areas. At the ITD inlet, two pairs of counter-rotating vortices at the shroud and the hub are, respectively, captured by the axial velocity mode. Large tip gaps enhance endwall vortices near the shroud and make the up vortex pairs merge into one pair.

The Effects of Incoming Vortex and Wake on the Aerodynamics of an Intermediate Turbine Duct

Abstract In a high bypass ratio aircraft engine, the high-pressure and low-pressure turbines are connected by an intermediate turbine duct (ITD). The aerodynamic performance of the ITD is affected by the incoming flow from the high-pressure turbine. This paper investigates the effects of an incoming wake or/and a near casing streamwise vortex on the flow field and loss of an ITD. For the case with only an incoming wake, the wake interacts with the boundary layer (BL), forming a pair of vortices and causing additional loss. With an incoming streamwise vortex, the casing boundary layer interacts with it and a loss core forms near the casing. When both a wake and a streamwise vortex are present at the inlet, apart from interacting with the boundary layer, the wake and the streamwise vortex could interact with each other. It is found that the distance between the wake and streamwise vortex has a major effect on the flow pattern and aerodynamic loss of ITD. Three different distances between the wake and the incoming streamwise vortex are investigated. When the distance between the wake and incoming streamwise vortex is large, the two flow structures develop relatively independently and the combined effect is small. As the distance between them reduces, the flow structure induced by the wake interacts with the incoming streamwise vortex and suppresses the loss production. However, for the case with the shortest distance, the interaction enhances the loss generation. A simplified analytical model is proposed to explain this loss mechanism.

Investigation on the flow-control strategy for an aggressive turbine transition ducts

After being studied for years, aggressive intermediate turbine duct is being attempted to be applied in turbine design to further improve the engine-performance. With such design, the shaft could be shortened effectively. However, under the influence of the more distorted coming-flow and stronger pressure-gradient in a real engine, the flow field would be more complicated definitely. Besides that, the upstream-rotor tip-leakage flow is a key loss-source by inducing separation. Flow-control strategies are necessary in this situation. In this paper, the flow field in an aggressive duct has been analyzed to declare the source of separation primarily. Then wide-chord blade design concept has been adopted as a control strategy firstly to realize the purpose of improving the areo-performance. After being verified, numerical method has been used in this study. Under the same aero-condition, the prototype and the modified turbine are analyzed. With this novel flow-control strategy, separation has been improved, even diminished. However, the flow structures within the blade passage are altered correspondingly. An instrumental conclusion is that the pressure loss could be decreased successfully by designing the wide-chord blade specially.

Streamwise vortex transportation and loss generation in an intermediate turbine duct

Annular S-shaped intermediate turbine ducts are used in modern turbofan engines with large by-pass ratios. To reduce the weight of an engine, the intermediate turbine ducts should be as short as possible, while keeping the loss at an acceptable level. Understanding the flow physics within the intermediate turbine ducts is the key to improve the intermediate turbine duct design. This paper aims to understand the transportation of the inlet streamwise vortices and loss generation in intermediate turbine ducts. First, cases with isolate incoming streamwise vortices at different spanwise locations and different axial velocities are investigated. The transportation of isolated vortex and loss generation are highly related to the interaction between vortex and boundary layer, which are mainly determined by the streamwise pressure gradient. When the axial velocity of the streamwise vortex is different to the main flow, the radial pressure gradient also has an effect. Then, the inlet condition of the intermediate turbine ducts is setup based on the flow field at the exit of a cascade, which contains the flow structures such as the tip leakage vortex, hub secondary vortex and the wake. The flow physics and the loss mechanism are analysed in detail. The formation mechanism of counter-rotating vortices pair and the influence of inlet vortex on loss generation within the intermediate turbine ducts are also presented.

Numerical Investigation on the Effects of Cavity-Blowing Jet on Intermediate Turbine Duct Flowfield

Intermediate turbine duct is an important part of engine, which guides the hot gas from upstream high-pressure turbine to downstream low-pressure turbine without much loss. To promise such goal, much work has been done to investigate flow mechanism in this kind of duct as well as its design criterion with numerical and experimental methods. Usually intermediate turbine duct simplified from real engine structure was adopted with upstream and downstream blades. However, cavity-blowing jet exists to disturb the duct flow field in real engine to change its performance. Naturally, the wall vortex pair would develop in different ways. In addition to that, the blowing jet flow rate changes at different engine representative operating conditions. This paper deals with the influence of cavity-blowing jet on the aerodynamic performance of an aggressive intermediate turbine duct. The objective is to reveal the physical mechanism of blowing jet ejected from the wheel-space and its effects on the duct flow field. First, ten cases with and without cavity are simulated simultaneously. On one hand, the influence of cavity structure without blowing jet on the flow field inside duct would be discussed. On the other hand, the effect of blowing jet rate on flow field could be analyzed to investigate the mechanisms at different engine operating conditions. Second, seventy other more configurations with different cavity inlet swirl angle have been discussed to study its influence on the flow mechanisms in the ducts.

Effects of axial length and integrated design on the aggressive intermediate turbine duct

With the increasing demand of high bypass ratio and thrust-to-weight ratio in civil aero-engine, the intermediate turbine duct between the high pressure and low pressure turbines of a modern gas turbine tends to shorter axial length, larger outlet-to-inlet area ratio and high pressure-to-low pressure radial offset. This paper experimentally and numerically investigated the three-dimensional flow characteristics of traditional (ITD1) and aggressive intermediate turbine duct (ITD2) at low Reynolds number. The baseline case of ITD1 is representative of a traditional intermediate turbine duct of aero-engine design with non-dimensional length of L/dR = 2.79 and middle angle of 20.12°. The detailed flow fields inside ITD1 and flow visualization were measured. Results showed the migration of boundary layer and a pair of counter-rotating vortexes were formed due to the radial migration of low momentum fluid. With the decreasing axial length of intermediate turbine duct, the radial and streamwise reverse pressure gradient in aggressive intermediate turbine duct (ITD2) were increased resulting in severe three-dimensional separation of boundary layer near casing surface and higher total pressure loss. The secondary flow and separation of boundary layer near the endwall were deeply analyzed to figure out the main source of high total pressure loss in the aggressive intermediate turbine duct (ITD2). Based on that, employing wide-chord guide vane to substitute “strut + guide vane”, this paper designed the super-aggressive intermediate turbine duct and realized the suppression of the three-dimensional separation and secondary flow.

Influence of Reynolds Number on the Unsteady Aerodynamics of Integrated Aggressive Intermediate Turbine Duct

The ultra-high bypass ratio turbofan engine attracts more and more attention in modern commercial engine due to advantages of high efficiency and low Specific Fuel Consumption (SFC). One of the characteristics of ultra-high bypass ratio turbofan is the intermediate turbine duct which guides the flow leaving high pressure turbine (HPT) to low pressure turbine (LPT) at a larger diameter, and this kind of design will lead to aggressive intermediate turbine duct (AITD) design concept. Thus, it is important to design the AITD without any severe loss. From the unsteady flow’s point of view, in actual operating conditions, the incoming wake generated by HPT is unsteady which will take influence on boundary layer’s transition within the ITD and LPT. In this paper, the three-dimensional unsteady aerodynamics of an AITD taken from a real engine is studied. The results of fully unsteady three-dimensional numerical simulations, performed with ANSYS-CFX (RANS simulation with transitional model), are critically evaluated against experimental data. After validation of the numerical model, the physical mechanisms inside the flow channel are analyzed, with an aim to quantify the sensitivities of different Reynolds number effect on both the ITD and LPT nozzle. Some general physical mechanisms can be recognized in the unsteady environment. It is recognized that wake characteristics plays a crucial role on the loss within both the ITD and LPT nozzle section, determining both time-averaged and time-resolved characteristics of the flow field. Meanwhile, particular attention needs to be paid to the unsteady effect on the boundary layer of LPT nozzle’s suction side surface.

Steady and unsteady numerical investigation of flow interaction between low-pressure turbine blade, intermediate turbine duct and power turbine vane

Flows in an intermediate turbine duct connecting low-pressure turbines and power turbines are very complex, affected by the upstream low-pressure turbine flow structures. Non-uniformities originating from the duct with struts also affect the power turbine inflow conditions, resulting in reduced efficiency. The present investigation is done to clarify the flow and loss mechanisms within the intermediate turbine duct and the power turbine. Steady and unsteady numerical investigations of the flow interaction between low-pressure turbine blade, intermediate turbine duct and power turbine vane were conducted. Effects of upstream low-pressure turbine blade on intermediate turbine duct flow fields and loss characteristics, and that of intermediate turbine duct with big and small struts on power turbine aerodynamics are explored. The generation and propagation of wake and secondary flows through the whole configuration are described. The fast Fourier transformation analyses of the flow in the low-pressure turbine blade, intermediate turbine duct and power turbine vane are also presented. Results from the steady and unsteady investigations show complex flow patterns resulted from blade–strut–vane flow interactions, which are not obtainable from intermediate turbine duct-only or power turbine-only simulations. The intermediate turbine duct has a great amplifying influence on the distorted inflow, and the inlet flow with upstream wakes and secondary flows introduces a high-loss area along the casing at intermediate turbine duct exit. Detailed results are presented and discussed for the flow physics and loss mechanisms as well as the unsteady flow evolution through the low-pressure turbine blade, intermediate turbine duct and power turbine vane.

Numerical investigation of the effects of rising angle on intermediate turbine duct and nearby turbines

In order to improve the efficiency, ultra-high bypass ratio engine attracts more and more attention because of its huge advantage, which has larger diameter low pressure turbine (LPT). This trend will lead to aggressive (high diffusion) intermediate turbine duct (ITD) design. It is necessary to guide the flow leaving high pressure turbine (HPT) to LPT at a larger diameter without any severe loss generating separation or flow disturbances. In this paper, eight ITDs with upstream swirl vanes and downstream LPT nozzle are investigated with the aid of numerical method. These models are modified from a unique ITD prototype, which comes from a real engine. Key parameters like area ratio, inlet height, and non-dimensional length of the ITDs are kept unchanged, while the rising angle (radial offset) is the only changed parameter which ranges from 8 degrees to 45 degrees. In this paper, the effects of rising angle (RA) on ITD, as well as nearby turbines, will be analyzed in detail. According to the investigation results, RA could be as large as 40 degrees in such model of this paper to escape separation; When RA increases, local inlet flow field of LPT nozzle appears to be with apparent variation; while a positive result is that outlet flow field could be kept almost unchanged through modifying blade profile. On the other hand, it seems optimistic that the overall total pressure loss could be kept nearly equivalent among different RA cases. And a valuable conclusion is that outer wall curvature is more important for pressure loss, which advises a clear direction for optimizing ITD.

Numerical investigation of the effects of ITD length on low pressure nozzle

The advantage of high efficiency, low SFC (Specific Fuel Consumption), ultra-high bypass ratio turbofan engine attracts more and more attention in modern commercial engine. The intermediate turbine duct (ITD), which connects high pressure turbine (HPT) with low pressure turbine (LPT), has a critical impact on the overall performance of turbine by guiding flow coming from HPT to LPT without too much loss. Therefore, it becomes more and more urgent to master the technique of designing aggressive, even super-aggressive ITD. Much more concerns have been concentrated on the duct. However, in order to further improve turbine, LPT nozzle is arranged into ITD to shorten low pressure axle. With such design concept, it is obvious that LPT nozzle flow field is easily influenced by upstream duct structure, but receives much less interests on the contrary. In this paper, numerical method is used to investigate the effects of length of ITD with upstream swirl blades on LPT nozzle. Nine models with the same swirl and nozzle blades, while the length of ITD is the only parameter to be changed, will be discussed. Finally, several conclusions and advices for designers are summarized. After changing axial length of ducts, inlet and outlet flow field of nozzle differs, correspondingly. On the other hand, the shearing stress on nozzle blade (suction and pressure) surface presents individual feature under various inlet flow. In addition to that, “Clocking-like effect” is described in this paper, which will contribute much to the pressure loss and should be paid enough attention.

Effect of Low-NOX Combustor Swirl Clocking on Intermediate Turbine Duct Vane Aerodynamics With an Upstream High Pressure Turbine Stage—An Experimental and Computational Study

Flow in an intermediate turbine duct (ITD) is highly complex, influenced by the upstream turbine stage flow structures, which include tip leakage flow and nonuniformities originating from the upstream high pressure turbine (HPT) vane and rotor. The complexity of the flow structures makes predicting them using numerical methods difficult, hence there exists a need for experimental validation. To evaluate the flow through an intermediate turbine duct including a turning vane, experiments were conducted in the Oxford Turbine Research Facility (OTRF). This is a short duration high speed test facility with a 3/4 engine-sized turbine, operating at the correct nondimensional parameters for aerodynamic and heat transfer measurements. The current configuration consists of a high pressure turbine stage and a downstream duct including a turning vane, for use in a counter-rotating turbine configuration. The facility has the ability to simulate low-NOx combustor swirl at the inlet to the turbine stage. This paper presents experimental aerodynamic results taken with three different turbine stage inlet conditions: a uniform inlet flow and two low-NOx swirl profiles (different clocking positions relative to the high pressure turbine vane). To further explain the flow through the 1.5 stage turbine, results from unsteady computational fluid dynamics (CFD) are included. The effect of varying the high pressure turbine vane inlet condition on the total pressure field through the 1.5 stage turbine, the intermediate turbine duct vane loading, and intermediate turbine duct exit condition are discussed and CFD results are compared with experimental data. The different inlet conditions are found to alter the flow exiting the high pressure turbine rotor. This is seen to have local effects on the intermediate turbine duct vane. With the current stator–stator vane count of 32-24, the effect of relative clocking between the two is found to have a larger effect on the aerodynamics in the intermediate turbine duct than the change in the high pressure turbine stage inlet condition. Given the severity of the low-NOx swirl profiles, this is perhaps surprising.

Effects of rising angle on upstream blades and intermediate turbine duct

With the improvement of requirement, design and manufacture technology, aero-engines for the future are characterized by further reduction in fuel consumption, cost, but increment in propulsion efficiency, which leads to ultra-high bypass ratio. The intermediate turbine duct (ITD), which connects the high pressure turbine (HPT) with the low pressure turbine (LPT), has a critical impact on the overall performances of such future engines. Therefore, it becomes more and more urgent to master the design technique of aggressive, even super-aggressive ITDs. Over the last years, a lot of research works about the flow mechanism in the diffuser ducts were carried out. Many achievements were reported, but further investigation should be performed. With the aid of numerical method, this paper focuses on the change of performance and flow field of ITD, as well as nearby turbines, brought by rising angle (RA). Eight ITDs with the same area ratio and length, but different RAs ranges from 8 degrees to 45 degrees, are compared. According to the investigation, flow field, especially outlet Ma of swirl blade is influenced by RA under potential effect, which is advisable for designers to modify HPT rotor blades after changing ITD. In addition to that, low velocity area moves towards upstream until the first bend as RA increases, while pressure loss distribution at S2 stream surface shows that hub boundary layer is more sensitive to RA, and casing layer keeps almost constant. On the other hand, the overall total pressure loss could keep nearly equivalent among different RA cases, which implies the importance of optimization.