Secondary Flows in LPT Cascades: Numerical and Experimental Investigation of the Impact of the Inner Part of the Boundary Layer

2018 ◽  
Author(s):  
Matteo Giovannini ◽  
Filippo Rubechini ◽  
Michele Marconcini ◽  
Daniele Simoni ◽  
Vianney Yepmo ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Low Pressure ◽  
Secondary Flows ◽  
Flow Angle ◽  
Pressure Losses ◽  
Current Design ◽  
Inlet Conditions ◽  
Correct Understanding ◽  
The Impact

Due to the low level of profile losses already reached in the design of modern low-pressure turbines for turbofan applications, a renewed interest is devoted to the other sources of loss, and namely to the secondary losses. At the same time, the importance of secondary losses has been reinforced by the current design trend towards high-lift profiles. A great attention, therefore, is dedicated to reliable and effective prediction methods as well as on the correct understanding of the mechanisms that drive the secondary flows. In this context, a systematic numerical and experimental campaign was carried out focusing on the impact of different inlet boundary layer (BL) profiles and considering a state-of-the-art low-pressure turbine cascade. Starting from a computational environment representative of a design standard, detailed RANS analyses were carried out in order to establish dependable guidelines for the computational setup. As a major result, such analyses also underlined the importance of the shape of the inlet BL very close to the endwall, hence suggesting tight requirements for the characterization of the experimental environment. The impact of the inlet BL profile on the secondary flow development was experimentally investigated by varying the profile shape very close to the endwall as well as on the external part with respect to a reference condition. The effects on the cascade performance were evaluated focusing on the intensity of the over-under-turning as well as on the associated losses (intensity and penetration) by measuring the span-wise distributions of flow angle and total pressure losses at the cascade exit plane. For all the inlet conditions, comparisons between CFD and experimental results are discussed. Besides providing guidelines for a proper numerical and experimental setup, the present paper underlines the importance of a detailed characterization of the inlet BL for an accurate assessment of the secondary flows. From a broader perspective, when aiming at reproducing (numerically or experimentally) a real engine environment, this suggests that an in-depth matching of the inlet profiles is crucial for reliable estimates of the secondary losses.

Secondary Flows in Low-Pressure Turbines Cascades: Numerical and Experimental Investigation of the Impact of the Inner Part of the Boundary Layer

2018 ◽  
Vol 140 (11) ◽  
Author(s):  
Matteo Giovannini ◽  
Filippo Rubechini ◽  
Michele Marconcini ◽  
Daniele Simoni ◽  
Vianney Yepmo ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Low Pressure ◽  
Secondary Flows ◽  
Navier Stokes ◽  
Flow Angle ◽  
Pressure Losses ◽  
Inlet Conditions ◽  
External Part ◽  
The Impact

Due to the low level of profile losses reached in low-pressure turbines (LPT) for turbofan applications, a renewed interest is devoted to other sources of loss, e.g., secondary losses. At the same time, the adoption of high-lift profiles has reinforced the importance of these losses. A great attention, therefore, is dedicated to reliable prediction methods and to the understanding of the mechanisms that drive the secondary flows. In this context, a numerical and experimental campaign on a state-of-the-art LPT cascade was carried out focusing on the impact of different inlet boundary layer (BL) profiles. First of all, detailed Reynolds Averaged Navier-Stokes (RANS) analyzes were carried out in order to establish dependable guidelines for the computational setup. Such analyzes also underlined the importance of the shape of the inlet BL very close to the endwall, suggesting tight requirements for the characterization of the experimental environment. The impact of the inlet BL on the secondary flow was experimentally investigated by varying the inlet profile very close to the endwall as well as on the external part of the BL. The effects on the cascade performance were evaluated by measuring the span-wise distributions of flow angle and total pressure losses. For all the inlet conditions, comparisons between Computational Fluid Dynamics (CFD) and experimental results are discussed. Besides providing guidelines for a proper numerical and experimental setup, the present paper underlines the importance of a detailed characterization of the inlet BL for an accurate assessment of the secondary flows.

Shorten the Intermediate Turbine Duct Length by Applying an Integrated Concept

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
A. Marn ◽  
E. Göttlich ◽  
D. Cadrecha ◽  
H. P. Pirker
Keyword(s):  
High Pressure ◽  
Flow Distribution ◽  
Low Pressure ◽  
Secondary Flows ◽  
Base Line ◽  
Flow Angle ◽  
Intermediate Turbine Duct ◽  
Integrated Concept ◽  
Inlet Conditions ◽  
Base Design

The demand of further increased bypass ratio of aero engines will lead to low pressure turbines with larger diameters, which rotate at lower speed. Therefore, it is necessary to guide the flow leaving the high pressure turbine to the low pressure turbine at larger diameters minimizing the losses and providing an adequate flow at the low pressure (LP)-turbine inlet. Due to costs and weight, this intermediate turbine duct has to be as short as possible. This would lead to an aggressive (high diffusion) s-shaped duct geometry. It is possible to shorten the duct simply by reducing the length but the risk of separation is rising and losses increase. Another approach to shorten the duct and thus the engine length is to apply a so called integrated concept. These are novel concepts where the struts, mounted in the transition duct, replace the usually following LP-vane row. This configuration should replace the first LP-vane row from a front bearing engine architecture where the vane needs a big area to hold bearing services. That means the rotor is located directly downstream of the strut. This means that the struts have to provide the downstream blade row with undisturbed inflow with suitable flow angle and Mach number. Therefore, the (lifting) strut has a distinct three-dimensional design in the more downstream part, while in the more upstream part, it has to be cylindrical to be able to lead through supply lines. In spite of the longer chord compared with the base design, this struts have a thickness to chord ratio of 18%. To apply this concept, a compromise must be found between the number of struts (weight), vibration, noise, and occurring flow disturbances due to the secondary flows and losses. The struts and the outer duct wall have been designed by Industria de Turbopropulsores. The inner duct was kept the same as for the base line configuration (designed by Motoren und Turbinen Union). The aim of the design was to have similar duct outflow conditions (exit flow angle and radial mass flow distribution) as the base design with which it is compared in this paper. This base design consists of a single transonic high pressure (HP)-turbine stage, an aggressive s-shaped intermediate turbine duct, and a LP-vane row. Both designs used the same HP-turbine and were run in the continuously operating Transonic Test Turbine Facility at Graz University of Technology under the same engine representative inlet conditions. The flow field upstream and downstream the LP-vane and the strut, respectively, has been investigated by means of five hole probes. A rough estimation of the overall duct loss is given as well as the upper and lower weight reduction limit for the integrated concept.

scholarly journals Reducing Secondary Flow Losses in Low-Pressure Turbines: The “Snaked” Blade

2019 ◽  
Vol 4 (3) ◽  
pp. 28
Author(s):  
Matteo Giovannini ◽  
Filippo Rubechini ◽  
Michele Marconcini ◽  
Andrea Arnone ◽  
Francesco Bertini
Keyword(s):  
Detailed Comparison ◽  
Low Pressure ◽  
Secondary Flows ◽  
Wall Region ◽  
Flow Angle ◽  
Pressure Loss Coefficient ◽  
Flow Losses ◽  
Parametric Description ◽  
Stator Blade ◽  
The Impact

This paper presents an innovative design for reducing the impact of secondary flows on the aerodynamics of low-pressure turbine (LPT) stages. Starting from a state-of-the-art LPT stage, a local reshaping of the stator blade was introduced in the end-wall region in order to oppose the flow turning deviation. This resulted in an optimal stator shape, able to provide a more uniform exit flow angle. The detailed comparison between the baseline stator and the redesigned one allowed for pointing out that the rotor row performance increased thanks to the more uniform inlet flow, while the stator losses were not significantly affected. Moreover, it was possible to derive some design rules and to devise a general blade shape, named ‘snaked’, able to ensure such results. This generalization translated in an effective parametric description of the ‘snaked’ shape, in which few parameters are sufficient to describe the optimal shape modification starting from a conventional design. The “snaked” blade concept and its design have been patented by Avio Aero. The stator redesign was then applied to a whole LPT module in order to evaluate the potential benefit of the ‘snaked’ design on the overall turbine performance. Finally, the design was validated by means of an experimental campaign concerning the stator blade. The spanwise distributions of the flow angle and pressure loss coefficient at the stator exit proved the effectiveness of the redesign in providing a more uniform flow to the successive row, while preserving the original stator losses.

Shorten the Intermediate Turbine Duct Length by Applying an Integrated Concept

2008 ◽  
Author(s):  
A. Marn ◽  
E. Go¨ttlich ◽  
D. Cadrecha ◽  
H. P. Pirker
Keyword(s):  
Three Dimensional ◽  
Flow Distribution ◽  
Low Pressure ◽  
Secondary Flows ◽  
Base Line ◽  
Flow Angle ◽  
Intermediate Turbine Duct ◽  
Integrated Concept ◽  
Inlet Conditions ◽  
Base Design

The demand of further increased bypass ratio of aero engines will lead to low pressure turbines with larger diameters which rotate at lower speed. Therefore, it is necessary to guide the flow leaving the high pressure turbine to the low pressure turbine at larger diameters minimising the losses and providing an adequate flow at the LP-turbine inlet. Due to costs and weight this intermediate turbine duct has to be as short as possible. This would lead to an aggressive (high diffusion) s-shaped duct geometry. It is possible to shorten the duct simply by reducing the length but the risk of separation is rising and losses increase. Another approach to shorten the duct and thus the engine length is to apply a so called integrated concept. These are novel concepts where the struts, mounted in the transition duct, replace the usually following LP-vane row. This configuration should replace the first LP-vane row from a front bearing engine architecture where the vane needs a big area to hold bearing services. That means the rotor is located directly downstream of the strut. This means that the struts have to provide the downstream blade row with undisturbed inflow with suitable flow angle and Mach number. Therefore, the (lifting) strut has a distinct three dimensional design in the more downstream part while in the more upstream part it has to be cylindrical to be able to lead through supply lines. In spite of the longer chord compared with the base design this struts have a thickness to chord ratio of 18%. To apply this concept a compromise must be found between the number of struts (weight), vibration, noise and occurring flow disturbances due to secondary flows and losses. The struts and the outer duct wall have been designed by ITP. The inner duct was kept the same as for the base line configuration (designed by MTU). The aim of the design was to have similar duct outflow conditions (exit flow angle and radial mass flow distribution) as the base design with which it is compared in this paper. This base design consists of a single transonic HP-turbine stage, an aggressive s-shaped intermediate turbine duct and an LP-vane row. Both designs used the same HP-turbine and were run in the continuously operating Transonic Test Turbine Facility (TTTF) at Graz University of Technology under the same engine representative inlet conditions. The flow field upstream and downstream the LP-vane and the strut, respectively has been investigated by means of five hole probes. A rough estimation of the overall duct loss is given as well as the upper and lower weight reduction limit for the integrated concept. This work is part of the EU-project AIDA (Aggressive Intermediate Duct Aerodynamics, Contract: AST3-CT-2003-502836).

Improving Characteristics of a Cooled Transonic Vane of Low Pressure Turbine Under Nonuniform Inlet Conditions

2020 ◽  
Author(s):  
A. V. Granovskiy ◽  
I. V. Afanasiev ◽  
V. K. Kostege ◽  
E. Yu. Marchukov
Keyword(s):  
Cooling System ◽  
Pressure Ratio ◽  
Low Pressure ◽  
Secondary Flows ◽  
Gas Temperature ◽  
Flow Angle ◽  
Low Pressure Turbine ◽  
Large Pressure ◽  
Negative Effect ◽  
Inlet Conditions

Abstract Vanes of low-pressure turbines (LPT) run under inlet conditions generated by a preceding high-pressure turbine (HPT). HP stages are generally cooled and transonic as well due to the large pressure ratio necessary to reduce the gas temperature upstream of the downstream stages. Therefore radial distributions of inlet flow angle, total pressure and total temperature at the boundary upstream of the LPT are highly non–uniform. Such non-uniform inlet conditions can result in enhanced level of the total losses including the secondary losses. Moreover, vanes of LPT have meridional openings along inner and outer boundaries of the flow path, which causes intensification of the secondary flows leading to an increase in secondary losses. In this case the special meridional contouring of the vanes’ outer and inner surfaces allows a decrease in the flare angle namely meridional opening in the rear part of the vane. In this work, in order to compensate the negative effect of non-uniform inlet conditions, meridional opening and low aspect ratio, 3D profiling of the vane row is used as a way of reducing secondary losses. Some variants of LPT vanes with various complex 3D shapes are investigated. In particular, vane variants with a “reversed bow”, a “bowed” and a “lean” in the circumferential direction have been examined. Significant modification of the vane row is limited by cooling system design, which has to incorporate a deflector in the inner hollow of the vane to improve cooling effectiveness. A compromise between aerodynamic quality and cooling limitations has been achieved.

scholarly journals LES and RANS Analysis of the End-Wall Flow in a Linear LPT Cascade: Part I — Flow and Secondary Vorticity Fields Under Varying Inlet Condition

2018 ◽  
Author(s):  
R. Pichler ◽  
Yaomin Zhao ◽  
R. D. Sandberg ◽  
V. Michelassi ◽  
R. Pacciani ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Secondary Flow ◽  
Flow Characteristics ◽  
Flow Region ◽  
Secondary Flows ◽  
Wall Boundary Layer ◽  
Wall Boundary ◽  
Wall Flow ◽  
End Wall ◽  
The Impact

In low-pressure-turbines (LPT) around 60–70% of losses are generated away from end-walls, while the remaining 30–40% is controlled by the interaction of the blade profile with the end-wall boundary layer. Experimental and numerical studies have shown how the strength and penetration of the secondary flow depends on the characteristics of the incoming end-wall boundary layer. Experimental techniques did shed light on the mechanism that controls the growth of the secondary vortices, and scale-resolving CFD allowed to dive deep into the details of the vorticity generation. Along these lines, this paper discusses the end-wall flow characteristics of the T106 LPT profile at Re = 120K and M = 0.59 by benchmarking with experiments and investigating the impact of the incoming boundary layer state. The simulations are carried out with proven Reynolds-averaged Navier–Stokes (RANS) and large-eddy simulation (LES) solvers to determine if Reynolds Averaged models can capture the relevant flow details with enough accuracy to drive the design of this flow region. Part I of the paper focuses on the critical grid needs to ensure accurate LES, and on the analysis of the overall time averaged flow field and comparison between RANS, LES and measurements when available. In particular, the growth of secondary flow features, the trace and strength of the secondary vortex system, its impact on the blade load variation along the span and end-wall flow visualizations are analysed. The ability of LES and RANS to accurately predict the secondary flows is discussed together with the implications this has on design.

Engine Design Strategy for Boundary Layer Ingesting Propulsion Systems With Multiple Non-Symmetric Engine Inlet Conditions

2013 ◽  
Author(s):  
Jonathan C. Gladin ◽  
Brian K. Kestner ◽  
Jeff S. Schutte ◽  
Dimitri N. Mavris
Keyword(s):  
Boundary Layer ◽  
Design Strategy ◽  
Total Power ◽  
Design Strategies ◽  
Fuel Burn ◽  
Practical Strategy ◽  
Engine Design ◽  
Vehicle Aerodynamics ◽  
Inlet Conditions ◽  
The Impact

Boundary layer ingesting inlets for hybrid wing body aircraft have been investigated at some depth in recent years due to the theoretical potential for fuel burn savings. Such savings derive from the ingestion of a portion of the low momentum wake into the propulsor to reenergize the flow, thus yielding total power savings and reducing required block fuel burn. A potential concern for BLI is that traditional concepts such as “thrust” and “drag” become less clearly defined due to the interaction between the vehicle aerodynamics and the propulsive thrust achieved. One such interaction for the HWB concept is the lateral location of the inlet on the upper surface which determines the effective Reynolds number at the point of ingestion. This is an important factor in determining the amount of power savings achieved by the system, since the boundary layer, displacement, and momentum thicknesses are functions of the local chord length and airfoil shape which are all functions of the lateral location of the engine. This poses a design challenge for engine layouts with more than two engines as at least one or more of the total engines will be operating at a different set of changing inlet conditions throughout the flight envelope. As a result, the engine operating point and propulsive performance will be different between outboard and inboard engines at flight conditions with appreciable boundary layer influence including key flight conditions for engine design: takeoff, top of climb, and cruise. The optimal engine design strategy in terms of performance to address this issue is to design separate engines with similar thrust performance. This strategy has significant challenges such as requiring the manufacturing and certification of two different engines for one vehicle. A more practical strategy is to design a single engine that performs adequately at the different inlet conditions but may not achieve the full benefits of BLI. This paper presents a technique for cycle analysis which can account for the disparity between inlet conditions. This technique was used for two principal purposes: first to determine the effect of the inlet disparity on the performance of the system; second, to analyze the various design strategies that might mitigate the impact of this effect. It is shown that a single engine can be sized when considering both inboard and outboard engines simultaneously. Additionally, it is shown that there is a benefit to ingesting larger mass flows in the inboard engine for the case with large disparity between the engine inlets.

Production and Development of Secondary Flows and Losses in Two Types of Straight Turbine Cascades: Part 1—A Stator Case

1987 ◽  
Vol 109 (2) ◽  
pp. 186-193 ◽  
Author(s):  
A. Yamamoto
Keyword(s):  
Secondary Flow ◽  
Total Pressure ◽  
Experimental Information ◽  
Secondary Flows ◽  
Accumulation Process ◽  
Flow Angle ◽  
Turning Angle ◽  
Pressure Losses ◽  
Flow Vectors ◽  
Turbine Cascades

The present study intends to give some experimental information on secondary flows and on the associated total pressure losses occurring within turbine cascades. Part 1 of the paper describes the mechanism of production and development of the loss caused by secondary flows in a straight stator cascade with a turning angle of about 65 deg. A full representation of superimposed secondary flow vectors and loss contours is given at fourteen serial traverse planes located throughout the cascade. The presentation shows the mechanism clearly. Distributions of static pressures and of the loss on various planes close to blade surfaces and close to an endwall surface are given to show the loss accumulation process over the surfaces of the cascade passage. Variation of mass-averaged flow angle, velocity and loss through the cascade, and evolution of overall loss from upstream to downstream of the cascade are also given. Part 2 of the paper describes the mechanism in a straight rotor cascade with a turning angle of about 102 deg.

Heat Transfer Investigation of an Aggressive Intermediate Turbine Duct: Part 1—Experimental Investigation

2010 ◽  
Author(s):  
Carlos Arroyo Osso ◽  
T. Gunnar Johansson ◽  
Fredrik Wallin
Keyword(s):  
Heat Transfer ◽  
Large Scale ◽  
Computational Study ◽  
Convective Heat Transfer Coefficient ◽  
Low Pressure ◽  
Flow Measurements ◽  
Pressure Losses ◽  
Turbofan Engines ◽  
Intermediate Turbine Duct ◽  
Inlet Conditions

In most designs of two-spool turbofan engines, intermediate turbine duct (ITD’s) are used to connect the high-pressure turbine (HPT) with the low-pressure turbine (LPT). Demands for more efficient engines with reduced emissions require more “aggressive ducts”, ducts which provide both a higher radial offset and a larger area ratio in the shortest possible length, while maintaining low pressure losses and avoiding non-uniformities in the outlet flow that might affect the performance of the downstream LPT. The work presented in this paper is part of a more comprehensive experimental and computational study of the flowfield and the heat transfer in an aggressive ITD. The main objectives of the study were to obtain an understanding of the mechanisms governing the heat transfer in ITD’s and to obtain high quality experimental data for the improvement of the CFD-based design tools. This paper consists of two parts. The first one, this one, presents and discusses the results of the experimental study. In the second part, a comparison between the experimental results and a numerical analysis is presented. The duct studied was a state-of-the-art “aggressive” design with nine thick non-turning structural struts. It was tested in a large-scale low-speed experimental facility with a single-stage HPT. In this paper measurements of the steady convective heat transfer coefficient (HTC) distribution on both endwalls and on the strut for the duct design inlet conditions are presented. The heat transfer measurement technique used is based on infrared-thermography. Part of the results of the flow measurements is also included.

Aerodynamic Performance of a Very High Lift Low Pressure Turbine Blade With Emphasis on Separation Prediction

2004 ◽  
Vol 126 (3) ◽  
pp. 406-413 ◽  
Author(s):  
Re´gis Houtermans ◽  
Thomas Coton ◽  
Tony Arts
Keyword(s):  
Turbine Blade ◽  
Separation Bubble ◽  
Separated Flow ◽  
Low Pressure ◽  
Secondary Flows ◽  
Flow Mode ◽  
High Lift ◽  
Flow Angle ◽  
Low Pressure Turbine ◽  
Very High

The present paper is based on an experimental study of a front-loaded very high lift, low pressure turbine blade designed at the VKI. The experiments have been carried out in a low-speed wind tunnel over a wide operating range of incidence and Reynolds number. The aim of the study is to characterize the flow through the cascade in terms of losses, mean outlet flow angle, and secondary flows. At low inlet freestream turbulence intensity, a laminar separation bubble is present, and a prediction model for a separated flow mode of transition has been developed.

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