Clocking in Low-Pressure Turbines

2017 ◽  
Vol 139 (10) ◽  
Author(s):  
Kathryn R. Evans ◽  
John P. Longley
Keyword(s):  
Leading Edge ◽  
Low Pressure ◽  
Two Stage ◽  
Low Speed ◽  
Low Pressure Turbine ◽  
Lost Work ◽  
Blade Row ◽  
Stage 1

The effect of stator clocking has been experimentally and computationally investigated using a low-speed, two-stage, low-pressure turbine (LPT) which was specifically designed to maximize the clocking potential by aligning the stator 1 wake segments with the stator 2 leading edge along the span. It was verified that the wake segments are aligned to within 10% of stator pitch across the span. The measured clocking effect on the work extraction is 0.12% and on efficiency is 0.08%. Although the effect of clocking is small, it is repeatable, periodic across four stator pitches and consistent between independent measurements. Furthermore, factors to consider for a reliable clocking investigation are discussed. The measurements revealed that the majority of the clocking effect on the work extraction occurs in stage 2 and it originates at stator 2 exit. This indicates that the flow is being processed differently within stator 2. There is also an effect on the stage 1 work. In each blade row, the measured clocking effect on the lost work is similar across the span. The computations with meshed cavities do not capture any clocking effects in stage 1. This indicates that an unsteady viscid phenomenon within rotor 1 is not captured by the fully turbulent calculation, e.g., unsteady transition. However, the computations do capture the measured clocking effect on the stage 2 work extraction. It is hypothesized that the clocking effect on stator 2 flow turning is dominated by a steady, inviscid process.

Clocking in Low-Pressure Turbines

2016 ◽  
Author(s):  
K. R. Evans ◽  
J. P. Longley
Keyword(s):  
Leading Edge ◽  
Low Pressure ◽  
Two Stage ◽  
Low Speed ◽  
Low Pressure Turbine ◽  
Lost Work ◽  
Blade Row ◽  
Stage 1

The effect of stator clocking has been experimentally and computationally investigated using a low-speed, two-stage, Low-Pressure Turbine which was specifically designed to maximise the clocking potential by aligning the Stator 1 wake segments with the Stator 2 leading edge along the span. It was verified that the wake segments are aligned to within 10% of stator pitch across the span. The measured clocking effect on the work extraction is 0.12% and on efficiency is 0.08%. Although the effect of clocking is small, it is repeatable, periodic across four stator pitches and consistent between independent measurements. Furthermore, factors to consider for a reliable clocking investigation are discussed. The measurements revealed that the majority of the clocking effect on the work extraction occurs in Stage 2 and it originates at Stator 2 exit. This indicates that the flow is being processed differently within Stator 2. There is also an effect on the Stage 1 work. In each blade row the measured clocking effect on the lost work is similar across the span. The computations with meshed cavities do not capture any clocking effects in Stage 1. This indicates that an unsteady viscid phenomenon within Rotor 1 is not captured by the fully turbulent calculation e.g. unsteady transition. However, the computations do capture the measured clocking effect on the Stage 2 work extraction. It is hypothesised that the clocking effect on Stator 2 flow turning is dominated by a steady, inviscid process.

Endwall Boundary Layer Development in an Engine Representative Four-Stage Low Pressure Turbine Rig

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Maria Vera ◽  
Elena de la Rosa Blanco ◽  
Howard Hodson ◽  
Raul Vazquez
Keyword(s):  
Boundary Layer ◽  
Leading Edge ◽  
Low Pressure ◽  
The State ◽  
Linear Cascade ◽  
Low Speed ◽  
Cold Flow ◽  
Low Pressure Turbine ◽  
Transitional Boundary Layer ◽  
Passage Vortex

Research by de la Rosa Blanco et al. (“Influence of the State of the Inlet Endwall Boundary Layer on the Interaction Between the Pressure Surface Separation and the Endwall Flows,” Proc. Inst. Mech. Eng., Part A, 217, pp. 433–441) in a linear cascade of low pressure turbine (LPT) blades has shown that the position and strength of the vortices forming the endwall flows depend on the state of the inlet endwall boundary layer, i.e., whether it is laminar or turbulent. This determines, amongst other effects, the location where the inlet boundary layer rolls up into a passage vortex, the amount of fluid that is entrained into the passage vortex, and the interaction of the vortex with the pressure side separation bubble. As a consequence, the mass-averaged stagnation pressure loss and therefore the design of a LPT depend on the state of the inlet endwall boundary layer. Unfortunately, the state of the boundary layer along the hub and casing under realistic engine conditions is not known. The results presented in this paper are taken from hot-film measurements performed on the casing of the fourth stage of the nozzle guide vanes of the cold flow affordable near term low emission (ANTLE) LPT rig. These results are compared with those from a low speed linear cascade of similar LPT blades. In the four-stage LPT rig, a transitional boundary layer has been found on the platforms upstream of the leading edge of the blades. The boundary layer is more turbulent near the leading edge of the blade and for higher Reynolds numbers. Within the passage, for both the cold flow four-stage rig and the low speed linear cascade, the new inlet boundary layer formed behind the pressure leg of the horseshoe vortex is a transitional boundary layer. The transition process progresses from the pressure to the suction surface of the passage in the direction of the secondary flow.

Turbulence Measurements in a Multistage Low-Pressure Turbine

1989 ◽  
Vol 111 (2) ◽  
pp. 153-161 ◽  
Author(s):  
A. Binder ◽  
Th. Schroeder ◽  
J. Hourmouziadis
Keyword(s):  
Fourier Transforms ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Low Pressure ◽  
Rotor Blades ◽  
Time Averaging ◽  
Ensemble Averaging ◽  
Low Pressure Turbine ◽  
Blade Row ◽  
Hot Film

The flow in the rotor blades of a five-stage low-pressure turbine was investigated experimentally using hot-film probes. Time averaging, Fourier transforms, and ensemble averaging are applied for data reduction. The techniques prove to be a very helpful instrument for the assessment of the flow characteristics in the relative frame. A strong interaction is identified between two successive rows of rotor blades. A physical model, developed from velocity and turbulence results, gives a comprehensive understanding of the phenomenon. The main parameter is the nonuniformity of the flow entering the downstream blade row. Separation occurs when the wake of the upstream rotor blades enters the blade passage near the leading edge, preferably on the pressure side. The interaction is quasi-steady in the relative frame and rotates with the rotor speed. It was observed only in one of three investigated blade rows. Further studies are necessary to identify the mechanism correlating the nonuniformity to the separation.

Endwall Boundary Layer Development in an Engine Representative Four-Stage Low Pressure Turbine Rig

2007 ◽  
Author(s):  
Maria Vera ◽  
Elena de la Rosa Blanco ◽  
Howard Hodson ◽  
Raul Vazquez
Keyword(s):  
Boundary Layer ◽  
Leading Edge ◽  
Low Pressure ◽  
The State ◽  
Linear Cascade ◽  
Low Speed ◽  
Cold Flow ◽  
Low Pressure Turbine ◽  
Transitional Boundary Layer ◽  
Passage Vortex

In a linear cascade of low pressure turbine, LPT, blades, the position and strength of the vortices forming the endwall flows depends on the state of the inlet endwall boundary layer, i.e., whether it is laminar or turbulent. The latter will determine, amongst other effects, the location where the inlet boundary layer rolls up into a passage vortex, the amount of fluid that gets swept up by the passage vortex and the interaction with the pressure side separation bubble, de la Rosa Blanco et al. [1]. As a consequence, the mass-averaged stagnation pressure loss and therefore the design of a low-pressure turbine are influenced by the state of the inlet endwall boundary layer. The paragraph above highlights the importance of determining the state of the boundary layer along the endwalls if an understanding of the endwall flows in a LPT at realistic engine conditions is sought. The results presented in this paper are taken from hot film measurements performed on the endwalls of selected nozzle guide vanes from the fourth stage of the Affordable Near Term Low Emission, ANTLE, LPT rig. These results are compared with those from a low speed linear cascade of similar LPT blades. In the cold flow four-stage LPT rig, a transitional boundary layer has been found on the platforms upstream of the leading edge of the blades. The boundary layer is more turbulent nearer the leading edge of the blade and for higher Reynolds numbers. As for the passage, for both the cold flow four-stage rig and the low speed linear cascade, the new inlet boundary layer formed behind the pressure leg of the horseshoe vortex is a transitional boundary layer. The transition process progresses from the pressure to the suction surface of the passage in the direction of the secondary flow.

Redesign of High-Lift LP-Turbine Airfoils for Low Speed Testing

2010 ◽  
Author(s):  
Michele Marconcini ◽  
Filippo Rubechini ◽  
Roberto Pacciani ◽  
Andrea Arnone ◽  
Francesco Bertini
Keyword(s):  
Separated Flow ◽  
Low Pressure ◽  
High Lift ◽  
Low Speed ◽  
Low Pressure Turbine ◽  
Wide Range ◽  
Flow Configurations ◽  
Artificial Neural Network Ann ◽  
Lp Turbine ◽  
Turbine Airfoils

Low pressure turbine airfoils of the present generation usually operate at subsonic conditions, with exit Mach numbers of about 0.6. To reduce the costs of experimental programs it can be convenient to carry out measurements in low speed tunnels in order to determine the cascades performance. Generally speaking, low speed tests are usually carried out on airfoils with modified shape, in order to compensate for the effects of compressibility. A scaling procedure for high-lift, low pressure turbine airfoils to be studied in low speed conditions is presented and discussed. The proposed procedure is based on the matching of a prescribed blade load distribution between the low speed airfoil and the actual one. Such a requirement is fulfilled via an Artificial Neural Network (ANN) methodology and a detailed parameterization of the airfoil. A RANS solver is used to guide the redesign process. The comparison between high and low speed profiles is carried out, over a wide range of Reynolds numbers, by using a novel three-equation, transition-sensitive, turbulence model. Such a model is based on the coupling of an additional transport equation for the so-called laminar kinetic energy (LKE) with the Wilcox k–ω model and it has proven to be effective for transitional, separated-flow configurations of high-lift cascade flows.

On the Simulation of Unsteady Turbulence and Transition Effects in a Multistage Low Pressure Turbine: Part III — Comparison of Harmonic Balance and Full Wheel Simulation

2018 ◽  
Author(s):  
Edmund Kügeler ◽  
Georg Geiser ◽  
Jens Wellner ◽  
Anton Weber ◽  
Anselm Moors
Keyword(s):  
Harmonic Balance ◽  
Leading Edge ◽  
Suction Side ◽  
Low Pressure ◽  
Transition Model ◽  
Higher Harmonics ◽  
Low Pressure Turbine ◽  
The Third ◽  
Transition Effects ◽  
Transition Models

This is the third part of a series of three papers on the simulation of turbulence and transition effects in a multistage low pressure turbine. The third part of the series deals with the detailed comparison of the Harmonic Balance calculations with the full wheel simulations and measurements for the two-stage low-pressure turbine. The Harmonic Balance simulations were carried out in two confingurations, either using only the 0th harmonic in the turbulence and transition model or additional in all harmonics. The same Menter SST two-equation k–ω turbulence model along with Menter and Langtrys two-equation γ–Reθ transition model is used in the Harmonic Balance simulation as in the full wheel simulations. The measurements on the second stator ofthe low-pressure turbine have been carried out separately for downstream and upstream influences. Thus, a dedicated comparison of the downstream and upstream influences of the flow to the second stator is possible. In the Harmonic Balance calculations, the influences of the not directly adjacent blade, i.e. the first stator, were also included in the second stator In the first analysis, however, it was shown that the consistency with the full wheel configuration and the measurement in this case was not as good as expected. From the analysis ofthe full wheel simulation, we found that there is a considerable variation in the order ofmagnitude ofthe unsteady values in the second stator. In a further deeper consideration of the configuration, it is found that modes are reflected in upstream rows and influences the flow in the second stator. After the integration of these modes into the Harmonic Balance calculations, a much better agreement was reached with results ofthe full wheel simulation and the measurements. The second stator has a laminar region on the suction side starting at the leading edge and then transition takes place via a separation or in bypass mode, depending on the particular blade viewed in the circumferential direction. In the area oftransition, the clear difference between the calculations without and with consideration ofthe higher harmonics in the turbulence and transition models can be clearly seen. The consideration ofthe higher harmonics in the turbulence and transition models results an improvement in the consistency.

Numerical and Experimental Investigation of the Reynolds Number and Reduced Frequency Effects on Low-Pressure Turbine Airfoils

2021 ◽  
Vol 143 (2) ◽  
Author(s):  
M. Bolinches-Gisbert ◽  
David Cadrecha Robles ◽  
Roque Corral ◽  
Fernando Gisbert
Keyword(s):  
Experimental Data ◽  
Numerical Data ◽  
Low Pressure ◽  
Reconstruction Method ◽  
Low Speed ◽  
Low Pressure Turbine ◽  
Reduced Frequency ◽  
Aerodynamic Properties ◽  
Numerical Solver ◽  
Turbine Airfoils

Abstract This article compares experimental and numerical data for a low-speed high-lift low pressure turbine (LPT) cascade under unsteady flow conditions. Three Reynolds numbers representative of LPTs have been tested, namely, 5 × 104, 105, and 2 × 105; at two reduced frequencies, fr = 0.5 and 1, also representative of LPTs. The experimental data were obtained at the low-speed linear cascade wind tunnel at the Polytechnic University of Madrid using hot wire, Laser Doppler Velocimetry (LDV), and pressure tappings. The numerical solver employs a sixth-order compact scheme based on the flux reconstruction method for spatial discretization and a fourth-order Runge–Kutta method to march in time. The longest case ran 550 h on 40 GPUs to reach a statistically periodic state. Pressure coefficients around the profile, boundary layer profiles and exit cross section distributions of velocity, pressure loss defect, shear Reynolds stress, and angle are compared against high-quality experimental data. Cascade loss and exit angle have also been compared against the experimental data. Very good agreement between experimental and numerical data is seen. The results demonstrate the suitability of the present methodology to predict the aerodynamic properties of unsteady flows around LPT linear cascades accurately.

Effect of Leading-Edge Optimization on the Loss Characteristics in a Low-Pressure Turbine Linear Cascade

2019 ◽  
Vol 28 (5) ◽  
pp. 886-904
Author(s):  
Tao Cui ◽  
Songtao Wang ◽  
Xiaolei Tang ◽  
Fengbo Wen ◽  
Zhongqi Wang
Keyword(s):  
Leading Edge ◽  
Low Pressure ◽  
Linear Cascade ◽  
Low Pressure Turbine

Highly Resolved Large Eddy Simulation Study of Gap Size Effect on Low-Pressure Turbine Stage

2017 ◽  
Vol 140 (2) ◽  
Author(s):  
R. Pichler ◽  
V. Michelassi ◽  
R. Sandberg ◽  
J. Ong
Keyword(s):  
Kinetic Energy ◽  
Cross Sections ◽  
Control Volume ◽  
Leading Edge ◽  
Suction Side ◽  
Low Pressure ◽  
Small Time ◽  
Gap Size ◽  
Low Pressure Turbine ◽  
Large Eddy

Blade-to-blade interactions in a low-pressure turbine (LPT) were investigated using highly resolved compressible large eddy simulations (LESs). For a realistic setup, a stator and rotor configuration with profiles typical of LPTs was used. Simulations were conducted with an in-house solver varying the gap size between stator and rotor from 21.5% to 43% rotor chord. To investigate the effect of the gap size on the prevailing loss mechanisms, a loss breakdown was conducted. It was found that in the large gap (LG) size case, the turbulence kinetic energy (TKE) levels of the stator wake close to the rotor leading edge were only one third of those in the small gap (SG) case, due to the longer distance of constant area mixing. The small time-averaged suction side separation on the blade, found in the LG case, disappeared in the SG calculations, confirming how stronger wakes can keep the boundary layer attached. The higher intensity wake impinging on the blade, however, did not affect the time-averaged losses calculated using the control volume approach of Denton. On the other hand, losses computed by taking cross sections upstream and downstream of the blade revealed a greater distortion loss generated by the stator wakes in the SG case. Despite the suction side separation suppression, the SG case gave higher losses overall due to the incoming wake turbulent kinetic energy amplification along the blade passage.

The Effect of Wake Passing on a Flow Separation in a Low-Pressure Turbine Cascade

2004 ◽  
Vol 126 (2) ◽  
pp. 250-256 ◽  
Author(s):  
Michael J. Brear ◽  
Howard P. Hodson
Keyword(s):  
Separation Bubble ◽  
Phase Locking ◽  
Experimental Studies ◽  
Leading Edge ◽  
Low Pressure ◽  
Pressure Surface ◽  
Low Pressure Turbine ◽  
Numerical Predictions ◽  
Unsteady Interaction ◽  
Wake Passing

This paper describes an investigation into the effect that passing wakes have on a separation bubble that exists on the pressure surface and near the leading edge of a low-pressure turbine blade. Previous experimental studies have shown that the behavior of this separation is strongly incidence dependent and that it responds to its disturbance environment. The results presented in this paper examine the effect of wake passing in greater detail. Two-dimensional, Reynolds averaged, numerical predictions are first used to examine qualitatively the unsteady interaction between the wakes and the separation bubble. The separation is predicted to consist of spanwise vortices whose development is in phase with the wake passing. However, comparison with experiments shows that the numerical predictions exaggerate the coherence of these vortices and also overpredict the time-averaged length of the separation. Nonetheless, experiments strongly suggest that the predicted phase locking of the vortices in the separation onto the wake passing is physical.

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