Aerodynamic Design of High End Wall Angle Turbine Stages—Part I: Methodology Development

2013 ◽  
Vol 136 (2) ◽  
Author(s):  
A. W. Cranstone ◽  
G. Pullan ◽  
E. M. Curtis ◽  
S. Bather
Keyword(s):  
Surface Pressure ◽  
Design Methodology ◽  
Low Pressure ◽  
Similar Magnitude ◽  
Aerodynamic Design ◽  
Wall Angle ◽  
Methodology Development ◽  
Low Pressure Turbine ◽  
Turbine Vanes ◽  
End Wall

A design methodology is presented for turbines in an annulus with high end wall angles. Such stages occur where large radial offsets between the stage inlet and stage outlet are required, for example in the first stage of modern low pressure turbines, and are becoming more prevalent as bypass ratios increase. The turbine vanes operate within s-shaped ducts which result in meridional curvature being of a similar magnitude to the blade-to-blade curvature. Through a systematic series of idealized computational cases, the importance of two aspects of vane design are shown. First, the region of peak end wall meridional curvature is best located within the vane row. Second, the vane should be leant so as to minimize spanwise variations in surface pressure—this condition is termed “ideal lean.” This design philosophy is applied to the first stage of a low pressure turbine with high end wall angles.

Aerodynamic Design of High Endwall Angle Turbine Stages: Part 1—Methodology Development

2012 ◽  
Author(s):  
A. W. Cranstone ◽  
G. Pullan ◽  
E. M. Curtis ◽  
S. Bather
Keyword(s):  
Surface Pressure ◽  
Design Methodology ◽  
Low Pressure ◽  
Similar Magnitude ◽  
Aerodynamic Design ◽  
Methodology Development ◽  
Low Pressure Turbine ◽  
Design Philosophy ◽  
Turbine Vanes

A design methodology is presented for turbines in an annulus with high endwall angles. Such stages occur where large radial offsets between the stage inlet and stage outlet are required, for example in the first stage of modern low pressure turbines, and are becoming more prevalent as bypass ratios increase. The turbine vanes operate within s-shaped ducts which result in meridional curvature being of a similar magnitude to the blade-to-blade curvature. Through a systematic series of idealised computational cases, the importance of two aspects of vane design are shown. First, the region of peak endwall meridional curvature is best located with the vane row. Second, the vane should be leant so as to minimise spanwise variations in surface pressure — this condition is termed ‘ideal lean’. This design philosophy is applied to the first stage of a low pressure turbine with high endwall angles.

Profiled End-Wall Design Using an Adjoint Navier-Stokes Solver

2006 ◽  
Author(s):  
Roque Corral ◽  
Fernando Gisbert
Keyword(s):  
Kinetic Energy ◽  
Cost Function ◽  
Unstructured Mesh ◽  
Low Pressure ◽  
Navier Stokes ◽  
Low Pressure Turbine ◽  
Gradient Based ◽  
Parallel Multigrid ◽  
End Wall ◽  
Discrete Formulation

A methodology to minimize blade secondary losses by modifying turbine end-walls is presented. The optimization is addressed using a gradient-based method, where the computation of the gradient is performed using an adjoint code and the secondary kinetic energy is used as a cost function. The adjoint code is implemented on the basis of the discrete formulation of a parallel multigrid unstructured mesh Navier-Stokes solver. The results of the optimization of two end-walls of a low pressure turbine row are shown.

A Low Pressure Turbine With Profiled End Walls and Purge Flow Operating With a Pressure Side Bubble

2011 ◽  
Author(s):  
P. Jenny ◽  
R. S. Abhari ◽  
M. G. Rose ◽  
M. Brettschneider ◽  
J. Gier
Keyword(s):  
Computational Study ◽  
Leading Edge ◽  
Low Pressure ◽  
Fast Response ◽  
Turbine Rotor ◽  
Operating Point ◽  
Pressure Side ◽  
Low Pressure Turbine ◽  
Purge Flow ◽  
End Wall

This paper presents an experimental and computational study of non-axisymmetric rotor end wall profiling in a low pressure turbine. End wall profiling has been proven to be an effective technique to reduce both turbine blade row losses and the required purge flow. For this work a rotor with profiled end walls on both hub and shroud is considered. The rotor tip and hub end walls have been designed using an automatic numerical optimisation that is implemented in an in-house MTU code. The end wall shape is modified up to the platform leading edge. Several levels of purge flow are considered in order to analyze the combined effects of end wall profiling and purge flow. The non-dimensional parameters match real engine conditions. The 2-sensor Fast Response Aerodynamic Probe (FRAP) technique system developed at ETH Zurich is used in this experimental campaign. Time-resolved measurements of the unsteady pressure, temperature and entropy fields between the rotor and stator blade rows are made. For the operating point under investigation the turbine rotor blades have pressure side separations. The unsteady behavior of the pressure side bubble is studied. Furthermore, the results of unsteady RANS simulations are compared to the measurements and the computations are also used to detail the flow field with particular emphasis on the unsteady purge flow migration and transport mechanisms in the turbine main flow containing a rotor pressure side separation. The profiled end walls show the beneficial effects of improved measured efficiency at this operating point, together with a reduced sensitivity to purge flow.

Predicting Transition in Turbomachinery—Part II: Model Validation and Benchmarking

2004 ◽  
Vol 129 (1) ◽  
pp. 14-22 ◽  
Author(s):  
T. J. Praisner ◽  
E. A. Grover ◽  
M. J. Rice ◽  
J. P. Clark
Keyword(s):  
Experimental Testing ◽  
Local Heat Transfer ◽  
Low Pressure ◽  
Boundary Layer Transition ◽  
Transfer Coefficients ◽  
Layer Transition ◽  
Low Pressure Turbine ◽  
Rans Simulations ◽  
Transition Modeling ◽  
End Wall

The ability to predict boundary layer transition locations accurately on turbomachinery airfoils is critical both to evaluate aerodynamic performance and to predict local heat-transfer coefficients with accuracy. Here we report on an effort to include empirical transition models developed in Part I of this report in a Reynolds averaged Navier-Stokes (RANS) solver. To validate the new models, two-dimensional design optimizations utilizing transitional RANS simulations were performed to obtain a pair of low-pressure turbine airfoils with the objective of increasing airfoil loading by 25%. Subsequent experimental testing of the two new airfoils confirmed pre-test predictions of both high and low Reynolds number loss levels. In addition, the accuracy of the new transition modeling capability was benchmarked with a number of legacy cascade and low-pressure turbine (LPT) rig data sets. Good agreement between measured and predicted profile losses was found in both cascade and rig environments. However, use of the transition modeling capability has elucidated deficiencies in typical RANS simulations that are conducted to predict component performance. Efficiency-versus-span comparisons between rig data and multi-stage steady and time-accurate LPT simulations indicate that loss levels in the end wall regions are significantly under predicted. Possible causes for the under-predicted end wall losses are discussed as well as suggestions for future improvements that would make RANS-based transitional simulations more accurate.

Development of Blade Profiles for Low Pressure Turbine Applications

1996 ◽  
Author(s):  
E. M. Curtis ◽  
H. P. Hodson ◽  
M. R. Banieghbal ◽  
J. D. Denton ◽  
R. J. Howell ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Surface Pressure ◽  
Low Pressure ◽  
Blade Profile ◽  
Suction Surface ◽  
Number Range ◽  
Low Pressure Turbine ◽  
Pressure Distributions ◽  
Wide Range ◽  
Highly Loaded

This paper describes a programme of work, largely experimental, which was undertaken with the objective of developing an improved blade profile for the low-pressure turbine in aero-engine applications. Preliminary experiments were conducted using a novel technique. An existing cascade of datum blades was modified to enable the pressure distribution on the suction surface of one of the blades to be altered. Various means, such as shaped inserts, an adjustable flap at the trailing edge, and changing stagger were employed to change the geometry of the passage. These experiments provided boundary layer and lift data for a wide range of suction surface pressure distributions. The data was then used as a guide for the development of new blade profiles. The new blade profiles were then investigated in a low-speed cascade that included a set of moving bars upstream of the cascade of blades 10 simulate the effect of the incoming wakes from the previous blade row in a multistage turbine environment. Results are presented for two improved profiles that are compared with a datum representative of current practice. The experimental results include loss measurements by wake traverse, surface pressure distributions, and boundary layer measurements. The cascades were operated over a Reynolds Number range from 0.7 × 105 to 4.0 × 105. The first profile is a “laminar flow” design that was intended to improve the efficiency at the same loading as the datum. The other is a more highly loaded blade profile intended to permit a reduction in blade numbers. The more highly loaded profile is the most promising candidate for inclusion in future designs. It enables blade numbers to be reduced by 20%, without incurring any efficiency penalty. The results also indicate that unsteady effects must be taken into consideration when selecting a blade profile for the low-pressure turbine.

Aerodynamic Design of a New Five Stage Low Pressure Turbine for the Rolls Royce Trent 500 Turbofan

2001 ◽  
Author(s):  
I. Ulizar ◽  
P. González
Keyword(s):  
Low Pressure ◽  
Previous Experience ◽  
Aerodynamic Design ◽  
Design Work ◽  
Cost Performance ◽  
Detailed Design ◽  
Low Pressure Turbine ◽  
Lp Turbine ◽  
The Moment ◽  
Turbine Design

Almost a decade ago, ITP (Industria de Turbo Propulsores, S.A.) started to participate in Low Pressure turbine design supported by Rolls-Royce. The Trent 500 LP turbine aerodynamic design is the most challenging and extensive design work carried out to the moment. The Trent 500 is part of the Rolls Royce Trent family. It has been designed to enter in service in the Airbus 340-600. This engine has very aggressive targets in terms of cost, performance, weight and noise. An optimization process was carried out during the preliminary and detailed design phases to accomplish these targets. This paper describes the most outstanding characteristics of the LP turbine, how the previous experience and Research and Technology results have been employed in this design and also some of the new advanced features, e.g. the introduction of spoon aerofoils.

End Wall Loss Reduction of High Lift Low Pressure Turbine Airfoils Using Profile Contouring—Part II: Validation

2014 ◽  
Vol 136 (8) ◽  
Author(s):  
Keith Sangston ◽  
Jesse Little ◽  
M. Eric Lyall ◽  
Rolf Sondergaard
Keyword(s):  
Flow Field ◽  
Low Pressure ◽  
Stereoscopic Particle Image Velocimetry ◽  
Loss Reduction ◽  
High Lift ◽  
Low Pressure Turbine ◽  
Wall Loss ◽  
Wall Flow ◽  
End Wall ◽  
Stagger Angle

The hypothesis, posed in Part I, that excessive end wall loss of high lift low pressure turbine (LPT) airfoils is due to the influence of high stagger angles on the end wall pressure distribution and not front loading is evaluated in a linear cascade at Re = 100,000 using both experimental and computational studies. A nominally high lift and high stagger angle front-loaded profile (L2F) with aspect ratio 3.5 is contoured at the end wall to reduce the stagger angle while maintaining the front loading. The contouring process effectively generates a fillet at the end wall, so the resulting airfoil is referred to as L2F-EF (end wall fillet). Although referred to as a fillet, this profile contouring process is novel in that it is designed to isolate the effect of stagger angle on end wall loss. Total pressure loss measurements downstream of the blade row indicate that the use of the lower stagger angle at the end wall reduces mixed out mass averaged end wall and passage losses approximately 23% and 10%, respectively. This is in good agreement with computational results used to design the contour which predict 18% and 7% loss reductions. The end wall flow field of the L2F and L2F-EF models is measured using stereoscopic particle image velocimetry (PIV) in the passage. These data are used to quantify changes in the end wall flow field due to the contouring. PIV results show that this loss reduction is characterized by reduced inlet boundary layer separation as well as a change in strength and location of the suction side horseshoe vortex (SHV) and passage vortex (PV). The end wall profile contouring also produces a reduction in all terms of the Reynolds stress tensor consistent with a decrease in deformation work and overall flow unsteadiness. These results confirm that the stagger angle has a significant effect on high-lift front-loaded LPT end wall loss. Low stagger profiling is successful in reducing end wall loss by limiting the development and migration of the low momentum fluid associated with the SHV and PV interaction.

Application of Nonaxisymmetric Endwall Contouring to Conventional and High-Lift Turbine Airfoils

2013 ◽  
Vol 135 (6) ◽  
Author(s):  
T. J. Praisner ◽  
E. Allen-Bradley ◽  
E. A. Grover ◽  
D. C. Knezevici ◽  
S. A. Sjolander
Keyword(s):  
Design Methodology ◽  
Three Dimensional ◽  
Low Pressure ◽  
Free Form ◽  
Published Data ◽  
High Lift ◽  
Flow Solver ◽  
Low Pressure Turbine ◽  
Gradient Based ◽  
Endwall Contouring

Here, we report on the application of nonaxisymmetric endwall contouring to mitigate the endwall losses of one conventional and two high-lift low-pressure turbine airfoil designs. The design methodology presented combines a gradient-based optimization algorithm with a three-dimensional computational fluid dynamics (CFD) flow solver to systematically vary a free-form parameterization of the endwall. The ability of the CFD solver employed in this work to predict endwall loss modifications resulting from nonaxisymmetric contouring is demonstrated with previously published data. Based on the validated trend accuracy of the solver for predicting the effects of endwall contouring, the magnitude of predicted viscous losses forms the objective function for the endwall design methodology. This system has subsequently been employed to optimize contours for the conventional-lift Pack B and high-lift Pack D-F and Pack D-A low-pressure turbine airfoil designs. Comparisons between the predicted and measured loss benefits associated with the contouring for Pack D-F design are shown to be in reasonable agreement. Additionally, the predictions and data demonstrate that the Pack D-F endwall contour is effective at reducing losses primarily associated with the passage vortex. However, some deficiencies in predictive capabilities demonstrated here highlight the need for a better understanding of the physics of endwall loss-generation and improved predictive capabilities.

Predictions of Unsteady Interactions Between Closely Coupled High Pressure- and Low Pressure-Turbines With Co- and Counterrotation

2013 ◽  
Vol 135 (6) ◽  
Author(s):  
T. J. Praisner ◽  
E. A. Grover ◽  
R. Mocanu ◽  
R. J. Jurek ◽  
R. E. Gacek
Keyword(s):  
High Pressure ◽  
Surface Pressure ◽  
Analytical Study ◽  
Low Pressure ◽  
Tangential Load ◽  
Low Pressure Turbine ◽  
Unsteady Aerodynamic ◽  
Complex Interactions ◽  
Unsteady Surface Pressure ◽  
Turbine Vane

Here, we report on an analytical study of the unsteady aerodynamic interactions of a closely coupled, corotating, high- and low-pressure turbine configuration. The effort was focused on the prediction of unsteady surface pressures imparted on the first blade of the low-pressure turbine (LPT). As a first step, a baseline three-row time-accurate prediction was carried out for the first three rows of the low-pressure turbine (vane-blade-vane). In contrast to the three-row results, a four-row analysis, which included the blade of the high-pressure turbine, revealed that the temporally varying tangential load on the LPT blade was increased in amplitude by a factor of five compared to the three-row case with a shift in primary unsteady energy to unexpected frequencies. In the four-row analysis, a region of unusually high unsteadiness near the tip of the LPT blade was also characterized by an increase in the amplitude of the fluctuating surface pressure by a factor of nearly seven, again, with unexpected attendant frequencies. A model is presented which explains the unexpected frequencies realized in the four-row results and allows the predetermination of these frequencies without the use of computational fluid dynamics. In an effort to better understand the complex interactions between the high- and low-pressure turbines, the first vane of the low-pressure turbine was redesigned, and the remaining airfoils were reoriented, to establish a counterrotating turbine configuration. While substantial reductions in unsteady surface-pressure amplitudes were realized near the tip of the LPT blade with the switch to counterrotation, the amplitude of the temporally varying tangential load on the blade remained notably higher than that from the three-row analysis. The precise physical cause for the high levels of local unsteadiness near the tip of the first LPT blade in the corotating configuration remains unclear.

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