Influence of Sweep on Axial Flow Turbine Aerodynamics at Midspan

2006 ◽  
Vol 129 (3) ◽  
pp. 591-598 ◽  
Author(s):  
Graham Pullan ◽  
Neil W. Harvey
Keyword(s):  
Pressure Distribution ◽  
Axial Flow ◽  
Surface Velocity ◽  
Simple Method ◽  
Pressure Surface ◽  
Blade Area ◽  
Wetted Area ◽  
Loading Parameter ◽  
Turbine Design ◽  
Profile Loss

Sweep, when the stacking axis of the blade is not perpendicular to the axisymmetric streamsurface in the meridional view, is often an unavoidable feature of turbine design. Although a high aspect ratio swept blade can be designed to achieve the same pressure distribution as an unswept design, this paper shows that the swept blade will inevitably have a higher profile loss. A modified Zweifel loading parameter, taking sweep into account, is first derived. If this loading coefficient is held constant, it is shown that sweep reduces the required pitch-to-chord ratio and thus increases the wetted area of the blades. Assuming fully turbulent boundary layers and a constant dissipation coefficient, the effect of sweep on profile loss is then estimated. A combination of increased blade area and a raised pressure surface velocity means that the profile loss rises with increasing sweep. The theory is then validated using experimental results from two linear cascade tests of highly loaded blade profiles of the type found in low-pressure aeroengine turbines: one cascade is unswept, the other has 45deg of sweep. The swept cascade is designed to perform the same duty with the same loading coefficient and pressure distribution as the unswept case. The measurements show that the simple method used to estimate the change in profile loss due to sweep is sufficiently accurate to be a useful aid in turbine design.

The Influence of Sweep on Axial Flow Turbine Aerodynamics at Mid-Span

2006 ◽  
Author(s):  
Graham Pullan ◽  
Neil W. Harvey
Keyword(s):  
Pressure Distribution ◽  
Axial Flow ◽  
Surface Velocity ◽  
Simple Method ◽  
Pressure Surface ◽  
Blade Area ◽  
Wetted Area ◽  
Loading Parameter ◽  
Turbine Design ◽  
Profile Loss

Sweep, when the stacking axis of the blade is not perpendicular to the axi-symmetric streamsurface in the meridional view, is often an unavoidable feature of turbine design. Although a high aspect ratio swept blade can be designed to achieve the same pressure distribution as an unswept design, this paper shows that the swept blade will inevitably have a higher profile loss. A modified Zweifel loading parameter, taking sweep into account, is first derived. If this loading coefficient is held constant, it is shown that sweep reduces the required pitch-to-chord ratio and so increases the wetted area of the blades. Assuming fully turbulent boundary layers, and a constant dissipation coefficient, the effect of sweep on profile loss is then estimated. A combination of increased blade area and a raised pressure surface velocity means that the profile loss rises with increasing sweep. The theory is then validated using experimental results from two linear cascade tests of highly loaded blade profiles of the type found in low pressure aeroengine turbines: one cascade is unswept, the other has 45 degrees of sweep. The swept cascade is designed to perform the same duty with the same loading coefficient and pressure distribution as the unswept case. The measurements show that the simple method used to estimate the change in profile loss due to sweep is sufficiently accurate to be a useful aid in turbine design.

Improved Blade Profile Loss and Deviation Angle Models for Advanced Transonic Compressor Bladings: Part I—A Model for Subsonic Flow

1996 ◽  
Vol 118 (1) ◽  
pp. 73-80 ◽  
Author(s):  
W. M. Ko¨nig ◽  
D. K. Hennecke ◽  
L. Fottner
Keyword(s):  
Axial Flow ◽  
Deviation Angle ◽  
Simple Method ◽  
Subsonic Flows ◽  
New Model ◽  
Transonic Compressor ◽  
Blade Row ◽  
Inlet Conditions ◽  
Improved Accuracy ◽  
Profile Loss

New blading concepts as used in modern transonic axial-flow compressors require improved loss and deviation angle correlations. The new model presented in this paper incorporates several elements and treats blade-row flows having subsonic and supersonic inlet conditions separately. In the first part of this paper two proved and well-established profile loss correlations for subsonic flows are extended to quasi-two-dimensional conditions and to custom-tailored blade designs. Instead of a deviation angle correlation, a simple method based on singularities is utilized. The comparison between the new model and a recently published model demonstrates the improved accuracy in prediction of cascade performance achieved by the new model.

A Simple Method for Estimating Secondary Losses in Turbines at the Preliminary Design Stage

1992 ◽  
Author(s):  
M. B. Okan ◽  
D. G. Gregory-Smith
Keyword(s):  
Boundary Layer ◽  
Design Stage ◽  
Accurate Estimation ◽  
Test Cases ◽  
Simple Method ◽  
Early Design Stage ◽  
Preliminary Design Stage ◽  
Turbine Design ◽  
End Wall ◽  
Profile Loss

Reasonably accurate estimation of losses at an early design stage plays an important part in the success of a turbine design. Although various computational methods exist for estimating the profile loss, for secondary losses which are equally important, designers still rely on emprical estimates. A method has been developed for estimating the secondary flow and secondary losses within an axial turbine cascade. It is assumed that the inlet boundary layer is convected into a loss core within the blade passage while extra loss has been generated due to the secondary kinetic energy and a new boundary layer that is developing on the end wall. The method has been applied to various test cases and the results show that the basic approach is reliable.

Analysis of Hot Streak Effects on Turbine Rotor Heat Load

1997 ◽  
Vol 119 (3) ◽  
pp. 544-553 ◽  
Author(s):  
T. Shang ◽  
A. H. Epstein
Keyword(s):  
Heat Load ◽  
Three Dimensional ◽  
Axial Flow ◽  
Turbine Rotor ◽  
Inlet Temperature ◽  
Pressure Surface ◽  
Physical Mechanisms ◽  
Design Variables ◽  
Hot Streak ◽  
Turbine Design

The influence of inlet hot streak temperature distortion on turbine blade heat load was explored on a transonic axial flow turbine stage test article using a three-dimensional, multiblade row unsteady Euler code. The turbine geometry was the same as that used for a recently reported testing of hot streak influence. Emphasis was placed on elucidating the physical mechanisms by which hot streaks affect turbine durability. It was found that temperature distortion significantly increases both blade surface heat load nonuniformity and total blade heat load by as much as 10–30 percent (mainly on the pressure surface), and that the severity of this influence is a strong function of turbine geometry and flow conditions. Three physical mechanisms were identified that drive the heat load nonuniformity: buoyancy, wake convection (the Kerrebrock–Mikolajczak effect), and Rotor–Stator interactions. The latter can generate significant nonuniformity of the time-averaged relative frame rotor inlet temperature distribution. Dependence of these effects on turbine design variables was investigated to shed light on the design space, which minimizes the adverse effects of hot streaks.

Improved Blade Profile Loss and Deviation Angle Models for Advanced Transonic Compressor Bladings: Part I — A Model for Subsonic Flow

1994 ◽  
Author(s):  
W. M. König ◽  
D. K. Hennecke ◽  
L. Fottner
Keyword(s):  
Axial Flow ◽  
Deviation Angle ◽  
Simple Method ◽  
Subsonic Flows ◽  
New Model ◽  
Transonic Compressor ◽  
Blade Row ◽  
Inlet Conditions ◽  
Improved Accuracy ◽  
Profile Loss

New blading concepts as used in modern transonic axial-flow compressors require improved loss and deviation angle correlations. The new model presented in this paper incorporates several elements and treats separately blade-row flows having subsonic and supersonic inlet conditions. In the first part of this paper two proved and well-established profile loss correlations for subsonic flows are extended to quasi twodimensional conditions and to custom-tailored blade designs. Instead of a deviation angle correlation a simple method based on singularities is utilized. The comparison between the new model and a recently published model demonstrates the improved accuracy in prediction of cascade performance achieved by the new model.

The Influence of Sweep on Axial Flow Turbine Aerodynamics in the Endwall Region

2007 ◽  
Author(s):  
Graham Pullan ◽  
Neil W. Harvey
Keyword(s):  
Secondary Flow ◽  
Computational Study ◽  
Axial Flow ◽  
Secondary Flows ◽  
The Other ◽  
Blade Loading ◽  
Reported Study ◽  
Secondary Flow Structure ◽  
Turbine Design ◽  
Profile Loss

Sweep, when the stacking axis of the blade is not perpendicular to the axi-symmetric streamsurface in the meridional view, is often an unavoidable feature of turbine design. In a previously reported study, the authors demonstrated that sweep leads to an inevitable increase in mid-span profile loss. In this paper, the influence on the flowfield close to the endwalls is investigated. Experimental data from two linear cascades, one unswept, the other swept at 45 degrees but having the same overall turning and mid-span pressure distribution, are presented. It is shown that sweep causes the blade to become more rear-loaded at the hub and fore-loaded at the casing. This is further shown to reduce the penetration of the secondary flow at the hub, and to produce a highly unusual secondary flow structure, with low endwall over-turning, at the casing. A computational study is then presented in which the development of the secondary flows of both blades is studied. The differences in the endwall flowfields are found to be caused by a combination of the effect of sweep on both the endwall blade loading distribution, and on the bulk movements of the primary irrotational flow.

Analysis of Hot Streak Effects on Turbine Rotor Heat Load

1996 ◽  
Author(s):  
Tonghuo Shang ◽  
Alan H. Epstein
Keyword(s):  
Heat Load ◽  
Three Dimensional ◽  
Axial Flow ◽  
Turbine Rotor ◽  
Inlet Temperature ◽  
Pressure Surface ◽  
Physical Mechanisms ◽  
Design Variables ◽  
Hot Streak ◽  
Turbine Design

The influence of inlet hot streak temperature distortion on turbine blade heat load was explored on a transonic axial flow turbine stage test article using a three-dimensional, multi-blade row unsteady Euler code. The turbine geometry was the same as that used for a recently reported testing of hot streak influence. Emphasis was placed elucidating the physical mechanisms by which hot streaks affect turbine durability. It was found that temperature distortion significantly increases both blade surface heat load nonuniformity and total blade heat load by as much as 10–30% (mainly on the pressure surface), and that the severity of this influence is a strong function of turbine geometry and flow conditions. Three physical mechanisms were identified which drive the heat load nonuniformity — buoyancy, wake convection (the Kerrebrock-Mikolajczak effect), and rotor-stator interactions. The latter can generate significant nonuniformity of the time-averaged relative frame rotor inlet temperature distribution. Dependence of these effects on turbine design variables was investigated to shed light on the design space which minimizes the adverse effects of hot streaks.

Inverse Design of Axial-Flow Compressor Blades Using Elastic Surface Algorithm in Subsonic and Transonic Flow Regimes With Separation

2016 ◽  
Author(s):  
M. H. Noorsalehi ◽  
M. Nili-Ahamadabadi ◽  
E. Shirani ◽  
M. Safari
Keyword(s):  
Pressure Distribution ◽  
Transonic Flow ◽  
Design Method ◽  
Axial Flow ◽  
Flow Regimes ◽  
Inverse Design ◽  
Elastic Surface ◽  
Axial Flow Compressor ◽  
Inverse Design Method ◽  
Flow Compressor

In this study, a new inverse design method called Elastic Surface Algorithm (ESA) is developed and enhanced for axial-flow compressor blade design in subsonic and transonic flow regimes with separation. ESA is a physically based iterative inverse design method that uses a 2D flow analysis code to estimate the pressure distribution on the solid structure, i.e. airfoil, and a 2D solid beam finite element code to calculate the deflections due to the difference between the calculated and target pressure distributions. In order to enhance the ESA, the wall shear stress distribution, besides pressure distribution, is applied to deflect the shape of the airfoil. The enhanced method is validated through the inverse design of the rotor blade of the first stage of an axial-flow compressor in transonic viscous flow regime. In addition, some design examples are presented to prove the effectiveness and robustness of the method. The results of this study show that the enhanced Elastic Surface Algorithm is an effective inverse design method in flow regimes with separation and normal shock.

scholarly journals Changes in the Behaviour of the Unteraargletscher in the Last 125 Years

1970 ◽  
Vol 9 (56) ◽  
pp. 195-212 ◽  
Author(s):  
R. Haefeli
Keyword(s):  
Marked Decrease ◽  
Decisive Role ◽  
Surface Velocity ◽  
Ice Thickness ◽  
Surface Slope ◽  
Simple Method ◽  
Glacier Tongue ◽  
Slowing Down ◽  
Shear Component ◽  
Glacier Flow

All the measurements involved concern the glacier tongue between its end and 2 600 m a.s.l. The total loss of volume of the Unteraargletscher since its last maximum advance (1871) is estimated to be 2.4 km3, which corresponds to a mean surface lowering of 0.67 m/year (referred to a total glacierized area of c. 40 km2 on average). The considerable slowing down of the glacier flow velocity over the 125 years is primarily attributable to the marked decrease in the sliding component, whereas the shear component has only changed slightly. This behaviour is connected with the fact that the decrease in ice thickness has been accompanied by an increase in surface slope, so that the two effects on the shear component partially compensate each other. The seasonal variations in surface velocity were measured simultaneously at two profiles by Agassiz and his team in 1845/46. These variations are due to the variable amount of melt water and the resulting variations in hydrostatic pressure in the contact zone between ice and bedrock, in which the plastic contraction of the water channels plays a decisive role. This leads to the problem of water circulation in the interior of a glacier and its importance in the sliding process. Finally a simple method for the approximate calculation of the longitudinal profile of the surface of a glacier tongue in a steady state and with constant ablation is indicated.

Optimum stage design in axial-flow gas turbines

2002 ◽  
Vol 216 (6) ◽  
pp. 433-445 ◽  
Author(s):  
K V J Rao ◽  
S Kolla ◽  
Ch Penchalayya ◽  
M Ananda Rao ◽  
J Srinivas
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Axial Flow ◽  
Sensitivity Analyses ◽  
Multiple Objective ◽  
Stage Design ◽  
Effective Dimensions ◽  
On Line ◽  
Turbine Design ◽  
Root Stress

This paper proposes the formulation and solution procedures in the stage optimization of the effective dimensions of an axial-flow gas turbine. Increasing the stage efficiency and minimizing the overall mass of components per stage are the common objectives in gas turbine design. This multiple objective function, with important constraints like natural frequency limits, root stress values, and tip deflection in blades, constitutes the overall optimization problem. The problem is solved by using a modified nonlinear simplex method with a built-in user interactive program that helps in on-line modifications of parameters other than variables in the problem. Results are presented with single objective and multiple objective criteria, including sensitivity analyses about the optimum point.

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