Improving the Performance of a Turbine With Low Aspect Ratio Stators by Aft-Loading

2004 ◽  
Vol 128 (3) ◽  
pp. 492-499 ◽  
Author(s):  
Graham Pullan ◽  
John Denton ◽  
Eric Curtis
Keyword(s):  
Aspect Ratio ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Loss Reduction ◽  
Low Aspect Ratio ◽  
Surface Pressure Distribution ◽  
Loaded Surface ◽  
Nozzle Guide ◽  
Nozzle Guide Vanes ◽  
Stage Efficiency

Experimental data and numerical simulations are presented from a research turbine with low aspect ratio nozzle guide vanes (NGVs). The combined effects of mechanical and aerodynamic constraints on the NGV create very strong secondary flows. This paper describes three designs of NGV that have been tested in the turbine, using the same rotor row in each case. NGV 2 used three-dimensional design techniques in an attempt to improve the performance of the datum NGV 1 blade, but succeeded only in creating an intense vortex shed from the trailing edge (as previously reported) and lowering the measured stage efficiency by 1.1% points. NGV 3 was produced to avoid the “shed vortex” while adopting a highly aft-loaded surface pressure distribution to reduce the influence of the secondary flows. The stage with NGV 3 had an efficiency 0.5% points greater than that with NGV 1. Detailed comparisons between experiment and computations, including predicted entropy generation rates, are used to highlight the areas where the loss reduction has occurred and hence to quantify the effects of employing highly aft-loaded NGVs.

Improving the Performance of a Turbine With Low Aspect Ratio Stators by Aft-Loading

2005 ◽  
Author(s):  
Graham Pullan ◽  
John Denton ◽  
Eric Curtis
Keyword(s):  
Aspect Ratio ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Loss Reduction ◽  
Low Aspect Ratio ◽  
Surface Pressure Distribution ◽  
Loaded Surface ◽  
Nozzle Guide ◽  
Nozzle Guide Vanes ◽  
Stage Efficiency

Experimental data and numerical simulations are presented from a research turbine with low aspect ratio nozzle guide vanes (NGVs). The combined effects of mechanical and aerodynamic constraints on the NGV create very strong secondary flows. This paper describes three designs of NGV that have been tested in the turbine, using the same rotor row in each case. NGV 2 used three-dimensional design techniques in an attempt to improve the performance of the datum NGV 1 blade but succeeded only in creating an intense vortex shed from the trailing edge (as previously reported) and lowering the measured stage efficiency by 1.1% points. NGV 3 was produced to avoid the “shed vortex” while adopting a highly aft-loaded surface pressure distribution to reduce the influence of the secondary flows. The stage with NGV 3 had an efficiency 0.5% points greater than that with NGV 1. Detailed comparisons between experiment and CFD, including predicted entropy generation rates, are used to highlight the areas where the loss reduction has occurred and hence to quantify the effects of employing highly aft-loaded NGVs.

Blade Lean and Shroud Leakage Flows in Low Aspect Ratio Turbines

2008 ◽  
Author(s):  
Budimir Rosic ◽  
Liping Xu
Keyword(s):  
Aspect Ratio ◽  
Numerical Study ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Leakage Flow ◽  
Industrial Practice ◽  
Leakage Flows ◽  
Low Aspect Ratio ◽  
Stator Blade ◽  
Different Levels

Blade lean, i.e. non-radial blade stacking, has been intensively used over the past in the design process of low aspect ratio gas and steam turbines. Although its influence on turbine efficiency is not completely understood, it has been proved as an effective way of controlling blade loading and secondary flows on blade passage endwalls. Three-dimensional blade designs in modern industrial practice are usually carried out using clean endwalls. The influence of the leakage flows on three-dimensional blade design is traditionally neglected. This paper presents an experimental study where two different stator blades, with different levels of compound lean, were tested in a low speed three-stage model turbine with the shroud leakage flow geometry representative of industrial practice. The experimental measurements were compared with numerical tests, conducted on the same blade geometries. The influence of the compound lean on the stator flow field was analysed in detail. In order to analyse the combined effects of both the stator hub and rotor shroud leakage flow on the blade lean, in the second part of the paper a numerical study on a two stage turbine with both leakage flow paths representative of a real turbine was carried out. Performance of three different stator blade designs (two different levels of compound lean and a straight blade) was investigated. The aim of this study is to understand the mechanism and the consequence of the stator blade lean on stage performance in an environment with leakage flows and associated cavities.

Effects of Tip Endwall Contouring on the Three-Dimensional Flow Field in an Annular Turbine Nozzle Guide Vane: Part 1—Experimental Investigation

1985 ◽  
Vol 107 (4) ◽  
pp. 983-990 ◽  
Author(s):  
E. Boletis
Keyword(s):  
Experimental Investigation ◽  
Aspect Ratio ◽  
Guide Vane ◽  
Three Dimensional ◽  
Three Dimensional Flow ◽  
Low Aspect Ratio ◽  
Dimensional Flow ◽  
Nozzle Guide Vane ◽  
Endwall Contouring ◽  
Nozzle Guide

Tip endwall contouring is one of the most effective methods to improve the performance of low aspect ratio turbine vanes [1]. In view of the wide variety of geometric parameters, it appears that only the physical understanding of the three-dimensional flow field will allow us to evaluate the probable benefits of a particular endwall contouring. The paper describes the experimental investigation of the three-dimensional flow through a low-speed, low aspect ratio, high-turning annular turbine nozzle guide vane with meridional tip endwall contouring. The full impact of the effects of tip contouring is evaluated by comparison with the results of a previous study in an annular turbine nozzle guide vane of the same blade and cascade geometry with cylindrical endwalls [12]. In parallel, the present experimental study provides a fully three-dimensional test case for comparison with advanced theoretical calculation methods [15]. The flow is explored by means of double-head, four-hole pressure probes in five axial planes from far upstream to downstream of the blade row. The results are presented in the form of contour plots and spanwise pitch-averaged distributions.

Challenges and Opportunities for the Turbine Performance Improvement Through Stator Clocking and Vane Bowing

2007 ◽  
Author(s):  
Antoni Smolny ◽  
Jaroslaw R. Blaszczak ◽  
Jan Krysinski ◽  
Tomasz Borzecki
Keyword(s):  
Aspect Ratio ◽  
Secondary Flow ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Flow Structures ◽  
Major Influence ◽  
Two Stage ◽  
Local Flow ◽  
Low Aspect Ratio ◽  
The Impact

The paper describes experimental and numerical investigations of turbine vane clocking effects on the flow process in a two-stage turbine with low-aspect ratio stators. The data present clocking effects that can be observed both for local flow patterns and external characteristics for the entire machine in terms of efficiency. A low-aspect ratio and high turning create a highly three-dimensional flow that is dominated by secondary flows. The aim was to reduce the impact of the secondary flows by bowing the first stator vanes by means of different vane bending and the stator clocking. Another major objective was to show how wake trajectory features can be applied in a turbine design. The changes in the secondary flow structures of the first stator were performed by leaning and bowing the airfoils to achieve load reduction near end walls. This can lead to a weaker end wall secondary flow structures and lower losses. Bowed blades are nowadays often adopted for high-pressure gas and steam turbines. The results demonstrate that incoming interacting streamwise vortices have a major influence on the secondary flows and loss generation mechanisms of the downstream airfoil rows. Using the clocking concept, the secondary flow structures are forced to interact one with another at different positions of the stators. This procedure reveals the best nature of such interactions and shows the resulting benefits. The data acquired by clocking the upstream cascade can identify the effects of incoming vortices, particularly when they entering the leading edge regions of the downstream cascade airfoil. The results for this test indicate that the size and strength of the secondary flows for the downstream cascade should be lower than those obtained without interaction. It is apparent from these investigations that incoming stream-wise vortices may have a potential effect on the flow distribution for downstream airfoil rows. The first part of the paper presents results of the stator clocking identification for different geometries of the first stator. An introduction of the vane bowing has redesigned the first stator. The cylindrical version and two combinations of the bowed vanes with low and high curvature have been considered for the first stator. The authors have found that modified vanes produce smaller and weaker secondary flow structures. The second part presents experimental and numerical results of the clocking investigations for the above-mentioned versions. The experiments have shown that clocking effects seem to be related to the stator wake and vortex structures which produce low momentum fluid areas. These areas interact with boundary layers or secondary flow regions of the second stator where the fluid momentum is already low. Clocking effects on external flow parameter are analyzed versus the low momentum area trajectories due to the first stator vane bowing. The present work focuses on the structures that are formed downstream as a result of the exit flow field of the upstream stage, and examines the implication for efficiency improvement. This paper therefore deals with an interaction of complex three-dimensional stator-rotor flow structures in the two-stage axial turbine.

Blade Lean and Shroud Leakage Flows in Low Aspect Ratio Turbines

2011 ◽  
Vol 134 (3) ◽  
Author(s):  
Budimir Rosic ◽  
Liping Xu
Keyword(s):  
Aspect Ratio ◽  
Numerical Study ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Leakage Flow ◽  
Industrial Practice ◽  
Leakage Flows ◽  
Low Aspect Ratio ◽  
Stator Blade ◽  
Different Levels

Blade lean, i.e., nonradial blade stacking, has been intensively used over the past in the design process of low aspect ratio gas and steam turbines. Although its influence on turbine efficiency is not completely understood, it has been proved as an effective way of controlling blade loading and secondary flows on blade passage endwalls. Three-dimensional blade designs in modern industrial practice are usually carried out using clean endwalls. The influence of the leakage flows on three-dimensional blade design is traditionally neglected. This paper presents an experimental study where two different stator blades, with different levels of compound lean, were tested in a low speed three-stage model turbine with the shroud leakage flow geometry representative of industrial practice. The experimental measurements were compared with numerical tests, conducted on the same blade geometries. The influence of the compound lean on the stator flow field was analyzed in detail. In order to analyze the combined effects of both the stator hub and the rotor shroud leakage flow on the blade lean, in the second part of the paper a numerical study on a two stage turbine with both leakage flow paths representative of a real turbine was carried out. Performance of three different stator blade designs (two different levels of compound lean and a straight blade) was investigated. The aim of this study is to understand the mechanism and the consequence of the stator blade lean on stage performance in an environment with leakage flows and associated cavities.

scholarly journals Secondary Flow Control in Low Aspect Ratio Vanes Using Splitters

2016 ◽  
Author(s):  
Christopher Clark ◽  
Graham Pullan ◽  
Eric Curtis ◽  
Frederic Goenaga
Keyword(s):  
Kinetic Energy ◽  
Aspect Ratio ◽  
Secondary Flow ◽  
Current Practice ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
Secondary Flows ◽  
Optimization Approach ◽  
Flow Strength ◽  
Low Aspect Ratio

Low aspect ratio vanes, often the result of overall engine architecture constraints, create strong secondary flows and high endwall loss. In this paper, a splitter concept is demonstrated that reduces secondary flow strength and improves stage performance. An analytic conceptual study, corroborated by inviscid computations, shows that the total secondary kinetic energy of the secondary flow vortices is reduced when the number of passages is increased and, for a given number of vanes, when the inlet endwall boundary layer is evenly distributed between the passages. Viscous computations show that, for this to be achieved in a splitter configuration, the pressure-side leg of the low aspect ratio vane horseshoe vortex, must enter the adjacent passage (and not “jump” in front of the splitter leading edge). For a target turbine application, four vane designs were produced using a multi-objective optimization approach. These designs represent: current practice for a low aspect ratio vane; a design exempt from thickness constraints; and two designs incorporating splitter vanes. Each geometry is tested experimentally, as a sector, within a low-speed turbine stage. The vane designs with splitters geometries were found to reduce the measured secondary kinetic energy, by up to 85%, to a value similar to the design exempt from thickness constraints. The resulting flowfield was also more uniform in both the circumferential and radial directions. One splitter design was selected for a full annulus test where a mixed-out loss reduction, compared to the current practice design, of 15.3% was measured and the stage efficiency increased by 0.88%.

Calculation of the Rise and Pitch of a Three-Dimensional Low-Aspect-Ratio Flat Ship

1991 ◽  
Vol 35 (04) ◽  
pp. 314-324
Author(s):  
Todd McComb
Keyword(s):  
Aspect Ratio ◽  
Three Dimensional ◽  
Static Case ◽  
Equilibrium Flow ◽  
Low Aspect Ratio ◽  
Fast Speed ◽  
Flow Past

Using low-aspect-ratio flat ship theory, this paper defines a procedure to determine the position of a hull which is in equilibrium at some "fast" speed in terms of a given hull shape for the same hull at rest. This procedure is then used to find the equilibrium flow past a moving ship, when given the shape of the hull at rest. The method is then extended to find the hull configuration at various speeds based on either the configuration in the static case or at some other equilibrium speed, leading to a calculation of drag versus speed. Some general formulas and some simple examples are given.

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