Multistage Aspects and Unsteady Effects of Stator and Rotor Clocking in an Axial Turbine With Low Aspect Ratio Blading

2005 ◽  
Vol 128 (1) ◽  
pp. 11-22 ◽  
Author(s):  
T. Behr ◽  
L. Porreca ◽  
T. Mokulys ◽  
A. I. Kalfas ◽  
R. S. Abhari
Keyword(s):  
Aspect Ratio ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Fast Response ◽  
Test Case ◽  
Systematic Analysis ◽  
Number Count ◽  
Low Aspect Ratio ◽  
Multi Stage ◽  
Flow Interactions

This paper presents the outcome of a recent study in clocking-related flow features and multistage effects occurring in high-pressure turbine blade geometries. The current investigation deals with an experimentally based systematic analysis of the effects of both stator-stator and rotor-rotor clocking. Due to the low aspect ratio of the turbine geometry, the flow field is strongly three-dimensional and is dominated by secondary flow structures. The investigation aims to identify the flow interactions involved and the associated effects on performance improvement or degradation. Consequently a three-dimensional numerical analysis has been undertaken to provide the numerical background to the test case considered. The experimental studies were performed in a two-stage axial research turbine facility. The turbine provides a realistic multi-stage environment, in which both stator blade rows and the two rotors can be clocked relative to each other. All blade rows have the same blade number count, which tends to amplify clocking effects. Unsteady and steady measurements were obtained in the second stage using fast response aerodynamic probes and miniature pneumatic five-hole probes. The current comprehensive investigation has shown that multistage and unsteady flow effects of stator and rotor clocking in low aspect ratio turbines are combined in a nonlinear fashion caused by axial and radial redistribution of low energy fluid. The integral result of clocking on stage efficiency is compensated by competing loss generating mechanisms across the span.

Multistage Aspects and Unsteady Effects of Stator and Rotor Clocking in an Axial Turbine With Low Aspect Ratio Blading

2004 ◽  
Author(s):  
T. Behr ◽  
L. Porreca ◽  
T. Mokulys ◽  
A. I. Kalfas ◽  
R. S. Abhari
Keyword(s):  
Aspect Ratio ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Fast Response ◽  
Test Case ◽  
Systematic Analysis ◽  
Number Count ◽  
Low Aspect Ratio ◽  
Multi Stage ◽  
Flow Interactions

This paper presents the outcome of a recent study in clocking-related flow features and multistage effects occurring in high-pressure turbine blade geometries. The current investigation deals with an experimentally based systematic analysis of the effects of both stator-stator and rotor-rotor clocking. Due to the low aspect ratio of the turbine geometry, the flow field is strongly three-dimensional and is dominated by secondary flow structures. The investigation aims to identify the flow interactions involved and the associated effects on performance improvement or degradation. Consequently a three-dimensional numerical analysis has been undertaken to provide the numerical background to the test case considered. The experimental studies were performed in a two-stage axial research turbine facility. The turbine provides a realistic multi-stage environment, in which both stator blade rows and the two rotors can be clocked relative to each other. All blade rows have the same blade number count, which tends to amplify clocking effects. Unsteady and steady measurements were obtained in the second stage using fast response aerodynamic probes (FRAP) and miniature pneumatic 5-hole probes. The current comprehensive investigation has shown that multistage and unsteady flow effects of stator and rotor clocking in low aspect ratio turbines are combined in a nonlinear fashion caused by axial and radial redistribution of low energy fluid. The integral result of clocking on stage efficiency is compensated by competing loss generating mechanisms across the span.

Unsteady Aerodynamics of a Low Aspect Ratio Turbine Stage: Modeling Issues and Flow Physics

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
G. Persico ◽  
A. Mora ◽  
P. Gaetani ◽  
M. Savini
Keyword(s):  
Aspect Ratio ◽  
Coming Out ◽  
Three Dimensional ◽  
Unsteady Aerodynamics ◽  
Fast Response ◽  
Operating Conditions ◽  
Pressure Probe ◽  
Turbine Stage ◽  
Time Resolved ◽  
Low Aspect Ratio

In this paper the three-dimensional unsteady aerodynamics of a low aspect ratio, high pressure turbine stage are studied. In particular, the results of fully unsteady three-dimensional numerical simulations, performed with ANSYS-CFX, are critically evaluated against experimental data. Measurements were carried out with a novel three-dimensional fast-response pressure probe in the closed-loop test rig of the Laboratorio di Fluidodinamica delle Macchine of the Politecnico di Milano. An analysis is first reported about the strategy to limit the CPU and memory requirements while performing three-dimensional simulations of blade row interaction when the rotor and stator blade numbers are prime to each other. What emerges as the best choice is to simulate the unsteady behavior of the rotor alone by applying the stator outlet flow field as a rotating inlet boundary condition (scaled on the rotor blade pitch). Thanks to the reliability of the numerical model, a detailed analysis of the physical mechanisms acting inside the rotor channel is performed. Two operating conditions at different vane incidence are considered, in a configuration where the effects of the vortex-blade interaction are highlighted. Different vane incidence angles lead to different size, position, and strength of secondary vortices coming out from the stator, thus promoting different interaction processes in the subsequent rotor channel. However some general trends can be recognized in the vortex-blade interaction: the sense of rotation and the spanwise position of the incoming vortices play a crucial role on the dynamics of the rotor vortices, determining both the time-mean and the time-resolved characteristics of the secondary field at the exit of the stage.

Unsteady Aerodynamics of a Low Aspect Ratio Turbine Stage: Modeling Issues and Flow Physics

2010 ◽  
Author(s):  
G. Persico ◽  
A. Mora ◽  
P. Gaetani ◽  
M. Savini
Keyword(s):  
Aspect Ratio ◽  
Coming Out ◽  
Cfd Simulation ◽  
Three Dimensional ◽  
Unsteady Aerodynamics ◽  
Fast Response ◽  
Pressure Probe ◽  
Turbine Stage ◽  
Aerodynamic Pressure ◽  
Low Aspect Ratio

In this paper the three-dimensional unsteady aerodynamics of a low aspect ratio, high pressure turbine stage is studied. Fully unsteady, three-dimensional numerical simulations are performed using the commercial code ANSYS-CFX The numerical model is critically evaluated against experimental data. Measurements were performed with a three-dimensional fast-response aerodynamic pressure probe in the closed-loop test rig operating in the Laboratorio di Fluidodinamica delle Macchine of the Politecnico di Milano (Italy). An analysis is first reported about the strategy to reduce the CPU and memory requirements while performing three-dimensional simulations of stator-rotor interaction in actual turbomachinery. What emerges as the best choice, at least for subsonic stages, is to simulate the unsteady behaviour of the rotor blade row alone by applying the stator outlet flow field as rotating inlet boundary condition. When measurements are available upstream of the rotor the best representation of the experimental results downstream of the stage is achieved. The agreement with the experiments achieved at the rotor exit makes the CFD simulation a key-tool for the comprehension and the interpretation of the physical mechanisms acting inside the rotor channel (often difficult to achieve using experiments only). Numerical investigations have been carried out by varying the incidence at the vane entrance. Different vane incidence angles lead to different size, position, and strength of secondary vortices coming out from the stator. The configuration is chosen is such a way to isolate the effects of the vortex-blade interaction. Results show that some general trends can be recognized in the vortex-blade interaction. The sense of rotation and the spanwise position of the incoming vortices play a crucial role on their interaction with the rotor vortices, thus determining both the time-mean and the time-resolved characteristics of the stage-exit secondary field.

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.

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.

The Lift on Wings at Sonic Speeds by Means of an Electrical Resistance Analogue

1956 ◽  
Vol 60 (542) ◽  
pp. 137-139
Author(s):  
P. J. Palmer
Keyword(s):  
Aspect Ratio ◽  
Electrical Resistance ◽  
Close Agreement ◽  
Velocity Potential ◽  
Three Dimensional ◽  
Sonic Velocity ◽  
Dimensional Problem ◽  
Low Aspect Ratio ◽  
Small Incidence ◽  
Low Aspect Ratio Wings

This note shows how a pure resistance analogue can be used to find the lift on low aspect ratio wings travelling, with small incidence, at speeds close to the sonic velocity.The method is applicable to flat, twisted or cambered wings and is simple in operation; the results obtained being in close agreement with those obtained by calculations based on the same theory.The solutions given in this note are essentially those corresponding to the Jones theory, which is applicable to low aspect ratio wings at small incidence, travelling with velocity close to the sonic value. Under these conditions it has been shown that the three-dimensional problem reduces to a series of two-dimensional problems in planes perpendicular to the direction of motion. Thus the wing can be considered as a series of spanwise sections, the solution for each section, in terms of the velocity potential, being considered in turn.

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