scholarly journals Spanwise Transport in Axial-Flow Turbines: Part 2 — Throughflow Calculations Including Spanwise Transport

1993 ◽  
Author(s):  
K. L. Lewis
Keyword(s):  
Aspect Ratio ◽  
Temperature Profile ◽  
Turbulent Diffusion ◽  
Axial Flow ◽  
Low Aspect Ratio ◽  
Loss Distributions ◽  
Diffusive Term ◽  
Two Stages ◽  
Throughflow Model

In Part 1 of this paper, a repeating stage condition was shown to occur in two low aspect ratio turbines, after typically two stages. Both turbulent diffusion and convective mechanisms were responsible for spanwise transport. In this part, two scaling expressions are determined that account for the influence of these mechanisms in effecting spanwise transport. These are incorporated into a throughflow model using a diffusive term. The inclusion of spanwise transport allows the use of more realistic loss distributions by the designer as input to the throughflow model and therefore focuses attention on areas where losses are generated. In addition, modelling of spanwise transport is shown to be crucial in predicting the attenuation of a temperature profile through a turbine.

Spanwise Transport in Axial-Flow Turbines: Part 2—Throughflow Calculations Including Spanwise Transport

1994 ◽  
Vol 116 (2) ◽  
pp. 187-193 ◽  
Author(s):  
K. L. Lewis
Keyword(s):  
Aspect Ratio ◽  
Temperature Profile ◽  
Turbulent Diffusion ◽  
Axial Flow ◽  
Low Aspect Ratio ◽  
Loss Distributions ◽  
Diffusive Term ◽  
Two Stages ◽  
Throughflow Model

In Part 1 of this paper, a repeating stage condition was shown to occur in two low aspect ratio turbines, typically after two stages. Both turbulent diffusion and convective mechanisms were responsible for spanwise transport. In this part, two scaling expressions are determined that account for the influence of these mechanisms in effecting spanwise transport. These are incorporated into a throughflow model using a diffusive term. The inclusion of spanwise transport allows the use of more realistic loss distributions by the designer as input to the throughflow model and therefore focuses attention on areas where losses are generated. In addition, modeling of spanwise transport is shown to be crucial in predicting the attenuation of a temperature profile through a turbine.

Spanwise Transport in Axial-Flow Turbines: Part 1 — The Multistage Environment

1993 ◽  
Author(s):  
K. L. Lewis
Keyword(s):  
Aspect Ratio ◽  
Axial Flow ◽  
Secondary Flows ◽  
Tracer Transport ◽  
Tracer Gas ◽  
Relative Significance ◽  
Low Aspect Ratio ◽  
Scaling Models ◽  
Two Stages ◽  
Throughflow Model

Selected experimental results, obtained from a detailed investigation into the flowfields within two low speed multistage turbines, are presented. A repeating stage condition occurred typically after two stages, with the secondary flows an important factor in the low aspect ratio geometry. A tracer gas technique was employed to identify the dominant mechanisms of spanwise transport and their relative significance. In the first stages of both machines, tracer transport was more intense near the endwalls than at mid-span whilst in the multistage environment the transport was approximately constant across the whole span. The convective influence of classical secondary flow, shroud leakage and wake passage through a downstream blade was identified and shown to be as significant as turbulent diffusion in effecting cross-passage and spanwise transport. The data show that spanwise transport should be included within any throughflow model and are used to calibrate two scaling models. These models are presented in Part 2 where the influence of incorporating spanwise transport into a throughflow model is investigated.

Spanwise Transport in Axial-Flow Turbines: Part 1—The Multistage Environment

1994 ◽  
Vol 116 (2) ◽  
pp. 179-186 ◽  
Author(s):  
K. L. Lewis
Keyword(s):  
Aspect Ratio ◽  
Axial Flow ◽  
Secondary Flows ◽  
Tracer Transport ◽  
Tracer Gas ◽  
Relative Significance ◽  
Low Aspect Ratio ◽  
Scaling Models ◽  
Two Stages ◽  
Throughflow Model

Selected experimental results, obtained from a detailed investigation into the flow fields within two low-speed multistage turbines, are presented. A repeating stage condition occurred typically after two stages, with the secondary flows an important factor in the low aspect ratio geometry. A tracer gas technique was employed to identify the dominant mechanisms of spanwise transport and their relative significance. In the first stages of both machines, tracer transport was more intense near the endwalls than at midspan, while in the multistage environment the transport was approximately constant across the whole span. The convective influence of classical secondary flow, shroud leakage, and wake passage through a downstream blade was identified and shown to be as significant as turbulent diffusion in effecting cross-passage and spanwise transport. The data show that spanwise transport should be included within any throughflow model and are used to calibrate two scaling models. These models are presented in Part 2, where the influence of incorporating spanwise transport into a throughflow model is investigated.

Influence of Blade Sweep on the Energetic Behavior of Axial Flow Turbomachinery Rotors at Design Flow Rate

2004 ◽  
Author(s):  
Ja´nos Vad ◽  
Ali R. A. Kwedikha ◽  
Helmut Jaberg
Keyword(s):  
Aspect Ratio ◽  
Flow Rate ◽  
Axial Flow ◽  
Pressure Rise ◽  
Design Flow ◽  
Tip Clearance ◽  
Total Efficiency ◽  
Low Aspect Ratio ◽  
Axial Velocity Profile ◽  
Bladed Rotor

Experimental and computational studies were carried out in order to survey the energetic aspects of forward and backward sweep in axial flow rotors of low aspect ratio blading for incompressible flow. It has been pointed out that negative sweep tends to increase the lift, the flow rate and the ideal total pressure rise in the vicinity of the endwalls. Just the opposite tendency was experienced for positive sweep. The local losses were found to develop according to combined effects of sweep near the endwalls, endwall and tip clearance losses, and profile drag influenced by re-arrangement of the axial velocity profile. The forward-swept bladed rotor showed reduced total efficiency compared to the unswept and swept-back bladed rotors. This behavior has been explained on the basis of analysis of flow details. It has been found that the swept bladings of low aspect ratio tend to retain the performance of the unswept datum rotor even in absence of sweep correction.

The Control of Shroud Leakage Flows to Reduce Aerodynamic Losses in a Low Aspect Ratio, Shrouded Axial Flow Turbine

2000 ◽  
Author(s):  
A. M. Wallis ◽  
J. D. Denton ◽  
A. A. J. Demargne
Keyword(s):  
Aspect Ratio ◽  
Turbine Blades ◽  
Significant Proportion ◽  
Axial Flow ◽  
Experimental Investigations ◽  
Leakage Flow ◽  
Leakage Flows ◽  
Low Aspect Ratio ◽  
Leakage Fraction ◽  
Aerodynamic Losses

The losses generated by fluid leaking across the shrouds of turbine blade rows are known to form a significant proportion of the overall loss generated in low aspect ratio turbines. The use of shrouds to encase the tips of turbine blades has encouraged the development of many innovative sealing arrangements, all of which are intended to reduce the quantity of fluid (the leakage fraction) leaking across the shroud. Modern sealing arrangements have reduced leakage fractions considerably, meaning that further improvements can only be obtained by controlling the leakage flow in such a way so as to minimise the aerodynamic losses incurred by the extraction and re-injection of the leakage flow into the mainstream. There are few published experimental investigations on the interaction between mainstream and leakage flows to provide guidance on the best means of managing the leakage flows to do this. This paper describes the development and testing of a strategy to turn the fluid leaking over shrouded turbine rotor blade rows with the aim of reducing the aerodynamic losses associated with its re-injection into the mainstream flow. The intent was to extract work from the leakage flow in the process. A four stage research turbine was used to test in detail the sealing design resulting from this strategy. A reduction in brake efficiency of 3.5% was measured. Further investigation suggested that much of the increase in loss could be attributed to the presence of axial gaps upstream and downstream of the shroud cavity which facilitated the periodic ingress and egress of mainstream fluid into the shroud cavity under the influence of the rotor potential field. This process was exacerbated by reductions in the leakage fraction.

Low Aspect Ratio Axial Flow Compressors: Why and What It Means

1989 ◽  
Vol 111 (4) ◽  
pp. 357-365 ◽  
Author(s):  
A. J. Wennerstrom
Keyword(s):  
Aspect Ratio ◽  
Mechanical Design ◽  
Axial Flow ◽  
Early Years ◽  
Turbine Engine ◽  
Low Aspect Ratio ◽  
Aspect Ratios ◽  
Design Systems ◽  
The 1960S ◽  
Axial Flow Compressors

One of the more visible changes that has occurred in fans and compressors for aircraft turbine engines that have entered development since about 1970 has been a significant reduction in the aspect ratio of the blading. This has brought with it a greatly reduced engine parts count and improved ruggedness and aeroelastic stability. This paper traces the evolution of thinking concerning appropriate aspect ratios for axial flow compressors since the early years of the aircraft turbine engine. In the 1950’s, moderate aspect ratios were favored for reasons of mechanical design. As mechanical design capability became more sophisticated, several attempts were made, primarily in the 1960s, to employ very high aspect ratios to reduce engine size and weight. Four of these programs are described that were largely unsuccessful for both mechanical and aerodynamic reasons. After 1970, the pendulum swung strongly in the other direction and designs of very low aspect ratio began to emerge. This has had a significant impact on compressor design systems, and a number of the ways in which design systems have been affected are discussed. Some concluding remarks are made concerning the author’s opinion of trends in the near future in aerodynamic design technology.

scholarly journals Effect of Partial Shrouds on the Performance and Flow Field of a Low-Aspect-Ratio Axial-Flow Fan Rotor

2011 ◽  
Vol 2011 ◽  
pp. 1-11 ◽  
Author(s):  
N. Sitaram ◽  
G. Ch. V. Sivakumar
Keyword(s):  
Aspect Ratio ◽  
Flow Field ◽  
Axial Flow ◽  
Flow Coefficient ◽  
Axial Flow Fan ◽  
Low Velocity ◽  
Flow Measurements ◽  
Low Aspect Ratio ◽  
Partial Shroud ◽  
Velocity Region

The flow field at the rotor exit of a low aspect ratio axial flow fan for different tip geometries and for different flow coefficients is measured in the present study. The following configurations are tested: (1) rotor without partial shroud, designated as rotor (wos), (2) rotor with partial shroud, designated as rotor (ws), and (3) rotor with perforated (perforations in the shape of discrete circular holes) partial shroud, designated as rotor (wps). From steady state measurements, the performance of rotor (wps) is found to be the best. Both the rotors with partial shrouds have stalled at a higher flow coefficient compared to that of rotor (wos). From periodic flow measurements, it is concluded that the low velocity region near the tip section is considerably reduced with the use of partial shrouds with perforations. The extent of this low velocity region for both rotor (wos) and rotor (wps) increases with decreasing flow coefficient due to increased stage loading. This core of low momentum fluid has moved inwards of the annulus and towards the pressure side as the flow coefficient decreases. The extent of the low momentum fluid is smaller for rotor (wps) than that of rotor (wos) at all flow coefficients.

Sign in / Sign up

Export Citation Format

Share Document