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.

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.

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.

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%.

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.

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.

Performance Prediction for High Turning Low Aspect Ratio Stator Cascades in the Transonic Regime

1970 ◽  
Vol 92 (4) ◽  
pp. 390-398
Author(s):  
H. F. L. Griepentrog
Keyword(s):  
Boundary Layer ◽  
Aspect Ratio ◽  
Flow Field ◽  
Performance Prediction ◽  
Transonic Flow ◽  
Secondary Flows ◽  
Compressor Stage ◽  
Low Aspect Ratio ◽  
Aspect Ratios ◽  
Boundary Layer Interaction

This paper describes a method for the prediction of the transonic flow field in a high solidity, high turning cascade, suitable for use as stator of a shock-in-rotor supersonic compressor stage. Effects of shock boundary layer interaction is taken into account by empirical correlation, valid for blade aspect ratios below unity. Use of partial slots for reduction of the secondary flows is briefly discussed and a correlation on slot efficiency is presented.

Control of Shock Structure and Secondary Flow Field Inside Transonic Compressor Rotors Through Aerodynamic Sweep

1998 ◽  
Author(s):  
C. Hah ◽  
S. L. Puterbaugh ◽  
A. R. Wadia
Keyword(s):  
Aspect Ratio ◽  
Shock Structure ◽  
Secondary Flows ◽  
Operating Conditions ◽  
Numerical Analyses ◽  
Peak Efficiency ◽  
Stall Margin ◽  
Transonic Compressor ◽  
Low Aspect Ratio ◽  
Through Flow

The present paper reports a numerical study on the effects of aerodynamic sweep applied to a low-aspect-ratio, high-through-flow, state-of-the-art, axial transonic compressor design. Numerical analyses based on the Reynolds-averaged Navier-Stokes equations were used to obtain the performance of a conventional unswept rotor, a forward swept rotor, and an aft-swept rotor, at both design and off-design operating conditions. The numerical analyses predicted that the forward-swept rotor has a higher peak efficiency and a substantially larger stall margin than the baseline unswept rotor, and that the aft-swept rotor has a similar peak efficiency as the unswept rotor with a significantly smaller stall margin. The rig test confirmed the numerical assessment of the effects of aerodynamic sweep on the low-aspect-ratio, high-through-flow, transonic compressor rotor. Detailed analyses of the measured and calculated flow fields indicate that two mechanisms are primarily responsible for the differences in aerodynamic performance among these rotors. The first mechanism is a change in the radial shape of the passage shock near the casing by the endwall effect, and the second is the radial migration of low-momentum fluid to the blade tip region. Aerodynamic sweep can be used to control the shock structure near the endwall and the migration of secondary flows and, consequently, flow structures near the tip area for improved performance.

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