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%.

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

2017 ◽  
Vol 139 (9) ◽  
Author(s):  
Christopher J. Clark ◽  
Graham Pullan ◽  
Eric Curtis ◽  
Frederic Goenaga
Keyword(s):  
Kinetic Energy ◽  
Aspect Ratio ◽  
Secondary Flow ◽  
Current Practice ◽  
Leading Edge ◽  
Secondary Flows ◽  
Optimization Approach ◽  
Flow Strength ◽  
Low Aspect Ratio ◽  
End Wall

Low aspect ratio vanes, often the result of overall engine architecture constraints, create strong secondary flows and high end-wall 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 (SKE) of the secondary flow vortices is reduced when the number of passages is increased and, for a given number of vanes, when the inlet end-wall 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 splitter 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 flow field 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%.

Secondary flows and developing, turbulent boundary layers in a rotating duct

1998 ◽  
Vol 373 ◽  
pp. 1-32 ◽  
Author(s):  
I. MACFARLANE ◽  
P. N. JOUBERT ◽  
T. B. NICKELS
Keyword(s):  
Aspect Ratio ◽  
Secondary Flow ◽  
Boundary Layers ◽  
Suction Side ◽  
Turbulent Boundary Layers ◽  
Secondary Flows ◽  
Turbulent Shear ◽  
Mean Flow ◽  
Flow Strength ◽  
Aspect Ratios

The work presented in this paper represents an experimental investigation into secondary flows, turbulent boundary layers and the interaction of the two as they develop in a zero-pressure-gradient rotating flow field. A duct of intermediate aspect ratio was used to examine secondary flows and determine when they begin to govern the boundary layer development. The aspect ratio (A) was defined as duct height/width at the upstream end of the working section. Measurements were taken at three aspect ratios: A=1, 2 and 4.A qualitative indication of secondary flow strength was established with mean-cross-stream-plane velocity measurements. A first-order analysis of the secondary flow is presented which provides a reasonable estimation of their strength. Mid-span mean-flow, turbulence and spectra profiles were measured on the duct walls parallel to the axis of rotation. Results are generally presented for A=2 and 1. For A=4 and 2 there were minor effects of secondary flows observed on the mid-span mean flow parameters. The turbulent shear measurements showed some secondary flow effect for A=2. All turbulence and mean-flow quantities were strongly affected by secondary flows for A=1. Spectra results presented for A=2 showed most variation at the low-to-mid wavenumber end. Spectra results for A=1 showed a bodily shift of the whole spectrum towards low wavenumber on the pressure side and high wavenumber on the suction side.

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.

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.

Leading Edge and Wing Tip Flow Control on Low Aspect Ratio Wings

2010 ◽  
Author(s):  
Stefan Vey ◽  
David Greenblatt ◽  
Christian Nayeri ◽  
Christian Paschereit
Keyword(s):  
Aspect Ratio ◽  
Flow Control ◽  
Leading Edge ◽  
Low Aspect Ratio ◽  
Wing Tip ◽  
Low Aspect Ratio Wings

scholarly journals On the lift-optimal aspect ratio of a revolving wing at low Reynolds number

2018 ◽  
Vol 15 (143) ◽  
pp. 20170933 ◽  
Author(s):  
T. Jardin ◽  
T. Colonius
Keyword(s):  
Aspect Ratio ◽  
Lift Coefficient ◽  
Leading Edge ◽  
Rossby Number ◽  
Subsequent Work ◽  
High Lift ◽  
Low Aspect Ratio ◽  
Axis Of Rotation ◽  
Edge Vortex ◽  
Convergent Solution

Lentink & Dickinson (2009 J. Exp. Biol. 212 , 2705–2719. ( doi:10.1242/jeb.022269 )) showed that rotational acceleration stabilized the leading-edge vortex on revolving, low aspect ratio (AR) wings and hypothesized that a Rossby number of around 3, which is achieved during each half-stroke for a variety of hovering insects, seeds and birds, represents a convergent high-lift solution across a range of scales in nature. Subsequent work has verified that, in particular, the Coriolis acceleration plays a key role in LEV stabilization. Implicit in these results is that there exists an optimal AR for wings revolving about their root, because it is otherwise unclear why, apart from possible morphological reasons, the convergent solution would not occur for an even lower Rossby number. We perform direct numerical simulations of the flow past revolving wings where we vary the AR and Rossby numbers independently by displacing the wing root from the axis of rotation. We show that the optimal lift coefficient represents a compromise between competing trends with competing time scales where the coefficient of lift increases monotonically with AR, holding Rossby number constant, but decreases monotonically with Rossby number, when holding AR constant. For wings revolving about their root, this favours wings of AR between 3 and 4.

An Experimental Study of Heat Transfer and Film Cooling on Low Aspect Ratio Turbine Nozzles

1990 ◽  
Vol 112 (3) ◽  
pp. 488-496 ◽  
Author(s):  
K. Takeishi ◽  
M. Matsuura ◽  
S. Aoki ◽  
T. Sato
Keyword(s):  
Heat Transfer ◽  
Secondary Flow ◽  
Film Cooling ◽  
Three Dimensional ◽  
Horseshoe Vortex ◽  
Three Dimensional Flow ◽  
Flow Passage ◽  
Pressure Surface ◽  
Low Aspect Ratio ◽  
Complex Phenomena

The effects of the three-dimensional flow field on the heat transfer and the film cooling on the endwall, suction, and pressure surface of an airfoil were studied using a low speed, fully annular, low aspect h/c = 0.5 vane cascade. The predominant effects on the horseshoe vortex, secondary flow, and nozzle wake of increases in the heat transfer and decreases in the film cooling on the suction vane surface and the endwall were clearly demonstrated. In addition, it was demonstrated that secondary flow has little effect on the pressure surface. Pertinent flow visualization of the flow passage was also carried out for better understanding of these complex phenomena. Heat transfer and film cooling on the fully annular vane passage surface are discussed.

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