Experimental Investigation of Secondary Flow Structure in a Blade Passage With and Without Leading Edge Fillets

2006 ◽  
Vol 129 (3) ◽  
pp. 253-262 ◽  
Author(s):  
G. I. Mahmood ◽  
S. Acharya
Keyword(s):  
Cross Section ◽  
Pressure Loss ◽  
Leading Edge ◽  
Suction Side ◽  
Horseshoe Vortex ◽  
Secondary Flows ◽  
Blade Passage ◽  
Pressure Loss Coefficient ◽  
Passage Vortex ◽  
Loss Coefficients

Velocity and pressure measurements are presented for a blade passage with and without leading edge contouring in a low speed linear cascade. The contouring is achieved through fillets placed at the junction of the leading edge and the endwall. Two fillet shapes, one with a linear streamwise cross-section (fillet 1) and the other with a parabolic cross-section (fillet 2), are examined. Measurements are taken at a constant Reynolds number of 233,000 based on the blade chord and the inlet velocity. Data presented at different axial planes include the pressure loss coefficient, axial vorticity, velocity vectors, and yaw and pitch angles. In the early stages of the development of the secondary flows, the fillets are seen to reduce the size and strength of the suction-side leg of the horseshoe vortex with associated reductions in the pressure loss coefficients and pitch angles. Further downstream, the total pressure loss coefficients and vorticity show that the fillets lift the passage vortex higher above the endwall and move it closer to the suction side in the passage. Near the trailing edge of the passage, the size and strength of the passage vortex is smaller with the fillets, and the corresponding reductions in pressure loss coefficients extend beyond the mid-span of the blade. While both fillets reduce pressure loss coefficients and vorticity, fillet 1 (linear fillet profile) appears to exhibit greater reductions in pressure loss coefficients and pitch angles.

Experimental Investigation of Flow Structure and Nusselt Number in a Low-Speed Linear Blade Passage With and Without Leading-Edge Fillets

2005 ◽  
Vol 127 (5) ◽  
pp. 499-512 ◽  
Author(s):  
G. I. Mahmood ◽  
R. Gustafson ◽  
S. Acharya
Keyword(s):  
Nusselt Number ◽  
Thermal Loading ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
Secondary Flows ◽  
Suction Surface ◽  
Blade Passage ◽  
Low Speed ◽  
Passage Vortex ◽  
End Wall

The potential of contouring the leading edge of a blade to control the development of the secondary flows in the blade passage and to reduce the thermal loading to the end wall is investigated experimentally. Fillets placed at the junctions of the leading edge and the end wall are used for contouring. Four different types of fillet profiles are tested in a low-speed linear cascade a Reynolds numbers of 233,000 based on the inlet velocity. Images of instantaneous smoke flow patterns show a smaller horseshoe vortex along the leading edge with the fillets. In the passage, the fillets cause the passage vortex to be located closer to the suction surface. Upstream of the throat, the normalized axial vorticity values for the passage vortex and the turbulence intensity levels are smaller with the fillets compared to the baseline. For the leading-edge fillet with a concave profile, the end-wall Nusselt number distributions show significant reductions compared to the baseline.

Volumetric Velocimetry Measurements of Purge–Mainstream Interaction in a One-Stage Turbine

2021 ◽  
Vol 143 (4) ◽  
Author(s):  
A. J. Carvalho Figueiredo ◽  
B. D. J. Schreiner ◽  
A. W. Mesny ◽  
O. J. Pountney ◽  
J. A. Scobie ◽  
...  
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Gas Turbines ◽  
Suction Side ◽  
Secondary Flows ◽  
Blade Passage ◽  
One Stage ◽  
Passage Vortex ◽  
Purge Flow ◽  
Secondary Flow Field

Abstract Air-cooled gas turbines employ bleed air from the compressor to cool vulnerable components in the turbine. The cooling flow, commonly known as purge air, is introduced at low radius, before exiting through the rim-seal at the periphery of the turbine discs. The purge flow interacts with the mainstream gas path, creating an unsteady and complex flowfield. Of particular interest to the designer is the effect of purge on the secondary-flow structures within the blade passage, the extent of which directly affects the aerodynamic loss in the stage. This paper presents a combined experimental and computational fluid dynamics (CFD) investigation into the effect of purge flow on the secondary flows in the blade passage of an optically accessible one-stage turbine rig. The experimental campaign was conducted using volumetric velocimetry (VV) measurements to assess the three-dimensional inter-blade velocity field; the complementary CFD campaign was carried out using unsteady Reynolds-averaged Navier–Stokes (URANS) computations. The implementation of VV within a rotating environment is a world first and offers an unparalleled level of experimental detail. The baseline flow-field, in the absence of purge flow, demonstrated a classical secondary flow-field: the rollup of a horseshoe vortex, with subsequent downstream convection of a pressure-side and suction-side leg, the former transitioning in to the passage vortex. The introduction of purge, at 1.7% of the mainstream flowrate, was shown to modify the secondary flow-field by enhancing the passage vortex, in both strength and span-wise migration. The computational predictions were in agreement with the enhancement revealed by the experiments.

Volumetric Velocimetry Measurements of Purge-Mainstream Interaction in a 1-Stage Turbine

2020 ◽  
Author(s):  
A. J. Carvalho Figueiredo ◽  
B. D. J. Schreiner ◽  
A. W. Mesny ◽  
O. J. Pountney ◽  
J. A. Scobie ◽  
...  
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Gas Turbines ◽  
Suction Side ◽  
Secondary Flows ◽  
Complex Flow ◽  
Blade Passage ◽  
Passage Vortex ◽  
Purge Flow ◽  
Secondary Flow Field

Abstract Air-cooled gas turbines employ bleed air from the compressor to cool vulnerable components in the turbine. The cooling flow, commonly known as purge air, is introduced at low radius, before exiting through the rim-seal at the periphery of the turbine discs. The purge flow interacts with the mainstream gas path, creating an unsteady and complex flow-field. Of particular interest to the designer is the effect of purge on the secondary flow structures within the blade passage, the extent of which directly affects the aerodynamic loss in the stage. This paper presents a combined experimental and Computational Fluid Dynamics (CFD) investigation into the effect of purge flow on the secondary flows in the blade passage of an optically-accessible 1-stage turbine rig. The experimental campaign was conducted using Volumetric Velocimetry (VV) measurements to assess the three-dimensional inter-blade velocity field; the complementary CFD campaign was carried out using URANS computations. The implementation of VV within a rotating environment is a world first and offers an unparalleled level of experimental detail. The baseline flow-field, in the absence of purge flow, demonstrated a classical secondary flow-field: the roll-up of a horseshoe-vortex, with subsequent downstream convection of a pressure-side and suction-side leg, the former transitioning in to the passage vortex. The introduction of purge, at 1.7% of the mainstream flow-rate, was shown to modify the secondary flow field by enhancing the passage vortex, both in strength and span-wise migration. The computational predictions were in agreement with the enhancement revealed by the experiments.

Endwall Vortex Effects on Turbulent Dispersion of Film Coolant in a Turbine Vane Cascade

2014 ◽  
Author(s):  
Sayuri D. Yapa ◽  
Christopher J. Elkins ◽  
John K. Eaton
Keyword(s):  
Cross Flow ◽  
Suction Side ◽  
Horseshoe Vortex ◽  
Secondary Flows ◽  
Turbulent Dispersion ◽  
Suction Surface ◽  
Full Field ◽  
Flow Vorticity ◽  
Passage Vortex ◽  
Turbine Vane

Turbine vane cascades produce strong secondary flows due to flow turning. The dominant flow feature is the passage vortex, located in the corner between the endwall and the suction surface of the airfoil. Full-field, 3D velocity and concentration measurements were made using magnetic resonance imaging to study turbulent mixing in a realistic film-cooled nozzle vane cascade. The passage vortex has large effects on the flow features in the vane wake and consequently, on coolant mixing. Cross-flow vorticity on the vane’s suction side rolls up and forms the suction-side leg of the horseshoe vortex, which then interacts with the cross-flow boundary layer and rolls up into the passage vortex. The passage vortex does not measurably increase the turbulent diffusivity, although it does strongly distort streamlines near the endwall.

Flow Visualization in a Linear Turbine Cascade of High Performance Turbine Blades

1995 ◽  
Author(s):  
Hai-Ping Wang ◽  
Steven J. Olson ◽  
Richard J. Goldstein ◽  
Ernst R. G. Eckert
Keyword(s):  
Flow Visualization ◽  
High Performance ◽  
Current Model ◽  
Turbine Blades ◽  
Leading Edge ◽  
Flow Region ◽  
Horseshoe Vortex ◽  
Secondary Flows ◽  
Suction Surface ◽  
Passage Vortex

Multiple smoke wires are used to investigate the secondary flow near the endwall of a plane cascade with blade shapes as used in high performance turbine stages. The wires are positioned parallel to the endwall and ahead of the cascade, within and outside the endwall boundary layer. The traces of the smoke generated by the wires are visualized within a laser light sheet arranged at various cross-sections around the cascade. During the experiment, a periodically fluctuating horseshoe vortex system of varying number of vortices is observed near the leading edge of the cascade. A series of photographs and video tapes was taken in the cascade to trace these vortices. The development and evolution of the horseshoe vortex and the passage vortex are clearly resolved in the photographs. The interaction between the suction side leg of the horseshoe vortex and the passage vortex is also observed in the experiment. A vortex induced by the passage vortex, starting about 1/4 of the curvilinear distance along the blade on the suction surface, is clearly shown in the photographs. This vortex stays close to the suction surface and above the passage vortex in the laminar flow region on the blade. From this flow visualization, a model describing the secondary flows in a cascade is proposed and compared with previous published models. Some naphthalene mass transfer results from a blade near an endwall are cited and compared with the current model. The flows inferred from both techniques agree well with each other.

scholarly journals Effect of Incidence on Secondary Flows in a Linear Turbine Cascade

1994 ◽  
Author(s):  
G. V. Ramana Murty ◽  
N. Venkatrayulu
Keyword(s):  
Pressure Loss ◽  
Total Pressure ◽  
Leading Edge ◽  
Loss Coefficient ◽  
Secondary Flows ◽  
Total Pressure Loss ◽  
Turbine Cascade ◽  
Local Loss ◽  
Pressure Loss Coefficient ◽  
Total Pressure Loss Coefficient

The effect of incidence on the generation and growth of secondary flows in a linear turbine cascade was studied in the present investigations using a Variable Density Cascade Tunnel at an exit Mach number of 0.43 and a Reynolds number of 8 × 105. The angles of incidence chosen were +15°, +50, 0°, −5° and −8.5°. The flow field was surveyed at five axial stations from cascade inlet to exit with a view to understanding the development of the secondary flow with the help of the variation of mass averaged total pressure loss coefficient and the contours of local loss coefficients in the pitch and spanwise directions. The total pressure loss coefficient and the net secondary loss coefficient have shown a steady growth along the cascade upto about 74 of the axial chord from the leading edge and thereafter rose very rapidly. The incidence is found to have an effect on the passage vortex and the loss cores due to the inlet boundary layer.

Review of Platform Cooling Technology for High Pressure Turbine Blades

2014 ◽  
Author(s):  
Lesley M. Wright ◽  
Malak F. Malak ◽  
Daniel C. Crites ◽  
Mark C. Morris ◽  
Vikram Yelavkar ◽  
...  
Keyword(s):  
Film Cooling ◽  
Turbine Blades ◽  
Leading Edge ◽  
Suction Side ◽  
Horseshoe Vortex ◽  
Secondary Flows ◽  
Gas Turbine Blades ◽  
Cooling Channels ◽  
Purge Flow ◽  
Cooling Technology

With the relatively large surface area of the platform of the gas turbine blades being exposed directly to the hot, mainstream gas, it is vital to efficiently cool this region of the blades. This region is particularly difficult to protect due to the strong secondary flows developed at the airfoil junction (formation of the leading edge horseshoe vortex) and circumferentially across the blade passage (strengthening passage vortex moving from the pressure side to the suction side of the passage). Over the past decade, researchers and engine designers have attempted to combat the enhanced heat transfer to the blade platform by implementing both frontside and backside novel cooling techniques. This paper presents a review of platform cooling technology ranging from frontside film cooling via stator-rotor purge flow, mid-passage purge flow, and discrete film holes to backside cooling achieved via impinging jet arrays or cooling channels. To gain a full understanding of state-of-the-art cooling technology, recent patents, journal articles, and conference proceedings are included in this review.

Flow Visualization in a Linear Turbine Cascade of High Performance Turbine Blades

1997 ◽  
Vol 119 (1) ◽  
pp. 1-8 ◽  
Author(s):  
H. P. Wang ◽  
S. J. Olson ◽  
R. J. Goldstein ◽  
E. R. G. Eckert
Keyword(s):  
Flow Visualization ◽  
High Performance ◽  
Current Model ◽  
Turbine Blades ◽  
Leading Edge ◽  
Flow Region ◽  
Horseshoe Vortex ◽  
Secondary Flows ◽  
Suction Surface ◽  
Passage Vortex

Multiple smoke wires are used to investigate the secondary flow near the endwall of a plane cascade with blade shapes used in high-performance turbine stages. The wires are positioned parallel to the endwall and ahead of the cascade, within and outside the endwall boundary layer. The traces of the smoke generated by the wires are visualized with a laser light sheet illuminating various cross sections around the cascade. During the experiment, a periodically fluctuating horseshoe vortex system of varying number of vortices is observed near the leading edge of the cascade. A series of photographs and video tapes was taken in the cascade to trace these vortices. The development and evolution of the horseshoe vortex and the passage vortex are clearly resolved in the photographs. The interation between the suction side leg of the horseshoe vortex and the passage vortex is also observed in the experiment. A vortex induced by the passage vortex, starting about one-fourth of the curvilinear distance along the blade on the suction surface, is also found. This vortex stays close to the suction surface and above the passage vortex in the laminar flow region on the blade. From this flow visualization, a model describing the secondary flows in a cascade is proposed and compared with previous published models. Some naphthalene mass transfer results from a blade near an endwall are cited and compared with the current model. The flows inferred from the two techniques are in good agreement.

scholarly journals Investigation of Separation Phenomena in a Radial Pump at Reduced Flow Rate by Large-Eddy Simulation

2016 ◽  
Vol 138 (12) ◽  
Author(s):  
Antonio Posa ◽  
Antonio Lippolis ◽  
Elias Balaras
Keyword(s):  
Reverse Flow ◽  
Leading Edge ◽  
Suction Side ◽  
Secondary Flows ◽  
Vaned Diffuser ◽  
Flow Rates ◽  
Turbulent Statistics ◽  
Large Eddy ◽  
Radial Pump ◽  
Reduced Flow

Turbopumps operating at reduced flow rates experience significant separation and backflow phenomena. Although Reynolds-Averaged Navier–Stokes (RANS) approaches proved to be usually able to capture the main flow features at design working conditions, previous numerical studies in the literature verified that eddy-resolving techniques are required in order to simulate the strong secondary flows generated at reduced loads. Here, highly resolved large-eddy simulations (LES) of a radial pump with a vaned diffuser are reported. The results are compared to particle image velocimetry (PIV) experiments in the literature. The main focus of the present work is to investigate the separation and backflow phenomena occurring at reduced flow rates. Our results indicate that the effect of these phenomena extends up to the impeller inflow: they involve the outer radii of the impeller vanes, influencing significantly the turbulent statistics of the flow. Also in the diffuser vanes, a strong spanwise evolution of the flow has been observed at the reduced load, with reverse flow, located mainly on the shroud side and on the suction side (SS) of the stationary channels, especially near the leading edge of the diffuser blades.

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%.

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