Effect of Purge on the Secondary Flow-Field of a Gas Turbine Blade-Row

2020 ◽  
Vol 142 (10) ◽  
Author(s):  
B. D. J Schreiner ◽  
M. Wilson ◽  
Y. S. Li ◽  
C. M. Sangan
Keyword(s):  
Computational Study ◽  
Suction Side ◽  
Horseshoe Vortex ◽  
Secondary Flows ◽  
Pressure Side ◽  
Suction Surface ◽  
Blade Row ◽  
Purge Flow ◽  
Rotational Direction ◽  
Secondary Flow Field

Abstract Turbine disc cooling is required to protect vulnerable components from exposure to the high temperatures found in the mainstream gas path. Purge air, bled from the latter stages of the compressor, is introduced to the turbine wheelspace at low radius before exiting through the rim-seal at the periphery of the discs. The unsteady, complex flowfield that arises from the interaction between the purge and mainstream gases modifies the structure of secondary flows within the blade passage. A computational study was conducted using an unsteady Reynolds-averaged Navir–Stokes (RANS) solver, modeling an engine-representative turbine stage. Preliminary results were validated using experimental data from a test rig. The baseline secondary flowfield was described, in the absence of purge flow, demonstrating the classical rollup of the horseshoe vortex and subsequent convection of the two legs downstream. The unsteady behavior of the model was investigated and addressed, resulting in recommendations for modeling interaction phenomena in turbines. A superposed purge flow, resulting in egress through the upstream rim-seal, was shown to modify the secondary flowfield in the turbine annulus. The most notable effect of egress was the formation of a large plume forming near the pressure minima associated with the blade suction surface. The egress was turned by the mainstream flow, creating a vortical structure consistent in rotational direction to the pressure-side leg of the horseshoe vortex; the pressure-side leg was subsequently strengthened and showed an increased radial migration relative to the unpurged case. The egress plume was also shown to overwhelm the suction-side leg of the horseshoe vortex, reducing its strength.

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.

Visualizations of the Unsteady Flow Field Near the Endwall of a Turbine Cascade

2002 ◽  
Author(s):  
Hongwei Ma ◽  
Haokang Jiang ◽  
Yaxi Qiu
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Incidence Angle ◽  
Suction Side ◽  
Horseshoe Vortex ◽  
Radial Clearance ◽  
Pressure Side ◽  
Turbine Cascade ◽  
Suction Surface ◽  
Vortex System

The unsteady flow field near the endwall of a turbine cascade was visualized in a water tunnel using the hydrogen bubble technique. With the help of a light sheet, the experiment was carried out at different incidences without a radial clearance. A fluctuating horseshoe vortex system of varying number of vortices is observed near the leading-edge endwall. The pressure-side leg of the vortex moves toward the suction side after it enters the passage, while the suction-side leg develops along the corner of the suction surface. With the incidence increase, the pressure-side leg of the horseshoe vortex becomes stronger and can directly kick on the suction surface, causing a considerable influence nearby. The interaction and the flow mixing among the counter-rotating horseshoe legs, the endwall boundary layer and the main flow occur in the passage, forming a vortex system traditionally called the passage vortex. The vortex patterns and the interactions are related to the incidence angle.

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.

Formation and Transport of Secondary Flows Caused by Vortex-Blade Interaction in a High Pressure Turbine

2015 ◽  
Author(s):  
Zuo-Jun Wei ◽  
Wei-Yang Qiao ◽  
Ping-Ping Chen ◽  
Jian Liu
Keyword(s):  
Boundary Layer ◽  
High Pressure ◽  
Pressure Gradient ◽  
Suction Side ◽  
Secondary Flows ◽  
Pressure Side ◽  
High Pressure Turbine ◽  
Suction Surface ◽  
Blade Loading ◽  
Passage Vortex

As modern turbines are designed with low aspect ratio and high blade loading, secondary flow interactions become more important. In the present work, numerical simulation is performed in a two-stage high-pressure turbine with divergent meridional passage to investigate the transport and interaction of secondary vortex from the first stage rotor within the second stage’s stator. Scale-Adaptive Simulation model coupled with Shear Stress Transport model (SAS-SST turbulence model) is used to capture the flow structures caused by the interaction in the second stator. Coupled with the passage vortex of the first rotor, the shed vortex rotates opposite in the direction and has comparable strength. As both of these vortices convect downstream to the stator bladerow, each deforms into two legs on the pressure and suction sides in the passage. In the passage due to the cross pressure gradient by blade loading, all the low-momentum fluid contained in these vortices moves towards the suction side. Besides, with the existing static pressure gradient in radial direction and vortex dynamics, the suction-side leg and the pressure-side leg move in different radial directions. The suction side leg of incoming passage vortex moves towards the endwall along the suction surface and interacts with the developing passage vortex of the second stator. The incoming shed vortex moves towards the midspan and rolls up the boundary layer fluid from suction surface. Due to the interactions between the incoming shed vortices from the hub and casing and the boundary layer of second stator, two counter-rotating vortices are formed near the midspan. Additional high loss is found there at the outlet plane, which has a comparable magnitude to the endwall secondary loss. The pressure side leg of the incoming passage vortex remains in a certain span with that of the incoming shed vortex and is not engulfed by the developing passage vortex.

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.

Design of Contoured Turbine Endwalls in the Presence of Purge Flow: A Feature-Based Approach

2019 ◽  
Author(s):  
B. D. J. Schreiner ◽  
M. Wilson ◽  
Y. S. Li ◽  
C. M. Sangan
Keyword(s):  
Gas Turbines ◽  
Computational Study ◽  
Leading Edge ◽  
Suction Side ◽  
Horseshoe Vortex ◽  
Geometric Features ◽  
Efficiency Gain ◽  
Pressure Side ◽  
Secondary Air ◽  
Edge Feature

Abstract Endwall contouring is used to increase the aerodynamic efficiency of both compressor and turbine stages in industrial gas turbines and aeroengines. The complex interaction between the secondary air-leakage, used to cool the turbine disc, and the mainstream gas path, leads to an unsteady flow field that is challenging to compute. Current endwall designs have shown sensitivity to the introduction of secondary air, with stage efficiency improvements being reduced, or in the limit, eliminated altogether. A computational study of an engine-representative turbine stage was conducted using an unsteady RANS solver. Previously published computations of the baseline axisymmetric endwall were validated with experimental data from a geometrically similar test rig. Understanding from this prior study was used to inform the design process for contoured endwalls, namely through the identification of three key geometric features: the leading-edge feature; the suction-side trough; the pressure-side trough. The baseline axisymmetric endwall showed periodic unsteadiness, large secondary flow features and an egress plume which dominated the aerodynamics of the stage. The implementation of a suction-side trough (i.e. making the endwall non-axisymmetric) reduced the magnitude of the unsteadiness by controlling the path of the egress plume. The trough also reduced the span-wise migration of the egress plume through the passage and provided modest control over pitchwise position. In corroboration with the findings of other authors, the introduction of a leading-edge feature was also used to reduce the leading edge horseshoe vortex,. The pressure-side trough enabled the prominence of the leading-edge feature to be enhanced, however it increased the span-wise migration of the egress plume. Insight generated from computations of the three distinct geometric features resulted in an improved endwall concept; the improved endwall demonstrated a 0.4% net efficiency gain for the stage relative to the cylindrical baseline.

Investigations on the interaction between the front and aft purge flow and the downstream vane of 1.5-stage turbine

2022 ◽  
Vol 0 (0) ◽  
Author(s):  
He Zhenpeng ◽  
Zhou Jiaxing ◽  
Xin Jia ◽  
Yang Chengquan ◽  
Li Baichun
Keyword(s):  
Flow Field ◽  
Flow Rate ◽  
Suction Side ◽  
Secondary Flows ◽  
Wall Structure ◽  
Pressure Side ◽  
Turbine Efficiency ◽  
Passage Vortex ◽  
Purge Flow ◽  
End Wall

Abstract The present work reports the influence of the 1.5-stage turbine flow field by the front and aft rim seal flow. The interaction between the front and aft purge flow and the mainstream of a 1.5-stage turbine was numerically simulated, and the influence of the front and aft purge flow on the downstream vane was analyzed separately. The results show that the front purge flow is distributed at the higher radius of second vane inlet, which changes the position of the blade hub secondary flows, and the aft purge flow is distributed at the low radius. The purge flow at different locations in the aft cavity exit forms shear induced vortex, pressure and suction side legs of the egress, which converges with the suction and pressure side legs of the horse vortex to form vane hub passage vortex. The increased purge flow rate in both the front and aft cavities significantly increases the sealing effectiveness of the rim seal, but also causes a reduction in turbine efficiency. The combined effect of the front and aft purge flow reduces the turbine efficiency of the end-wall structure by 0.3619, 0.9062, 1.5004, 2.0188 and 2.509% at IR = 0, IR = 0.5%, IR = 0.9%, IR = 1.3% and IR = 1.7%.

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.

Numerical Predictions of Turbine Cascade Secondary Flows and Heat Transfer With Inflow Turbulence

2020 ◽  
Author(s):  
Yousef Kanani ◽  
Sumanta Acharya ◽  
Forrest Ames
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Leading Edge ◽  
Suction Side ◽  
Lateral Spreading ◽  
Secondary Flows ◽  
Pressure Side ◽  
Initial Flow ◽  
Numerical Predictions ◽  
Inflow Turbulence

Abstract Turbine passage secondary flows are studied for a large rounded leading edge airfoil geometry considered in the experimental investigation of Varty et al. (J. Turbomach. 140(2):021010) using high resolution Large Eddy Simulation (LES). The complex nature of secondary flow formation and evolution are affected by the approach boundary layer characteristics, components of pressure gradients tangent and normal to the passage flow, surface curvature, and inflow turbulence. This paper presents a detailed description of the secondary flows and heat transfer in a linear vane cascade at exit chord Reynolds number of 5 × 105 at low and high inflow turbulence. Initial flow turning at the leading edge of the inlet boundary layer leads to a pair of counter-rotating flow circulation in each half of the cross-plane that drive the evolution of the pressure-side and suction side of the near-wall vortices such as the horseshoe and leading edge corner vortex. The passage vortex for the current large leading-edge vane is formed by the amplification of the initially formed circulation closer to the pressure side (PPC) which strengthens and merges with other vortex systems while moving toward the suction side. The predicted suction surface heat transfer shows good agreement with the measurements and properly captures the augmented heat transfer due to the formation and lateral spreading of the secondary flows towards the vane midspan downstream of the vane passage. Effects of various components of the secondary flows on the endwall and vane heat transfer are discussed in detail.

Comparison of Steady and Unsteady Secondary Flows in a Turbine Stator Cascade

1989 ◽  
Author(s):  
Gregory J. Hebert ◽  
William G. Tiederman
Keyword(s):  
Secondary Flows ◽  
Rotor Blades ◽  
Velocity Measurements ◽  
Flow Loop ◽  
Suction Surface ◽  
Linear Cascade ◽  
Turbine Stator ◽  
Passage Vortex ◽  
Blade Row ◽  
Secondary Flow Structure

The effect of periodic rotor wakes on the secondary flow structure in a turbine stator cascade was investigated. A mechanism simulated the wakes shed from rotor blades bypassing cylindrical rods across the inlet to a linear cascade installed in a recirculating water flow loop. Velocity measurements showed a passage vortex, similar to that seen in steady flow, during the time associated with undisturbed fluid. However, as the rotor wake passed through the blade row, a large crossflow toward the suction surface was observed in the midspan region. This caused the development of two large areas of circulation between the midspan and endwall regions, significantly distorting and weakening the passage vortices.

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