The Effect of Secondary Air Injection on the Performance of a Transonic Turbine Stage

2002 ◽  
Author(s):  
S. Girgis ◽  
E. Vlasic ◽  
J.-P. Lavoie ◽  
S. H. Moustapha
Keyword(s):  
Turbine Stage ◽  
Cfd Simulations ◽  
Secondary Air Injection ◽  
Flow Test ◽  
Mainstream Flow ◽  
Purge Flow ◽  
Simulated Test ◽  
Transonic Turbine ◽  
Secondary Air ◽  
Stage Efficiency

This paper presents results of rig testing of a transonic, single stage turbine with various modifications made to the injection of secondary air into the mainstream. Results show that significant improvements in stage efficiency can be realized by optimizing the injection of upstream disk purge and rotor upstream shroud leakage flow into the mainstream flow. Results of CFD simulations of the rotor upstream disk purge flow test conditions and closely simulated test geometry agree well with test data.

Experimental Investigation of Turbine Stage Flow Field and Performance at Varying Cavity Purge Rates and Operating Speeds

2016 ◽  
Author(s):  
Johan Dahlqvist ◽  
Jens Fridh
Keyword(s):  
Mach Number ◽  
Flow Field ◽  
High Speed ◽  
Control Volume ◽  
Spatial Average ◽  
Turbine Stage ◽  
Wide Range ◽  
Annulus Flow ◽  
Purge Flow ◽  
Secondary Air

The aspect of hub cavity purge has been investigated in a high-pressure axial low-reaction turbine stage. The cavity purge is an important part of the secondary air system, used to isolate the hot main annulus flow from cavities below the hub level. A full-scale cold-flow experimental rig featuring a rotating stage was used in the investigation, quantifying main annulus flow field impact with respect to purge flow rate as it was injected upstream of the rotor. Five operating speeds were investigated of which three with respect to purge flow, namely a high loading case, the peak efficiency, and a high speed case. At each of these operating speeds, the amount of purge flow was varied across a very wide range of ejection rates. Observing the effect of the purge rate on measurement plane averaged parameters, a minor outlet swirl decrease is seen with increasing purge flow for each of the operating speeds while the Mach number is constant. The prominent effect due to purge is seen in the efficiency, showing a similar linear sensitivity to purge for the investigated speeds. An attempt is made to predict the efficiency loss with control volume analysis and entropy production. While spatial average values of swirl and Mach number are essentially unaffected by purge injection, important spanwise variations are observed and highlighted. The secondary flow structure is strengthened in the hub region, leading to a generally increased over-turning and lowered flow velocity. Meanwhile, the added volume flow through the rotor leads to higher outlet flow velocities visible in the tip region, and an associated decreased turning. A radial efficiency distribution is utilized, showing increased impact with increasing rotor speed.

Improving Turbine Stage Efficiency and Sealing Effectiveness Through Modifications of the Rim Seal Geometry

2012 ◽  
Author(s):  
I. Popović ◽  
H. P. Hodson
Keyword(s):  
Large Scale ◽  
Outer Part ◽  
Turbine Stage ◽  
Linear Cascade ◽  
Seal Design ◽  
Swirl Velocity ◽  
Different Types ◽  
Recirculation Zones ◽  
Secondary Air ◽  
Stage Efficiency

This paper presents an investigation of a range of engine realistic rim seals starting from a simple axial seal to different types of overlapping seals. The experiments were performed in a large-scale linear cascade equipped with a secondary air system capable of varying independently both the mass fraction as well as the swirl velocity of the leakage air. The experimental results were also complemented by CFD to provide better insight in the flow physics. It has been found that the key feature of the rim seals that affect their impact on overall loss generation and their ability to provide good sealing effectiveness was the location and the size of the recirculation zones within the rim seal. The requirements for good sealing and reduced spoiling effects on the main gaspath flow often led to contradictory designs. In general, the recirculation zones were found to improve sealing by reducing the effect of the pitchwise (circumferential) variation in the pressure distribution due to the blade’s potential field, and thus reduce ingestion. However, at the same time the recirculation zones tend to increase the loss generation. The best compromise was found when the outer part of the seal and its interface with the rotor platform was as smooth as possible to minimize the spoiling losses, while the recirculation zones were confined to the inner part of the seal to maintain acceptable levels of sealing effectiveness. A new rim seal design, which utilizes the best attributes of the above mentioned designs was developed. Linear cascade tests showed the losses due to the leakage-mainstream interaction were reduced by 33% compared to the datum seal design. Further validation was performed by examining the new configuration using unsteady full-stage calculations under engine realistic conditions. These calculations suggest an improvement of nearly 0.2% in the stage efficiency.

Aerothermal Impact of Stator-Rim Purge Flow and Rotor-Platform Film Cooling on a Transonic Turbine Stage

2008 ◽  
Author(s):  
M. Pau ◽  
G. Paniagua ◽  
D. Delhaye ◽  
A. de la Loma ◽  
P. Ginibre
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Pressure Fluctuations ◽  
Pressure Sensors ◽  
Suction Side ◽  
Turbine Stage ◽  
Purge Flow ◽  
Rotor Disk ◽  
Transonic Turbine ◽  
The Impact

This paper describes the effects on the mainstream flow of two types of cooling techniques in a transonic turbine stage: purge gas ejected out of the cavity between the stator rim and the rotor disk, as well as film cooling gas discharged from the rotor-platform. The tests were carried out in a full annular stage fed by a compression tube, at M2is = 1.1, Re = 1.1×106, and at temperature ratios reproducing engine conditions. The stator outlet was instrumented to allow the aerothermal characterization of the purge flow. The rotor blade was heavily instrumented with fast-response pressure sensors and double-layer thin film gauges. The tests are coupled with numerical calculations performed using the ONERA’s code elsA. The stator-rotor interaction is seen to be significantly affected by the stator-rim seal, both in terms of heat transfer and pressure fluctuations. The flow exchange between the rotor disk cavity and the mainstream passage is mainly governed by the vane shock patterns. The purge flow leads to the appearance of a large coherent vortex structure on the suction side of the blade which enhances the overall heat transfer coefficient due to the blockage effect created. Secondly, the impact of the platform cooling is observed to be restricted to the platform, with negligible effects on the blade suction side. The platform cooling results in a clear attenuation of pressure pulsations at some specific locations. Finally the turbine performance was analyzed, comparing measured and CFD results. A detailed loss breakdown analysis has been done using correlations, in order to isolate the different loss component contributions. The presented results should help designers improve the protection of the rotor platform and minimize the amount of coolant used.

Unsteady 360 CFD Validation of a Turbine Stage Mainstream/Disc Cavity Interaction

2014 ◽  
Author(s):  
A. V. Mirzamoghadam ◽  
S. Kanjiyani ◽  
A. Riahi ◽  
Reddaiah Vishnumolakala ◽  
Lavan Gundeti
Keyword(s):  
Fluid Velocity ◽  
Swirling Flows ◽  
Time Dependent ◽  
Cover Plate ◽  
Turbine Stage ◽  
Flow Conditions ◽  
Unstable Flow ◽  
Cfd Simulations ◽  
Cfd Validation ◽  
Purge Flow

The amount of cooling air assigned to seal high pressure turbine rim cavities is critical for performance as well as component life. Insufficient air leads to excessive hot annulus gas ingestion and its penetration deep into the cavity compromising disc or cover plate life. Excessive purge air, on the other hand, adversely affects performance. Experiments on a rotating turbine stage rig which included a rotor-stator forward disc cavity were performed at Arizona State University. The turbine rig has 22 vanes and 28 blades, while the cavity is composed of a single-tooth lab seal and a rim platform overlap seal. Time-averaged static pressures were measured in the gas path and the cavity, while mainstream gas ingestion into the cavity was determined by measuring the concentration distribution of tracer gas (carbon dioxide) under a range of purge flows from 0.435% (Cw = 1540) to 1.74% (Cw = 6161). Additionally, particle image velocimetry (PIV) was used to measure fluid velocity inside the cavity between the lab seal and the rim seal. The data from the experiments were compared to time-dependent CFD simulations using FLUENT CFD software. The CFD simulations brought to light the unsteadiness present in the flow during the experiment which the slower response data did not fully capture. An unsteady RANS, 360-degree CFD model of the complete turbine stage was employed in order to increase the understanding of the swirl physics which dominate cavity flows and better predict rim seal ingestion. Although the rotor-stator cavity is geometrically axisymmetric, it was found that the interaction between swirling flows in the cavity and swirling flows in the gas path create non-periodic/time-dependent unstable flow patterns which at the present are not accurately modeled by a 360 degree full stage unsteady analysis. At low purge flow conditions, the vortices that form inside the cavities are greatly influenced by mainstream ingestion. Conversely at high purge flow conditions the vortices are influenced by the purge flow, therefore ingestion is minimized. The paper also discusses details of meshing, convergence of time-dependent CFD simulations, and recommendations for future simulations in a rotor-stator disc cavity such as assessing the observed unsteadiness in the frequency domain in order to identify any critical frequencies driving the system.

Unsteady 360 Computational Fluid Dynamics Validation of a Turbine Stage Mainstream/Disk Cavity Interaction

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
A. V. Mirzamoghadam ◽  
S. Kanjiyani ◽  
A. Riahi ◽  
Reddaiah Vishnumolakala ◽  
Lavan Gundeti
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Swirling Flows ◽  
Time Dependent ◽  
Cover Plate ◽  
Turbine Stage ◽  
Flow Conditions ◽  
Unstable Flow ◽  
Cfd Simulations ◽  
Purge Flow

The amount of cooling air assigned to seal high pressure turbine (HPT) rim cavities is critical for performance as well as component life. Insufficient air leads to excessive hot annulus gas ingestion and its penetration deep into the cavity compromising disk or cover plate life. Excessive purge air, on the other hand, adversely affects performance. Experiments on a rotating turbine stage rig which included a rotor–stator forward disk cavity were performed at Arizona State University (ASU). The turbine rig has 22 vanes and 28 blades, while the cavity is composed of a single-tooth lab seal and a rim platform overlap seal. Time-averaged static pressures were measured in the gas path and the cavity, while mainstream gas ingestion into the cavity was determined by measuring the concentration distribution of tracer gas (carbon dioxide) under a range of purge flows from 0.435% (Cw = 1540) to 1.74% (Cw = 6161). Additionally, particle image velocimetry (PIV) was used to measure fluid velocity inside the cavity between the lab seal and the rim seal. The data from the experiments were compared to time-dependent computational fluid dynamics (CFD) simulations using fluent CFD software. The CFD simulations brought to light the unsteadiness present in the flow during the experiment which the slower response data did not fully capture. An unsteady Reynolds averaged Navier–Stokes (RANS), 360-deg CFD model of the complete turbine stage was employed in order to increase the understanding of the swirl physics which dominate cavity flows and better predict rim seal ingestion. Although the rotor–stator cavity is geometrically axisymmetric, it was found that the interaction between swirling flows in the cavity and swirling flows in the gas path create nonperiodic/time-dependent unstable flow patterns which at the present are not accurately modeled by a 360 deg full stage unsteady analysis. At low purge flow conditions, the vortices that form inside the cavities are greatly influenced by mainstream ingestion. Conversely at high purge flow conditions the vortices are influenced by the purge flow, therefore ingestion is minimized. The paper also discusses details of meshing, convergence of time-dependent CFD simulations, and recommendations for future simulations in a rotor–stator disk cavity such as assessing the observed unsteadiness in the frequency domain in order to identify any critical frequencies driving the system.

Experimental Investigation of Purge Flow Effects on a High Pressure Turbine Stage

2014 ◽  
Vol 137 (4) ◽  
Author(s):  
K. Regina ◽  
A. I. Kalfas ◽  
R. S. Abhari
Keyword(s):  
Experimental Investigation ◽  
High Pressure ◽  
Gas Turbines ◽  
Radial Displacement ◽  
Secondary Flows ◽  
Turbine Stage ◽  
Flow Factor ◽  
Purge Flow ◽  
The Impact ◽  
Stage Efficiency

In the present paper, an experimental investigation of the effects of rim seal purge flow on the performance of a highly loaded axial turbine stage is presented. The test configuration consists of a one-and-a-half stage, unshrouded, turbine, with a blading representative of high pressure (HP) gas turbines. Efficiency measurements for various purge flow injection levels have been carried out with pneumatic probes at the exit of the rotor and show a reduction of isentropic total-to-total efficiency of 0.8% per percent of injected mass flow. For three purge flow conditions, the unsteady aerodynamic flow field at rotor inlet and rotor exit has been measured with the in-house developed fast response aerodynamic probe (FRAP). The time-resolved data show the unsteady interaction of the purge flow with the secondary flows of the main flow and the impact on the radial displacement of the rotor hub passage vortex (HPV). Steady measurements at off-design conditions show the impact of the rotor incidence and of the stage flow factor on the resulting stage efficiency and the radial displacement of the rotor HPV. A comparison of the effect of purge flow and of the off-design conditions on the rotor incidence and stage flow factor shows that the detrimental effect of the purge flow on the stage efficiency caused by the radial displacement of the rotor HPV is dominated by the increase of stage flow factor in the hub region rather than by the increase of negative rotor incidence.

Numerical Investigations on the Aerodynamic Performance and Endwall Cooling Characteristics of Turbine During Acceleration Process With Lagging Effects

2021 ◽  
Author(s):  
Qingfeng Cong ◽  
Zhigang Li ◽  
Jun Li
Keyword(s):  
Flow Field ◽  
Rotational Speed ◽  
Aerodynamic Performance ◽  
Acceleration Process ◽  
Two Stage ◽  
Cooling Effectiveness ◽  
Mainstream Flow ◽  
Purge Flow ◽  
Secondary Air ◽  
Endwall Cooling

Abstract In the process of turbine acceleration, due to the influence of compressor and complex secondary air system, the change process of coolant purge flow is relatively lagging behind that of mainstream flow and rotational speed. The lagging egress of coolant flow influence the aerodynamic performance and endwall cooling effectiveness of turbine acceleration process. The flow field and aerothermal performance of two-stage axial turbines combined with rim seal structures and coolant purge flow lagging effects in the turbine acceleration process was numerically investigated using Unsteady Reynolds-Averaged Navier-Stokes (URANS) via SST turbulence model. The effects of lagging coolant purge flow across the rim seal on the turbine aerodynamics and endwall cooling effectiveness were analyzed. The obtained results show that the turbine aerodynamic efficiency obtains the maximum value when the coolant purge flow lagging time equals to half the acceleration time at the same rotational speed after the end of lagging times. The total-to-total efficiency for the second stage is more sensitive to lagging times. The turbine output power is almost un-changed due to combination of additional work capacity and aerodynamic loss with the introduction of coolant. The turbine endwalls have the maximum averaged cooling effectiveness in the turbine acceleration process without consideration of the coolant purge flow lagging time. And endwall cooling effectiveness decreases with the increase of coolant purge flow lagging time at the same rotational speed and mainstream flow conditions. The detailed flow field of two-stage turbine considering interaction between the coolant purge flow and mainstream was also discussed. The present work provides the reference for the match design between the turbine mainstream flow and secondary air flow system.

An Investigation of a Highly Loaded Transonic Turbine Stage With Compound Leaned Vanes

1986 ◽  
Vol 108 (2) ◽  
pp. 265-269 ◽  
Author(s):  
Jing Shi ◽  
Jianyuan Han ◽  
Shiying Zhou ◽  
Mingfu Zhu ◽  
Yaoko Zhang ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Velocity Profile ◽  
Three Dimensional ◽  
Turbine Stage ◽  
Time Marching ◽  
Overall Performance ◽  
Transonic Turbine ◽  
Volume Method ◽  
Stage Efficiency ◽  
Highly Loaded

An investigation was made to compare the performance of a highly loaded transonic turbine stage with and without compound leaned vanes. In both cases, velocity distribution along the vane surfaces was calculated from a full three-dimensional time-marching finite volume method. Nozzles were tested in a wind tunnel. Through rig tests, velocity profile at the stage exit was measured and the stage overall performance obtained. Performance in both tip and hub regions was improved by using the compound leaned vanes so that the stage efficiency increased by approximately 1 percent. The improvement is particularly remarkable at off-design points.

scholarly journals An Investigation of a Highly-Loaded Transonic Turbine Stage With Compound Leaned Vanes

1985 ◽  
Author(s):  
Shi Jing ◽  
Han Jianyuan ◽  
Zhou Shiying ◽  
Zhu Mingfu ◽  
Zhang Yaoko ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Velocity Profile ◽  
Turbine Stage ◽  
Test Velocity ◽  
Time Marching ◽  
Overall Performance ◽  
Transonic Turbine ◽  
Volume Method ◽  
Stage Efficiency ◽  
Highly Loaded

An investigation was made to compare the performance of a highly-loaded transonic turbine stage with and without compound leaned vanes. In both cases, velocity distribution along the vane surfaces was calculated from a full 3 D time-marching finite volume method. Nozzles were tested in a wind tunnel. Through rig test, velocity profile at the stage exit was measured and the stage overall performance obtained. Performance in both tip and hub regions was improved by using the compound leaned vanes so that the stage efficiency increased by 1% approximately. The improvement is payticylarly remarkable at off-design points.

Improving Turbine Stage Efficiency and Sealing Effectiveness Through Modifications of the Rim Seal Geometry

2013 ◽  
Vol 135 (6) ◽  
Author(s):  
Ivan Popovíc ◽  
Howard P. Hodson
Keyword(s):  
Large Scale ◽  
Outer Part ◽  
Turbine Stage ◽  
Linear Cascade ◽  
Seal Design ◽  
Swirl Velocity ◽  
Different Types ◽  
Recirculation Zones ◽  
Secondary Air ◽  
Stage Efficiency

This paper presents an investigation of a range of engine realistic rim seals starting from a simple axial seal to different types of overlapping seals. The experiments were performed in a large-scale linear cascade equipped with a secondary air system capable of varying independently both the mass fraction as well as the swirl velocity of the leakage air. The experimental results were also complemented by computationally fluid dynamics (CFD) to provide better insight in the flow physics. It has been found that the key feature of the rim seals that affect their impact on overall loss generation and their ability to provide good sealing effectiveness was the location and the size of the recirculation zones within the rim seal. The requirements for good sealing and reduced spoiling effects on the main gaspath flow often led to contradictory designs. In general, the recirculation zones were found to improve sealing by reducing the effect of the pitchwise (circumferential) variation in the pressure distribution due to the blade's potential field, and thus reduce ingestion. However, at the same time the recirculation zones tend to increase the loss generation. The best compromise was found when the outer part of the seal and its interface with the rotor platform was as smooth as possible to minimize the spoiling losses, while the recirculation zones were confined to the inner part of the seal to maintain acceptable levels of sealing effectiveness. A new rim seal design, which utilizes the best attributes of the above mentioned designs was developed. Linear cascade tests showed the losses due to the leakage-mainstream interaction were reduced by 33% compared to the datum seal design. Further validation was performed by examining the new configuration using unsteady full-stage calculations under engine realistic conditions. These calculations suggest an improvement of nearly 0.2% in the stage efficiency.

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