Modulation and Radial Migration of Turbine Hub Cavity Modes by the Rim Seal Purge Flow

2016 ◽  
Author(s):  
R. Schädler ◽  
A. I. Kalfas ◽  
R. S. Abhari ◽  
G. Schmid ◽  
S. Voelker
Keyword(s):  
Gas Turbines ◽  
Fast Response ◽  
Loss Mechanism ◽  
Axial Turbine ◽  
Pressure Transducers ◽  
Aerodynamic Loss ◽  
Numerical Predictions ◽  
Cavity Modes ◽  
Annulus Flow ◽  
Purge Flow

In the present paper, the results of an experimental and numerical investigation of the hub cavity modes and their migration into the main annulus flow are presented. A one-and-a-half stage, unshrouded and highly loaded axial turbine configuration with 3-dimensionally shaped blades and cylindrical end walls has been tested in an axial turbine facility. Both, the blade design and the rim seal purge flow path are representative to modern high pressure gas turbines. The unsteady flow field at the hub cavity exit region has been measured with the fast-response aerodynamic probe (FRAP) for two different rim seal purge flow rates. Furthermore, fast-response wall mounted pressure transducers have been installed inside the cavity. Unsteady full-annular CFD simulations have been employed in order to complement the experimental work. The time-resolved pressure measurements inside the hub cavity reveal clear cavity modes which show a strong dependency on the injected amount of rim seal purge flow. The numerical predictions provide information on the origin of these modes and relate them to pronounced ingestion spots around the circumference. The unsteady probe measurements at the rim seal interface show that the signature of the hub cavity induced modes migrates into the main annulus flow up to 30% blade span. Based on that, an aerodynamic loss mechanism has been found, showing that the benefit in loss reduction by decreasing the rim seal purge flow rate is weakened by the presence of turbine hub cavity modes.

Modulation and Radial Migration of Turbine Hub Cavity Modes by the Rim Seal Purge Flow

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
R. Schädler ◽  
A. I. Kalfas ◽  
R. S. Abhari ◽  
G. Schmid ◽  
S. Voelker
Keyword(s):  
Gas Turbines ◽  
Fast Response ◽  
Loss Mechanism ◽  
Axial Turbine ◽  
Pressure Transducers ◽  
Aerodynamic Loss ◽  
Numerical Predictions ◽  
Cavity Modes ◽  
Annulus Flow ◽  
Purge Flow

In the present paper, the results of an experimental and numerical investigation of the hub cavity modes and their migration into the main annulus flow are presented. A one-and-a-half stage, unshrouded and highly loaded axial turbine configuration with three-dimensionally shaped blades and cylindrical end walls has been tested in an axial turbine facility. Both the blade design and the rim seal purge flow path are representative to modern high-pressure gas turbines. The unsteady flow field at the hub cavity exit region has been measured with the fast-response aerodynamic probe (FRAP) for two different rim seal purge flow rates. Furthermore, fast-response wall-mounted pressure transducers have been installed inside the cavity. Unsteady full-annular computational fluid dynamics (CFD) simulations have been employed in order to complement the experimental work. The time-resolved pressure measurements inside the hub cavity reveal clear cavity modes, which show a strong dependency on the injected amount of rim seal purge flow. The numerical predictions provide information on the origin of these modes and relate them to pronounced ingestion spots around the circumference. The unsteady probe measurements at the rim seal interface show that the signature of the hub cavity induced modes migrates into the main annulus flow up to 30% blade span. Based on that, an aerodynamic loss mechanism has been found, showing that the benefit in loss reduction by decreasing the rim seal purge flow rate is weakened by the presence of turbine hub cavity modes.

Aerodynamic Robustness of End Wall Contouring Against Rim Seal Purge Flow

2014 ◽  
Author(s):  
K. Regina ◽  
A. I. Kalfas ◽  
R. S. Abhari ◽  
A. Lohaus ◽  
S. Voelker ◽  
...  
Keyword(s):  
Experimental Investigation ◽  
Flow Field ◽  
Gas Turbines ◽  
Fast Response ◽  
Axial Turbine ◽  
Purge Flow ◽  
The One ◽  
End Wall ◽  
Stage Efficiency ◽  
Higher Sensitivity

In the present study, the results of an experimental investigation are presented, which have been undertaken in the axial turbine facility LISA at ETH Zurich. The two test configurations consist of a one-and-a-half stage, unshrouded, highly loaded axial turbine with 3-dimensionally shaped blading representative of modern high pressure gas turbines. The two test configurations differ in the hub end walls: while one design has cylindrical end walls, the other design features non-axisymmetric end wall contouring (EWC). Both turbine designs have not been especially designed for the unsteady and complex interaction mechanisms of the hub rim seal purge flow with the main annulus flow. However, these turbine designs have been subject to measurements without (nominal) and with purge flow (0.8% of the main mass flow) with the purpose of studying the aerodynamic robustness of the performance of the stages with respect to the rim seal purge flow. In order to further analyze the robustness of both turbine designs, also measurements at off-design conditions have been taken. The steady and unsteady aerodynamic effects are measured, respectively, with pneumatic probes as well as with the in-house developed and manufactured Fast Response Aerodynamic Probe (FRAP) technology. With the aim of evaluating the aerodynamic performance and robustness of the end wall design, the one result of the experimental investigation is the quantification of the sensitivity of the stage efficiency with respect to the case with and without purge flow for both turbine designs. By means of the analysis of the time-resolved flow field and characterization of the secondary flow features, their reaction to the presence of purge flow is highlighted and used as an explanation for the efficiency deficits caused by the purge flow. The measurements show a benefit in stage efficiency of +0.2% by using the end wall contouring in the nominal case, confirming the design intention and effectiveness of the contoured end walls. However, the beneficial impact of the end wall contouring is taken back by a higher sensitivity of the stage efficiency with respect to the purge flow, which causes the efficiency benefit to vanish with the investigated purge flow injection rate of 0.8%. The off-design measurements show that also the sensitivity of the stage with end wall contouring with respect to the reduction of stage loading factor is by 1/3 higher than the one of the cylindrical end walls. The measurements imply that the cost of higher stage efficiency at nominal conditions by the use of end wall contouring is paid with a higher sensitivity of the stage to changes in the rotor incoming flow field and thus with a lower aerodynamic robustness of the turbine design.

scholarly journals Experimental and Analytical Assessment of Cavity Modes in a Gas Turbine Wheelspace

2017 ◽  
Author(s):  
Rachel A. Berg ◽  
C. S. Tan ◽  
Zhongman Ding ◽  
Gregory Laskowski ◽  
Pepe Palafox ◽  
...  
Keyword(s):  
Gas Turbine ◽  
High Speed ◽  
Flow Direction ◽  
Pressure Oscillation ◽  
Fast Response ◽  
Hot Gas ◽  
Modal Response ◽  
Cavity Modes ◽  
Oscillation Modes ◽  
Purge Flow

Fast response pressure data acquired in a high-speed 1.5-stage turbine Hot Gas Ingestion Rig shows the existence of pressure oscillation modes in the rim-seal-wheelspace cavity of a high pressure gas turbine stage with purge flow. The experimental results and observations are complemented by computational assessments of pressure oscillation modes associated with the flow in canonical cavity configurations. The cavity modes identified include shallow cavity modes and Helmholtz resonance. The response of the cavity modes to variation in design and operating parameters are assessed. These parameters include cavity aspect ratio, purge flow ratio, and flow direction defined by the ratio of primary tangential to axial velocity. Scaling the cavity modal response based on computational results and available experimental data in terms of the appropriate reduced frequencies appears to indicate the potential presence of a deep cavity mode as well. While the role of cavity modes on hot gas ingestion cannot be clarified based on the current set of data, the unsteady pressure field associated with turbine rim cavity modal response can be expected to drive ingress/egress.

Re-Ingestion of Upstream Egress in a 1.5-Stage Gas Turbine Rig

2018 ◽  
Vol 140 (7) ◽  
Author(s):  
James A. Scobie ◽  
Fabian P. Hualca ◽  
Marios Patinios ◽  
Carl M. Sangan ◽  
J. Michael Owen ◽  
...  
Keyword(s):  
Gas Turbines ◽  
Co2 Concentration ◽  
Test Facility ◽  
Operating Life ◽  
Annulus Flow ◽  
Purge Flow ◽  
Rotor Disk ◽  
First Time ◽  
Measured Mass ◽  
Insight Into

In gas turbines, rim seals are fitted at the periphery of stator and rotor discs to minimize the purge flow required to seal the wheel-space between the discs. Ingestion (or ingress) of hot mainstream gases through rim seals is a threat to the operating life and integrity of highly stressed components, particularly in the first-stage turbine. Egress of sealing flow from the first-stage can be re-ingested in downstream stages. This paper presents experimental results using a 1.5-stage test facility designed to investigate ingress into the wheel-spaces upstream and downstream of a rotor disk. Re-ingestion was quantified using measurements of CO2 concentration, with seeding injected into the upstream and downstream sealing flows. Here, a theoretical mixing model has been developed from first principles and validated by the experimental measurements. For the first time, a method to quantify the mass fraction of the fluid carried over from upstream egress into downstream ingress has been presented and measured; it was shown that this fraction increased as the downstream sealing flow rate increased. The upstream purge was shown to not significantly disturb the fluid dynamics but only partially mixes with the annulus flow near the downstream seal, with the ingested fluid emanating from the boundary layer on the blade platform. From the analogy between heat and mass transfer, the measured mass-concentration flux is equivalent to an enthalpy flux, and this re-ingestion could significantly reduce the adverse effect of ingress in the downstream wheel-space. Radial traverses using a concentration probe in and around the rim seal clearances provide insight into the complex interaction between the egress, ingress and mainstream flows.

Re-Ingestion of Upstream Egress in a 1.5-Stage Gas Turbine Rig

2017 ◽  
Author(s):  
James A. Scobie ◽  
Fabian P. Hualca ◽  
Marios Patinios ◽  
Carl M. Sangan ◽  
J. Michael Owen ◽  
...  
Keyword(s):  
First Principles ◽  
Gas Turbines ◽  
Co2 Concentration ◽  
Test Facility ◽  
Operating Life ◽  
Annulus Flow ◽  
Purge Flow ◽  
First Time ◽  
Measured Mass ◽  
Insight Into

In gas turbines, rim seals are fitted at the periphery of stator and rotor discs to minimise the purge flow required to seal the wheel-space between the discs. Ingestion (or ingress) of hot mainstream gases through rim seals is a threat to the operating life and integrity of highly-stressed components, particularly in the first-stage turbine. Egress of sealing flow from the first-stage can be re-ingested in downstream stages. This paper presents experimental results using a 1.5-stage test facility designed to investigate ingress into the wheel-spaces upstream and downstream of a rotor disc. Re-ingestion was quantified using measurements of CO2 concentration, with seeding injected into the upstream and downstream sealing flows. Here a theoretical mixing model has been developed from first principles and validated by the experimental measurements. For the first time, a method to quantify the mass fraction of the fluid carried over from upstream egress into downstream ingress has been presented and measured; it was shown that this fraction increased as the downstream sealing flow rate increased. The upstream purge was shown to not significantly disturb the fluid dynamics but only partially mixes with the annulus flow near the downstream seal, with the ingested fluid emanating from the boundary layer on the blade platform. From the analogy between heat and mass transfer, the measured mass-concentration flux is equivalent to an enthalpy flux and this re-ingestion could significantly reduce the adverse effect of ingress in the downstream wheel-space. Radial traverses using a concentration probe in and around the rim seal clearances provide insight into the complex interaction between the egress, ingress and mainstream flows.

scholarly journals Detection of Rotor Forced Response Vibrations Using Stationary Pressure Transducers in a Multistage Axial Compressor

2015 ◽  
Vol 2015 ◽  
pp. 1-10 ◽  
Author(s):  
William L. Murray ◽  
Nicole L. Key
Keyword(s):  
Gas Turbines ◽  
Axial Compressor ◽  
Fast Response ◽  
Forced Response ◽  
Vibration Monitoring ◽  
Blade Vibration ◽  
Response Condition ◽  
Pressure Transducers ◽  
Forcing Function ◽  
Cross Covariance

Blade row interactions in turbomachinery can lead to blade vibrations and even high cycle fatigue. Forced response conditions occur when a forcing function (such as impingement of stator wakes) occurs at a frequency that matches the natural frequency of a blade. The objective of this research is to develop the data processing techniques needed to detect rotor blade vibration in a forced response condition from stationary fast-response pressure transducers to allow for detection of rotor vibration from transient data and lead to techniques for vibration monitoring in gas turbines. This paper marks the first time in the open literature that engine-order resonant response of an embedded bladed disk in a 3-stage intermediate-speed axial compressor was detected using stationary pressure transducers. Experiments were performed in a stage axial research compressor focusing on the embedded rotor of blisk construction. Fourier waterfall graphs from a laser tip timing system were used to detect the vibrations after applying signal processing methods to uncover these pressure waves associated with blade vibration. Individual blade response was investigated using cross covariance to compare blade passage pressure signatures through resonance. Both methods agree with NSMS data that provide a measure of the exact compressor speeds at which individual blades enter resonance.

scholarly journals Experimental and Analytical Assessment of Cavity Modes in a Gas Turbine Wheelspace

2018 ◽  
Vol 140 (6) ◽  
Author(s):  
Rachel A. Berg ◽  
C. S. Tan ◽  
Zhongman Ding ◽  
Gregory Laskowski ◽  
Pepe Palafox ◽  
...  
Keyword(s):  
Gas Turbine ◽  
High Speed ◽  
Flow Direction ◽  
Pressure Oscillation ◽  
Fast Response ◽  
Hot Gas ◽  
Modal Response ◽  
Cavity Modes ◽  
Oscillation Modes ◽  
Purge Flow

Fast response pressure data acquired in a high-speed 1.5-stage turbine hot gas ingestion rig (HGIR) show the existence of pressure oscillation modes in the rim-seal-wheelspace cavity of a high pressure gas turbine stage with purge flow. The experimental results and observations are complemented by computational assessments of pressure oscillation modes associated with the flow in canonical cavity configurations. The cavity modes identified include shallow cavity modes and Helmholtz resonance. The response of the cavity modes to variation in design and operating parameters are assessed. These parameters include cavity aspect ratio (AR), purge flow ratio, and flow direction defined by the ratio of primary tangential to axial velocity. Scaling the cavity modal response based on computational results and available experimental data in terms of the appropriate reduced frequencies appears to indicate the potential presence of a deep cavity mode as well. While the role of cavity modes on hot gas ingestion cannot be clarified based on the current set of data, the unsteady pressure field associated with turbine rim cavity modal response can be expected to drive ingress/egress.

scholarly journals Sensitivity analysis on the impact of geometrical and operational variations on turbine hub cavity modes and practical methods to control them

2021 ◽  
Vol 5 ◽  
pp. 66-78
Author(s):  
Vahid Iranidokht ◽  
Anestis Kalfas ◽  
Reza Abhari ◽  
Shigeki Senoo ◽  
Kazuhiro Momma
Keyword(s):  
Experimental Investigation ◽  
Pressure Ratio ◽  
Fast Response ◽  
Test Facility ◽  
Flow Structures ◽  
Characteristic Parameters ◽  
Pressure Transducers ◽  
Cavity Modes ◽  
Layer Velocity ◽  
The Impact

This paper presents an experimental investigation on the impact of different design and operational variations on the instabilities induced at the hub cavity outlet of a turbine. The experiments were conducted at the “LISA” test facility at ETH Zurich. The axial gap at the 2nd stage hub cavity exit was varied, and also three different flow deflectors were implemented at the cavity exit to control the cavity modes (CMs). Furthermore, the turbine pressure ratio was altered to mimic the off-design condition and study the sensitivity of the CMs to this parameter. Measurements were performed using pneumatic, and Fast Response Aerodynamic Probes (FRAP) at stator and rotor exit. In addition, unsteady pressure transducers were installed at the cavity exit wall to measure the characteristic parameters of the CMs. For the small axial gap, distinct and strong CMs were generated, which actively interacted with stator and rotor hub flow structures. Increasing the gap damped the fluctuations; however, a broader range of frequencies was amplified. The flow deflectors successfully suppressed the CMs by manipulating the shear layer velocity profile and blocking the growing instabilities. Eventually, the increase in the turbine pressure ratio strengthened the CMs and vice versa.

scholarly journals Effect of purge air on rotor endwall heat transfer of an axial turbine

2017 ◽  
Vol 1 ◽  
pp. F29ZWY ◽  
Author(s):  
Sebastiano Lazzi Gazzini ◽  
Rainer Schädler ◽  
Anestis I. Kalfas ◽  
Reza S. Abhari ◽  
Sebastian Hohenstein ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Wall Temperature ◽  
Gas Turbines ◽  
Suction Side ◽  
Local Heat ◽  
Heat Fluxes ◽  
Secondary Flows ◽  
Adiabatic Wall ◽  
Axial Turbine ◽  
Purge Flow

AbstractIn order to gain in cycle efficiency, turbine inlet temperatures tend to rise, posing the challenge for designers to cool components more effectively. Purge flow injection through the rim seal is regularly used in gas turbines to limit the ingestion of hot air in the cavities and prevent overheating of the disks and shaft bearings. The interaction of the purge air with the main flow and the static pressure field of the blade rows results in a non-homogenous distribution of coolant on the passage endwall which poses questions on its effect on endwall heat transfer. A novel measurement technique based on infrared thermography has been applied in the rotating axial turbine research facility LISA of the Laboratory for Energy Conversion (LEC) of ETH Zürich. A 1.5 stage configuration with fully three-dimensional airfoils and endwall contouring is integrated in the facility. The effect of different purge air mass flow rates on the distribution of the heat transfer quantities has been observed for the rated operating condition of the turbine. Two-dimensional distributions of Nusselt number and adiabatic wall temperature show that the purge flow affects local heat loads. It does so by acting on the adiabatic wall temperature on the suction side of the passage until 30% of the axial extent of the rotor endwall. This suggests the possibility of effectively employing purge air also as rotor platform coolant in this specific region. The strengthening of the secondary flows due to purge air injection is observed, but plays a negligible role in varying local heat fluxes. For one test case, experimental data is compared to high-fidelity, unsteady Reynolds-Averaged Navier–Stokes simulations performed on a model of the full 1.5 stage configuration.

scholarly journals Novel high-pressure turbine purge control features for increased stage efficiency

2017 ◽  
Vol 1 ◽  
pp. 68MK5V ◽  
Author(s):  
Rainer Schädler ◽  
Anestis I. Kalfas ◽  
Reza S. Abhari ◽  
Gregor Schmid ◽  
Tilmann auf dem Kampe ◽  
...  
Keyword(s):  
High Pressure ◽  
Flow Field ◽  
Gas Turbines ◽  
High Pressure Turbine ◽  
Axial Turbine ◽  
Seal Design ◽  
Geometrical Features ◽  
Purge Flow ◽  
The Impact ◽  
Stage Efficiency

AbstractRim seals throttle flow and have shown to impact the aerodynamic performance of gas turbines. The results of an experimental investigation of a rim seal exit geometry variation and its impact on the high-pressure turbine flow field are presented. A one-and-a-half stage, unshrouded and highly loaded axial turbine configuration with 3-dimensionally shaped blades and non-axisymmetric end wall contouring has been tested in an axial turbine facility. The exit of the rotor upstream rim seal was equipped with novel geometrical features which are termed as purge control features (PCFs) and a baseline rim seal geometry for comparison. The time-averaged and unsteady aerodynamic effects at rotor inlet and exit have been measured with pneumatic probes and the fast-response aerodynamic probe (FRAP) for three rim seal purge flow injection rates. Measurements at rotor inlet and exit reveal the impact of the geometrical features on the rim seal exit and main annulus flow field, highlighting regions of reduced aerodynamic losses induced by the modified rim seal design. Measurements at the rotor exit with the PCFs installed show a benefit in the total-to-total stage efficiency up to 0.4% for nominal and high rim seal purge flow rates. The work shows the potential to improve the aerodynamic efficiency by means of a well-designed rim seal exit geometry without losing the potential to block hot gas ingestion from the main annulus.

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