On the Prediction of Unsteady Forces on Gas Turbine Blades: Part 2—Analysis of the Results

1992 ◽  
Vol 114 (1) ◽  
pp. 123-131 ◽  
Author(s):  
T. Korakianitis
Keyword(s):  
Potential Flow ◽  
Turbine Blades ◽  
Interaction Mechanism ◽  
Rotor Blades ◽  
Unsteady Forces ◽  
Flow Angle ◽  
Gas Turbine Blades ◽  
Flow Interaction ◽  
Unsteady Force ◽  
Outlet Flow

This article investigates the generation of unsteady forces on turbine blades due to potential-flow interaction and viscous-wake interaction from upstream blade rows. A computer program is used to calculate the unsteady forces on the rotor blades. Results for typical stator-to-rotor-pitch ratios and stator outlet-flow angles show that the first spatial harmonic of the unsteady force may decrease for higher stator-to-rotor-pitch ratios, while the higher spatial harmonics increase. This (apparently counterintuitive) trend for the first harmonic, and other blade row interaction issues, are explained by considering the mechanisms by which the viscous wakes and the potential-flow interaction affect the flow field. The interaction mechanism is shown to vary with the stator-to-rotor-pitch ratio and with the outlet flow angle of the stator. It is also shown that varying the axial gap between rotor and stator can minimize the magnitude of the unsteady part of the forces generated by the combined effects of the two interactions.

On the Prediction of Unsteady Forces on Gas-Turbine Blades: Part 1 — Typical Results and Potential-Flow-Interaction Effects

1988 ◽  
Author(s):  
Theodosios P. Korakianitis
Keyword(s):  
Computer Program ◽  
Potential Flow ◽  
Turbine Blades ◽  
Unsteady Forces ◽  
Flow Angle ◽  
Flow Calculation ◽  
Gas Turbine Blades ◽  
Flow Interaction ◽  
Unsteady Force ◽  
Outlet Flow

This paper is a contribution to the study of the generation of unsteady forces on turbine blades due to potential-flow interaction and viscous-wake interaction from upstream blade rows. A computer program is used to compute the unsteady forces on a rotor. The accuracy of the computer program is tested by comparing the results of a steady-flow calculation case and of an unsteady-flow calculation case with theory and experiment respectively. Results are shown for typical stator-to-rotor-pitch ratios and stator outlet-flow angles. These results show that the first spatial harmonic of the unsteady force may decrease for higher stator-to-rotor-pitch ratios. This trend is explained by considering the mechanisms by which the unsteady forces are generated. In this paper the mechanism by which the potential-flow interaction affects the flow field to generate these unsteady forces is shown to vary with the stator-to-rotor-pitch ratio and with the outlet flow angle of the stator.

scholarly journals On the Prediction of Unsteady Forces on Gas-Turbine Blades: Part 2 — Viscous-Wake-Interaction and Axial-Gap Effects

1988 ◽  
Author(s):  
Theodosios P. Korakianitis
Keyword(s):  
Potential Flow ◽  
Turbine Blades ◽  
Unsteady Forces ◽  
Flow Angle ◽  
Gas Turbine Blades ◽  
Flow Interaction ◽  
Wake Interaction ◽  
Unsteady Force ◽  
Outlet Flow ◽  
Pitch Ratio

This paper is a contribution to the study of the generation of unsteady forces on turbine blades due to viscous wake interaction and potential-flow interaction from upstream blade rows. A computer program is used to compute the unsteady forces on a rotor. Typical results for isolated viscous-wake interaction (no potential-flow interaction) are shown. These results indicate that the first spatial harmonic of the unsteady force may decrease for higher stator-to-rotor-pitch ratios. This trend is explained by considering the mechanisms by which the unsteady forces are generated. The mechanism by which the viscous wakes affect the flow field to generate these unsteady forces is shown to vary with the stator-to-rotor-pitch ratio and with the outlet flow angle of the stator. It is also shown that by varying the axial gap between rotor and stator one can attempt to minimize the magnitude of the unsteady part of the forces generated by the combined effects of viscous-wake interaction and potential-flow interaction.

On the Prediction of Unsteady Forces on Gas Turbine Blades: Part 1—Description of the Approach

1992 ◽  
Vol 114 (1) ◽  
pp. 114-122 ◽  
Author(s):  
T. Korakianitis
Keyword(s):  
Flow Field ◽  
Potential Flow ◽  
Turbine Blades ◽  
Turbine Rotor ◽  
Rotor Blades ◽  
Flow Disturbance ◽  
Unsteady Forces ◽  
Gas Turbine Blades ◽  
Wake Interaction ◽  
Flow Case

This article investigates the generation of unsteady forces on turbine blades due to potential-flow interaction and viscous-wake interaction from upstream blade rows. A computer program is used to calculate the unsteady forces on the rotor blades. Results are obtained by modeling the effects of the stator viscous wake and the stator potential-flow field on the rotor flow field. The results for one steady and one unsteady flow case are compared with known analytical and experimental data. The amplitudes for the two types of interaction are based on an analysis of available viscous wake data, on measurements of the potential-flow disturbance downstream of typical turbine stators, and on a parametric study of the effects of the amplitudes on the results of the unsteady forces generated on a typical turbine rotor cascade.

Unsteady Forces of Rotor Blades in Full and Partial Admission Turbines

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Narmin Baagherzadeh Hushmandi ◽  
Jens E. Fridh ◽  
Torsten H. Fransson
Keyword(s):  
Pressure Field ◽  
Dynamic Pressure ◽  
Turbine Blades ◽  
Leading Edge ◽  
Rotational Frequency ◽  
Rotor Blades ◽  
Computational Domain ◽  
Unsteady Forces ◽  
Partial Admission ◽  
Unsteady Force

A numerical and experimental study of partial admission in a low reaction two-stage axial air test turbine is performed in this paper. In order to model one part load configuration, corresponding to zero flow in one of the admission arcs, the inlet was blocked at one segmental arc, at the leading edge of the first stage guide vanes. Due to the unsymmetrical geometry, the full annulus of the turbine was modeled numerically. The computational domain contained the shroud and disk cavities. The full admission turbine configuration was also modeled for reference comparisons. Computed unsteady forces of the first stage rotor blades showed cyclic change both in magnitude and direction while moving around the circumference. Unsteady forces of first stage rotor blades were plotted in the frequency domain using Fourier analysis. The largest amplitudes caused by partial admission were at first and second multiples of rotational frequency due to the existence of single blockage and change in the force direction. Unsteady forces of rotating blades in a partial admission turbine could cause unexpected failures in operation; therefore, knowledge about the frequency content of the unsteady force vector and the related amplitudes is vital to the design process of partial admission turbine blades. The pressure plots showed that the nonuniformity in the static pressure field decreases considerably downstream of the second stage’s stator row, while the nonuniformity in the dynamic pressure field is still large. The numerical results between the first stage’s stator and rotor rows showed that the leakage flow leaves the blade path down into the disk cavity in the admitted sector and re-enters downstream of the blocked channel. This process compensates for the sudden pressure drop downstream of the blockage but reduces the momentum of the main flow.

Heat Transfer and Pressure Drop in Pin-Fin Trapezoidal Ducts

1999 ◽  
Vol 121 (2) ◽  
pp. 264-271 ◽  
Author(s):  
J.-J. Hwang ◽  
D.-Y. Lai ◽  
Y.-P. Tsia
Keyword(s):  
Nusselt Number ◽  
Pressure Drop ◽  
Turbine Blades ◽  
Total Flow ◽  
Gas Turbine Blades ◽  
Pin Fin ◽  
Flow Reynolds Number ◽  
Outlet Flow ◽  
Pin Configuration ◽  
Flow Duct

Experiments are conducted to determine the log-mean averaged Nusselt number and overall pressure-drop coefficient in a pin-fin trapezoidal duct that models the cooling passages in modern gas turbine blades. The effects of pin arrangement (in-line and staggered), flow Reynolds number (6,000 ≦ Re ≦ 40,000) and ratio of lateral-to-total flow rate (0 ≦ ε ≦ 1.0) are examined. The results of smooth trapezoidal ducts without pin arrays are also obtained for comparison. It is found that, for the single-outlet-flow duct, the log-mean averaged Nusselt number in the pin-fin trapezoidal duct with lateral outlet is insensitive to the pin arrangement, which is higher than that in straight-outlet-flow duct with the corresponding pin array. As for the trapezoidal ducts having both outlets, the log-mean averaged Nusselt number has a local minimum value at about ε = 0.3. After about ε ≧ 0.8, the log-mean averaged Nusselt number is nearly independent of the pin configuration. Moreover, the staggered pin array pays more pressure-drop penalty as compared with the in-line pin array in the straight-outlet-flow duct; however, in the lateral-outlet-flow duct, the in-line and staggered pin arrays yield almost the same overall pressure drop.

On the Propagation of Viscous Wakes and Potential Flow in Axial-Turbine Cascades

1993 ◽  
Vol 115 (1) ◽  
pp. 118-127 ◽  
Author(s):  
T. Korakianitis
Keyword(s):  
Flow Field ◽  
Potential Flow ◽  
Leading Edge ◽  
Local Pressure ◽  
Flow Disturbance ◽  
Unsteady Forces ◽  
Flow Interaction ◽  
Wake Interaction ◽  
Pitch Ratio ◽  
Relative Flow

This paper investigates the propagation of pressure disturbances due to potential-flow interaction and viscous-wake interaction from upstream blade rows in axial-turbine-blade rotor cascades. Results are obtained by modeling the effects of the upstream stator viscous wake and potential-flow fields as incoming disturbances on the downstream rotor flow field, where the computations are performed. A computer program is used to calculate the unsteady rotor flow fields. The amplitudes for the rotor inlet distortions due to the two types of interaction are based on a review of available experimental and computational data. We study the propagation of the isolated potential-flow interaction (no viscous-wake interaction), of the isolated viscous wake interaction (no potential-flow interaction), and of the combination of interactions. The discussion uses as example a lightly loaded cascade for a stator-to-rotor-pitch ratio R = 2. We examine the relative magnitudes of the unsteady forces for two different stator-exit angles. We also explain the expected differences when the stator-to-rotor pitch ratio is decreased (to R = 1) and increased (to R = 4). We offer new and previously unpublished explanations of the mechanisms of generation of unsteady forces on the rotor blades. The potential flow field of the rotor cuts into the potential flow field of the stator. After the potential-flow disturbance from the stator is cut into a rotor cascade, it propagates into the relative flow field of the rotor passage as a potential-flow disturbance superimposed on the rotor-relative flow. The potential flow field of the rotor near the leading edge and the leading edge itself cut into the wake and generate two counterrotating vortical patterns flanking the wake centerline in the passage. The vortical pattern upstream of the wake centerline generates an increase in the local pressure (and in the forces acting on the sides of the passage). The vortical pattern downstream of the wake centerline generates a decrease in the local pressure (and in the forces acting on the sides of the passage). The resulting unsteady forces on the blades are generated by the combined (additive) interaction of the two disturbances.

Degradation of Protective Al - Si Coatings during Exploitation of Gas Turbine Blades

2007 ◽  
Vol 567-568 ◽  
pp. 309-312 ◽  
Author(s):  
Marta Kianicová ◽  
Jaroslav Pokluda
Keyword(s):  
Turbine Blades ◽  
High Temperature Corrosion ◽  
Rotor Blades ◽  
Aircraft Engines ◽  
Relative Thickness ◽  
Surface Layers ◽  
Gas Turbine Blades ◽  
Oxide Phases ◽  
Exploitation Parameter ◽  
Sudden Decrease

Diffusion Al-Si coatings are often used to protect rotor blades of aircraft engines against high-temperature corrosion in environments containing sulfur compounds. Besides other microstructural changes, the degradation of AlSi layers can be indicated by an increasing amount of surface oxide phases and changes in parameters of the layer geometry. In practice, the timetemperature area beyond a critical temperature of the outgoing gas is used as an empirical exploitation parameter D indicating a degradation level. The efficiency of such approach was investigated by analyzing degradation features in the surface layers of rotor blades after exploitations corresponding to different values of D. Determined simple relationships between the relative thickness of degraded layer and the parameter D verify the methodology and yield its clear geometrical interpretation. However, this method fails to provide reasonable information in case when the gas is burning outside the combustion chamber due to a sudden decrease of turbine revolutions.

On the Propagation of Viscous Wakes and Potential Flow in Axial-Turbine Cascades

1991 ◽  
Author(s):  
Theodosios Korakianitis
Keyword(s):  
Flow Field ◽  
Potential Flow ◽  
Leading Edge ◽  
Local Pressure ◽  
Flow Disturbance ◽  
Unsteady Forces ◽  
Axial Turbine ◽  
Flow Interaction ◽  
Wake Interaction ◽  
Pitch Ratio

This paper investigates the propagation of pressure disturbances due to potential-flow interaction and viscous-wake interaction from upstream blade rows in axial-turbine-blade rotor cascades. Results are obtained by modeling the effects of the stator viscous wake and the stator potential-flow field on the rotor flow field. A computer program is used to calculate the unsteady flow fields. The amplitudes for the two types of interaction are based on a review of available experimental and computational data. We study the propagation of the isolated potential-flow interaction (no viscous-wake interaction), of the isolated viscous wake interaction (no potential-flow interaction), and of the combination of interactions. The discussion uses as example a lightly-loaded cascade for a stator-to-rotor-pitch ratio R = 2. We examine the relative magnitudes of the unsteady forces for two different stator-exit angles. We also explain the expected differences when the stator-to-rotor pitch ratio is decreased (to R = 1) and increased (to R = 4). We offer new and previously unpublished explanations of the mechanisms of generation of unsteady forces on the blades. The potential flow field of the rotor cuts into the potential flow field of the stator. After the potential-flow disturbance from the stator is cut into a rotor cascade, it propagates into the relative flow field of the rotor passage as a potential-flow disturbance. The potential flow field of the rotor near the leading edge and the leading edge itself cut into the wake and generate two counter-rotating vortical patterns flanking the wake centerline in the passage. The vortical pattern upstream of the wake centerline generates an increase in the local pressure (and in the forces acting on the sides of the passage). The vortical pattern downstream of the wake centerline generates a decrease in the local pressure (and in the forces acting on the sides of the passage). The resulting unsteady forces on the blades are generated by the combined (additive) interaction of the two disturbances.

scholarly journals Enhancement of Free Vortex Filament Method for Aerodynamic Loads on Rotor Blades

2017 ◽  
Vol 139 (3) ◽  
Author(s):  
Hamidreza Abedi ◽  
Lars Davidson ◽  
Spyros Voutsinas
Keyword(s):  
Wind Turbine ◽  
Potential Flow ◽  
Turbine Blades ◽  
Boundary Layer Separation ◽  
Operating Conditions ◽  
Rotor Blades ◽  
Dynamic Stall ◽  
Aerodynamic Loads ◽  
Operational Conditions ◽  
Blade Element

The aerodynamics of a wind turbine is governed by the flow around the rotor, where the prediction of air loads on rotor blades in different operational conditions and its relation to rotor structural dynamics is one of the most important challenges in wind turbine rotor blade design. Because of the unsteady flow field around wind turbine blades, prediction of aerodynamic loads with high level of accuracy is difficult and increases the uncertainty of load calculations. An in-house vortex lattice free wake (VLFW) code, based on the inviscid, incompressible, and irrotational flow (potential flow), was developed to study the aerodynamic loads. Since it is based on the potential flow, it cannot be used to predict viscous phenomena such as drag and boundary layer separation. Therefore, it must be coupled to tabulated airfoil data to take the viscosity effects into account. Additionally, a dynamic approach must be introduced to modify the aerodynamic coefficients for unsteady operating conditions. This approach, which is called dynamic stall, adjusts the lift, the drag, and the moment coefficients for each blade element on the basis of the two-dimensional (2D) static airfoil data together with the correction for separated flow. Two different turbines, NREL and MEXICO, are used in the simulations. Predicted normal and tangential forces using the VLFW method are compared with the blade element momentum (BEM) method, the GENUVP code, and the MEXICO wind tunnel measurements. The results show that coupling to the 2D static airfoil data improves the load and power predictions while employing the dynamic stall model to take the time-varying operating conditions into consideration is crucial.

Rainbow Field Test of Coatings for Hot Corrosion Protection of Gas Turbine Blades and Vanes: I — Blade Coatings

1989 ◽  
Author(s):  
Mark Van Roode ◽  
Jose Aurrecoechea
Keyword(s):  
Gas Turbine ◽  
Field Test ◽  
Coating Thickness ◽  
Hot Corrosion ◽  
Turbine Blades ◽  
Rotor Blades ◽  
Lower Grade ◽  
Corrosion Morphology ◽  
Metallographic Examination ◽  
Gas Turbine Blades

A rainbow field test sponsored by the Electric Power Research Institute (EPRI) under contract RP2465-1 was performed to evaluate the comparative hot corrosion resistance of commercially available coatings for gas turbine blades and vanes. The 10,307-hr field test was carried out on a Solar Turbines Incorporated Centaur T-4000 gas turbine operating on a lower grade liquid fuel at the Favianca site of the Owens-Illinois, Inc. glass manufacturing facility in Valera, Venezuela. This paper reviews the results of an evaluation of the performance of three modified aluminides, three MCrAlY overlays, and one duplex NiCoCrAlY/ZrO2-2OY2O3 overlay applied as coatings to the first-stage MAR-M421 and IN-738LC rotor blades, Visual and metallographic examination and remnant coating thickness measurements established that the MCrAlY overlay coatings were generally more effective than a Cr-aluminide and two Pt-aluminides protecting the first-stage blades. Individual differences between the various coatings were established. A remnant coating thickness index (RCTI) was defined to express coating survival and protectiveness quantitatively. The results of blade airfoil temperature estimates were correlated with the hot corrosion morphology.

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