On the Importance of Engine-Representative Models for Fan Flutter Predictions

2018 ◽  
Vol 140 (8) ◽  
Author(s):  
Sina Stapelfeldt ◽  
Mehdi Vahdati
Keyword(s):  
Inlet Temperature ◽  
Pressure System ◽  
Blade Vibration ◽  
Cfd Models ◽  
Numerical Predictions ◽  
Reduced Frequency ◽  
Aerodynamic Properties ◽  
Acoustic Liner ◽  
Flutter Boundary ◽  
Fan Blade

Discrepancies between rig tests and numerical predictions of the flutter boundary for fan blades are usually attributed to the deficiency of computational fluid dynamics (CFD) models for resolving flow at off-design conditions. However, as will be demonstrated in this paper, there are a number of other factors, which can influence the flutter stability of fan blades and lead to differences between measurements and numerical predictions. This research was initiated as a result of inconsistencies between the flutter predictions of two rig fan blades. The numerical results agreed well with rig test data in terms of flutter speed and nodal diameter (ND) for both fans. However, they predicted a significantly higher flutter margin for one of the fans, while measured flutter margins were similar for both blades. A new set of flutter computations including the whole low-pressure system was therefore performed. The new set of computations considered the effects of the acoustic liner and mistuning for both blades. The results of this work indicate that the previous discrepancies between CFD and tests were caused by, first, differences in the effectiveness of the acoustic liner in attenuating the pressure wave created by the blade vibration and second, differences in the level of unintentional mistuning of the two fan blades. In the second part of this research, the effects of blade mis-staggering and inlet temperature on aerodynamic damping were investigated. The data presented in this paper clearly show that manufacturing and environmental uncertainties can play an important role in the flutter stability of a fan blade. They demonstrate that aeroelastic similarity is not necessarily achieved if only aerodynamic properties and the traditional aeroelastic parameters, reduced frequency and mass ratio, are maintained. This emphasizes the importance of engine-representative models, in addition to accurate and validated CFD codes, for the reliable prediction of the flutter boundary.

On the Importance of Engine-Representative Models for Fan Flutter Predictions

2017 ◽  
Author(s):  
Sina Stapelfeldt ◽  
Mehdi Vahdati
Keyword(s):  
Inlet Temperature ◽  
Blade Vibration ◽  
Cfd Models ◽  
Numerical Predictions ◽  
Reduced Frequency ◽  
Aerodynamic Properties ◽  
Acoustic Liner ◽  
Flutter Boundary ◽  
Fan Blade ◽  
Flutter Margin

This paper examines the factors which can result in discrepancies between rig tests and numerical predictions of the flutter boundary for fan blades. Differences are usually attributed to the deficiency of CFD models for resolving the flow at off-design conditions. This work was initiated as a result of inconsistencies between the flutter prediction of two rig fan blades, called here Fan F1 and Fan F2. The numerical results agreed well with the test data in terms of flutter speed and nodal diameter for both fans. However, they predicted a significantly higher flutter margin for F2 than for Fan F1, while rig tests showed that the two blades had similar flutter margins. A new set of flutter computations for both blades using the whole LP domain (intake, fan, OGV and ESS) was therefore performed. The new set of computations considered the effects of the acoustic liner and mistuning for both blades. The results of this work indicate that the previous discrepancies between CFD and tests were due to: 1. Differences in the effectiveness of the acoustic liner in attenuating the pressure wave created by the blade vibration as a result of differences in flutter frequencies between the two fan blades. 2. Differences in the level of unintentional mistuning of the two fan blades due to manufacturing tolerances. In the second part of this research, the effects of blade misstaggering and inlet temperature on aerodynamic damping were investigated. The data presented in this paper clearly show that manufacturing and environmental uncertainties can play an important role in the flutter stability of a fan blade. They demonstrate that aeroelastic similarity is not necessarily achieved if only aerodynamic properties and the traditional aeroelastic parameters, reduced frequency and mass ratio, are maintained. This emphasises the importance of engine-representative models, in addition to an accurate and validated CFD code, for the reliable prediction of the flutter boundary.

Numerical Predictions of Rotating Stall in an Axial Multi-Stage-Compressor

2011 ◽  
Author(s):  
Caetano Peng
Keyword(s):  
Rotating Stall ◽  
Blade Vibration ◽  
Angle Variation ◽  
Cfd Models ◽  
Numerical Studies ◽  
Numerical Predictions ◽  
Multi Stage ◽  
Engine Part ◽  
Stagger Angle ◽  
Variable Stator

This paper describes a numerical investigation of rotating stall in an axial multi-stage compressor using an in-house CFD (Computational Fluid Dynamics) based aeroelasticity code. This study investigates the effects of VSV (variable stator vanes) schedule on the occurrence of rotating stall at engine part-speed. Moreover, the effects of VSV circumferential mis-stagger angles (e.g. vane stagger angle variation) on the inception of rotating stall are also investigated. Virtual pressure probes are used here in the CFD models to extract unsteady pressure levels at locations of interest. These numerical studies have also enabled to evaluate the blade peak displacements due to rotating stall and hence to predict the blade vibration levels. In general, the numerical results would appear to be in line with past experience from rig and development engine data.

Influence of Intake on Fan Blade Flutter

2015 ◽  
Vol 137 (8) ◽  
Author(s):  
Mehdi Vahdati ◽  
Nigel Smith ◽  
Fanzhou Zhao
Keyword(s):  
Correct Prediction ◽  
Blade Vibration ◽  
Reflected Waves ◽  
Reflection Model ◽  
Flutter Analysis ◽  
Flutter Boundary ◽  
Blade Flutter ◽  
Computational Fluid Dynamics Cfd ◽  
Fan Blade ◽  
Insight Into

The main aim of this paper is to study the influence of upstream reflections on flutter of a fan blade. To achieve this goal, flutter analysis of a complete fan assembly with an intake duct and the downstream outlet guide vanes (OGVs) (whole low pressure (LP) domain) is undertaken using a validated computational fluid dynamics (CFD) model. The computed results show good correlation with measured data. Due to space constraints, only upstream (intake) reflections are analyzed in this paper. It will be shown that the correct prediction of flutter boundary for a fan blade requires modeling of the intake and different intakes would produce different flutter boundaries for the same fan blade. However, the “blade only” and intake damping are independent and the total damping can be obtained from the sum of the two contributions. In order to gain further insight into the physics of the problem, the pressure waves created by blade vibration are split into an upstream and a downstream traveling wave in the intake. The splitting of the pressure wave allows one to establish a relationship between the phase and amplitude of the reflected waves and flutter stability of the blade. By using this approach, a simple reflection model can be used to model the intake effects.

Influence of Intake on Fan Blade Flutter

2014 ◽  
Author(s):  
Mehdi Vahdati ◽  
Nigel Smith ◽  
Fanzhou Zhao
Keyword(s):  
Correct Prediction ◽  
Pressure Waves ◽  
Blade Vibration ◽  
Reflected Waves ◽  
Reflection Model ◽  
Flutter Analysis ◽  
Flutter Boundary ◽  
Blade Flutter ◽  
Fan Blade ◽  
Insight Into

The main aim of this paper is to study the influence of upstream reflections on flutter of a fan blade. To achieve this goal, flutter analysis of a complete fan assembly with an intake duct and the downstream OGVs (whole LP domain) is undertaken using a validated CFD model. The computed results show good correlation with measured data. Due to space constraints, only upstream (intake) reflections are analyzed in this paper. It will be shown that the correct prediction of flutter boundary for a fan blade requires modeling of the intake and different intakes would produce different flutter boundaries for the same fan blade. However, the ‘blade only’ and intake damping are independent and the total damping can be obtained from the sum of the two contributions. In order to gain further insight into the physics of the problem, the pressure waves created by blade vibration are split into an upstream and a downstream traveling wave in the intake. The splitting of the pressure wave allows one to establish a relationship between the phase and amplitude of the reflected waves and flutter stability of the blade. By using this approach, a simple reflection model can be used to model the intake effects.

Numerical Investigation of the Cooling Performance on the Endwall With and Without Fillet

2018 ◽  
Author(s):  
Qingzong Xu ◽  
Qiang Du ◽  
Pei Wang ◽  
Jun Liu ◽  
Guang Liu
Keyword(s):  
Secondary Flow ◽  
Turbulence Model ◽  
Film Cooling ◽  
Computational Method ◽  
Inlet Temperature ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Numerical Predictions ◽  
Turbine Vane

High inlet temperature of turbine vane increases the demand of high film cooling effectiveness. Vane endwall region was extensively cooled due to the high and flat exit temperature distribution of combustor. Leakage flow from the combustor-turbine gap was used to cool the endwall region except for preventing hot gas ingestion. Numerical predictions were conducted to investigate the flow structure and adiabatic film cooling effectiveness of endwall region in a linear cascade with vane-endwall junction fillet. The simulations were completed by solving the three-dimensional Reynolds-Averaged Navier-Stokes(RANS) equations with shear stress transport(SST) k-ω turbulence model, meanwhile, the computational method and turbulence model were validated by comparing computational result with the experiment. Three types of linear fillet with the length-to-height ratio of 0.5, 1 and 2, named fillet A, fillet B and fillet C respectively, were studied. In addition, circular fillet with radius of 2mm was compared with linear fillet B. The interrupted slot, produced by changing the way of junction of combustor and turbine vane endwall, is introduced at X/Cax = −0.2 upstream of the vane leading edge. Results showed that fillet can significantly affect the cooling performance on the endwall due to suppressing the strength of the secondary flow. Fillet C presented the best cooling performance comparing to fillet A and fillet B because a portion of the coolant which climbs to the fillet was barely affected by secondary flow. Results also showed the effect of fillet on the total pressure loss. The result indicated that only fillet A slightly decreases endwall loss.

Numerical and Experimental Investigation of the Reynolds Number and Reduced Frequency Effects on Low-Pressure Turbine Airfoils

2021 ◽  
Vol 143 (2) ◽  
Author(s):  
M. Bolinches-Gisbert ◽  
David Cadrecha Robles ◽  
Roque Corral ◽  
Fernando Gisbert
Keyword(s):  
Experimental Data ◽  
Numerical Data ◽  
Low Pressure ◽  
Reconstruction Method ◽  
Low Speed ◽  
Low Pressure Turbine ◽  
Reduced Frequency ◽  
Aerodynamic Properties ◽  
Numerical Solver ◽  
Turbine Airfoils

Abstract This article compares experimental and numerical data for a low-speed high-lift low pressure turbine (LPT) cascade under unsteady flow conditions. Three Reynolds numbers representative of LPTs have been tested, namely, 5 × 104, 105, and 2 × 105; at two reduced frequencies, fr = 0.5 and 1, also representative of LPTs. The experimental data were obtained at the low-speed linear cascade wind tunnel at the Polytechnic University of Madrid using hot wire, Laser Doppler Velocimetry (LDV), and pressure tappings. The numerical solver employs a sixth-order compact scheme based on the flux reconstruction method for spatial discretization and a fourth-order Runge–Kutta method to march in time. The longest case ran 550 h on 40 GPUs to reach a statistically periodic state. Pressure coefficients around the profile, boundary layer profiles and exit cross section distributions of velocity, pressure loss defect, shear Reynolds stress, and angle are compared against high-quality experimental data. Cascade loss and exit angle have also been compared against the experimental data. Very good agreement between experimental and numerical data is seen. The results demonstrate the suitability of the present methodology to predict the aerodynamic properties of unsteady flows around LPT linear cascades accurately.

Improving the Flutter Margin of an Unstable Fan Blade

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
Sina Stapelfeldt ◽  
Mehdi Vahdati
Keyword(s):  
Steady Flow ◽  
Leading Edge ◽  
Measured Data ◽  
Optimization Approach ◽  
Speed Range ◽  
Final Design ◽  
Flutter Boundary ◽  
Fan Blade ◽  
Flutter Margin ◽  
Stagger Angle

The aim of this paper is to introduce design modifications that can be made to improve the flutter stability of a fan blade. A rig fan blade, which suffered flutter in the part-speed range and for which good quality measured data in terms of steady flow and flutter boundary is available, is used for this purpose. The work is carried out numerically using the aeroelasticity code AU3D. Two different approaches are explored: aerodynamic modifications and aero-acoustic modifications. In the first approach, the blade is stabilized by altering the radial distribution of the stagger angle based on the steady flow on the blade. The re-staggering patterns used in this work are therefore particular to the fan blade under investigation. Moreover, the modifications made to the blade are very simple and crude, and more sophisticated methods and/or an optimization approach could be used to achieve the above objectives with a more viable final design. This paper, however, clearly demonstrates how modifying the steady blade aerodynamics can prevent flutter. In the second approach, flutter is removed by drawing bleed air from the casing above the tip of the blade. Only a small amount of bleed (0.2% of the total inlet flow) is extracted such that the effect on the operating point of the fan is small. The purpose of the bleed is merely to attenuate the pressure wave that propagates from the trailing edge to the leading edge of the blade. The results show that extracting bleed over the tip of the fan blade can improve the flutter margin of the fan significantly.

Improving the Flutter Margin of an Unstable Fan Blade

2018 ◽  
Author(s):  
Sina Stapelfeldt ◽  
Mehdi Vahdati
Keyword(s):  
Steady Flow ◽  
Leading Edge ◽  
Measured Data ◽  
Optimization Approach ◽  
Speed Range ◽  
Final Design ◽  
Flutter Boundary ◽  
Fan Blade ◽  
Flutter Margin ◽  
Stagger Angle

The aim of this paper is to introduce design modifications which can be made to improve the flutter stability of a fan blade. A rig fan blade, which suffered from flutter in the part-speed range and for which good quality measured data in terms of steady flow and flutter boundary is available, is used for this purpose. The work is carried out numerically using the aeroelasticity code AU3D. Two different approaches are explored; aerodynamic modifications and aero-acoustic modifications. In the first approach, the blade is stabilized by altering the radial distribution of the stagger angle based on the steady flow on the blade. The re-staggering patterns used in this work are therefore particular to the fan blade under investigation. Moreover, the modifications made to the blade are very simple and crude and more sophisticated methods and/or an optimization approach could be used to achieve the above objectives with a more viable final design. This paper, however, clearly demonstrates how modifying the steady blade aerodynamics can prevent flutter. In the second approach, flutter is removed by drawing bleed air from the casing above the tip of the blade. Only a small amount of bleed (0.2% of the total inlet flow) is extracted such that the effect on the operating point of the fan is small. The purpose of the bleed is merely to attenuate the pressure wave which propagates from the trailing edge to the leading edge of the blade. The results show that extracting bleed over the tip of the fan blade can improve the flutter margin of the fan significantly.

Test Validation of Flamelet Model Predictions of NOx

1999 ◽  
Author(s):  
Yu. Buriko ◽  
V. Zakharov ◽  
A. Belokon ◽  
G. Opdyke
Keyword(s):  
Gas Turbines ◽  
Prediction Method ◽  
Inlet Temperature ◽  
Nox Emissions ◽  
Load Curve ◽  
Flamelet Model ◽  
Numerical Predictions ◽  
Air Supply ◽  
Model Predictions ◽  
The Relationship

Calculations of NOx emissions were made for the original high pressure combustor and for the original and a modified design of the low pressure combustor used in a Compressed Air Energy Storage (CAES) plant. All were typical diffusion flame combustors. Since a CAES plant has an independent air supply, the relationship between combustor inlet temperature and pressure is not typical for gas turbines, and the pressure level for the HP combustor is unusually high (up to 4.5 MPa). Vitiated air from HP combustor exhaust is used as combustion air in the LP combustor. The NOx emissions prediction method, which was used, for calculations is based on a flamelet model which takes detailed kinetic schemes for fuel oxidation, NOx generation and turbulence/chemistry interaction into account. Site measurements over the entire load curve confirmed the numerical predictions for both the original combustors and the newly developed LP combustor design.

A Framework for Flutter Clearance of Aeroengine Blades

2001 ◽  
Author(s):  
Asif Khalak
Keyword(s):  
Test Procedure ◽  
Inlet Temperature ◽  
Mass Ratio ◽  
Reduced Frequency ◽  
Damping Parameter ◽  
Individual Effects ◽  
Performance Effects ◽  
The Individual ◽  
Operability Assessment ◽  
Selection Of

A framework for flutter operability assessment, based upon a new set of similarity parameters, has been developed. This set consists of four parameters which embrace both the performance characteristics in terms of corrected mass flow and corrected speed, and the flight condition in terms of inlet temperature and density (or, equivalently, inlet pressure). It is shown that a combined mass-damping parameter, g/ρ*, novel in the field of turbomachinery aeroelasticity, can summarize the individual effects of mechanical damping, g, and blade mass ratio, μ. A particular selection of four nondimensional parameters, including g/ρ* and a compressible reduced frequency parameter, K*, allows for a decoupling of corrected performance effects from purely aeroelastic effects, for a given machine and a specific modeshape. This view of flutter operability is applied to the analysis of full-scale engine data. The data exhibits the trend that increasing K* and increasing g/ρ* have stabilizing effects, which is consistent with previous work in flutter stability. We propose that these trends hold generally, and apply the trends towards constructing a flutter clearance methodology, a test procedure which satisfies the requirements for comprehensive flutter stability testing.

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