Transonic Fan Blade Redesign Approach to Attenuate Nonsynchronous Vibration

2021 ◽  
Author(s):  
Yaozhi Lu ◽  
Bharat Lad ◽  
Mehdi Vahdati
Keyword(s):  
High Cycle Fatigue ◽  
Wave Pattern ◽  
Travelling Wave ◽  
Peak Efficiency ◽  
Aerodynamic Loads ◽  
Manufacturing Tolerance ◽  
Unsteady Effect ◽  
Fan Blade ◽  
Transonic Fan ◽  
Stagger Angle

Abstract Due to manufacturing tolerance and deterioration during operation, different blades in a fan assembly exhibit geometric variability. This leads to asymmetry which will be amplified in the running geometry by centrifugal and aerodynamic loads. This study investigates a phenomenon known as Alternate Passage Divergence (APD), where the blade untwist creates an alternating pattern in passage geometry and stagger angle around the circumference. After the formation of alternating tip stagger pattern, APD's unsteady effect, APD-induced Non-Synchronous Vibration (APD-NSV), can cause the blades from one group to switch to the other creating a travelling wave pattern around the circumference. Thus, it can potentially lead to high cycle fatigue issues. More importantly, this phenomenon occurs close to, or at, peak efficiency conditions and can significantly reduce overall efficiency. Therefore, it is vital to attenuate the NSV behaviour. In this study, an redesign approach is investigated.

Transonic Fan Blade Redesign Approach to Attenuate Nonsynchronous Vibration

2020 ◽  
Author(s):  
Yaozhi Lu ◽  
Bharat Lad ◽  
Mehdi Vahdati
Keyword(s):  
High Cycle Fatigue ◽  
Wave Pattern ◽  
Travelling Wave ◽  
Peak Efficiency ◽  
Aerodynamic Loads ◽  
Manufacturing Tolerance ◽  
Unsteady Effect ◽  
Fan Blade ◽  
Transonic Fan ◽  
Stagger Angle

Abstract Due to manufacturing tolerance and deterioration during operation, different blades in a fan assembly exhibit geometric variability. This leads to asymmetry which will be amplified in the running geometry by centrifugal and aerodynamic loads. This study investigates a phenomenon known as Alternate Passage Divergence (APD), where the blade untwist creates an alternating pattern in passage geometry and stagger angle around the circumference. After the formation of alternating tip stagger pattern, APD’s unsteady effect, APD-induced Non-Synchronous Vibration (APD-NSV), can cause the blades from one group to switch to the other creating a travelling wave pattern around the circumference. Thus, it can potentially lead to high cycle fatigue issues. More importantly, this phenomenon occurs close to, or at, peak efficiency conditions and can significantly reduce overall efficiency. Therefore, it is vital to attenuate the NSV behaviour. In this study, an redesign approach is investigated.

Nonsynchronous Vibration Associated With Transonic Fan Blade Untwist

2019 ◽  
Author(s):  
Yaozhi Lu ◽  
Bharat Lad ◽  
Mehdi Vahdati ◽  
Sina C. Stapelfeldt
Keyword(s):  
Underlying Mechanism ◽  
Wave Pattern ◽  
Travelling Wave ◽  
Manufacturing Tolerance ◽  
Numerical Assessment ◽  
Aero Engine ◽  
Unsteady Effect ◽  
Fan Blade ◽  
Transonic Fan ◽  
Stagger Angle

Abstract Due to manufacturing tolerance and deterioration during operation, fan blades in the aero-engine exhibit geometric variability. This leads to asymmetry in the assembly which will be amplified in the running geometry by centrifugal and aerodynamic loads. This study investigates a phenomenon known as Alternative Passage Divergence (APD), where the blade untwist creates an alternating pattern in passage geometry and stagger angle around the circumference, resulting in two groups of blades. This phenomenon occurs close to, or at, peak efficiency conditions and can significantly reduce overall efficiency. This study focuses on a type of non-integral vibration which occurs during APD. After the formation of alternating tip stagger pattern, APDs unsteady effect can cause the blades from one group to switch to the other, creating a travelling wave pattern around the circumference.It was found from numerical assessment on a randomly mis-staggered assembly that real engines can potentially experience such travelling disturbance and suffer fatigue damage. An idealised case is used to capture the bulk behaviour from the more complex cases in real engines and to decipher the underlying mechanism of this travelling disturbance. The results indicate that the driving force originates from the interaction between passage shock displacement and the passage geometry.

Detecting Nonsynchronous Vibration in Transonic Fans Using Machine Learning Techniques

2020 ◽  
Author(s):  
Yaozhi Lu ◽  
Mehdi Vahdati
Keyword(s):  
Machine Learning ◽  
Wave Pattern ◽  
Travelling Wave ◽  
Machine Learning Techniques ◽  
Manufacturing Tolerance ◽  
Learning Techniques ◽  
Unsteady Effect ◽  
Two Parameters ◽  
Stagger Angle ◽  
Random Nature

Abstract Due to manufacturing tolerance and deterioration during operation, different blades in a fan assembly exhibit geometric variability. This leads to asymmetry which will be amplified in the running geometry by centrifugal and aerodynamic loads. This study investigates a phenomenon known as Alternate Passage Divergence (APD), where the blade untwist creates an alternating pattern in passage geometry and stagger angle around the circumference. After the formation of alternating tip stagger pattern, APD’s unsteady effect, APD-induced Non-Synchronous Vibration (APD-NSV, abbreviated as NSV), can cause the blades from one group to switch to the other creating a travelling wave pattern around the circumference. Thus, it can potentially lead to high cycle fatigue issues. More importantly, this phenomenon occurs close to, or at, peak efficiency conditions and can significantly reduce overall efficiency. Therefore, it is vital to attenuate the NSV behaviour. The random nature of mis-staggering patterns complicate the evolution of NSV significantly. Thus, machine learning techniques are used to analyse mis-stagger patterns to identify patterns that can lead to NSV and thus help avoid it. Numerical results from 113 numerical cases (1.6 million CPU hours) are used to train and test the classifier. From the results, two parameters contributing to NSV behaviour have been identified with one of them enhancing the understanding found in the previous study.

scholarly journals Effect of Geometry Variability on Transonic Fan Blade Untwist †

2019 ◽  
Vol 4 (3) ◽  
pp. 24
Author(s):  
Yaozhi Lu ◽  
Bharat Lad ◽  
Jeff Green ◽  
Sina Stapelfeldt ◽  
Mehdi Vahdati
Keyword(s):  
High Cycle Fatigue ◽  
Related Phenomenon ◽  
Peak Efficiency ◽  
Fan Performance ◽  
Manufacturing Tolerance ◽  
Efficiency Condition ◽  
Fatigue Characteristics ◽  
Fan Blade ◽  
Adverse Influence ◽  
Transonic Fan

Due to manufacturing tolerance and deterioration during operation, fan blades in the same engine exhibit geometric variability. The absence of symmetry will inevitably exacerbate and contribute to the complexities of running geometry prediction as the blade variability is bound to be amplified by aerodynamic and centrifugal loading. In this study, we aim to address the fan blade untwist related phenomenon known as alternate passage divergence (APD). As the name suggests, APD manifests as alternating passage geometry (and hence alternating tip stagger pattern) when the fan stage is operating close to/at peak efficiency condition. APD can introduce adverse influence on fan performance, aeroacoustics behaviour, and high cycle fatigue characteristics of the blade. The main objective of the study is to identify the parameters contributing to the APD phenomenon. In this study, the APD behaviours of two transonic fan blade designs are compared.

Effect Of Manufacturing Tolerance In Flow Past A Compressor Blade

2021 ◽  
pp. 1-24
Author(s):  
Venkatesh Suriyanarayanan ◽  
Quentin Rendu ◽  
Mehdi Vahdati ◽  
Loic Salles
Keyword(s):  
Pressure Ratio ◽  
Compressor Blade ◽  
Test Case ◽  
Optimal Arrangement ◽  
Stability Boundaries ◽  
Manufacturing Tolerance ◽  
Simulation Based ◽  
The Stability ◽  
Transonic Fan ◽  
Stagger Angle

Abstract This paper presents the effect of manufacturing tolerance on performance and stability boundaries of a transonic fan using a RANS simulation. The effect of tip gap and stagger angle was analysed through a series of single passage and double passage simulation; based on which an optimal arrangement was proposed for random tip gap and random stagger angle in case of a whole annulus rotor. All simulations were carried out using NASA rotor 67 as a test case and AU3D an in-house CFD solver. Results illustrate that the stagger angle mainly affects efficiency and hence its circumferential variation must be as smooth as possible. Furthermore, the tip gap affects the stability boundaries, pressure ratio and efficiency. Hence its optimal configuration mandates that the blades be configured in a zigzag arrangement around the annulus i.e. larger tip gap between two smaller ones.

Flutter of a Fan Blade in Supersonic Axial Flow

1989 ◽  
Vol 111 (4) ◽  
pp. 462-467 ◽  
Author(s):  
R. E. Kielb ◽  
J. K. Ramsey
Keyword(s):  
Mode Coupling ◽  
Axial Flow ◽  
Axial Flow Fan ◽  
Compressor Blades ◽  
Torsional Mode ◽  
Aerodynamic Loads ◽  
Aeroelastic Model ◽  
Parametric Studies ◽  
Fan Blade ◽  
Stagger Angle

An application of a simple aeroelastic model to an advanced supersonic axial flow fan is presented. Lane’s cascade theory is used to determine the unsteady aerodynamic loads. Parametric studies are performed to determine the effects of mode coupling, Mach number, damping, pitching axis location, solidity, stagger angle, and mistuning. The results show that supersonic axial flow fan and compressor blades are susceptible to a strong torsional mode flutter having critical reduced velocities that can be less than one.

Transonic Fan Blade Redesign Approach to Attenuate Nonsynchronous Vibration

2021 ◽  
Author(s):  
Yaozhi Lu ◽  
Bharat Lad ◽  
Mehdi Vahdati
Keyword(s):  
Fan Blade ◽  
Transonic Fan

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.

scholarly journals Investigation of Flow Phenomena in a Transonic Fan Rotor Using Laser Anemometry

1985 ◽  
Vol 107 (2) ◽  
pp. 427-435 ◽  
Author(s):  
A. J. Strazisar
Keyword(s):  
Pressure Rise ◽  
Peak Efficiency ◽  
Laser Anemometry ◽  
Low Aspect Ratio ◽  
Laser Anemometer ◽  
Flow Phenomena ◽  
Shock System ◽  
Shock Oscillation ◽  
Transonic Fan ◽  
System Geometry

Several flow phenomena, including flow field periodicity, rotor shock oscillation, and rotor shock system geometry have been investigated in a transonic low aspect ratio fan rotor using laser anemometry. Flow periodicity is found to increase with increasing rotor pressure rise and to correlate with blade geometry variations. Analysis of time-accurate laser anemometer data indicates that the rotor shock oscillates about its mean location with an amplitude of 3–4 percent of rotor chord. The shock surface is nearly two-dimensional for levels of rotor pressure rise at and above the peak efficiency level but becomes more complex for lower levels of pressure rise. Spanwise shock lean generates radial flows due to streamline deflection in the hub-to-shroud streamsurface.

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.

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