Flutter of Swept Fan Blades

1985 ◽  
Vol 107 (2) ◽  
pp. 394-398
Author(s):  
R. E. Kielb ◽  
K. R. V. Kaza
Keyword(s):  
Detrimental Effect ◽  
Structural Model ◽  
Aerodynamic Loads ◽  
Unsteady Aerodynamic ◽  
Aeroelastic Analysis ◽  
Flutter Analysis ◽  
Blade Flutter ◽  
Fan Blade ◽  
Element Technique ◽  
Nonuniform Beam

The purpose of the research presented in this paper is to study the effect of sweep on fan blade flutter by applying the analytical methods developed for aeroelastic analysis of advanced turboprops. Two methods are used. The first method utilizes an approximate structural model in which the blade is represented by a swept, nonuniform beam. The second method utilizes a finite element technique to conduct modal flutter analysis. For both methods, the unsteady aerodynamic loads are calculated using two-dimensional cascade theories that are modified to account for sweep. An advanced fan stage is analyzed with 0, 15, and 30 deg of sweep. It is shown that sweep has a beneficial effect on predominantly torsional flutter and a detrimental effect on predominantly bending flutter. This detrimental effect is shown to be significantly destabilizing for 30 deg of sweep.

Annular Cascade Study of Low Back-Pressure Supersonic Fan Blade Flutter

1990 ◽  
Vol 112 (4) ◽  
pp. 768-777 ◽  
Author(s):  
H. Kobayashi
Keyword(s):  
Back Pressure ◽  
Low Back ◽  
Aerodynamic Forces ◽  
Unsteady Aerodynamic ◽  
Reduced Frequency ◽  
Blade Flutter ◽  
Fan Blade ◽  
Cascade Flutter ◽  
Annular Cascade ◽  
Phase Angles

Low back-pressure supersonic fan blade flutter in the torsional mode was examined using a controlled-oscillating annular cascade test facility. Precise data of unsteady aerodynamic forces generated by shock wave movement, due to blade oscillation, and the previously measured data of chordwise distributions of unsteady aerodynamic forces acting on an oscillating blade, were joined and, then, the nature of cascade flutter was evaluated. These unsteady aerodynamic forces were measured by direct and indirect pressure measuring methods. Our experiments covered a range of reduced frequencies based on a semichord from 0.0375 to 0.547, six interblade phase angles, and inlet flow velocities from subsonic to supersonic flow. The occurrence of unstalled cascade flutter in relation to reduced frequency, interblade phase angle, and inlet flow velocity was clarified, including the role of unsteady aerodynamic blade surface forces on flutter. Reduced frequency of the flutter boundary increased greatly when the blade suction surface flow became transonic flow. Interblade phase angles that caused flutter were in the range from 40 to 160 deg for flow fields ranging from high subsonic to supersonic. Shock wave movement due to blade oscillation generated markedly large unsteady aerodynamic forces which stimulated blade oscillation.

Aerolelastic Analysis of a Thin-Walled Composite Aircraft Wing With an External Store Subjected to a Follower Force

2014 ◽  
Author(s):  
Alev Kacar Aksongur ◽  
Seher Eken ◽  
Metin O. Kaya
Keyword(s):  
Transverse Shear ◽  
Structural Model ◽  
Follower Force ◽  
Beam Model ◽  
Aircraft Wing ◽  
Sweep Angle ◽  
Aerodynamic Loads ◽  
Unsteady Aerodynamic ◽  
Thin Walled ◽  
The Time Domain

This study reports dynamic aeroelastic analyses of an aircraft wing with an attached mass subjected a lateral follower force in an incompressible flow. A swept thin-walled composite beam with a biconvex cross-section is used as the structural model that incorporates a number of non-classical effects such as material anisotropy, transverse shear deformation and warping restraint. A symmetric lay-up configuration i.e. circumferentially asymmetric stiffness (CAS) is further adapted to this model to generate the coupled motion of flapwise bending-torsion-transverse shear. For this beam model, the unsteady aerodynamic loads are expressed using Wagners function in the time-domain as well as using Theodorsen function in the frequency-domain. The flutter speeds are evaluated for several ply angles and the effects of follower force, transverse shear, fiber-orientation and sweep angle on the aeroelastic instabilities are further discussed.

Mechanisms for Wide-Chord Fan Blade Flutter

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Mehdi Vahdati ◽  
George Simpson ◽  
Mehmet Imregun
Keyword(s):  
Flow Separation ◽  
Pressure Wave ◽  
Geometric Features ◽  
The Third ◽  
Reflected Wave ◽  
Flutter Analysis ◽  
Parametric Studies ◽  
Blade Flutter ◽  
Stall Flutter ◽  
Fan Blade

This paper describes a detailed wide-chord fan blade flutter analysis with emphasis on flutter bite. The same fan was used with three different intakes of increasing complexity to explain flutter mechanisms. Two types of flutter, namely, stall and acoustic flutters, were identified. The first intake is a uniform cylinder, in which there are no acoustic reflections. Only the stall flutter, which is driven by flow separation, can exist in this case. The second intake, based on the first one, has a “bump” feature to reflect the fan’s forward pressure wave at a known location so that detailed parametric studies can be undertaken. The analysis revealed a mechanism for acoustic flutter, which is driven by the phase of the reflected wave. The third intake has the typical geometric features of a flight intake. The results indicate that flutter bite occurs when both stall and acoustic flutters happen at the same speed. It is also found that blade stiffening has no effect on aero-acoustic flutter.

Annular Cascade Study of Low Back-Pressure Supersonic Fan Blade Flutter

1989 ◽  
Author(s):  
Hiroshi Kobayashi
Keyword(s):  
Back Pressure ◽  
Low Back ◽  
Aerodynamic Forces ◽  
Unsteady Aerodynamic ◽  
Reduced Frequency ◽  
Blade Flutter ◽  
Fan Blade ◽  
Cascade Flutter ◽  
Annular Cascade ◽  
Phase Angles

Low back-pressure supersonic fan blade flutter in the torsional mode was examined using a controlled-oscillating annular cascade test facility. Precise data of unsteady aerodynamic forces generated by shock wave movement due to blade oscillation and the previously measured data of chordwise distributions of unsteady aerodynamic forces acting, on an oscillating blade were joined, and then the nature of cascade flutter was evaluated. These unsteady aerodynamic forces were measured by direct and indirect pressure measuring methods. Our experiments covered a range of reduced frequencies based on a semi-chord from 0.0375 to 0.547, 6 interblade phase angles and inlet flow velocities from subsonic to supersonic flow. The occurrence of unstalled cascade flutter in relation to reduced frequency, interblade phase angle and inlet flow velocity was clarified including the role of unsteady aerodynamic blade surface forces on flutter. Reduced frequency of the flutter boundary increased greatly when the blade suction surface flow became transonic flow. Interblade phase angles which caused flutter were in the range from 40° to 160° for flow fields ranging from high subsonic to supersonic. Shock wave movement due to blade oscillation generated markedly large unsteady aerodynamic forces which stimulated blade oscillation.

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.

scholarly journals An Analysis of the Aeroelastic Behaviour of a Typical Fan-Blade With Emphasis on the Flutter Mechanism

1996 ◽  
Author(s):  
J. G. Marshall ◽  
M. Imregun
Keyword(s):  
Structural Model ◽  
Navier Stokes ◽  
Test Case ◽  
Flow Measurements ◽  
Structural Domains ◽  
Flutter Analysis ◽  
Shape Correction ◽  
Fan Blade ◽  
Integrated Or ◽  
Phase Angles

Aeroelasticity phenomena are characterised by the interaction of fluid and structural domains, whose describing equations are nonlinear. Classical prediction methods are generally based on treating the two domains separately while integrated (or coupled) approaches link them via boundary conditions throughout the solution phase. In turbomachinery environments, the aeroelasticity problem is further compounded by the fact that blades vibrate with a relative phase with respect to each other, the value of which is not necessarily known. Using a 3D thin-layer Reynolds-averaged Navier-Stokes solver and a 3D structural model, various coupled and uncoupled flutter analysis methods are compared with particular emphasis on inter-blade phase angle. A typical fan geometry, the NASA Rotor 67 blade, was chosen as the test case since steady-flow measurements are available for this particular structure. Two flow conditions, near peak-efficiency and near stall, were investigated for inter-blade phase angles of −90°, 0°, 90° & 180°. The performance of the uncoupled analysis with shape correction was first compared with that of the uncoupled multi-passage analysis. A coupled multi-passage analysis was performed next in order to highlight the importance of fluid/structure interaction. It was found that significant natural frequency shifts could exist between the structural and aeroelastic modes of the system, which suggests that coupled analyses may be more appropriate for such cases.

A Review of the Research on Aeroelasticity in Aero Turbomachinery

2013 ◽  
Vol 651 ◽  
pp. 694-700 ◽  
Author(s):  
Li Cheng Fang ◽  
Shun Ming Li
Keyword(s):  
Research And Development ◽  
Structural Model ◽  
Prediction Methods ◽  
Coupling Effects ◽  
Unsteady Aerodynamic ◽  
Aerodynamic Model ◽  
Blade Flutter ◽  
Fundamental Mechanism

Aeroelasticity in the form of blade flutter is a major concern for designers in the field of turbomachinery. This paper presents a review of the research and development on blade flutter modeling, including the unsteady aerodynamic model, the structural model and flutter prediction methods. Based on the presentation of these models, the fundamental mechanism and effects of different treatments are discussed. At the end of paper, some deficiencies in the research of flutter and difficulties in modeling fluid-solid coupling effects are pointed out, to which attention should be paid in future.

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.

Flutter Analysis of Hypersonic Wings Subject to Thermal Load

2011 ◽  
Vol 105-107 ◽  
pp. 466-469
Author(s):  
Yao Bin Niu ◽  
Zhong Wei Wang
Keyword(s):  
Elevated Temperature ◽  
Material Properties ◽  
Thermal Load ◽  
Thermal Stresses ◽  
Vital Role ◽  
Aerodynamic Loads ◽  
Flutter Speed ◽  
Aeroelastic Analysis ◽  
Flutter Analysis ◽  
Nature Frequency

Aeroelastic analysis plays a vital role in the design of hypersonic wings. The thermal flutter of hypersonic tail under different materials at different temperature is analyzed by using MSC.NASTRAN, and the hypersonic piston theory is used for the modeling of supersonic aerodynamic loads. The research results showed: nature frequency is reduced as temperature increased, elevated temperature tend to reduce model stiffness due to changes in material properties and development of thermal stresses. Increased temperature will decrease the flutter velocity, flutter speed of tail is different with different material of titanium, but the trend and the value of variety of flutter speed are same as temperature increase. When material is different, the value of variety of flutter speed is also different.

Mechansims for Wide-Chord Fan Blade Flutter

2009 ◽  
Author(s):  
Mehdi Vahdati ◽  
George Simpson ◽  
Mehmet Imregun
Keyword(s):  
Flow Separation ◽  
Pressure Wave ◽  
Geometric Features ◽  
The Third ◽  
Reflected Wave ◽  
Flutter Analysis ◽  
Parametric Studies ◽  
Blade Flutter ◽  
Stall Flutter ◽  
Fan Blade

This paper describes a detailed wide-chord fan blade flutter analysis with emphasis on flutter bite. The same fan was used with three different intakes of increasing complexity to explain flutter mechanisms. Two types of flutter, namely stall flutter and acoustic flutter, were identified. The first intake is a uniform cylinder for which there are no acoustic reflections. Only stall flutter, driven by flow separation, can exist in this case. The second intake, based on the first one, has a ‘bump’ feature to reflect the fan’s forward pressure wave at a known location so that detailed parametric studies can be undertaken. The analysis revealed a mechanism for acoustic flutter, which is driven by the phase of the reflected wave. The third intake has the typical geometric features of a flight intake. The results indicate that flutter bite occurs when both stall and acoustic flutter happen at the same speed. It is also found that blade stiffening has no effect on aero-acoustic flutter.

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