Fan Blade Flutter: Single Blade Instability or Blade to Blade Coupling?

1985 ◽  
Author(s):  
Edmond Széchényi
Keyword(s):  
Wind Tunnel ◽  
Flow Regimes ◽  
Single Degree Of Freedom ◽  
Single Degree ◽  
Different Types ◽  
Blade Flutter ◽  
Physical Insight ◽  
Fan Blade ◽  
Cascade Effects ◽  
Mode Order

Different types of fan blade flutter occur at the various compressor flow regimes. Sub/transonic stall flutter and two forms of supersonic started flow flutter have been studied in a straight cascade wind tunnel. Results show clearly that these three common forms of flutter can exist as single-degree-of-freedom (single-blade instabilities). Cascade effects, though at times important, are never the only flutter mechanism: flutter limits are essentially controlled by single-blade aeroelastic coefficients, though blade-to-blade coupling arising from cascade effects can modify these limits according to the mode order. Thus, contrary to widespread practice, the fundamental approach to flutter problems should lie at least as much in the study of single blade flutter as in that of unsteady cascade effects. The two should anyhow best be considered separately when searching for a better physical insight.

The Response of Nonlinear Systems to Modulated High-Frequency Input

1993 ◽  
Author(s):  
S. A. Nayfeh ◽  
A. H. Nayfeh
Keyword(s):  
Nonlinear Systems ◽  
Natural Frequency ◽  
Amplitude Modulation ◽  
Carrier Frequency ◽  
High Frequency ◽  
Degree Of Freedom ◽  
Resonant Excitation ◽  
Single Degree Of Freedom ◽  
Single Degree ◽  
Different Types

Abstract We study the response of a single-degree-of-freedom system with cubic nonlinearities to an amplitude-modulated excitation whose carrier frequency is much higher than the natural frequency of the system. The only restriction on the amplitude modulation is that it contain frequencies much lower than the carrier frequency of the excitation. We apply the theory to different types of amplitude modulation and find that resonant excitation of the system may occur under some conditions.

The Determination of Fan Blade Aerodynamic Loading From a Measured Response

2015 ◽  
Author(s):  
Jacques Muiyser ◽  
Daniel N. J. Els ◽  
Sybrand J. van der Spuy ◽  
Albert Zapke
Keyword(s):  
Fourier Series ◽  
Strain Gauge ◽  
Full Scale ◽  
Aerodynamic Forces ◽  
Single Degree Of Freedom ◽  
Single Degree ◽  
Aerodynamic Loading ◽  
Fan Blade ◽  
Strain Gauge Measurements ◽  
Measured Response

Large-scale cooling system fans often operate under distorted inlet air flow conditions due to the presence of other fans and the prevalent wind conditions. Strain gauge measurements have been used to determine the blade loading as a result of the unsteady aerodynamic forces. However, these measurements are of the blade’s response to the aerodynamic forces and include the deformation as a result of the first natural frequency being excited. When considering the dominant first natural frequency and bending mode of the fan blade, one can approximate the fan blade as a cantilever beam that acts as a single degree-of-freedom system. The response of a single degree-of-freedom system can be calculated analytically for any excitation if the system’s properties are known. The current investigation focuses on using these equations to create an algorithm that can be applied to the measured response of a fan blade to then extract the aerodynamic forces exciting it. This is performed by using a simple non-linear, least-squares optimization algorithm to fit a complex Fourier series to the response and using the coefficients of each harmonic term to determine the Fourier series representing the excitation function. The algorithm was first tested by applying it to the response of a finite element cantilever beam representing a simplified model of the fan blade. Good results were obtained for a variety of excitation forces and as such the algorithm was then applied to the measured response of a full-scale fan blade. The full-scale blade was excited with a shaker where the forcing function could be accurately controlled. Once validated, the algorithm was applied to a set of strain gauge measurements that were recorded at a full-scale fan while in operation. The reconstructed aerodynamic loading showed increased forces when the blade passed beneath the fan bridge as well as when it approached the windward side of the casing.

Influence of Friction Dampers on Torsional Blade Flutter

1986 ◽  
Vol 108 (2) ◽  
pp. 313-318 ◽  
Author(s):  
A. Sinha ◽  
J. H. Griffin ◽  
R. E. Kielb
Keyword(s):  
Dry Friction ◽  
Fluid Velocity ◽  
Supersonic Flows ◽  
Degree Of Freedom ◽  
Lumped Parameter Model ◽  
Single Degree Of Freedom ◽  
Friction Dampers ◽  
Single Degree ◽  
Lumped Parameter ◽  
Blade Flutter

This paper deals with the stabilizing effects of dry friction on torsional blade flutter. A lumped parameter model with single degree of freedom per blade has been used to represent the rotor stage. The well-known cascade theories for incompressible and supersonic flows have been used to determine the allowable increase in fluid velocity relative to the blade. It has been found that the effectiveness of friction dampers in controlling flutter can be substantial.

The Virtual Cam – Hexagon Method Authentication on Locating Key Instant Centers of All Planar Single Degree of Freedom Kinematically Indeterminate Linkages up to Ten-Bar

2018 ◽  
Author(s):  
Zhengqi Liu ◽  
Yin-ping Chang
Keyword(s):  
Degree Of Freedom ◽  
Universal Method ◽  
Single Degree Of Freedom ◽  
Graphical Approach ◽  
Single Degree ◽  
Wide Range ◽  
Different Types ◽  
Limited Application ◽  
Complete Sets ◽  
Improved Technique

At this moment all the methods which had been proposed have extremely limited application to only several specific constructions of kinematically indeterminate linkages, i.e. their complete sets of instant centers cannot be obtained simply from Kennedy Theorem due to lack of enough four-bar loop information in their constructions. Planar single degree of freedom linkages up to ten-bar include two different types of mechanisms, i.e. pure bar linkages, such as four-, six-, eight-, and ten-bar; and geared-bar linkages, i.e. geared-five, seven, and nine-bar. The huge varieties of different types and constructions can serve as great testbeds for these methods. This research systematically investigates and modifies the graphical approach, i.e. virtual cam method, whose employment will show it to be an almost-universal method which can be compliantly applied on very wide range of kinematically indeterminate linkages. The procedures and criteria of the methodology are proposed and examined thoroughly to help locate key instant centers of all planar single degree of freedom kinematically indeterminate linkages up to ten-bar so that their complete sets of instant centers can be located successfully. We call this modified and improved technique as Virtual Cam – Hexagon Method. The results are verified carefully against traditional Kennedy Theorem approach and CAD modeling.

Detection of Improper General Spatial Kinematic Chains With Different Types of Pairs

1994 ◽  
Author(s):  
Xian-Wen Kong ◽  
Ting-Li Yang
Keyword(s):  
Unsolved Problem ◽  
Degree Of Freedom ◽  
Sufficient Condition ◽  
Necessary And Sufficient Condition ◽  
Single Degree Of Freedom ◽  
Kinematic Chains ◽  
Single Degree ◽  
Different Types ◽  
Necessary And Sufficient ◽  
Topological Synthesis

Abstract Improper general spatial kinematic chains (GSKCs) due to the effect of pair types may be generated during the process of topological synthesis of GSKCs with different types of pairs. Thus, detection of improper GSKCs is necessary in topological synthesis of GSKCs with different types of pairs. Unfortunately, it is still an unsolved problem. In this paper, a method for detecting improper GSKCs is presented. Both a necessary and sufficient condition and a sufficient condition for proper GSKCs with R, P, H, T and C pairs are introduced at first. Based on these two conditions, an algorithm to detect improper GSKCs is then developed which is very efficient and suitable for topological synthesis of GSKCs with R, P, H, T and C pairs. The proposed algorithm has been applied to topological synthesis of 1- and 2-loop, single degree of freedom GSKCs with R, P, H, T and C pairs and the corresponding atlas is obtained.

Motion Patterns at Rotor Stator Contact

2005 ◽  
Author(s):  
Ulrich Ehehalt ◽  
Eric Hahn ◽  
Richard Markert
Keyword(s):  
Dry Friction ◽  
Viscoelastic Model ◽  
Single Degree Of Freedom ◽  
Motion Patterns ◽  
System Parameters ◽  
Single Degree ◽  
Synchronous Motion ◽  
Different Types ◽  
Run Up ◽  
Motion Types

The present paper discusses the various movement patterns during rotor stator contact. Both rotor and stator are assumed to be flexible damped single degree of freedom systems. The contact is described by a flexible viscoelastic model. Dry friction between rotor and stator is taken into account. Despite strong non-linearity due to contact, rotor unbalance causes purely synchronous motions. However, in some circumstances, the synchronous motion may become unstable and the rotor motion turns into a non-synchronous state, which can be very destructive. Non-synchronous motions include backward whirl, sub- and super-harmonic vibration and chaotic motion. The influence of various system parameters on the different types of motion is investigated by numerical simulation. The transients between synchronous to non-synchronous motions are exemplarily demonstrated by run-up and run-down processes. It is shown that different motion types may co-exist. Even in speed regions where the synchronous whirl is stable, non-synchronous motions with rotor stator contact are possible.

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