An Analysis of Aeroengine Fan Flutter Using Twin Orthogonal Vibration Modes

1980 ◽  
Vol 102 (2) ◽  
pp. 376-381
Author(s):  
R. A. J. Ford ◽  
C. A. Foord
Keyword(s):  
Mechanical Response ◽  
Aerodynamic Force ◽  
Frequency Separation ◽  
Practical Case ◽  
Temporal Phase ◽  
Excited Vibration ◽  
Sophisticated Model ◽  
Vibration Pattern ◽  
Frequency Split ◽  
Phase Angles

Flutter prediction methods for aeroengine fans at present typically combine a complex aerodynamic analysis with a simple model of the mechanical behavior of the fan. In this paper a more sophisticated model of the mechanical response is used to investigate flutter and provide additional insight into the physical mechanisms involved. The model incorporates twin orthogonal modes, which are two independent vibration patterns similar in shape and resonant frequency but displaced 1/4 wave circumferentially in space. Flutter can be thought of as a self excited vibration in which the response of each blade in one mode generates aerodynamic forces on the blades which drive the twin mode—and vice versa. The flutter frequency can be determined by considering the phasing between the twin modes; whether flutter does actually occur (at this frequency) depends upon the relationship between the aerodynamic force coefficients and the amplitude response of each mode. The greatest tendency to flutter occurs when the twin modes are identical in frequency. For the more practical case of a frequency split between the modes the tendency to flutter decreases with increased frequency separation, and the vibration pattern becomes non-uniform. The non-uniformities include unequal blade amplitudes, unequal interblade phase angles, variation from blade to blade in the temporal phase between twist and flap within each individual blade, and a deflected shape which is not sinusoidal circumferentially.

scholarly journals Piezoelectric Wind Energy Harvesting from Self-Excited Vibration of Square Cylinder

2016 ◽  
Vol 2016 ◽  
pp. 1-12 ◽  
Author(s):  
Junlei Wang ◽  
Sheng Wen ◽  
Xingqiang Zhao ◽  
Min Zhang ◽  
Jingyu Ran
Keyword(s):  
Wind Energy ◽  
Aerodynamic Force ◽  
Load Resistance ◽  
Open Circuit ◽  
Transverse Displacement ◽  
Square Cylinder ◽  
Force Output ◽  
Vortex Induced Vibration ◽  
Wind Speeds ◽  
Excited Vibration

Self-excited vibration of a square cylinder has been considered as an effective way in harvesting piezoelectric wind energy. In present work, both of the vortex-induced vibration and unstable galloping phenomenon process are investigated in a reduced velocity (Ur=U/ωn·D) range of4≤Ur≤20with load resistance ranging in100 Ω≤R≤1 MΩ. The vortex-induced vibration covers presynchronization, synchronization, and postsynchronization branches. An aeroelectromechanical model is given to describe the coupling of the dynamic equation of the fluid-structure interaction and the equation of Gauss law. The effects of load resistance are investigated in both the open-circuit and close-circuit system by a linear analysis, which covers the parameters of the transverse displacement, aerodynamic force, output voltage, and harvested power utilized to measure the efficiency of the system. The highest level of the transverse displacement and the maximum value of harvested power of synchronization branch during the vortex-induced vibration and galloping are obtained. The results show that the large-amplitude galloping at high wind speeds can generate energy. Additionally, energy can be harvested by utilization of the lock-in phenomenon of vortex-induced vibration under low wind speed.

Effects of Frequency Separation and Diotic/Dichotic Presentations on the Alternation Frequency Limits in Audition Derived from a Temporal Phase Discrimination Task

Perception ◽  
10.1068/p7753 ◽  
2015 ◽  
Vol 44 (2) ◽  
pp. 198-214 ◽  
Author(s):  
Shoko Kanaya ◽  
Waka Fujisaki ◽  
Shin'ya Nishida ◽  
Shigeto Furukawa ◽  
Kazuhiko Yokosawa
Keyword(s):  
Discrimination Task ◽  
Frequency Separation ◽  
Phase Discrimination ◽  
Temporal Phase

Numerical analysis of flows and aerodynamic forces in honeycomb and labyrinth seals

2012 ◽  
Vol 227 (9) ◽  
pp. 1965-1979 ◽  
Author(s):  
Hai Zhang ◽  
Qun Zheng ◽  
Guoqiang Yue ◽  
Jie Gao
Keyword(s):  
Aerodynamic Force ◽  
Flow Characteristics ◽  
Labyrinth Seal ◽  
Structure Design ◽  
Rotor Vibration ◽  
Aerodynamic Forces ◽  
Labyrinth Seals ◽  
Sealing Performance ◽  
Excited Vibration ◽  
Unsteady Fluid

Rotor dynamics and flow characteristics are computed for a honeycomb seal and a corresponding labyrinth seal. Firstly, rotor dynamic parameters, such as amplitude and frequency of vibration are calculated. Then these parameters are used for unsteady fluid flow computation. Numerical results indicate that the rotor vibration can reduce sealing performance and result in additional aerodynamic force on rotor. Further, the aerodynamic forces tend to reduce the self-excited vibration of rotor, and this effect becomes more apparent with the increase of pressure difference. Vortex in seal cavities is deemed to be the primary cause of the above mentioned results. The differences between the two types of seals are presented in this article. Finally, authors conclude that suitable structure design of honeycomb and labyrinth seals, or their combination can minimize rotor vibration.

Measurement of Fan Vibration Using Double Pulse Holography

1978 ◽  
Vol 100 (4) ◽  
pp. 655-663 ◽  
Author(s):  
B. S. Hockley ◽  
R. A. J. Ford ◽  
C. A. Foord
Keyword(s):  
Vibration Mode ◽  
Mechanical Vibration ◽  
Propagation Speed ◽  
Double Pulse ◽  
Mode Shapes ◽  
Vibration Modes ◽  
Television System ◽  
Temporal Phase ◽  
Frequency Split ◽  
Laser Holography

Supersonic unstalled flutter in gas turbine fans is a self-excited instability in which mechanical vibrations give rise to unsteady aerodynamic forces which drive the mechanical vibration. The phenomenon is very sensitive to the deflected shapes of the blades and to the spatial and temporal phases of the blades’ responses. This paper is concerned with the measurement of vibrational behavior on static fans and relating it to flutter. Accurate detailed data on the blade and disk vibration mode shapes of fans up to 2.2 m diameter has been measured using double pulse laser holography. Both axial and tangential components of the blade mode shape are obtained by taking holograms from two directions. The analysis of the holograms is performed with the aid of a computer linked television system which generates the required blade mode shapes directly from the photographs of the hologram reconstructions. The disk mode measurements on real fans have shown the existence of pairs of spatially orthogonal vibration modes which have similar shapes (e.g. both 4D) but slightly different natural frequencies. This frequency split between modes means that the flutter wave will experience a cyclic variation in amplitude and propagation speed as it travels round the fan. In addition, the temporal phase angle between twist and flap in a single blade, which is generally assumed to be 90 deg, will vary from blade to blade.

Phase Angles of the Vibrations and Hydrodynamic Forces of the Flexible Risers Undergoing Vortex-Induced Vibration

2017 ◽  
Vol 139 (3) ◽  
Author(s):  
Leijian Song ◽  
Shixiao Fu ◽  
Tie Ren ◽  
Ziqi Lu
Keyword(s):  
Phase Angle ◽  
Cross Sections ◽  
Cross Flow ◽  
Hydrodynamic Forces ◽  
Uniform Flow ◽  
Vortex Induced Vibration ◽  
Excited Vibration ◽  
Phase Angles ◽  
Euler Bernoulli Beam ◽  
Two Sides

This paper investigates the phase angles of the vibrations and hydrodynamic forces by the model testing of a flexible riser's vortex-induced vibration (VIV) under uniform flow. The VIV displacement of the riser is derived from the measured strains in the cross-flow (CF) and inline (IL) directions. Then, the hydrodynamic forces are obtained by the dynamic equation of an Euler–Bernoulli beam based on the results of VIV displacement. The characteristics of the phase angle of displacement and the hydrodynamic forces are analyzed. The results show that the phase angles of displacement and the hydrodynamic forces are almost identical at different cross sections of the riser under uniform flow. Moreover, within two adjacent vibration nodes in IL direction, the phase angle almost kept constant, while had a 180 deg change at the two sides of each vibration node. When the reduced velocity varies from 5.25 to 7.5, the phase angles of displacement derived from the flexible riser's VIV are 45 deg larger than those from the rigid cylinder's self-excited vibration.

Numerical investigation of wing–wing interaction and its effect on the aerodynamic force of a hovering dragonfly

2021 ◽  
pp. 095441002098210
Author(s):  
Prafulla Kumar Swain ◽  
Siva Prasad Dora ◽  
Suryanarayana Murthy Battula ◽  
Ashok K Barik
Keyword(s):  
Aerodynamic Force ◽  
Flow Analysis ◽  
Simulation Method ◽  
Hovering Flight ◽  
Dipole Structure ◽  
Flight Mode ◽  
Phase Angles ◽  
System Coupling ◽  
D Model ◽  
Wing Interaction

The present research focuses on the timing of wing–wing interaction that benefits the aerodynamic force of a dragonfly in hovering flight at Reynolds number 1350. A 3-D numerical simulation method, called the system coupling, was utilised by implementing a two-way coupling between the transient structural and flow analysis. We further explore the aerodynamic forces produced at different phase angles on the forewing and hindwing during the hovering flight condition of a dragonfly. A pair of dragonfly wings is simulated to obtain the force generated during flapping at a 60° inclination stroke plane angle with respect to the horizontal. The hovering flight is simulated by varying the phase angle and the inter-distance between the two wings. We observe a significant enhancement in the lift (16%) of the hindwing when it flaps in-phase with the forewing and closer to the forewing, maintaining an inter-wing distance of 1.2 cm (where centimetre is the mean chord length). However, for the same condition, the lift of the hindwing reduces by 9% when the wings are out of phase/counterstroke flapping. These benefits and drawbacks are dependent on the timing of the interactions between the forewing and hindwing. The time of interaction of wake capture, wing–wing interaction, dipole structure and development of root vortex are examined by 2-D vorticity of the flow field and isosurface of the 3-D model dragonfly. From the isosurface, we found that the root vortex elicited at the root of the hindwing in counter-flapping creates an obstacle for the shedding of wake vortices, which results in reduction of vertical lift during the upstroke of flapping. Hence, at the supination stage, a dragonfly uses a high rotation angle for the hovering flight mode. It is observed that the system coupling method was found to be more efficient and exhibited better performance. The present numerical methodology shows a very close match to the previously reported results.

Self-excited vibration of workpieces in a turning process

2012 ◽  
Vol 226 (8) ◽  
pp. 1958-1970 ◽  
Author(s):  
Xianguo Han ◽  
Huajiang Ouyang ◽  
Minjie Wang ◽  
Nurhafizzah Hassan ◽  
Yuming Mao
Keyword(s):  
Dynamic Model ◽  
Moving Load ◽  
Longitudinal Axis ◽  
Dynamic Interaction ◽  
Turning Process ◽  
Turning Operations ◽  
Excited Vibration ◽  
Vibration Pattern ◽  
Quality Of Products

Vibration occurring during machining is a major limitation to the productivity and quality of products. The dynamic interaction between the cutter and the workpiece during a turning process causes self-excited vibration. If the level of vibration is sufficiently high, poor surface quality of the workpiece and excessive tool wear can occur. This article presents a dynamic model for the vibration in turning operations taking into account the time-dependent reduction of workpiece diameter and the regenerative chatter mechanism. The workpiece is modelled as a beam rotating about its longitudinal axis and the cutter provides a moving load that is a source of parametric excitation. Simulated numerical examples are presented. Turning experiments are conducted that demonstrate vibration and chatter in turning operations. It is found through comparison between the theoretical and numerical results that the established dynamic model can predict the vibration pattern of the workpieces fairly well but underestimates the magnitude of workpiece oscillation.

The Eclipsing Binary WX Eridani

1979 ◽  
Vol 46 ◽  
pp. 385
Author(s):  
M.B.K. Sarma ◽  
K.D. Abhankar
Keyword(s):  
Light Curve ◽  
Spectral Type ◽  
Orbital Period ◽  
Primary Component ◽  
Light Curves ◽  
Absorption Feature ◽  
Primary Star ◽  
Eclipsing Binary ◽  
The Times ◽  
Phase Angles

AbstractThe Algol-type eclipsing binary WX Eridani was observed on 21 nights on the 48-inch telescope of the Japal-Rangapur Observatory during 1973-75 in B and V colours. An improved period of P = 0.82327038 days was obtained from the analysis of the times of five primary minima. An absorption feature between phase angles 50-80, 100-130, 230-260 and 280-310 was present in the light curves. The analysis of the light curves indicated the eclipses to be grazing with primary to be transit and secondary, an occultation. Elements derived from the solution of the light curve using Russel-Merrill method are given. From comparison of the fractional radii with Roche lobes, it is concluded that none of the components have filled their respective lobes but the primary star seems to be evolving. The spectral type of the primary component was estimated to be F3 and is found to be pulsating with two periods equal to one-fifth and one-sixth of the orbital period.

Comparison of Substructures Between Uniaxial and Biaxial Deformation in 1100-0 Aluminum

1981 ◽  
Vol 39 ◽  
pp. 52-53
Author(s):  
D. L. Rohr ◽  
S. S. Hecker
Keyword(s):  
Plastic Strain ◽  
Cell Walls ◽  
Room Temperature ◽  
Mechanical Response ◽  
Biaxial Tension ◽  
Initial Deformation ◽  
Uniaxial Deformation ◽  
Biaxial Deformation ◽  
Stress States ◽  
Comprehensive Study

As part of a comprehensive study of microstructural and mechanical response of metals to uniaxial and biaxial deformations, the development of substructure in 1100 A1 has been studied over a range of plastic strain for two stress states.Specimens of 1100 aluminum annealed at 350 C were tested in uniaxial (UT) and balanced biaxial tension (BBT) at room temperature to different strain levels. The biaxial specimens were produced by the in-plane punch stretching technique. Areas of known strain levels were prepared for TEM by lapping followed by jet electropolishing. All specimens were examined in a JEOL 200B run at 150 and 200 kV within 24 to 36 hours after testing.The development of the substructure with deformation is shown in Fig. 1 for both stress states. Initial deformation produces dislocation tangles, which form cell walls by 10% uniaxial deformation, and start to recover to form subgrains by 25%. The results of several hundred measurements of cell/subgrain sizes by a linear intercept technique are presented in Table I.

Construction of plastic contact deformation maps on ceramics: a case study on aluminum nitride

1996 ◽  
Vol 54 ◽  
pp. 636-637
Author(s):  
D. L. Callahan
Keyword(s):  
Plastic Deformation ◽  
Aluminum Nitride ◽  
Mechanical Response ◽  
Three Dimensional ◽  
Bright Field Image ◽  
Perfectly Plastic ◽  
Contrast Analysis ◽  
Deformation Patterns

Modern polishing, precision machining and microindentation techniques allow the processing and mechanical characterization of ceramics at nanometric scales and within entirely plastic deformation regimes. The mechanical response of most ceramics to such highly constrained contact is not predictable from macroscopic properties and the microstructural deformation patterns have proven difficult to characterize by the application of any individual technique. In this study, TEM techniques of contrast analysis and CBED are combined with stereographic analysis to construct a three-dimensional microstructure deformation map of the surface of a perfectly plastic microindentation on macroscopically brittle aluminum nitride.The bright field image in Figure 1 shows a lg Vickers microindentation contained within a single AlN grain far from any boundaries. High densities of dislocations are evident, particularly near facet edges but are not individually resolvable. The prominent bend contours also indicate the severity of plastic deformation. Figure 2 is a selected area diffraction pattern covering the entire indentation area.

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