Aeroelastic Behavior of Low-Aspect-Ratio Metal and Composite Blades

1987 ◽  
Vol 109 (2) ◽  
pp. 168-175 ◽  
Author(s):  
J. F. White ◽  
O. O. Bendiksen
Keyword(s):  
Aspect Ratio ◽  
Opposite Effect ◽  
Design Parameters ◽  
Aeroelastic Stability ◽  
Low Aspect Ratio ◽  
Supersonic Flutter ◽  
Type Mode ◽  
The Stability ◽  
Composite Blades ◽  
Plate Type

The aeroelastic stability of titanium and composite blades of low aspect ratio is examined over a range of design parameters, using a Rayleigh-Ritz formulation. The blade modes include a plate-type mode to account for chordwise bending. Chord-wise flexibility is found to have a significant effect on the unstalled supersonic flutter of low-aspect-ratio blades, and also on the stability of tip sections of shrouded fan blades. For blades with a thickness of less than approximately 4 percent of chord, the chordwise, second bending, and first torsion branches are all unstable at moderately high supersonic Mach numbers. For composite blades, the important structural coupling between bending and torsion cannot be modeled properly unless chordwise bending is accounted for. Typically, aft fiber sweep produces beneficial bending-torsion coupling that is stabilizing, whereas forward fiber sweep has the opposite effect. By using crossed-ply laminate configurations, critical aeroelastic modes can be stabilized.

scholarly journals Aeroelastic Behavior of Low Aspect Ratio Metal and Composite Blades

1986 ◽  
Author(s):  
James F. White ◽  
Oddvar O. Bendiksen
Keyword(s):  
Aspect Ratio ◽  
Opposite Effect ◽  
Design Parameters ◽  
Aeroelastic Stability ◽  
Low Aspect Ratio ◽  
Supersonic Flutter ◽  
Type Mode ◽  
The Stability ◽  
Composite Blades ◽  
Plate Type

The aeroelastic stability of titanium and composite blades of low aspect ratio is examined over a range of design parameters, using a Rayleigh-Ritz formulation. The blade modes include a plate-type mode to account for chordwise bending. Chordwise flexibility is found to have a significant effect on the unstalled supersonic flutter of low aspect ratio blades, and also on the stability of tip sections of shrouded fan blades. For blades with a thickness of less than approximately four percent of chord, the chordwise, second bending, and first torsion branches are all unstable at moderately high supersonic Mach numbers. For composite blades, the important structural coupling between bending and torsion cannot be modeled properly unless chordwise bending is accounted for. Typically, aft fiber sweep produces beneficial bending-torsion coupling that is stabilizing, whereas forward fiber sweep has the opposite effect. By using crossed-ply laminate configurations, critical aeroelastic modes can be stabilized.

Investigation of sustainability of lubricated journal bearing under relevant design parameters

2018 ◽  
Vol 70 (4) ◽  
pp. 789-804 ◽  
Author(s):  
M.M. Shahin ◽  
Mohammad Asaduzzaman Chowdhury ◽  
Md. Arefin Kowser ◽  
Uttam Kumar Debnath ◽  
M.H. Monir
Keyword(s):  
Aspect Ratio ◽  
Elastic Strain ◽  
Journal Bearing ◽  
Design Parameters ◽  
Content Type ◽  
Computational Fluid Dynamics Cfd ◽  
Stress Formation ◽  
Bearing Design ◽  
The Stability ◽  
Bearing Friction

Purpose The purposes of the present study are to ensure higher sustainability of journal bearings under different applied loads and to observe bearing performances such as elastic strain, total deformation and stress formation. Design/methodology/approach A journal bearing test rig was used to determine the effect of the applied load on the bearing friction, film thickness, lubricant film pressure, etc. A steady-state analysis was performed to obtain the bearing performance. Findings An efficient aspect ratio (L/D) range was obtained to increase the durability or the stability of the bearing while the bearing is in the working condition by using SAE 5W-30 oil. The results from the study were compared with previous studies in which different types of oil and water, such as Newtonian fluid (NF), magnetorheological fluid (MRF) and nonmagnetorheological fluid (NMRF), were used as the lubricant. To ensure a preferable aspect ratio range (0.25-0.50), a computational fluid dynamics (CFD) analysis was conducted by ANSYS; the results show a lower elastic strain and deformation within the preferable aspect ratio (0.25-0.50) rather than a higher aspect ratio using the SAE 5W-30 oil. Originality/value It is expected that the findings of this study will contribute to the improvement of the bearing design and the bearing lubricating system.

The development of the winged keel for twelve-metre yachts

1986 ◽  
Vol 173 ◽  
pp. 55-71 ◽  
Author(s):  
P. Van Oossanen ◽  
P. N. Joubert
Keyword(s):  
Wind Tunnel ◽  
Aspect Ratio ◽  
Experimental Analysis ◽  
Design Parameters ◽  
Low Aspect Ratio ◽  
Lifting Surface ◽  
Wind Tunnel Measurements ◽  
America’S Cup

In this paper the authors present a numerical and experimental analysis of the winged keel originally developed for the International twelve-metre class yacht Australia II that won the America's Cup in 1983. After briefly explaining why this keel was evolved in 1981, some basic considerations are presented relating keel performance to various design parameters. The results of numerical flow analyses and wind-tunnel measurements on a model of a winged keel are then presented and compared. The differences between the performance with and without winglets fitted to the keel are discussed. The fitting of winglets appreciably enhances the performance of a low-aspect-ratio lifting surface such as the keel of a twelve-metre yacht.

Results of supersonic flutter characteristics of low aspect-ratio flat-plate surfaces.

AIAA Journal ◽  
1967 ◽  
Vol 5 (9) ◽  
pp. 1715-1717 ◽  
Author(s):  
EIICHI NAKAI ◽  
TOSHIRO TAKAGI ◽  
KOJI ISOGAI
Keyword(s):  
Aspect Ratio ◽  
Flat Plate ◽  
Low Aspect Ratio ◽  
Supersonic Flutter

scholarly journals Low Aspect Ratio Transonic Rotors: Part 2 — Influence of Location of Maximum Thickness on Transonic Compressor Performance

1992 ◽  
Author(s):  
A. R. Wadia ◽  
C. H. Law
Keyword(s):  
Aspect Ratio ◽  
Test Data ◽  
Three Dimensional ◽  
Leading Edge ◽  
Chord Length ◽  
Design Parameters ◽  
Transonic Compressor ◽  
Low Aspect Ratio ◽  
Maximum Thickness ◽  
Design Speed

Transonic compressor rotor performance is sensitive to variations in several known design parameters. One such parameter is the chordwise location of maximum thickness. This article reports on the design and experimental evaluation of two versions of a low aspect ratio transonic rotor that had the location of the tip blade section maximum thickness moved forward in two increments from the nominal 70 percent to 55 and 40 percent chord length, respectively. The original hub characteristics were preserved and the maximum thickness location was adjusted proportionately along the span. Although designed to satisfy identical design speed requirements, the experimental results reveal significant variation in the performance of the rotors. At design speed, the rotor with its maximum thickness located at 55 percent chord length attains the highest peak efficiency amongst the three rotors but has lowest flow rollback relative to the other two versions. To focus on current ruggedization issues for transonic blading (e.g. bird, ice ingestion), detailed comparison of test data and analysis to characterize the aerodynamic flow details responsible for the measured performance differences was confined to the two rotors with the most forward location of maximum thickness. A three-dimensional viscous flow analysis was used to identify the performance enhancing features of the higher efficiency rotor and to provide guidance in the interpretation of the experimental measurements. The computational results of the viscous analysis shows that the difference in performance between the two rotors can be attributed to the higher shock losses that result from the increased leading edge “wedge angle” as the maximum thickness is moved closer to the leading edge. The test data and the three-dimensional viscous analysis also reveal that the higher efficiency rotor achieves the same static pressure rise potential and loading at a higher flow level than its lesser efficient counterpart and this is responsible for its resulting lower flow rollback and apparent loss in stall margin. Comparison of the peak efficiencies attained by the two rotors described in this article with the baseline ruggedized rotor performance presented in part 1 of this paper suggests the existence of an optimum maximum thickness location at 55 to 60 percent chord length for such low aspect ratio transonic rotors.

Finite element supersonic flutter analysis of low aspect ratio stiffened wing

2012 ◽  
Vol 19 (14) ◽  
pp. 2187-2198
Author(s):  
Shirko Faroughi ◽  
Kramet Malekzadeh ◽  
Ieraje Mirzaee
Keyword(s):  
Finite Element ◽  
Aspect Ratio ◽  
Low Aspect Ratio ◽  
Flutter Analysis ◽  
Supersonic Flutter

scholarly journals Direct Use of Unsteady Aerodynamic Pressures in the Flutter Analysis of Mistuned Blades

1994 ◽  
Author(s):  
A. V. Srinivasan ◽  
G. G. Tavares
Keyword(s):  
Stability Analysis ◽  
Aspect Ratio ◽  
Unique Feature ◽  
Mode Shapes ◽  
Complex Eigenvalue ◽  
Aeroelastic Stability ◽  
Low Aspect Ratio ◽  
Unsteady Aerodynamic ◽  
Flutter Analysis ◽  
Direct Use

An aeroelastic stability analysis of a cascade of engine blades coupled only through aerodynamica is developed. The unique feature of the analysis is the direct use of unsteady aerodynamic pressures, rather than lifts and moments, in calculating the susceptibility of a cascade to flutter. The approach developed here is realistic and relevant for analysis of low aspect ratio blades. However, in the calculations presented in this paper, the surface is assumed to be divided into equal elemental areas. The formulation leads to a complex eigenvalue problem, the solution of which determines the susceptibility of the cascade to flutter. The eigenvalues of an assembly of alternately mistuned blades, operating at high reduced frequencies, appear to be very sensitive to the level of mistuned frequencies. The locus of eigenvalues shows a strong tendency to split even for very small percentage differences between the frequencies of the two sets of blades. Further, blades with identical frequencies, but alternately mistuned mode shapes, operating at high reduced frequencies show a tendency towards instability.

Low Aspect Ratio Transonic Rotors: Part 2—Influence of Location of Maximum Thickness on Transonic Compressor Performance

1993 ◽  
Vol 115 (2) ◽  
pp. 226-239 ◽  
Author(s):  
A. R. Wadia ◽  
C. H. Law
Keyword(s):  
Aspect Ratio ◽  
Test Data ◽  
Three Dimensional ◽  
Leading Edge ◽  
Chord Length ◽  
Design Parameters ◽  
Transonic Compressor ◽  
Low Aspect Ratio ◽  
Maximum Thickness ◽  
Design Speed

Transonic compressor rotor performance is sensitive to variations in several known design parameters. One such parameter is the chordwise location of maximum thickness. This article reports on the design and experimental evaluation of two versions of a low aspect ratio transonic rotor that had the location of the tip blade section maximum thickness moved forward in two increments from the nominal 70 percent to 55 and 40 percent chord length, respectively. The original hub characteristics were preserved and the maximum thickness location was adjusted proportionately along the span. Although designed to satisfy identical design speed requirements, the experimental results reveal significant variation in the performance of the rotors. At design speed, the rotor with its maximum thickness located at 55 percent chord length attains the highest peak efficiency among the three rotors but has lowest flow rollback relative to the other two versions. To focus on current ruggedization issues for transonic blading (e.g., bird and ice ingestion), detailed comparison of test data and analysis to characterize the aerodynamic flow details responsible for the measured performance differences were confined to the two rotors with the most forward location of maximum thickness. A three-dimensional viscous flow analysis was used to identify the performance-enhancing features of the higher efficiency rotor and to provide guidance in the interpretation of the experimental measurements. The computational results of the viscous analysis show that the difference in performance between the two rotors can be attributed to the higher shock losses that result from the increased leading edge “wedge angle” as the maximum thickness is moved closer to the leading edge. The test data and the three-dimensional viscous analysis also reveal that the higher efficiency rotor achieves the same static pressure rise potential and loading at a higher flow level than its less efficient counterpart and this is responsible for its resulting lower flow rollback and apparent loss in stall margin. Comparison of the peak efficiencies attained by the two rotors described in this article with the baseline ruggedized rotor performance presented in part 1 of this paper suggests the existence of an optimum maximum thickness location at 55 to 60 percent chord length for such low aspect ratio transonic rotors.

Secondary Flow Reduction by Blade Redesign and Endwall Contouring Using an Adjoint Optimization Method

2010 ◽  
Author(s):  
Jiaqi Luo ◽  
Juntao Xiong ◽  
Feng Liu ◽  
Ivan McBean
Keyword(s):  
Aspect Ratio ◽  
Secondary Flow ◽  
Adjoint Method ◽  
Turbine Blades ◽  
Adjoint Equations ◽  
Design Parameters ◽  
Flow Equations ◽  
Secondary Loss ◽  
Low Aspect Ratio ◽  
Endwall Contouring

For low-aspect-ratio turbine blades secondary loss reduction is important for improving performance. This paper presents the application of a viscous adjoint method to reduce secondary loss of a linear cascade. A scalable wall function is implemented in an existing Navier-Stokes flow solver to simulate the secondary flow with reduced requirements on grid density. The simulation result is in good agreement with the experimental data. Entropy production through a blade row is used as the objective function in the optimization of blade redesign and endwall contouring. With the adjoint method, the complete gradient information needed for optimization can be obtained by solving the governing flow equations and their corresponding adjoint equations only once, regardless of the number of design parameters. Three design cases are performed with a low-aspect-ratio steam turbine blade tested by Perdichizzi and Dossena. The results demonstrate that it is feasible to reduce flow loss through the redesign of the blade while maintaining the same mass-averaged turning angle. The effects on the profile loss and secondary loss due to the geometry modification of stagger angle, blade shape and endwall profile are presented and analyzed.

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