Unsteady Aerodynamic Analysis of Subsonic Oscillating Cascade

1994 ◽  
Vol 116 (3) ◽  
pp. 501-512
Author(s):  
S. H. Chen ◽  
A. H. Eastland ◽  
E. D. Jackson
Keyword(s):  
Minimum Cost ◽  
Flow Speed ◽  
Flow Coefficient ◽  
Aerodynamic Load ◽  
Influence Coefficient ◽  
Unsteady Aerodynamic ◽  
Grid Deformation ◽  
Influence Coefficient Method ◽  
Phase Angles ◽  
Interblade Phase Angle

This paper describes the development of the source-doublet-based potential paneling method for oscillating cascade unsteady aerodynamic load predictions. By using the integral influence coefficient method and by using the interblade phase angles, the unsteady loads on an oscillating cascade can be accurately predicted at a minimum cost. As the grids are placed only on the blade surfaces, the blades are allowed to vibrate without grid deformation problems. Four notable subsonic oscillating cascade test cases that cover most important parameters, e.g., blade geometry, interblade phase angle, flow coefficient, flow speed, frequency, etc., are studied in this paper. The agreement between the present solutions and other numerical/experimental results demonstrates the robustness of the present model. Applicability of the method for realistic compressible flow cascades is also discussed.

Unsteady Aerodynamic Characteristics of Oscillating Cascade With Separation Bubble in High Subsonic Flow

2005 ◽  
Author(s):  
Toshinori Watanabe ◽  
Mizuho Aotsuka
Keyword(s):  
Subsonic Flow ◽  
Separation Bubble ◽  
Leading Edge ◽  
Aerodynamic Characteristics ◽  
Influence Coefficient ◽  
Unsteady Aerodynamic ◽  
Key Factor ◽  
Influence Coefficient Method ◽  
Airfoil Blades ◽  
High Subsonic Flow

Unsteady aerodynamic characteristics of an oscillating cascade composed of DCA (Double Circular Arc airfoil) blades were studied both experimentally and numerically. The test cascade was operated in high subsonic flow fields with incidence angles up to 5 degrees. Above 3 degrees of the incidence, a separation bubble was produced at the leading edge. The principal concern of the present study was placed on the influence of the separated region on the vibration instability of the cascade blades. The experiment was conducted in a linear cascade wind tunnel in which seven DCA blades were equipped. The central one could be oscillated in a pitching mode. The influence coefficient method was adopted for the measurement, where the unsteady aerodynamic moments were measured on the central blade and neighboring ones. For the numerical analysis, a quasi 3-D N-S code with k–ε turbulence model was developed. The experimental and numerical results complemented each other to obtain detailed understanding of the unsteady aerodynamic behavior of the cascade. It was found that the separation bubble at the leading edge governed the vibration characteristics of blades through the oscillation of the separation bubble itself on the blade surfaces. From the results of parametric studies, the phase shift of the oscillation of the separation bubble was found to be a key factor for determining the unsteady aerodynamic characteristics of the oscillating blades.

Mistuning and Structural Coupling Effects on Flutter of Turbomachinery Blades

2013 ◽  
Vol 482 ◽  
pp. 311-314
Author(s):  
Zhi Zhong Fu ◽  
Yan Rong Wang
Keyword(s):  
Influence Coefficient ◽  
Aeroelastic Stability ◽  
Disk System ◽  
Structural Coupling ◽  
Bladed Disk ◽  
Unsteady Aerodynamic ◽  
Simplified Method ◽  
Influence Coefficient Method ◽  
Turbomachinery Blades ◽  
Coefficient Method

A fast numerical method based on aeroelastic eigenvalue analysis is applied to study the effects of mistuning on the aeroelastic stability of turbomachinery blades in which the structural coupling is included by a simplified method and an influence coefficient method is employed to deal with the unsteady aerodynamic effects. Results show that there exists an optimal mistuning amount at which the system has the best aeroelastic stability. Structural coupling almost has no effects on aeroelastic stability of a tuned system. But the benefit of alternate frequency mistuning to aeroelastic stability is inhibited drastically when structural coupling is introduced into the bladed disk system.

Analytical and Experimental Study on Balancing Using Influence Coefficient Method

2013 ◽  
Vol 393 ◽  
pp. 694-702
Author(s):  
Wan Sulaiman Wan Mohamad ◽  
A.A. Mat Isa ◽  
M.A. Ismail
Keyword(s):  
Experimental Study ◽  
Experimental Verification ◽  
Mass Concentration ◽  
Vibration Reduction ◽  
Influence Coefficient ◽  
Centrifugal Forces ◽  
Experimental Procedure ◽  
Influence Coefficient Method ◽  
Phase Angles ◽  
Coefficient Method

Unbalance effect on rotating element happens as a result of an off centered mass concentration which will generate centrifugal forces with increasing running speeds. This unwanted situation requires correction to avoid failure due to excessive vibration. In this study, unbalance problem are studied by using theoretical influence coefficient method followed by the experimental verification. Experimental procedure is performed by using trial mass to calculate the influence coefficient and the corrected mass values as well as the phase angles. Finally, the vibration reduction of the rotor is compared theoretically and experimentally. Based on the results, the improved vibration reduction could be obtained reasonably for both single and two-plane balancing by using influence coefficient method.

scholarly journals Design and Experimentation of New Balancing Technique Based on the Jeffcott Rotor Model

2020 ◽  
pp. 186-194
Keyword(s):  
Influence Coefficient ◽  
Rotating Speed ◽  
Vibration Data ◽  
Jeffcott Rotor ◽  
Common Causes ◽  
Influence Coefficient Method ◽  
Phase Angles ◽  
The Mathematical Model ◽  
Rotor Model

Unbalance is one of the most common causes of machinery vibrations, present in rotating machines. The influence coefficient method of balancing used for in-situ balancing requires vibration data (Phase angles and vibration values) of many trial runs which may result in a lengthy balancing process. The vibration data can be measured with the help state-of-the-art four channel Adash 4400 VA4 Pro FFT analyzer platform along with data acquisition system and electronic instrumentation. It has been identified in the literature that it is possible to balance the rotor without the use of trial weight. This paper presents a new systematic approach of balancing method based on the Jeffcott rotor dynamic model. The mathematical model on Jeffcott rotor model is presented here. The proposed method requires vibration data of two test runs at different speeds without trial weight. For experimental verification of proposed method, a test rig has been developed. Systematic experiments done on the Jeffcott rotor model at different rotating speed are described in this paper. The experimental results shows the success of proposed balancing method. The importance of identifying type of rotor unbalance (static, couple, quasi-static, or dynamic) and the method to detect type of unbalance present in the rotor is presented.

Effect of Shock Wave Behavior on Unsteady Aerodynamic Characteristics of Oscillating Transonic Compressor Cascade

2021 ◽  
Author(s):  
Jiuliang Gan ◽  
Toshinori Watanabe ◽  
Takehiro Himeno
Keyword(s):  
Shock Wave ◽  
Aerodynamic Force ◽  
Aerodynamic Characteristics ◽  
Fast Response ◽  
Influence Coefficient ◽  
Compressor Cascade ◽  
Blade Vibration ◽  
Unsteady Pressure ◽  
Transonic Compressor ◽  
Unsteady Aerodynamic

Abstract The unsteady behavior of the shock wave was studied in an oscillating transonic compressor cascade. The experimental measurement and corresponding numerical simulation were conducted on the cascade with different shock patterns based on influence coefficient method. The unsteady pressure distribution on blade surface was measured with fast-response pressure-sensitive paint (PSP) to capture the unsteady aerodynamic force as well as the shock wave movement. It was found that the movement of shock waves in the neighboring flow passages of the oscillating blade was almost anti-phase between the two shock patterns, namely, the double shocks pattern and the merged shock pattern. It was also found that the amplitude of the unsteady pressure caused by the passage shock wave was very large under the merged shock pattern compared with the double shocks pattern. The stability of blade vibration was also analyzed for both shock patterns including 3-D flow effect. These findings were thought to shed light on the fundamental understanding of the unsteady aerodynamic characteristics of oscillating cascade caused by the shock wave behavior.

scholarly journals Aerodynamic Damping Characteristics of a Transonic Turbine Cascade

1999 ◽  
Author(s):  
Mizuho Aotsuka ◽  
Toshinori Watanabe ◽  
Yasuo Machida
Keyword(s):  
Phase Angle ◽  
Aerodynamic Force ◽  
Turbine Blades ◽  
Aerodynamic Characteristics ◽  
Influence Coefficient ◽  
Suction Surface ◽  
Aerodynamic Damping ◽  
Unsteady Aerodynamic ◽  
Design Case ◽  
Oscillation Instability

The unsteady aerodynamic characteristics of oscillating thin turbine blades were studied both experimentally and numerically to obtain the comprehensive knowledge on the aerodynamic damping of the blades operating in transonic flows. The experiment was carried out in a linear cascade tunnel by use of the influence coefficient method. The two flow conditions were adopted, namely, a near-design condition and an off-design condition with a higher back pressure. In the results for the near-design case, a strong vibration instability was observed in the positive side of the interblade phase angle. In the off-design case, however, the instability did not appear for almost all the interblade phase angles. A drastic change was found in the phase angle of unsteady aerodynamic force between the two cases, which change was a governing factor for the oscillation instability. Numerical simulation based on 2-D Euler equation revealed that the phase change came from the change in phase of the unsteady surface pressure across the shock impingement point on the blade suction surface in the off-design case. The numerical results also showed that the aerodynamic damping increased with increasing reduced frequency, and that the oscillation instability disappeared.

Modified Harmonic Balance Method for Nonlinear Aeroelastic Analysis of Two Degree-of-Freedom Airfoils in Supersonic Flow

2018 ◽  
Vol 18 (06) ◽  
pp. 1871006 ◽  
Author(s):  
Yaobin Niu ◽  
Zhongwei Wang
Keyword(s):  
Harmonic Balance ◽  
Harmonic Balance Method ◽  
Current Method ◽  
Degree Of Freedom ◽  
Balance Method ◽  
Aerodynamic Load ◽  
Nonlinear Aeroelasticity ◽  
Unsteady Aerodynamic ◽  
Aeroelastic Analysis ◽  
Two Degree Of Freedom

In this paper, a new modified harmonic balance method is presented for the nonlinear aeroelastic analysis of two degree-of-freedom airfoils. Using this method, the nonlinear problem is first translated into a minimization problem, and the Particle Swarm Optimization which has high calculation efficiency is adopted to solve the problem. The proposed method is used to solve the nonlinear aeroelastic behavior of supersonic airfoil, with the unsteady aerodynamic load evaluated by the piston theory. Three examples of nonlinear aeroelasticity with significantly different coefficients are prepared, in which the frequencies and amplitudes of the limit cycles are obtained. The results show that the present current method is computationally more efficient.

Influence Coefficients Obtained by Hammer Beat Permit Significant Time Savings When Balancing Simple Flexible Rotors

1999 ◽  
Author(s):  
D. Wiese ◽  
M. Breitwieser
Keyword(s):  
Influence Coefficient ◽  
Significant Time ◽  
Flexible Rotors ◽  
Influence Coefficients ◽  
Flexible Roll ◽  
Influence Coefficient Method ◽  
Time Savings ◽  
Positive Results ◽  
Coefficient Method

Abstract The following paper presents a method for balancing simple flexible rotors with the help of influence coefficients obtained by hammer beat. The method permits time savings of approx. 50% compared to the conventional influence coefficient method. Initial positive results obtained on a flexible roll are also presented.

Prototype design and size optimization of a hybrid lower extremity exoskeleton with a scissor mechanism for load-carrying augmentation

2014 ◽  
Vol 229 (1) ◽  
pp. 155-167 ◽  
Author(s):  
Yunjie Miao ◽  
Feng Gao ◽  
Dalei Pan
Keyword(s):  
Lower Extremity ◽  
Influence Coefficient ◽  
Input And Output ◽  
Flexion Extension ◽  
Load Carrying ◽  
Influence Coefficient Method ◽  
Prototype Design ◽  
Coefficient Method ◽  
Length Optimization ◽  
Scissor Mechanism

A hybrid lower extremity exoskeleton SJTU-EX which adopts a scissor mechanism as the hip and knee flexion/extension joint is proposed in Shanghai Jiao Tong University to augment load carrying for walking. The load supporting capabilities of a traditional serially connected mechanism and the scissor mechanism are compared in detail. The kinematic influence coefficient method of the kinematic and dynamic analysis is applied in the length optimization of the scissor sides to minimize the transmitting errors between the input and output motions in walking and the load capacities of different scissor mechanisms are illustrated. The optimization results are then verified by the walking simulations. Finally, the prototype of SJTU-EX is implemented with several improvements to enhance the working performances.

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