A Study of the Influence of Static Eccentricity and Unbalance on Cavitation Effects in a Squeeze Film Damped Flexible Rotor

2002 ◽  
Author(s):  
Philip Bonello ◽  
Michael J. Brennan ◽  
Roy Holmes
Keyword(s):  
Dynamic Systems ◽  
Harmonic Balance ◽  
Harmonic Balance Method ◽  
Squeeze Film ◽  
Flexible Rotor ◽  
Test Rig ◽  
Squeeze Film Damper ◽  
Static Eccentricity ◽  
Rotor Dynamic ◽  
Rigid Rotors

The study of eccentric squeeze film damped rotor dynamic systems has largely concentrated on rigid rotors. In this paper, a newly developed receptance harmonic balance method is used to efficiently analyze a squeeze film damped flexible rotor test rig. The aim of the study is to investigate the influence of damper static eccentricity and unbalance level on cavitation and its resulting effect on the vibration level. By comparing predictions for the rotor vibration levels obtained respectively with, and without, lower pressure limits for the eccentric squeeze film damper model, it is demonstrated that cavitation is promoted by increasing static eccentricity and/or unbalance level. This, in turn, is found to have a profound effect on the predictions for the critical vibration levels, which such dampers are designed to attenuate. The reported findings are backed by experimental evidence from the test rig.

A Study of the Nonlinear Interaction Between an Eccentric Squeeze Film Damper and an Unbalanced Flexible Rotor

2004 ◽  
Vol 126 (4) ◽  
pp. 855-866 ◽  
Author(s):  
Philip Bonello ◽  
Michael J. Brennan ◽  
Roy Holmes
Keyword(s):  
Periodic Solutions ◽  
Nonlinear Interaction ◽  
Harmonic Balance ◽  
Linear Part ◽  
Harmonic Balance Method ◽  
Squeeze Film ◽  
Flexible Rotor ◽  
Test Rig ◽  
Squeeze Film Damper ◽  
Static Eccentricity

In this paper, the nonlinear interaction between an eccentric squeeze film damper and an unbalanced flexible rotor is investigated, paying particular attention to the effect of cavitation in the damper. A harmonic balance method that uses the receptance functions of the rotating linear part of the system to determine periodic solutions to the nonlinear problem is used to predict vibration levels in a test rig. By comparing predictions obtained respectively with, and without, lower pressure limits for the squeeze film damper model, it is concluded that cavitation is promoted by increasing static eccentricity and/or unbalance level. This, in turn, is found to have a profound effect on the predictions for the critical vibration levels, which such dampers are designed to attenuate. Experimental results are presented to support the findings.

A theoretical and experimental investigation into the vibration response of a flexible rotor and squeeze-film damper assembly

2001 ◽  
Vol 215 (10) ◽  
pp. 1251-1269 ◽  
Author(s):  
C-C Siew ◽  
M Hill ◽  
R Holmes ◽  
M Brennan
Keyword(s):  
Harmonic Balance ◽  
Three Dimensional ◽  
Harmonic Balance Method ◽  
Vibration Response ◽  
Mode Shapes ◽  
Squeeze Film ◽  
Flexible Rotor ◽  
Linear Vibration ◽  
Squeeze Film Damper ◽  
Good Agreement

This paper presents two efficient methods to calculate the unbalance vibration response of a flexible rotor provided with a squeeze-film damper (SFD) with retainer springs. Both methods are iterative and combine the harmonic balance and receptance approaches. The first method, called the modified iteration method (MIM), is suitable for predicting the three-dimensional mode shapes of a concentric SFD-rotor system. The second method, called the modified harmonic balance method (MHBM), is developed to calculate the non-linear vibration response of a flexible shaft provided with either a concentric or eccentric SFD. The system is also investigated experimentally under different conditions. The predictions computed by these methods are compared with experimental measurements and reasonably good agreement is obtained.

A System to Measure the Response of a High-Speed Rotor to a Sudden Imbalance

1981 ◽  
Author(s):  
R. J. Trippett
Keyword(s):  
High Speed ◽  
Dynamic Test ◽  
Data Acquisition System ◽  
Squeeze Film ◽  
Sudden Increase ◽  
Test Rig ◽  
Dynamic Data ◽  
Squeeze Film Damper ◽  
Rotor Dynamic ◽  
Dynamic Data Acquisition

A unique rotor dynamic data acquisition system is described to control the gathering and display of rotor displacement data measured at rotor speeds up to 70 000 r/min. The first published results measured with this system are demonstrated with plots of measured transient shaft motion after a sudden increase in shaft imbalance at speeds up to 44 500 r/min. The displacements of the rotor in the forms of Lissajous plots with and without a squeeze film damper are presented at four axial shaft locations below and above the shafts critical speeds. The blade-loss, dynamic test rig is also described.

Experimental research on suppressing unbalanced vibration of rotor by integral squeeze film damper

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Wei Yan ◽  
Lidong He ◽  
Zhe Deng ◽  
Xingyun Jia
Keyword(s):  
Rotational Speed ◽  
Critical Speed ◽  
Structural Characteristics ◽  
Experimental Studies ◽  
Rotor System ◽  
Squeeze Film ◽  
Rigid Rotor ◽  
Flexible Rotor ◽  
Test Rig ◽  
Squeeze Film Damper

Abstract As a novel structural damper, the unique structural characteristics of the integral squeeze film damper (ISFD) solve the nonlinear problem of the traditional squeeze film damper (SFD), and it has good linear damping characteristics. In this research, the experimental studies of ISFD vibration reduction performance are carried out for various working conditions of unbalanced rotors. Two ball bearing-rotor system test rigs are built based on ISFD: a rigid rotor test rig and a flexible rotor test rig. When the rotational speed of rigid rotor is 1500 rpm, ISFD can reduce the amplitude of the rotor by 41.79%. Under different unbalance conditions, ISFD can effectively improve the different degrees of unbalanced faults in the rotor system, reduce the amplitude by 43.21%, and reduce the sensitivity of the rotor to unbalance. Under different rotational speed conditions, ISFD can effectively suppress the unbalanced vibration of rigid rotor, and the amplitude can be reduced by 53.51%. In the experiment of the unbalanced response of the flexible rotor, it is found that ISFD can improve the damping of the rotor system, effectively suppress the resonance of the rotor at the critical speed, and the amplitude at the first-order critical speed can be reduced by 31.72%.

scholarly journals The Effect of Squeeze Film Damper Parameters on the Unbalance Response and Stability of a Flexible Rotor

1996 ◽  
Author(s):  
F. Chu ◽  
R. Holmes
Keyword(s):  
Research Work ◽  
Stability Control ◽  
Squeeze Film ◽  
Flexible Rotor ◽  
Squeeze Film Damper ◽  
Significant Movement ◽  
Squeeze Film Dampers ◽  
Bearing Assembly ◽  
Static Eccentricity ◽  
Points Of View

There has been much research work carried out on various aspects of individual squeeze-film dampers (SFDs) but very little on the interplay between a damper and the rotating assembly of which it forms a part. In this paper, a flexible rotor-bearing assembly in a configuration, typical of a small centrifugal pump and incorporating an SFD is investigated theoretically and experimentally from the points of view of forced vibration control and stability control. It is found that change in rotor unbalance, SFD static eccentricity ratio and SFD supply pressure can cause significant movement of system resonances and vibration resulting from excessive damping. The provision of an SFD also delays the onset of instability and because of its nonlinearity, the SFD contributes more damping than can a linear damper when the vibration amplitude becomes large as instability develops. It is shown that this instability is curbed at some limit cycle, whose frequency is a system natural frequency.

Use of the Harmonic Balance Method for Flexible Aircraft Engine Rotors With Nonlinear Squeeze Film Dampers

2014 ◽  
Author(s):  
Feng He ◽  
Paul Allaire ◽  
Timothy Dimond
Keyword(s):  
Harmonic Balance ◽  
Harmonic Balance Method ◽  
Aircraft Engine ◽  
Balance Method ◽  
Squeeze Film ◽  
Spring Stiffness ◽  
Squeeze Film Damper ◽  
Flexible Rotors ◽  
Squeeze Film Dampers ◽  
Nonlinear Transient

Squeeze film dampers in flexible rotors such as those in compressors, steam turbines, aircraft engines and other rotating machines are often modeled as linear devices. This linearization is valid only for a specified orbit where appropriate equivalent stiffness and damping coefficients can be found. However, squeeze film dampers are inherently nonlinear devices which complicates the analysis. This paper develops the harmonic balance method with a direct force model of the SFDs. This model is used for flexible rotors with squeeze film dampers where the rotor is treated as linear and the squeeze film damper is treated as nonlinear. The predictor-corrector method is employed to obtain the system forced response in the frequency domain after separating the nonlinear components from the linear components of the equations of motion. This approach is much more efficient than conventional full nonlinear transient analysis. The application considered in this paper is the low pressure (LP) compressor of an aircraft engine. The LP compressor rotor has two roller bearings with squeeze film dampers and one ball bearing without a squeeze film damper. Orbits at the fan end dampers and the turbine end dampers for both the harmonic balance and nonlinear transient modeling are compared for accuracy and calculation time. The HB method is shown to be 5 to 12 times faster computationally for similar results. Fast Fourier transform results were obtained for various shaft operating speeds. Results were also obtained for the unbalance response at different locations with gravity loading. Finally, unbalance response of the rotor with varying centering spring stiffness values were obtained. The results show that the centering spring stiffness for the turbine end damper is less sensitive than the fan end damper.

Forced Response of a Flexible Rotor With Squeeze Film Damper Under Parametric Change

2013 ◽  
Author(s):  
Feng He ◽  
Paul E. Allaire ◽  
Saeid Dousti ◽  
Alexandrina Untaroiu
Keyword(s):  
Harmonic Balance Method ◽  
Forced Response ◽  
Squeeze Film ◽  
Flexible Rotor ◽  
Fluid Inertia ◽  
Inertia Effects ◽  
Squeeze Film Damper ◽  
Vibrational Response ◽  
Parametric Change ◽  
Gyroscopic Effects

Squeeze film dampers play an important role in the dynamics of modern turbomachinery by improving vibrational response and stability. The present paper develops an effective tool for evaluating the forced response of these systems under parametric changes. A flexible rotor with multiple masses supported on a squeeze film damper at one end is investigated. The forced response of this asymmetrically supported system is obtained using the harmonic balance method with a predictor-corrector procedure. This response is examined with various parameters including unbalance forces with and without fluid inertia effects, unidirectional loads, stiffness of centering spring of the damper and the gyroscopic effects of the disks. The developed tool predicts the nonlinear jump phenomenon of the damper with large unbalance forces, indicates the present of multiple harmonics within the response with high damper eccentricity and shows the insensitivity of the damper to surrounding gyroscopic variation.

The Effect of Squeeze Film Damper Parameters on the Unbalance Response and Stability of a Flexible Rotor

1998 ◽  
Vol 120 (1) ◽  
pp. 140-148 ◽  
Author(s):  
F. Chu ◽  
R. Holmes
Keyword(s):  
Research Work ◽  
Stability Control ◽  
Squeeze Film ◽  
Flexible Rotor ◽  
Squeeze Film Damper ◽  
Significant Movement ◽  
Squeeze Film Dampers ◽  
Bearing Assembly ◽  
Static Eccentricity ◽  
Points Of View

There has been much research work carried out on various aspects of individual squeeze-film dampers (SFDs) but very little on the interplay between a damper and the rotating assembly of which it forms a part. In this paper, a flexible rotor-bearing assembly in a configuration, typical of a small centrifugal pump and incorporating an SFD, is investigated theoretically and experimentally from the points of view of forced vibration control and stability control. It is found that change in rotor unbalance, SFD static eccentricity ratio, and SFD supply pressure can cause significant movement of system resonances and vibration resulting from excessive damping. The provision of an SFD also delays the onset of instability and because of its nonlinearity, the SFD contributes more damping than can a linear damper when the vibration amplitude becomes large as instability develops. It is shown that this instability is curbed at some limit cycle, whose frequency is a system natural frequency.

scholarly journals Application of Generalized Polynomial Expansion Method to Nonlinear Rotor Bearing Systems

1991 ◽  
Author(s):  
Jon Li Hwang ◽  
Ting Nung Shiau
Keyword(s):  
Hybrid Method ◽  
Harmonic Balance ◽  
Harmonic Balance Method ◽  
Expansion Method ◽  
Polynomial Expansion ◽  
Squeeze Film ◽  
Generalized Polynomial ◽  
Polynomial Expansion Method ◽  
Rotor Dynamic ◽  
Modal Coordinates

Abstract The Generalized Polynomial Expansion Method (GPEM) is utilized to model a large-order flexible-rotor system with nonlinear supports. With the application of GPEM, a set of nonlinear ordinary differential equations are obtained. A hybrid method which combines the merits of the Harmonic Balance Method (HBM) and the Trigonometric Collocation Method (TCM) is used to solve for the nonlinear response of the system. This hybrid method together with reduction techniques can efficiently solve for the motion of the system. The overall algorithm presented provides a very efficient technique for investigating the periodic response of large-order nonlinear rotor systems. Two examples are used to illustrate the merits of the method. One is the simple Jeffcott rotor which is used to check the accuracy of the present numerical algorithms. The other is a flexible shaft with multiple disks, supported by multiple bearings. It is used to show the advantages of the linkage between GPEM and the presented hybrid numerical algorithm. Some of the support bearings are modeled as a squeeze-film damper associated with a center spring. The center spring is considered to be linear and the squeeze-film damper is nonlinear. The nonlinear hydrodynamic forces are obtained using short-bearing theory. Based on the example results, the conclusions can be summarized as follows: (l) For a nonlinear flexible-rotor system, the number of equations needed for the system described by the Generalized Polynomial Expansion Method are always smaller than the number required by the finite element method before applying the condensation technique. This is also true for the linear case which has been discussed by Shiau and Hwang (1989, 1990). (2) A technique of component mode synthesis has been developed based on the modeling approach of the Generalized Polynomial Expansion Method. It is applied to decouple the nonlinear independent and dependent modal coordinates. With this technique, the number of non-zero elements in the generalized modal-forces vector is equal to the number of nonlinear, dependent modal coordinates. The results indicate that the use of GPEM together with component mode synthesis not only retains its merits in solving a linear rotor-dynamic problem, but also provides attainable solutions for the nonlinear rotor-dynamic problem. (3) The hybrid numerical algorithm developed in the present study combines both the advantages of the harmonic-balance method and the collocation method. The use of this hybrid method with condensation technique can significantly save computing time. Furthermore, it can be used to predict the periodic response, including the sub-harmonic response and the super-harmonic response, of a nonlinear system. (4) The time required for the initial formulation processing with this method may be a little more than that required by the finite-element approach. However, it is very small compared to the overall time savings that are accrued.

Imbalance Response of Nonlinear Rotor-SFD Dynamic Systems With Structure Modelled As FRFs Using Harmonic Balance Method

2017 ◽  
Author(s):  
Manoj Settipalli ◽  
Rahul Chandran ◽  
Venkatarao Ganji ◽  
Theodore Brockett
Keyword(s):  
Dynamic Systems ◽  
Harmonic Balance ◽  
Degrees Of Freedom ◽  
Fourier Coefficients ◽  
Harmonic Balance Method ◽  
Rotor System ◽  
Balance Method ◽  
Squeeze Film ◽  
Static Structure ◽  
The Impact

Squeeze-film-dampers (SFDs) used to couple rotor dynamic systems to linear static structures, such as those in aircraft engines and turbochargers, are often approximated as linear connections in dynamic simulations. Linearized stiffness and damping coefficients of the SFDs can be reasonably estimated for circular centered orbits. Selection of linearized properties for the SFD is challenged under more general whirling conditions, such as those occurring in non-centered dampers with steady gravity loading. In this paper, an efficient method for coupling the rotor system to a static structure modeled as frequency-response-functions (FRFs) through nonlinear SFDs is illustrated. The harmonic balance method (HBM) with arc length continuation technique is employed in the frequency domain to obtain the system periodic response. Degrees-of-freedom participating in the non-linear SFD model, when separated from the remaining linear degrees-of-freedom, are expanded in terms of Fourier coefficients. The algorithm allows the Fourier coefficients approximating the nonlinearity to be iteratively determined at each frequency of interest. The approach has a tremendous time advantage over a traditional nonlinear transient analysis. The method can be used to efficiently predict vibration response on the engine static structure to typical imbalance on the rotors to assess the risk of meeting the low vibration requirements typical of new designs. The prediction includes the primary driving frequencies and their harmonics in the vibration estimate. A flexible rotor system connected to structure through an SFD is used to demonstrate the approach and discuss the impact of results.

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