Improving Tilting-Pad Journal Bearing Predictions—Part II: Comparison of Measured and Predicted Rotor-Pad Transfer Functions for a Rocker-Pivot Tilting-Pad Journal Bearing

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
Jason C. Wilkes ◽  
Dara W. Childs
Keyword(s):  
Static Load ◽  
Journal Bearing ◽  
Transfer Functions ◽  
Model Development ◽  
Analytical Models ◽  
Dynamic Changes ◽  
Direct Measurements ◽  
Tilting Pad ◽  
Load Vector ◽  
Tilting Pad Journal Bearing

As described in Part I (Wilkes et al., 2012, “Improving Tilting-Pad Journal Bearing Predictions—Part I: Model Development and Impact of Rotor Excited Versus Bearing Excited Impedance Coefficients,” ASME J. Eng. Gas Turb. Power, 135(1), p. 012503), most analytical models for tilting-pad journal bearing (TPJBs) are based on the assumption that explicit dependence on pad motion can be eliminated by assuming harmonic rotor motion such that the amplitude and phase of pad motions resulting from radial and transverse rotor motions are predicted by rotor-pad transfer functions. In short, these transfer functions specify the amplitude and phase of pad motion (angular, radial, translational, etc.) in response to an input rotor motion. Direct measurements of pad motion during test excitation were recorded to produce measured transfer functions between rotor and pad motion, and a comparison between these measurements and predictions is given. Motion probes were added to the loaded pad (having the static load vector directed through its pivot) of a 5-pad TPJB to obtain accurate measurement of pad radial and tangential motion, as well as tilt, yaw, and pitch. Strain gauges were attached to the side of the loaded pad to measure static and dynamic bending strains, which were then used to determine static and dynamic changes in pad curvature (pad clearance).

Improving Tilting-Pad Journal Bearing Predictions: Part II—Comparison of Measured and Predicted Rotor-Pad Transfer Functions for a Rocker-Pivot Tilting-Pad Journal Bearing

2012 ◽  
Author(s):  
Jason C. Wilkes ◽  
Dara W. Childs
Keyword(s):  
Static Load ◽  
Journal Bearing ◽  
Transfer Functions ◽  
Analytical Models ◽  
Strain Gages ◽  
Dynamic Changes ◽  
Direct Measurements ◽  
Tilting Pad ◽  
Load Vector ◽  
Tilting Pad Journal Bearing

As described in Part I [1], most analytical models for TPJBs are based on the assumption that explicit dependence on pad motion can be eliminated by assuming harmonic rotor motion such that the amplitude and phase of pad motions resulting from radial and transverse rotor motions are predicted by rotor-pad transfer functions (TFs). In short, these transfer functions specify the amplitude and phase of pad motion (angular, radial, translational, etc.) in response to an input rotor motion. Direct measurements of pad motion during test excitation were recorded to produce measured transfer functions between rotor and pad motion, and a comparison between these measurements and predictions is given. Motion probes were added to the loaded pad (having the static load vector directed through its pivot) of a 5-pad TPJB to obtain accurate measurement of pad radial and tangential motion, as well as tilt, yaw, and pitch. Strain gages were attached to the side of the loaded pad to measure static and dynamic bending strains, which were then used to determine static and dynamic changes in pad curvature (pad clearance).

Identification of Dynamic Coefficients of a Five-Pad Tilting Pad Journal Bearing up to Highest Surface Speeds

2020 ◽  
Author(s):  
Philipp Zemella ◽  
Thomas Hagemann ◽  
Bastian Pfau ◽  
Hubert Schwarze
Keyword(s):  
Flow Rate ◽  
Time Domain ◽  
Static Load ◽  
Journal Bearing ◽  
Damping Coefficients ◽  
Dynamic Coefficients ◽  
Tilting Pad ◽  
Oil Flow ◽  
Tilting Pad Journal Bearing ◽  
The Impact

Abstract Tilting-pad journal bearings are widely used in turbomachinery industry due to their positive dynamic properties at high rotor speeds. However, the exact description of this dynamic behavior is still part of current research. This paper presents measurement results for a five-pad tilting-pad journal bearing in load between pivot configuration. The bearing is characterized by a nominal diameter of 100 mm, a length of 90 mm, and a pivot offset of 0.6. Investigations include results for surface speeds between 25 and 120 m/s and specific bearing loads ranging from 0.0 to 3.0 MPa. Results of theoretical predictions are commonly derived from perturbation of stationary operation under static load. Therefore, experimental results for stationary operation including pad deflection under static load are presented first to characterize the investigated bearing. Measured results indicate considerable non-laminar flow in the upper region of the investigated range of rotor speeds. Second, dynamic excitation test are performed with excitation frequencies up to 400 Hz to evaluate dynamic coefficients of a stiffness (K) and damping (C) KC-model, and additionally, a KCM-model using additional virtual mass (M) coefficients. KCM-coefficients are obtained by fitting frequency dependent KC-characteristics to the KCM-model structure using least square approach. The wide range of rotating and excitation frequencies leads to subsynchronous as well as supersynchronous vibrations. Excitation forces are applied with multi-sinus and single-sinus characteristics. The latter one allows evaluation of KC-coefficients at the particular frequency ratio in the time domain. Here, frequency and time domain evaluation algorithms for dynamic coefficients are used in order to assess their special properties and quality. The impact of surface speed, bearing load, and oil flow rate on measured and predicted KCM-coefficients is investigated. Measured and predicted results can be well fitted to a KCM-model and show a significant influence of the ratio between fluid film and pivot support stiffness on the speed dependent characteristic of bearing stiffness coefficients. However, the impact of this ratio on damping coefficients is considerably lower. Further investigations on the impact of oil flow rates indicate that a significant decrease of direct damping coefficients exists below a certain level of starvation. Above this limit, direct damping coefficients are nearly independent of oil flow rate. Results are analyzed in detail and demands on improvements for predictions are derived.

Calculation of Stiffness and Damping Properties of Gas Bearings

1968 ◽  
Vol 90 (4) ◽  
pp. 793-803 ◽  
Author(s):  
J. W. Lund
Keyword(s):  
Static Load ◽  
Journal Bearing ◽  
Computational Method ◽  
Gas Bearings ◽  
Rotating Speed ◽  
Damping Coefficients ◽  
Tilting Pad ◽  
Stiffness And Damping ◽  
Tilting Pad Journal Bearing ◽  
Gas Bearing

The dynamic characteristics of a gas bearing can be represented by a set of spring and damping coefficients (impedances) which are functions of the static load on the bearing, the rotating speed and the whirl frequency of the journal. For a rotor supported in gas bearings, these coefficients can be used directly in a critical speed calculation or an unbalance response calculation. In addition, the coefficients can be employed in a stability investigation. The paper gives the computational method for obtaining the spring and damping coefficients and, also, describes how they are used in rotor calculations and stability studies. Numerical results are given in graphical and tabular form for a tilting pad journal bearing and a three-lobe journal bearing.

Measured and Predicted Transfer Functions Between Rotor Motion and Pad Motion for a Rocker-Back Tilting-Pad Bearing in LOP Configuration

2011 ◽  
Author(s):  
Jason C. Wilkes
Keyword(s):  
Transfer Functions ◽  
Analytical Models ◽  
Single Frequency ◽  
Frequency Dependent ◽  
Damping Coefficients ◽  
Operating Region ◽  
Direct Measurements ◽  
Trailing Edges ◽  
Tilting Pad ◽  
Stiffness And Damping

Many researchers have compared predicted stiffness and damping coefficients for tilting-pad journal bearings (TPJBs) to measurements. Most have found that direct damping is consistently overpredicted. Continuing to test TBJBs in the same fashion is not likely to produce an explanation for the discrepancies between measured and predicted damping. Most analytical models for TPJBs are based on the assumption that explicit dependence on pad motion can be eliminated by assuming a solution for rotor motion such that the amplitude and phase of pad motions are predicted by rotor-pad transfer functions. Direct measurements of pad motion during test excitation are needed to produce measured transfer functions between rotor and pad motion, and a comparison between these measurements and predictions is needed to identify model discrepancies. A test setup was designed to fulfill these objectives. Motion probes were added to the loaded pad to obtain accurate measurement of pad radial and tangential motion, as well as tilt, yaw and pitch. For the remainder of this work, the loaded pad refers to the pad whose pivot sits on the static load line. Testing was performed primarily at low speeds and high loads, since this is the operating region for which predictions are most erroneous. Single frequency excitations were performed ranging from 10–350 Hz, producing rotor and pad motion, acceleration, and force vectors. This motion was used to determine frequency-dependent bearing impedances and rotor-pad transfer functions. A new pad perturbation model is proposed including the effects of pad angular, radial, and circumferential pad motion. This model was implemented in a Reynolds-based TPJB code to predict the frequency-dependent bearing impedances and rotor-pad transfer functions. These predictions are compared with measurements and discussed. Good agreement was found between the amplitude of the measured and predicted transfer functions concerning tilt and radial motions for low to moderate loads, but deviated in accuracy at the highest loaded case. Circumferential (sliding) pad motion was predicted and observed; however, the effect of this degree of freedom on dynamic bearing coefficients has not been quantitatively assessed. For the bearing investigated, radial motion accounted for more than 67% of total motion of the fluid-film height at the leading and trailing edges of the pad when operating at 4400 rpm under heavily loaded conditions. The measurements show that predicting TPJB stiffness and damping coefficients without accounting for pad pivot deformation will not produce satisfactory outcomes.

Improving Tilting-Pad Journal Bearing Predictions: Part I—Model Development and Impact of Rotor-Excited Versus Bearing-Excited Impedance Coefficients

2012 ◽  
Author(s):  
Jason C. Wilkes ◽  
Dara W. Childs
Keyword(s):  
Journal Bearing ◽  
Reaction Force ◽  
Model Development ◽  
Journal Bearings ◽  
Test Rig ◽  
Tilting Pad ◽  
Force Components ◽  
Rotor Journal ◽  
Tilting Pad Journal Bearing ◽  
Tilting Pad Journal Bearings

The floating-bearing-test-rig concept was initially developed by Glienicke in 1966 and has since been used to test many tilting-pad journal bearings (TPJBs). The impedances measured during these tests have been compared to rotor/journal perturbed impedance predictions. Since the inertial acceleration of a pad is different for bearing perturbed and rotor perturbed motions, the bearing’s reaction force components for bearing perturbed and journal perturbed motions will also differ. An understanding of how bearing perturbed and rotor perturbed impedances differ is needed to assess the validity of past, present, and future comparisons between TPJB test data and predictions. A new TPJB perturbation model is developed including the effects of angular, radial, and transverse pad motion and changes in pad clearance due to pad bending compliance. Though all of these pad variables have previously been included in different analyses, there are no publications containing perturbations of all four variables. In addition, previous researchers have only perturbed the rotor, while both the bearing and rotor motions are perturbed in the present analysis. The applicability of comparing rotor-perturbed bearing impedance predictions to impedances measured on a bearing-perturbed test rig is assessed by comparing rotor perturbed and bearing perturbed impedance predictions for an example bearing.

Chaotic Dynamics of Rotor Supported on Tilting-Pad Journal Bearing (TPJB): A Review and Current Work

2005 ◽  
Author(s):  
Issam Abu-Mahfouz
Keyword(s):  
Chaotic Dynamics ◽  
Static Load ◽  
Journal Bearing ◽  
State Of The Art ◽  
Nonlinear Behavior ◽  
Chaotic Motions ◽  
Strongly Nonlinear ◽  
Numerical Experimentation ◽  
Tilting Pad ◽  
Tilting Pad Journal Bearing

The use of tilting-pad journal bearing (TPJB) has increased in the recent past due to their stability effects on the rotor bearing system. The first part of this paper presents a review of the state of the art work on rotor response when supported on TPJB. Only few published work presented results relating to the strongly nonlinear behavior, especially chaos, resulting from the use of these types of bearings. In the second part of this paper, three loading mechanisms capable of producing instabilities in terms of sub-harmonic and chaotic motions are suggested. The first one is that of a centrally loaded pad with small rotor unbalance excitations. The second one is when the load is applied between two pads. And, the third represents a concentric rotor (zero static load) acted upon by centering sprigs and unbalance excitation. After a quite extensive numerical experimentation, the resulting response shows, for certain parameters, sub-harmonic, quasi-periodic and chaotic motions.

scholarly journals Static Characteristics of a Tilting Five-Pad Journal Bearing with an Asymmetric Geometry

Actuators ◽  
2020 ◽  
Vol 9 (3) ◽  
pp. 89
Author(s):  
Phuoc Vinh Dang ◽  
Steven Chatterton ◽  
Paolo Pennacchi
Keyword(s):  
Static Load ◽  
Journal Bearing ◽  
Experimental Tests ◽  
Experimental Measurements ◽  
Static Characteristics ◽  
Distribution Profile ◽  
Tilting Pad ◽  
Static Eccentricity ◽  
Temperature And Pressure ◽  
Tilting Pad Journal Bearing

In this paper, static characteristics of a tilting five-pad rocker-backed journal bearing with an asymmetric geometry, i.e., different clearance for each pad, are investigated. A thermo-elasto-hydrodynamic (TEHD) model considering the elasticity of the pad and pivot is used for the simulation. The pivot stiffness of each pad obtained by experiment is also introduced in the model. The experimental tests were carried out on a tilting pad journal bearing (TPJB) with a nominal diameter of 100 mm and a length-to-diameter (L/D) ratio of 0.7 with load-between-pad (LBP) and load-on-pad (LOP) arrangements. Several analyses, including numerical simulations and experimental measurements, are implemented in order to obtain the static behaviors of the tilting-pad bearing under variations of rotational speed, amplitude and direction of applied static load, such as clearance distribution profile, static eccentricity, temperature and pressure distribution. The results show that the effect of asymmetric geometry on the static characteristics is not negligible.

Frequency Effects on the TEHD Behavior of a Tilting-Pad Journal Bearing Under Dynamic Loading

1999 ◽  
Vol 121 (2) ◽  
pp. 321-326 ◽  
Author(s):  
P. Monmousseau ◽  
M. Fillon
Keyword(s):  
Dynamic Loading ◽  
Dynamic Load ◽  
Critical Frequency ◽  
Static Load ◽  
Journal Bearing ◽  
Loading Frequency ◽  
Tilting Pad ◽  
High Dynamic ◽  
Tilting Pad Journal Bearing ◽  
Rotating Load

In this paper, a theoretical nonlinear analysis of a tilting-pad journal bearing is presented when both a dynamic load and a static load are applied. This analysis is performed under TEHD regime which takes into account both thermal behavior and elastic deformations of the bearing. A comparison between numerical maximum journal amplitudes and experimental data in the case of synchronous dynamic loading is carried out in order to justify the TEHD analysis. The influence of the dynamic loading frequency, which can occur because of vibrations in a turbomachinery, will be studied at a constant rotational speed (15,000 rpm) and for a low (200 N) and a high (2652 N) rotating load and for a periodic dynamic load. It will be shown that, for a critical frequency, the amplitude of the shaft orbit is maximum and this changes the behavior of the tilting-pad journal bearing. It is apparent that the application of the dynamic load generates a thermal transient regime. The increase in the maximum bearing temperature is larger for high dynamic loading response. Consequently, the behavior of the bearing is mainly modified during the first few seconds when the loading frequency is near the critical frequency.

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