Methods and Procedures for Trim Balancing the LM2500 Marine Gas Turbine in the Test Cell and Aboard Ship

1989 ◽  
Author(s):  
Bruce D. Thompson ◽  
Robert H. Badgley ◽  
Richard Raczkowski
Keyword(s):  
Gas Turbines ◽  
Angle Measurement ◽  
Influence Coefficient ◽  
Gas Generator ◽  
Residual Vibration ◽  
Successful Development ◽  
Generator Rotor ◽  
Practical Procedure ◽  
Influence Coefficients ◽  
Speed Range

Extensive fleet experience with LM2500 marine gas turbines shows that engines with higher than normal vibration are more likely to show early wear. Gas generator rotor unbalance has been identified as the main cause of high vibration. Rotor rebalancing reduces vibration to acceptable levels, at the same time reducing or eliminating many wearout modes. Initially, the only rebalance option was to remove the gas generator from the ship and send it to the depot. The high cost of this option led to a search for alternatives, and the successful development of a procedure for rebalancing the gas generator rotor aboard ship. The method adopted was the well known influence coefficient procedure, developed by the National Aeronautics and Space Administration (NASA) in the late 1960’s. This method is well suited for implementation on portable computers, and fits readily into a practical procedure for use by trained technicians. The NASA program originally included a procedure to minimize peak residual vibration. Navy engineers added an improved optimizing procedure and a method to account for engine nonlinearities. Rebalancing involves mounting four external accelerometers on the engine, along with a tachometer to give a one-per-rev signal for phase angle measurement. Baseline vibration measurements, together with stored influence coefficients for the LM2500 engine series, permit first shot multi-plane, multi-speed trim correction weights to be calculated. The compressor case is readily opened and the weights installed without disturbing the engine. Application of this procedure has been highly successful: vibration levels of less than 0.001 inch peak-to-peak over the entire speed range have been achieved. The avoided cost of removal, replacement and repair of an LM2500 is estimated to be about $500,000.

scholarly journals An Optimum Balance Weight Search Algorithm

1993 ◽  
Author(s):  
James C. Austrow
Keyword(s):  
Search Algorithm ◽  
Least Square ◽  
Test Case ◽  
Influence Coefficient ◽  
Residual Vibration ◽  
Single Plane ◽  
Vibration Data ◽  
Influence Coefficients ◽  
Balance Weight ◽  
Optimum Balance

A mathematical description for an optimum balance weight search algorithm for single plane multipoint balance is presented. The algorithm uses influence coefficients, either measured or known beforehand, and measured complex vibration data to determine an optimum balance correction weight. The solution minimizes the maximum residual vibration. The algorithm allows user defined balance weights to be analyzed and evaluated. A test case is presented showing actual results and comparison with a least square solution algorithm. An efficient multiplane influence coefficient calculation scheme is also presented.

Optimization of LM2500 Gas Generator and Power Turbine Trim Balance Techniques

1991 ◽  
Author(s):  
Bruce D. Thompson
Keyword(s):  
Success Rate ◽  
Maximum Amplitude ◽  
Turbine Rotor ◽  
Theoretical Background ◽  
Influence Coefficient ◽  
Gas Generator ◽  
Imbalance Problem ◽  
Influence Coefficients ◽  
Power Turbine ◽  
Good Set

A procedure has been developed by the U.S. Navy to trim balance, in-place, the gas generator and power turbine rotor of the LM2500 Marine Gas Turbine Engine. This paper presents the theoretical background and the techniques necessary to optimize the procedure to balance the gas generator rotor. Additionally, a method was developed to trim balance LM2500 power turbines. To expand the implementation of both gas generator and power turbine trim balancing, a capability had to be developed to minimize the effort required (trial weight runs etc.). The objective was to able to perform consistently what are called “First Shot” trim balances. “First Shot” trim balances require only one weight placement to bring the engine vibration levels to within the specified goals (less than .002 of an inch maximum amplitude) and that being the final trim weight. It was realized that the Least Squares Influence Coefficient method, even with a good set of averaged influence coefficients, can lead to a number of trial weight experiments before the final trim weights can be placed. The method used to maximize the possibility of obtaining a “First Shot” trim balance was to use modal information to tailor the influence coefficient sets to correct the most predominant and correctable imbalance problem. Since the influence coefficients were tailored, it became necessary to be able to identify, in the initial vibration survey, the type of response a particular LM2500 has. Using modal information obtained from a LM2500 rotor dynamics model and from the early trim balance efforts it was possible to identify the modal response of a given LM2500 and optimize the trim balance of that engine. With these improved techniques a 70% success rate for “First Shot” trim balance has been achieved and the success rate of the trim balance procedure, as a whole, has been near 100%.

Optimization of LM2500 Gas Generator and Power Turbine Trim-Balance Techniques

1992 ◽  
Vol 114 (2) ◽  
pp. 222-229 ◽  
Author(s):  
B. D. Thompson
Keyword(s):  
Success Rate ◽  
Maximum Amplitude ◽  
Turbine Rotor ◽  
Theoretical Background ◽  
Influence Coefficient ◽  
Gas Generator ◽  
Imbalance Problem ◽  
Influence Coefficients ◽  
Power Turbine ◽  
Good Set

A procedure has been developed by the U.S. Navy to trim-balance, in-place, the gas generator and power turbine rotor of the LM2500 Marine Gas Turbine Engine. This paper presents the theoretical background and the techniques necessary to optimize the procedure to balance the gas generator rotor. Additionally, a method was developed to trim balance LM2500 power turbines. To expand the implementation of both gas generator and power turbine trim-balancing, a capability has to be developed to minimize the effort required (trial weight runs, etc.). The objective was to be able to perform consistently what are called “First-Shot” trim balances. First-Shot trim balances require only one weight placement to bring the engine vibration levels to within the specified goals (less than 0.002 of an in. maximum amplitude) and that being the final trim weight. It was realized that the Least-Squares Influence-Coefficient Method, even with a good set of averaged influence coefficients, can lead to a number of trial weight experiments before the final trim weights can be placed. The method used to maximize the possibility of obtaining a First-Shot trim balance was to use modal information to tailor the influence coefficient sets to correct the most predominant and correctable imbalance problem. Since the influence coefficients were tailored, it became necessary to be able to identify, in the initial vibration survey, the type of response a particular LM2500 has. Using modal information obtained from a LM2500 rotor dynamics model and from the early trim-balance efforts, it was possible to identify the modal response of a given LM2500 and optimize the trim balance of that engine. With these improved techniques a 70 percent success rate for First-Shot trim balance has been achieved and the success rate of the trim balance procedure, as a whole, has been near 100 percent.

An Optimum Balance Weight Search Algorithm

1994 ◽  
Vol 116 (3) ◽  
pp. 678-681 ◽  
Author(s):  
J. C. Austrow
Keyword(s):  
Search Algorithm ◽  
Solution Algorithm ◽  
Test Case ◽  
Influence Coefficient ◽  
Residual Vibration ◽  
Single Plane ◽  
Vibration Data ◽  
Influence Coefficients ◽  
Balance Weight ◽  
Optimum Balance

A mathematical description for an optimum balance weight search algorithm for single-plane multipoint balance is presented. The algorithm uses influence coefficients, either measured or known beforehand, and measured complex vibration data to determine an optimum balance correction weight. The solution minimizes the maximum residual vibration. The algorithm allows user-defined balance weights to be analyzed and evaluated. A test case is presented showing actual results and comparison with a least-squares solution algorithm. An efficient multiplane influence coefficient calculation scheme is also presented.

Advanced Control System Considerations for Small Shaft-Type Aircraft Gas Turbines

1970 ◽  
Author(s):  
D. A. Prue ◽  
T. L. Soule
Keyword(s):  
Control System ◽  
Gas Turbines ◽  
Evaluation Criteria ◽  
Open Loop ◽  
Engine Control ◽  
Gas Generator ◽  
Engine Control System ◽  
Power Turbine ◽  
Advanced Control ◽  
Temperature Load

The next generation of free-turbine engines in the 2 to 5-lb/sec airflow class will undergo vast improvements in performance and efficiency. The improvements will be achieved concurrent with overall reductions in size and weight. Effort is required at optimization and miniaturization of the engine control system to keep pace with these improvements. This paper describes a conceptual design of an advanced engine control system for this class of engine. It provides gas generator and power turbine control with torque, temperature, load sharing and overspeed limiting functions. The control system was concepted to accommodate, with minimum hardware changes, such variants as regenerative cycle and/or variable power turbine geometry. In addition, considerations for closed and open loop modes of control and fluidic, electronic and hydromechanical technologies were studied to best meet a defined specification and a weighted set of evaluation criteria.

Comparison of the Influence Coefficient Method and Travelling Wave Mode Approach for the Calculation of Aerodynamic Damping of Centrifugal Compressors and Axial Turbines

2017 ◽  
Author(s):  
K. Vogel ◽  
A. D. Naidu ◽  
M. Fischer
Keyword(s):  
Centrifugal Compressor ◽  
Travelling Wave ◽  
Wave Mode ◽  
Forced Response ◽  
Computational Time ◽  
Influence Coefficient ◽  
Average Deviation ◽  
Aerodynamic Damping ◽  
Influence Coefficients ◽  
Periodic Boundaries

The prediction of aerodynamic damping is a key step towards high fidelity forced response calculations. Without the knowledge of absolute damping values, the resulting stresses from forced response calculations are often afflicted with large uncertainties. In addition, with the knowledge of the aerodynamic damping the aeroelastic contribution to mistuning can be considered. The first section of this paper compares two methods of one-way-coupled aerodynamic damping computations on an axial turbine. Those methods are: the aerodynamic influence coefficient, and the travelling wave mode method. Excellent agreement between the two methods is found with significant differences in required computational time. The average deviation between all methods for the transonic turbine is 4%. Additionally, the use of transient blade row methods with phase lagged periodic boundaries are investigated and the influence of periodic boundaries on the aerodynamic influence coefficients are assessed. A total of 23 out of 33 passages are needed to remove all influence from the periodic boundaries for the present configuration. The second part of the paper presents the aerodynamic damping calculations for a centrifugal compressor. Simulations are predominantly performed using the aerodynamic influence coefficient approach. The influence of the periodic boundaries and the recirculation channel is investigated. All simulations are performed on a modern turbocharger turbine and centrifugal compressor using ANSYS CFX V17.0 with an inhouse pre- and post-processing procedure at ABB Turbocharging. The comparison to experimental results concludes the paper.

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.

Analysis of Complex Kinematic Chains With Influence Coefficients

1959 ◽  
Vol 26 (2) ◽  
pp. 184-188
Author(s):  
J. Modrey
Keyword(s):  
Simultaneous Equations ◽  
Influence Coefficient ◽  
Complex Mechanism ◽  
Direct Process ◽  
Kinematic Chains ◽  
Influence Coefficients

Abstract Highly complex kinematic chains such as Fig. 1(c) can be analyzed by the use of simple vector equations involving influence coefficients. The influence-coefficient equations are related to superposition of simple kinematic chains. The technique for determining the necessary influence coefficients is one of sequentially setting all variables but one to zero and relaxing appropriate constraints to maintain mobility. This “zero-relax” process creates a series of mechanisms each simple enough to be solved by a direct process rather than by simultaneous equations. The analysis of the velocities and accelerations for these simpler mechanisms yields the influence coefficients of the related but more highly complex mechanism.

Influence Coefficients for Hemispherical Shells With Small Openings at the Vertex

1955 ◽  
Vol 22 (1) ◽  
pp. 20-24
Author(s):  
G. D. Galletly
Keyword(s):  
Constant Thickness ◽  
Influence Coefficient ◽  
Circular Opening ◽  
Central Angle ◽  
Calculation Time ◽  
Numerical Example ◽  
Hemispherical Shell ◽  
Influence Coefficients ◽  
Hemispherical Shells

Abstract Three methods of obtaining the influence coefficients for a thin, constant-thickness, hemispherical shell with a circular opening at the vertex were investigated and utilized in a numerical example. Bearing in mind both accuracy and calculation time, it was concluded that when the total central angle subtended by the opening is less than approximately 30 deg, good results for the influence coefficient calculation will be obtained by using Method II in the text of the paper.

scholarly journals Usage of the influence coefficient during calculation of a nominal error of gas counters

2019 ◽  
Vol 298 ◽  
pp. 00009
Author(s):  
M.S. Ostapenko ◽  
M.A. Popova ◽  
A.M. Tveryakov
Keyword(s):  
Relative Error ◽  
Gas Flow ◽  
Oil And Gas ◽  
Great Influence ◽  
Operating Conditions ◽  
Effect Of Temperature ◽  
Influence Coefficient ◽  
Technical Documentation ◽  
Flow Meters ◽  
Influence Coefficients

In this paper, we evaluate the method of finding the relative error of gas flow meters taking into account the influence coefficients. A literature analysis was carried out, which showed that flow meters are used at oil and gas enterprises, which show its metrological characteristic, showing specific values of gas flow in operating conditions. Various types of gas flow meters are considered, with a description of the quality indicators of the devices. An additional error was investigated depending on changes in operating conditions. The calculations of the relative error of the meter taking into account the limiting values of the additional errors indicated in the technical documentation, as well as calculations taking into account the coefficients of influence under operating conditions. Based on the obtained values of the influence coefficients, graphs were constructed on which the effect of temperature and pressure on the error was determined. The article provides tabular values of the influence coefficients for petroleum gas, a conclusion is drawn on the applicability of this method.Oil and gas industry have a great influence on development of national economy in our country. Oil and gas have a leading position in energy industry and they are more effective and energy-intense in comparison with other natural substances.

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