scholarly journals The Computational Method of Estimating Vibration Stress Levels for GTE Compressor Blades

2021 ◽  
pp. 118-131
Author(s):  
M. V Pivovarova ◽  
V. A Besschetnov
Keyword(s):  
Rotor Blade ◽  
Dynamic Stress ◽  
Natural Frequencies ◽  
Estimation Method ◽  
Compressor Blades ◽  
Vibration Stress ◽  
Stress Estimation ◽  
High Level ◽  
Vibration Forms ◽  
Blade Geometry

At present, the process of designing a GTE involves a large amount of computational modeling. With the help of computational modeling, it is possible to predict a behavior of an engine part during engine operations before conducting experimental studies. For example, the numerical dynamic behavior analysis of compressor blades and prediction of dynamic stress levels during fluctuations in free modes are urgent problems. A high level of dynamic stress in the compressor blades in resonant modes can break a blade and stop an engine. In this paper, we propose a simple vibration stress estimation method for the compressor blades based on the calculation of natural frequencies and vibration forms. The method is based on a comparative analysis and scaling of stresses by the value of the total potential or kinetic energy. This estimation method is valid for local changes in the blade geometry, which do not lead to changes in the natural frequencies and vibration forms of the blades, assuming that the geometry change does not change the level of the aerodynamic excitation of the blade or its damping. At the stage of development or revision of the blade, a large number of variants of the blade geometry needs to be analyzed in order to reduce dynamic stresses. The proposed vibration stress estimation method has shown its high efficiency in developing and refining the geometry of the compressor blade. The vibration stress estimation method was tested using the rotor blade of a high-pressure compressor. As a result of the experimental study of the rotor blade, a high level of vibration stresses exceeding the permissible level was found for natural frequencies and vibration forms. To reduce the vibration stresses, measures were proposed to modify the geometry of the blade. For the modified blade geometry, the vibration stress estimation was performed with a prediction of the vibration stress values based on the manifested vibration forms. In order to verify the estimated vibration stress change, an experimental study of the modified blade was conducted. The vibration stress estimation method for the compressor blades was successfully verified.

Speed Dependency of Coupled Rotor-Blade Torsional Natural Frequencies

2013 ◽  
Author(s):  
Ulrich Ehehalt ◽  
Balazs Becs ◽  
Xiaoping Zhou ◽  
Stefan Güllenstern
Keyword(s):  
Natural Frequency ◽  
Rotor Blade ◽  
Natural Frequencies ◽  
Low Pressure ◽  
Campbell Diagram ◽  
Calculation Results ◽  
Measured Speed ◽  
High Level ◽  
Blade Model ◽  
Proper Analysis

The natural frequencies of blades depend on the rotational speed of the rotor train as the stiffness changes with centrifugal loading. In the case of low pressure turbines with shrunk-on-disc design the coupled rotor-blade torsional natural frequencies can also show this property. For proper analysis of the speed dependency, a complete rotor-blade model which takes the elasticity of the blades into account is required. In this paper the torsional natural frequencies calculated with a complete rotor-blade model are compared with those calculated with a model in which blade elasticity is not included. The analysis clearly demonstrates that calculations without blade elasticity lead to different natural frequencies. By modeling the complete rotor and taking blade elasticity into account, it is demonstrated that the torsional natural frequencies of a complete rotor-blade model can also become speed dependent. As a consequence, a distinction between the natural frequencies at nominal speed and natural frequency at critical speeds becomes necessary. In the following, measured torsional natural frequencies at different rotating speeds of an individual low pressure rotor are presented. A comparison of the measured speed dependency of the torsional natural frequency with calculation results thereby taking the blade elasticity into account is conducted. The analysis shows that the measured speed dependency can be predicted with a high level of accuracy and can become important for modes which are dominated by the blades of the last stages. As a consequence of this analysis, a clear distinction between natural frequency at nominal and at critical speed has to be made for certain rotor and blade designs. It is shown that the use of the Campbell diagram is highly beneficial for designing rotor trains with large blades with regard to their torsional vibration behavior.

Frequency Analysis Performed on Compressor Blades of Two Types of Gas Turbines Using Campbell and SAFE Diagrams

2017 ◽  
Author(s):  
Saeed Bab ◽  
Mohsen Behzadi ◽  
Ahmad Ahmadi ◽  
Ali Ramesh ◽  
Ali Reza Shahrabi ◽  
...  
Keyword(s):  
Frequency Analysis ◽  
Gas Turbines ◽  
Natural Frequencies ◽  
Compressor Blades ◽  
Blade Vibration ◽  
Nodal Diameter ◽  
Campbell Diagram ◽  
Bladed Disk ◽  
Three Stages ◽  
High Level

This paper investigates the results of a frequency analysis performed on the blades of the last three compressor stages of two different gas turbines (Case A and B). The axial compressors in A and B have ten and eleven stages, respectively. The studied stages have identical number of blades in both compressors. However turbine B has higher number of upstream vanes before each rotating stage. Turbine B is actually a modified version of A with higher power output. The manufacturer provides acceptable ranges for several natural frequencies of blades of stage No.8 to 10 in case A. One of the purposes of this study is to figure out the logic behind the abovementioned ranges. FEM has been used in order to determine the natural frequencies of a single blade (for Campbell diagram) and bladed disk (for SAFE diagram). By surveying the results of the Campbell diagrams for blades of case A’s mentioned stages, it is concluded that the manufacturer has obtained the acceptable ranges by considering a 10% difference (at least) between single blade natural frequencies and excitation frequencies (upstream vane passage frequencies (VPF)). On the other hand, according to Campbell diagram, there is no resonance for these blades within the operational speed while SAFE diagrams show the existence of one resonance mode within the same range. The reason of this contradiction is found to be ignoring the disk stiffness effect on the blades frequencies. A same procedure was also followed to study the critical frequencies of the blades of the last three stages of turbine B’s compressor by SAFE diagrams. By checking the critical modes, it is concluded that these modes in case B are transferred to one or two modes higher in comparison to A which results in a much better vibrational behavior. This has been acquired by increasing the number of the upstream vanes. In addition, in case A’s compressor, the blades of the stage No.10 have been designed with far thicker airfoils (approximately 50%) when compared to stage No.8 and 9, even though their other dimensions are almost identical. But, this fault has been corrected in turbine B and the airfoils of all three stages almost have the same thickness. To sum up, although the design of mentioned blades in turbine B looks better and more logical than A, still a more precise look at its stages bladed disk SAFE diagrams reveals another issue. In some references there are some hints that low number of critical nodal diameter (veering region) might cause high level of blade vibration due to mistuning and this means that even in turbine B the design might not be optimal. A cure could be an increase or decrease in the number of upstream vanes in order to have a higher critical nodal diameter.

scholarly journals The Sensitivity Analysis for Life Estimation of Turbine Blades

1997 ◽  
Author(s):  
O. Repetski ◽  
K. Zainchkovski
Keyword(s):  
Vibration Analysis ◽  
Dynamic Stress ◽  
Natural Frequencies ◽  
Turbine Blades ◽  
Stress Sensitivity ◽  
Life Estimation ◽  
Sensitivity Coefficients ◽  
Sensitivity Distribution ◽  
Design Variables ◽  
Forced Vibration Analysis

The proposed algorithm permits one to determine the sensitivity coefficients of natural frequencies and dynamic displacements and stresses in the free- and forced vibration analysis. This algorithm is presented in a computer program with the help of finite element method (FEM). The design variables is the thickness of the blades. Usually a maximum resonance accounts more than half the damage and deterioration of machine components. The analysis of dynamic stress sensitivity distribution for this resonance permits us to control for both the endurance of machines and their components based on the thickness. In this study the sensitivity coefficients for both free vibration, dynamic resonances are investigated by acceleration and braking the regimes.

scholarly journals Local stress fields in solids estimated by acoustical emission method

2021 ◽  
Vol 2103 (1) ◽  
pp. 012064
Author(s):  
V L Hilarov ◽  
E E Damaskinskaya
Keyword(s):  
Time Series ◽  
Acoustic Emission ◽  
Stress Field ◽  
Estimation Method ◽  
Local Stress ◽  
Stress Fields ◽  
Emission Method ◽  
Macroscopic Fracture ◽  
Stress Estimation ◽  
Kinetic Concept

Abstract Based on the Zhurkov’s kinetic concept of solids’ fracture a local internal stress estimation method is introduced. Stress field is computed from the time series of acoustic emission intervals between successive signals. For the case of two structurally different materials the time evolution of these stresses is examined. It is shown that temporal changes of these stresses’ accumulation law may serve as a precursor of incoming macroscopic fracture.

Optimization of Robust Transonic Compressor Blades

2016 ◽  
Author(s):  
Marcus Lejon ◽  
Niklas Andersson ◽  
Tomas Grönstedt ◽  
Lars Ellbrant ◽  
Hans Mårtensson
Keyword(s):  
Surface Roughness ◽  
Service Use ◽  
Axial Compressor ◽  
Optimization Approach ◽  
Optimized Design ◽  
Compressor Stage ◽  
Compressor Blades ◽  
Transonic Compressor ◽  
Long Period ◽  
High Level

Surface degradation in an axial compressor during its lifetime can have a considerable adverse effect on its performance. The present study investigates how the optimized design of compressor blades in a single compressor stage is affected by considering a high level of surface roughness on a level representative of a long period of in-service use. It is shown that including surface roughness in the optimization process is of relatively little importance, however, matching of compressor stages is shown to require consideration as the rotational speed must be increased to reach the design point as surface quality decrease. An increased surface roughness in itself is shown to have a large effect on performance. Two optimization approaches are compared. The first approach considers the compressor blades to be hydraulically smooth. The designs obtained from this approach are subsequently degraded by increasing the level of surface roughness. The compressor blades from the first approach are compared to designs obtained from a second optimization approach, which considers a high level of surface roughness from the outset. The degraded compressor stages from the first approach are shown to be among the best performing designs in terms of polytropic efficiency and stability when compared to designs obtained with the second approach.

Cold Blade Profile Generation Methodology for Compressor Rotor Blades Using FSI Approach

2017 ◽  
Author(s):  
Kirubakaran Purushothaman ◽  
Sankar Kumar Jeyaraman ◽  
Ajay Pratap ◽  
Kishore Prasad Deshkulkarni
Keyword(s):  
Aspect Ratio ◽  
Rotor Blade ◽  
Axial Compressor ◽  
Operating Conditions ◽  
Rotor Blades ◽  
Blade Profile ◽  
Interaction Technique ◽  
Compressor Rotor ◽  
Blade Shape ◽  
Blade Geometry

This paper describes a methodology for obtaining correct blade geometry of high aspect ratio axial compressor blades during running condition taking into account of blade untwist and bending. It discusses the detailed approach for generating cold blade geometry for axial compressor rotor blades from the design blade geometry using fluid structure interaction technique. Cold blade geometry represents the rotor blade shape at rest, which under running condition deflects and takes a new operating blade shape under centrifugal and aerodynamic loads. Aerodynamic performance of compressor primarily depends on this operating rotor blade shape. At design point it is expected to have the operating blade shape same as the intended design blade geometry and a slight mismatch will result in severe performance deterioration. Starting from design blade profile, an appropriate cold blade profile is generated by applying proper lean and pre-twist calculated using this methodology. Further improvements were carried out to arrive at the cold blade profile to match the stagger of design profile at design operating conditions with lower deflection and stress for first stage rotor blade. In rear stages, thermal effects will contribute more towards blade deflection values. But due to short blade span, deflection and untwist values will be of lower values. Hence difference between cold blade and design blade profile would be small. This methodology can especially be used for front stage compressor rotor blades for which aspect ratio is higher and deflections are large.

A Study on the Effects of Geometric Non Linearities on the Un-Running Transformation of Compressor Blades

2014 ◽  
Author(s):  
Vicente P. Timon ◽  
Roque Corral
Keyword(s):  
Elastic Modulus ◽  
Rotational Speed ◽  
Compressor Blade ◽  
Large Displacement ◽  
Mass Model ◽  
Compressor Blades ◽  
Linear Solver ◽  
The Given ◽  
Selection Of ◽  
Blade Geometry

A manufactured, cold, turbomachinery blade will deform elastically under the design centrifugal, aerodynamic and thermal loads, giving the hot blade geometry. The hot-to-cold transformation or blade unrunning process consist in the calculation of the cold blade geometry which, when subject to the design conditions, will deform to match the given hot blade geometry. This paper will use a simple spring-mass model to show how the selection of geometrically linear or large displacement, geometrically non-linear, structural solvers affect the hot-to-cold transformation for compressor blades. The geometrically linear solver gives good results below a certain value of the rotational speed, which depends on the blade geometry and on the ratio of density to elastic modulus of the blade material. Above that speed, the geometrically linear solver predicts unrealistically high deformations. This model is applied to a realistic compressor blade, showing the same behavior.

Diagonal Flow Pump Impeller With NACA65 Series Blade (Correction of Blade Geometry)

2011 ◽  
Author(s):  
Yoichi Kinoue ◽  
Norimasa Shiomi ◽  
Toshiaki Setoguchi ◽  
Kazuhiro Sawamura ◽  
Hideaki Maeda
Keyword(s):  
Rotor Blade ◽  
Design Flow ◽  
Numerical Calculations ◽  
Navier Stokes ◽  
Minimum Pressure ◽  
The One ◽  
Suction Performance ◽  
Flow Pump ◽  
Better Than ◽  
Blade Geometry

Using the design method based on the design for axial-flow type turbomachine, the diagonal flow pump impellers were designed for two cases of the centrifugal effect parameter a. In addition, three-dimensional Navier-Stokes numerical calculations for single-phase were conducted in order to examine the tendency of the suction performance as well as the head performance. The head increases from the NS calculation of the impeller are the same between for a = 0.4 and for a = 1.0 because major specification are the same between for a = 0.4 and for a = 1.0. For the minimum pressure on the rotor blade, however, there is a difference between for a = 0.4 and for a = 1.0. The value of minimum pressure for a = 0.4 is −324 kPa, whereas the value for a = 1.0 is −294 kPa. The blade geometry for a = 1.0 is better than the one for a = 0.4 in terms of the suction performance because the trough of the minimum pressure is shallower for a = 1.0 than a = 0.4. Furthermore, Navier-Stokes numerical calculations were also conducted for off-design flow rate. For all cases in this paper, the minimum pressure on the rotor blade occurred at both near the leading edge and near the tip on the suction side of the blade. In addition, for all cases in this paper, the blade geometry for a = 1.0 is better than the one for a = 0.4 in terms of the suction performance.

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