Forced Response Analysis of a Steam Turbine Shrouded Blade: Numerical Analysis and Experiments

2013 ◽  
Author(s):  
Francesco Piraccini ◽  
Salvatore Lorusso ◽  
Nicola Maceli ◽  
John Ryman
Keyword(s):  
Dynamic Response ◽  
Steam Turbine ◽  
Test Data ◽  
Element Model ◽  
Low Pressure ◽  
Forced Response ◽  
Operating Conditions ◽  
Response Analysis ◽  
Cfd Analysis ◽  
Pressure Development

Faced with the present transformation of the world economy, steam turbine manufacturers are seeking ways to remain competitive in their respective markets. Having longer Low Pressure (LP) blades and seeking for higher rotating speeds have always been two effective methods to improve the Steam Turbine efficiency, therefore to reduce steam consumption and related plant costs. Both trends have increased the risk of failure for forced response due to the occurrence of resonance or to the decrease of alternating stress margins. Because of large uncertainties in the estimation of friction damping and aerodynamic excitation, the prediction of dynamic response of the long blades in the LP section is still a challenge for the analytical tools; therefore, expensive activities for experimental validation are usually required. In order to reduce design costs and time, a set of tools has been developed and validated using the test data collected during a full-scale test vehicle campaign in steam (Low Pressure Development Turbine - LPDT). In this study, the validation activity related to the blade response due to nozzle stimulus is reported. As a first step, a steady state CFD analysis was performed at the operating conditions where significant response was observed, caused by the resonance with the Nozzle Passing Frequency (NPF). Then, an unsteady CFD analysis of the bucket blade was conducted considering the perturbation due to the nozzles. Subsequently, the computed unsteady pressure distribution on the blade airfoil was mapped onto a finite element model and forced response analyses were performed to estimate the bucket dynamic response. The predicted response was compared against measured test data and good correlation was found.

Impact of Turbine Center Frame Wakes on Downstream Rows in Heavy-Duty Low-Pressure Turbine

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Sara Biagiotti ◽  
Juri Bellucci ◽  
Michele Marconcini ◽  
Andrea Arnone ◽  
Gino Baldi ◽  
...  
Keyword(s):  
Experimental Data ◽  
Low Pressure ◽  
Numerical Approach ◽  
Forced Response ◽  
Operating Conditions ◽  
Response Analysis ◽  
Test Case ◽  
Low Pressure Turbine ◽  
Harmonic Content ◽  
The Impact

Abstract In this work, the effects of turbine center frame (TCF) wakes on the aeromechanical behavior of the downstream low-pressure turbine (LPT) blades are numerically investigated and compared with the experimental data. A small industrial gas turbine has been selected as a test case, composed of a TCF followed by the two low-pressure stages and a turbine rear frame (TRF) before the exhaust plenum. Full annulus unsteady computations of the whole low-pressure module have been performed. Two operating conditions, full (100%) and partial (50%) load, have been investigated with the aim of highlighting the impact of TCF wakes convection and diffusion through the downstream rows. Attention was paid to the harmonic content of rotors’ blades. The results show a slower decay of the wakes through the downstream rows in off-design conditions compared with the design point. The analysis of the rotors’ frequency spectrum reveals that moving from design to off-design conditions, the effect of the TCF does not change significantly. The harmonic contribution of all turbine components has been extracted, highlighting the effect of statoric parts on the last LPT blade. The TCF harmonic content remains the most relevant from an aeromechanic point of view as per experimental evidence, and it is considered for an forced response analysis (FRA) on the last LPT blade itself. Finally, aerodynamic and aeromechanic predictions have been compared with the experimental data to validate the numerical approach. Some general design solutions aimed at mitigating the TCF wakes impact are discussed.

Impact of Turbine Center Frame Wakes on Downstream Rows in Heavy Duty Low Pressure Turbine

2019 ◽  
Author(s):  
Sara Biagiotti ◽  
Juri Bellucci ◽  
Michele Marconcini ◽  
Andrea Arnone ◽  
Gino Baldi ◽  
...  
Keyword(s):  
Experimental Data ◽  
Low Pressure ◽  
Forced Response ◽  
Point Of View ◽  
Operating Conditions ◽  
Response Analysis ◽  
Low Pressure Turbine ◽  
Harmonic Content ◽  
Partial Load ◽  
The Impact

Abstract In this work, the effects of Turbine Center Frame (TCF) wakes on the aeromechanical behavior of the downstream Low Pressure Turbine (LPT) blades are numerically investigated and compared with experimental data. A small industrial gas turbine has been selected as a test case, composed of a TCF followed by the two low pressure stages and a Turbine Rear Frame (TRF) before the exhaust plenum. Full annulus unsteady computations of the whole low-pressure module have been performed. Two operating conditions, full (100%) and partial (50%) load, have been investigated with the aim of highlighting the impact of TCF wakes convection and diffusion through the downstream rows. Attention was paid to the harmonic content of rotors’ blades. From an aerodynamic point of view, the results show a slower decay of the wakes through the downstream rows in off-design conditions as compared to the design point. The wakes generated by the struts at partial load persist throughout the domain outlet, while they are chopped and circumferentially transported by the rotors motion. This is due to the strong incidence variation at which the TCF works, which induces the growth of wide regions of separated flow on the rear part of the struts. Nevertheless, the analysis of the rotors’ frequency spectrum reveals that moving from design to off-design conditions, the effect of the TCF does not change significantly, thanks to the filtering action of the first LPT stage movable Nozzle Guide Vane (NGV). From unsteady calculations the harmonic contribution of all turbine components has been extracted, highlighting the effect of statoric parts on the last LPT blade. Anyhow the TCF harmonic content remains the most relevant from an aeromechanic point of view as per experimental evidence, and it is considered for a Forced Response Analysis (FRA) on the last LPT blade itself. Finally, aerodynamic and aeromechanic predictions have been compared with the experimental data to validate the numerical approach. In the last part of this paper some general design solutions, that can help mitigation of the TCF wakes impact, are discussed.

Forced Response Prediction for Steam Turbine Last Stage Blade Subject to Low Engine Order Excitation

2011 ◽  
Author(s):  
Bin Zhou ◽  
Amir Mujezinovic ◽  
Andrew Coleman ◽  
Wei Ning ◽  
Asif Ansari
Keyword(s):  
Steam Turbine ◽  
Low Pressure ◽  
Forced Response ◽  
Operating Conditions ◽  
Low Flow ◽  
Analytical Prediction ◽  
Unsteady Pressure ◽  
Engine Order ◽  
Last Stage ◽  
Cfd Analyses

Low Engine Order (LEO) excitations on a steam turbine Last Stage low-pressure (LP) Bucket (or Blade) (LSB) are largely the result of flow unsteadiness (e.g. flow circulation and reversal) due to low steam exit velocity (Vax) off the LSB at the off-design conditions. These excitations at low frequencies impose major constraints on LP bucket aeromechanical design. In this study, bucket forced response under typical LEO excitation was analytically predicted and correlated to experimental measurements. First, transient CFD analyses were performed at typical low flow, low Vax operating conditions that had been previously tested in a subscale low pressure turbine test rig. The unsteady pressure distribution on the bucket was derived from the transient CFD analyses at frequencies corresponding to the bucket’s modes of vibration. Subsequently, these computed unsteady pressure were mapped onto a LSB finite element model, and forced response analyses were performed to estimate the bucket dynamic response, i.e. the alternating stresses and strains. The analytically predicted bucket response was compared against measured data from airfoil mounted strain gages and good correlation was found between the analytical prediction and the test data. Despite uncertainty associated with various parameters such as damping and unsteady steam forcing etc., the developed methodology provides a viable approach for predicting bucket forced response and in turn High Cycle Fatigue (HCF) capability during early phases of steam turbine LSB design.

Impact of Mistuning on the Vibration Behaviour of the Last Stage in a Model Three Stage Low Pressure Steam Turbine

2011 ◽  
Author(s):  
Christoph Heinz ◽  
Markus Schatz ◽  
Michael V. Casey ◽  
Heinrich Stu¨er
Keyword(s):  
Steam Turbine ◽  
Amplitude Distribution ◽  
Low Pressure ◽  
Forced Response ◽  
Operating Conditions ◽  
Scale Model ◽  
Resonance Frequencies ◽  
Pressure Steam ◽  
Last Stage ◽  
Operating Points

The last stages of a low-pressure steam turbine, with long freestanding blades, may experience forced response excitation during resonance crossing at start-up and shut-down and this can be responsible for blade failure. This paper presents an experimental investigation of the circumferential blade amplitude distribution at different operating conditions and for different mistuning configurations in a scale model of a state-of-the-art low pressure steam turbine. Five configurations are investigated; two with different intentionally mistuned frequency arrangements, where the blades are placed alternately in different high-low configurations and three randomly mistuned systems. For the randomly mistuned systems the standard deviation of the resonance frequencies of the last stage blades is varied. The maximum blade amplitude and the circumferential blade amplitude distribution of each mistuning configuration are compared at different operating points and at a repeatable rotational speed gradient. The behaviour of the blade amplitude distribution at different operating conditions shows that the vibration levels depend on both the mistuning configuration and the operating points.

Experimental and Analytical Investigations of a Low Pressure Model Turbine During Forced Response Excitation

2010 ◽  
Author(s):  
Christoph Heinz ◽  
Markus Schatz ◽  
Michael V. Casey ◽  
Heinrich Stu¨er
Keyword(s):  
Degrees Of Freedom ◽  
Timing Analysis ◽  
Dynamic Performance ◽  
Amplitude Distribution ◽  
Low Pressure ◽  
Forced Response ◽  
Operating Conditions ◽  
Linear Regression Method ◽  
Rotor Shaft ◽  
Aerodynamic Damping

To guarantee a faultless operation of a turbine it is necessary to know the dynamic performance of the machine especially during start-up and shut-down. In this paper the vibration behaviour of a low pressure model steam turbine which has been intentionally mistuned is investigated at the resonance point of an eigenfrequency crossing an engine order. Strain gauge measurements as well as tip timing analysis have been used, whereby a very good agreement is found between the methods. To enhance the interpretation of the data measured, an analytical mass-spring-model, which incorporates degrees of freedom for the blades as well as for the rotor shaft, is presented. The vibration amplitude varies strongly from blade to blade. This is caused by the mistuning parameters and the coupling through the rotor shaft. This circumferential blade amplitude distribution is investigated at different operating conditions. The results show an increasing aerodynamic coupling with increasing fluid density, which becomes visible in a changing circumferential blade amplitude distribution. Furthermore the blade amplitudes rise non-linearly with increasing flow velocity, while the amplitude distribution is almost independent. Additionally, the mechanical and aerodynamic damping parameters are calculated by means of a non-linear regression method. Based on measurements at different density conditions, it is possible to extrapolate the damping parameters down to vacuum conditions, where aerodynamic damping is absent. Hence the material damping parameter can be determined.

Detailed Numerical Study of the Main Sources of Loss and Flow Behavior in Low Pressure Steam Turbine Exhaust Hoods

2017 ◽  
Author(s):  
Dickson Munyoki ◽  
Markus Schatz ◽  
Damian M. Vogt
Keyword(s):  
Steam Turbine ◽  
Numerical Study ◽  
Flow Behavior ◽  
Low Pressure ◽  
Operating Conditions ◽  
Pressure Recovery ◽  
Exhaust Hood ◽  
Recovery Coefficient ◽  
Pressure Steam ◽  
Underlying Mechanisms

The performance of the axial-radial diffuser downstream of the last low-pressure steam turbine stages and the losses occurring subsequently within the exhaust hood directly influences the overall efficiency of a steam power plant. It is estimated that an improvement of the pressure recovery in the diffuser and exhaust hood by 10% translates into 1% of last stage efficiency [11]. While the design of axial-radial diffusers has been the object of quite many studies, the flow phenomena occurring within the exhaust hood have not received much attention in recent years. However, major losses occur due to dissipation within vortices and inability of the hood to properly diffuse the flow. Flow turning from radial to downward flow towards the condenser, especially at the upper part of the hood is essentially the main cause for this. This paper presents a detailed analysis of the losses within the exhaust hood flow for two operating conditions based on numerical results. In order to identify the underlying mechanisms and the locations where dissipation mainly occurs, an approach was followed, whereby the diffuser inflow is divided into different sectors and pressure recovery, dissipation and finally residual kinetic energy of the flow originating from these sectors is calculated at different locations within the hood. Based on this method, the flow from the topmost sectors at the diffuser inlet is found to cause the highest dissipation for both investigated cases. Upon hitting the exhaust hood walls, the flow on the upper part of the diffuser is deflected, forming complex vortices which are stretching into the condenser and interacting with flow originating from other sectors, thereby causing further swirling and generating additional losses. The detailed study of the flow behavior in the exhaust hood and the associated dissipation presents an opportunity for future investigations of efficient geometrical features to be introduced within the hood to improve the flow and hence the overall pressure recovery coefficient.

Effect of Gear Tooth Crack on Spur Gear Dynamic Response by Simulation

2011 ◽  
Author(s):  
Yimin Shao ◽  
Xi Wang ◽  
Zaigang Chen ◽  
Teik C. Lim
Keyword(s):  
Dynamic Response ◽  
Gear Tooth ◽  
Sudden Change ◽  
Element Model ◽  
Spur Gear ◽  
Operating Conditions ◽  
Lumped Parameter Model ◽  
Mesh Stiffness ◽  
Heavy Load ◽  
High Rotational Speed

Geared transmission systems are widely applied to transmit power, torque and high rotational speed, and as well as change the direction of rotational motion. Their performances and efficiencies depend greatly on the integrity of the gear structure. Hence, health monitoring and fault detection in geared systems have gained much attention. Often, as a result of inappropriate operating conditions, application of heavy load beyond the designed capacity or end of fatigue life, gear faults frequently occur in practice. When fault happens, gear meshing characteristics, including mesh stiffness that is one of the important dynamic parameters, can be affected. This sudden change in mesh stiffness can induce shock vibration as the faulty gear tooth passes through the engagement zone. In this study, a finite element model representing the crack at the tooth root of a spur gear is developed. The theory is applied to investigate the effect of different crack sizes and the corresponding change in mesh stiffness. In addition, a lumped parameter model is formulated to examine the effect of tooth fault on gear dynamic response.

Investigation of Damping Potential of Strip Damper on a Real Turbine Blade

2016 ◽  
Author(s):  
M. Afzal ◽  
I. Lopez Arteaga ◽  
L. Kari ◽  
V. Kharyton
Keyword(s):  
Boundary Conditions ◽  
Dynamic Properties ◽  
Equations Of Motion ◽  
Iterative Solution ◽  
Element Model ◽  
Forced Response ◽  
Contact Forces ◽  
Response Analysis ◽  
Bladed Disk ◽  
Different Types

This paper investigates the damping potential of strip dampers on a real turbine bladed disk. A 3D numerical friction contact model is used to compute the contact forces by means of the Alternate Frequency Time domain method. The Jacobian matrix required during the iterative solution is computed in parallel with the contact forces, by a quasi-analytical method. A finite element model of the strip dampers, that allows for an accurate description of their dynamic properties, is included in the steady-state forced response analysis of the bladed disk. Cyclic symmetry boundary conditions and the multiharmonic balance method are applied in the formulation of the equations of motion in the frequency domain. The nonlinear forced response analysis is performed with two different types of boundary conditions on the strip: (a) free-free and (b) elastic, and their influence is analyzed. The effect of the strip mass, thickness and the excitation levels on the forced response curve is investigated in detail.

Unsteady Wet Steam Flow Field Measurements in the Last Stage of Low Pressure Steam Turbine

2015 ◽  
Author(s):  
Ilias Bosdas ◽  
Michel Mansour ◽  
Anestis I. Kalfas ◽  
Reza S. Abhari ◽  
Shigeki Senoo
Keyword(s):  
Flow Field ◽  
Steam Turbine ◽  
Total Pressure ◽  
Low Pressure ◽  
Operating Conditions ◽  
Test Facility ◽  
Flow Structures ◽  
Wet Steam ◽  
Operating Condition ◽  
Last Stage

Modern steam turbines need to operate efficiently and safely over a wide range of operating conditions. This paper presents a unique unprecedented set of time-resolved steam flowfield measurements from the exit of the last two stages of a low pressure (LP) steam turbine under various volumetric massflow conditions. The measurements were performed in the steam turbine test facility in Hitachi city in Japan. A newly developed fast response probe equipped with a heated tip to operate in wet steam flows was used. The probe tip is heated through an active control system using a miniature high-power cartridge heater developed in-house. Three different operating points, including two reduced massflow conditions, are compared and a detailed analysis of the unsteady flow structures under various blade loads and wetness mass fractions is presented. The measurements show that at the exit of the second to last stage the flow field is highly three dimensional. The measurements also show that the secondary flow structures at the tip region (shroud leakage and tip passage vortices) are the predominant sources of unsteadiness at 85% span. The high massflow operating condition exhibits the highest level of periodical total pressure fluctuation compared to the reduced massflow conditions at the inlet of the last stage. In contrast at the exit of the last stage, the reduced massflow operating condition exhibits the largest aerodynamic losses near the tip. This is due to the onset of the ventilation process at the exit of the LP steam turbine. This phenomenon results in 3 times larger levels of relative total pressure unsteadiness at 93% span, compared to the high massflow condition. This implies that at low volumetric flow conditions the blades will be subjected to higher dynamic load fluctuations at the tip region.

Dynamic Response Analysis of NC Machine Tool's Bed on ANSYS

2013 ◽  
Vol 392 ◽  
pp. 122-126
Author(s):  
Hai Fei Qiu ◽  
Song Lin Wu
Keyword(s):  
Dynamic Response ◽  
Impact Load ◽  
Element Model ◽  
Response Analysis ◽  
Displacement Curve ◽  
Harmonic Load ◽  
Frequency Curve ◽  
Transient Dynamic Analysis ◽  
Nc Machine ◽  
Harmonic Response Analysis

Finite element model of NC machine tools bed was set up in ANSYS, natural frequencies and modal shapes in low order were calculated by modal analysis of the bed. Then displacement-frequency curve and stress-frequency curve between 300 Hz and 700 Hz were acquired based on harmonic response analysis of the bed, and dynamic response of the bed which affected by harmonic load was clear; Transient dynamic analysis of the bed was finished by Full method, then displacement curve and acceleration curve about time domain were acquired, and influence of impact load during the process of starting NC machine tool which affect on the bed was understand, in results, some important references and basis were offered to optimal design of the beds dynamics.

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