Natural Frequency Shift in a Centrifugal Compressor Impeller for High-Density Gas Applications

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
Yohei Magara ◽  
Kazuyuki Yamaguchi ◽  
Haruo Miura ◽  
Naohiko Takahashi ◽  
Mitsuhiro Narita
Keyword(s):  
Centrifugal Compressor ◽  
Natural Frequencies ◽  
Mass Density ◽  
Mass Effect ◽  
Added Mass ◽  
High Density ◽  
Experimental Results ◽  
Centrifugal Compressors ◽  
Resonance Frequencies ◽  
Discharge Gas

In designing an impeller for centrifugal compressors, it is important to predict the natural frequencies accurately in order to avoid resonance caused by pressure fluctuations due to rotor-stator interaction. However, the natural frequencies of an impeller change under high-density fluid conditions. The natural frequencies of pump impellers are lower in water than in air because of the added mass effect of water, and in high-pressure compressors the mass density of the discharge gas can be about one-third that of water. So to predict the natural frequencies of centrifugal compressor impellers, the influence of the gas must be considered. We previously found in the nonrotating case that some natural frequencies of an impeller decreased under high-density gas conditions but others increased and that the increase of natural frequencies is caused by fluid-structure interaction, not only the added mass effect but also effect of the stiffness of the gas. In order to develop a method for predicting natural frequencies of centrifugal compressor impellers for high-density gas applications, this paper presents experimental results obtained using a variable-speed centrifugal compressor with vaned diffusers. The maximum mass density of its discharge gas is approximately 300 kg/m3. The vibration stress on an impeller when the compressor was speeding up or slowing down was measured by strain gauges, and the natural frequencies were determined by resonance frequencies. The results indicate that for high-density centrifugal compressors, some natural frequencies of an impeller increased in high-density gas. To predict this behavior, we developed a calculation method based on the theoretical analysis of a rotating disk. Its predictions are in good agreement with experimental results.

Natural Frequency Shift in a Centrifugal Compressor Impeller for High-Density Gas Applications

2011 ◽  
Author(s):  
Yohei Magara ◽  
Kazuyuki Yamaguchi ◽  
Haruo Miura ◽  
Naohiko Takahashi ◽  
Mitsuhiro Narita
Keyword(s):  
Centrifugal Compressor ◽  
Natural Frequencies ◽  
Mass Density ◽  
Mass Effect ◽  
Added Mass ◽  
High Density ◽  
Experimental Results ◽  
Centrifugal Compressors ◽  
Resonance Frequencies ◽  
Discharge Gas

In designing an impeller for centrifugal compressors, it is important to predict the natural frequencies accurately in order to avoid resonance caused by pressure fluctuations due to rotorstator interaction. However, the natural frequencies of an impeller change under high-density fluid conditions. The natural frequencies of pump impellers are lower in water than in air because of the added mass effect of water, and in high-pressure compressors the mass density of the discharge gas can be about one-third that of water. So to predict the natural frequencies of centrifugal compressor impellers, the influence of the gas must be considered. We previously found in the non-rotating case that some natural frequencies of an impeller decreased under high-density gas conditions but others increased and that the increase of natural frequencies is caused by fluid-structure interaction, not only the added mass effect but also effect of the stiffness of the gas. In order to develop a method for predicting natural frequencies of centrifugal compressor impellers for high-density gas applications, this paper presents experimental results obtained using a variable-speed centrifugal compressor with vaned diffusers. The maximum mass density of its discharge gas is approximately 300 kg/m3. The vibration stress on an impeller when the compressor was speeding up or slowing down was measured by strain gages, and the natural frequencies were determined by resonance frequencies. The results indicate that for high-density centrifugal compressors, some natural frequencies of an impeller increased in high-density gas. To predict this behavior, we developed a calculation method based on the theoretical analysis of a rotating disc. Its predictions are in good agreement with experimental results.

Natural Frequencies of Centrifugal Compressor Impellers for High Density Gas Applications

2008 ◽  
Author(s):  
Yohei Magara ◽  
Mitsuhiro Narita ◽  
Kazuyuki Yamaguchi ◽  
Naohiko Takahashi ◽  
Tetsuya Kuwano
Keyword(s):  
Centrifugal Compressor ◽  
Natural Frequencies ◽  
Fluid Structure Interaction ◽  
Mass Effect ◽  
Added Mass ◽  
High Density ◽  
Experimental Results ◽  
Density Condition ◽  
Fluid Structure ◽  
Structure Interaction

Characteristics of natural frequencies of an impeller and an equivalent disc were investigated in high-density gas to develop a method for predicting natural frequencies of centrifugal compressor impellers for high-density gas applications. The equivalent disc had outer and inner diameters equal to those of the impeller. We expected that natural frequencies would decrease with increasing the gas density because of the added-mass effect. However, we found experimentally that some natural frequencies of the impeller and the disc in high-density gas decreased but others increased. Moreover, we observed, under high-density condition, some resonance frequencies that we did not observe under low-density condition. These experimental results cannot be explained by only the added-mass effect. For simplicity, we focused on the disc to understand the mechanism of the behavior of natural frequencies. We developed a theoretical analysis of fluid-structure interaction considering not only the mass but also stiffness of gas. The analysis gave a qualitative explanation of the experimental results. In addition, we carried out a fluid-structure interaction analysis using the finite element method. The behavior of natural frequencies of the disc in high-density gas was predicted with errors less than 6%.

Fluid Added Mass Effect in the Modal Response of a Pump-Turbine Impeller

2009 ◽  
Author(s):  
Eduard Egusquiza ◽  
Carme Valero ◽  
Quanwei Liang ◽  
Miguel Coussirat ◽  
Ulrich Seidel
Keyword(s):  
Natural Frequencies ◽  
Experimental Tests ◽  
Mass Effect ◽  
Added Mass ◽  
Mode Shapes ◽  
Pump Turbine ◽  
Modal Response ◽  
Surrounding Fluid ◽  
Turbine Impeller ◽  
Good Agreement

In this paper, the reduction in the natural frequencies of a pump-turbine impeller prototype when submerged in water has been investigated. The impeller, with a diameter of 2.870m belongs to a pump-turbine unit with a power of around 100MW. To analyze the influence of the added mass, both experimental tests and numerical simulations have been carried out. The experiment has been performed in air and in water. From the frequency response functions the modal characteristics such as natural frequencies and mode shapes have been obtained. A numerical simulation using FEM (Finite Elements Model) was done using the same boundary conditions as in the experiment (impeller in air and surrounded by a mass of water). The modal behaviour has also been calculated. The numerical results were compared with the available experimental results. The comparison shows a good agreement in the natural frequency values both in air and in water. The reduction in frequency due to the added mass effect of surrounding fluid has been calculated. The physics of this phenomenon due to the fluid structure interaction has been investigated from the analysis of the mode-shapes.

scholarly journals Structural seismic characteristics assessment of LMFR fuel assembly hexagonal wrapper over operational temperature range

2019 ◽  
Vol 34 (4) ◽  
pp. 313-324
Author(s):  
M. Khizer ◽  
Zhang Yong ◽  
Yang Guowei ◽  
Wu Qingsheng ◽  
Wu Yican
Keyword(s):  
Fuel Assembly ◽  
Fast Reactor ◽  
Natural Frequencies ◽  
Mass Effect ◽  
Added Mass ◽  
Reactor Fuel ◽  
Temperature Range ◽  
Fast Reactor Fuel ◽  
Lead Bismuth Eutectic ◽  
Reactor Fuel Assembly

In this study, the structural integrity of liquid metal fast reactor fuel assembly has been established for different parameters considering the optimum fuel design. Analytical calculation of added mass effect due to lead bismuth eutectic and verification through previously presented theories, has been established. The integrity of the hexagonal wrapper of fuel assembly has been guaranteed over the entire operating temperature range. Effect of temperature on the density of lead bismuth eutectic, the subsequent change in added mass of lead bismuth eutectic, the effect on natural frequencies and effect on stresses on wrapper, has been studied in detail. A simple empirical relationship is presented for estimation of added mass effect for lead bismuth eutectic type fast reactors for any desired temperature. An approach for assessment of fast reactor fuel assembly performance has been outlined and calculated results are presented. Nuclear seismic rules require that systems and components which are important to safety, shall be capable of bearing earthquake effects and their integrity and functionality should be guaranteed. Mode shapes, natural frequencies, stresses on wrapper and seismic aspect has also been considered using ANSYS. Modal analysis has been compared in vacuum and lead bismuth eutectic using the calculated added mass.

Numerical Simulation of the Added Mass of the Fluid Adjacent to the Ship Hull in Vibration Measured During Sea-Trials in Tanker Ships to be Converted to Offshore Construction Vessel

2012 ◽  
Author(s):  
Severino Fonseca Silva Neto ◽  
Silvia Ramscheid Figueiredo ◽  
Marta Cecilia Tapia Reyes ◽  
Luiza de Mesquita Ortiz
Keyword(s):  
Numerical Model ◽  
Kinetic Energy ◽  
Natural Frequencies ◽  
Three Dimensional ◽  
Added Mass ◽  
Vertical Vibration ◽  
Full Scale ◽  
Experimental Results ◽  
Vibration Velocity ◽  
Main Engine

This study aims to analyze the influence of the kinetic energy of the fluid adjacent to the hull of a tanker ship in its vertical vibration frequencies, comparing them with experimental measurements obtained during sea-trials. The one-dimensional modeling of ships allows the construction of simple finite element models from the structural elements of its master section, with structural and added masses, and their frequencies are verified by full-scale measurements, during the sea-trials. The numerical results of these models, with the value of the effective shear area as a fraction of the total area of the strength steel are compared to those obtained in full-scale measurements during sea trials of an oil tanker to be converted to Offshore Construction Vessel. Global vibration measurements were carried out in two of the six ships with the same hull. Accelerometers were installed in eleven strategic points of each hull. Vibration data acquisition was performed simultaneously for these locals in thirteen rotations of the main engine. The amplitude spectra of vibration velocity on the frequency range of measurements were obtained and were plotted graphs of the evolution of the main harmonics, depending on the rotation of the main engine, in order to identify four natural frequencies of the overall vibration of the hull, which were compared to the numerical model. The calculation is performed by the added mass formulations from Burrill, Todd, Kumay and Lewis/Landweber [8] curves, including in all three-dimensional effect by Townsin [17] coefficients, which is checked against the experimental results. The comparison between numerical and experimental results allows assessing the influence of the kinetic energy of the fluid surrounding the hull in the natural frequencies of vibration of the numerical model of the tanker ship and simulating their dynamic behavior after conversion in Offshore Construction Vessel.

scholarly journals Fluid Added-Mass Effect on Flexural Vibration of Hemispherical Shell Structure

2020 ◽  
Vol 25 (1) ◽  
pp. 104-111
Author(s):  
Shahrokh Sepehrirahnama ◽  
Felix Bob Wijaya ◽  
Darren Oon ◽  
Eng Teo Ong ◽  
Heow Pueh Lee ◽  
...  
Keyword(s):  
Shell Structure ◽  
Potential Flow ◽  
Natural Frequencies ◽  
Flexural Vibration ◽  
Mass Effect ◽  
Added Mass ◽  
Fluid Viscosity ◽  
Hemispherical Shell ◽  
Wide Range ◽  
Fluid Added Mass

In this hydroelasticity study, the fluid added-mass effect on a hemispherical shell structure under flexural vibration is investigated. The vibration response of the hemisphere is solved by using a commercial finite element software (ABAQUS) coupled with an in-house boundary element code that models the fluid as potential flow. The fluid-structure interaction is solved as a fully-coupled system by modal superposition to reduce the number of degrees of freedom. The need for an iterative scheme to pass displacement/force information between the two solvers is avoided by direct coupling between the fluid and structure equations. The numerical results on the downward shift in natural frequencies due to added-mass effect compare well with vibration measurements conducted on a stainless-steel bowl with interior and exterior fluid. For water and soap-water solution used in the experiments, the fluid viscosity (varying over a wide range) did not have any significant effect on the wet natural frequencies. This is due to the small viscous boundary layer (milimetre scale) compared to the nominal size of the bowl in centimetres. For such cases, the fluid-added mass only depends on the density of the fluid and the use of potential flow in the numerical model is applicable.

Parametric Performance of a Class of Standard Discharge Scrolls for Industrial Centrifugal Compressors

2014 ◽  
Author(s):  
Marco Giachi ◽  
Vidyasagar Ramalingam ◽  
Elisabetta Belardini ◽  
Fabio De Bellis ◽  
Chanukya Reddy
Keyword(s):  
Centrifugal Compressor ◽  
Point Of View ◽  
Experimental Results ◽  
The Other ◽  
Delivery Time ◽  
Centrifugal Compressors ◽  
Performance Point ◽  
Engineering Solution ◽  
Other Hand

For many reasons, the discharge volute of a centrifugal compressor is becoming more and more critical for the performance of the machine. The most important are the need to reduce the size of the casing and to minimize the delivery time and cost of the compressor. A database of standard geometries represents a good engineering solution to both these requirements. In fact, it is possible, from a mechanical point of view, to design a class of similar volutes to fit different casings and stages. On the other hand, from the performance point of view, very little has been done to describe families of similar scrolls and how the performance of a baseline geometry can be adapted to take into account the differences which exist in the scrolls of the same family. A lot of data are available in literature but they refer to single specific geometries and to optimized individual designs. In this paper, a description of the analysis which has been done to investigate which may be the most convenient parameters to describe the volute performance is presented together with some experimental results which have been used to validate the analysis.

Parker-Type Acoustic Resonances in the Return Guide Vane Cascade of a Centrifugal Compressor: Theoretical Modeling and Experimental Verification

2010 ◽  
Author(s):  
Sven Ko¨nig ◽  
Nico Petry
Keyword(s):  
High Pressure ◽  
Centrifugal Compressor ◽  
Vortex Shedding ◽  
Guide Vane ◽  
Experimental Results ◽  
Mode Shapes ◽  
Centrifugal Compressors ◽  
Acoustic Modes ◽  
Trailing Edges ◽  
Acoustic Resonances

The potential of acoustic resonances within vane arrays of turbomachinery has been known since the fundamental investigations of Parker back in the sixties and seventies. In his basic studies on flat plate arrays (and later on for an axial compressor) he could show that vortex shedding from the respective trailing edges may excite acoustic resonances that are localized to the vaned flow region. In principle, such phenomena are conceivable for any kind of turbomachinery; however, no such investigations are publicly available for the centrifugal type. The current investigation is one part of an extended research program to gain a better understanding of excitation and noise generating mechanism in centrifugal compressors, and focuses on Parker-type acoustic resonances within the return guide vane cascade of a high-pressure centrifugal compressor. A simplified model to calculate the respective acoustic eigenfrequencies is presented, and the results are compared with finite element analyses. Furthermore, the calculated mode shapes and frequencies are compared with experimental results. It is shown that for high-pressure centrifugal compressors, according to the nomenclature of Parker, acoustic modes of the α, β, γ, and δ type exist over a wide operating range within the return guide vane cascade. For engine representative Reynolds numbers, the experimental results indicate that the vortex shedding frequencies from the vane trailing edges cannot be characterized by a definite Strouhal number; the excitation of the Parker-type acoustic modes is mostly broadband due to the flow turbulence. No lock-in phenomenon between vortex shedding and acoustic modes takes place, and the amplitudes of the acoustic resonances are too small to cause machines failures or excessive noise levels.

scholarly journals Dynamics of Cilia-Based Microfluidic Devices

2011 ◽  
Author(s):  
Jiradech Kongthon ◽  
Jae-Hyun Chung ◽  
James Riley ◽  
Santosh Devasia
Keyword(s):  
Large Amplitude ◽  
Microfluidic Devices ◽  
Mass Effect ◽  
Added Mass ◽  
Liquid Sloshing ◽  
Experimental Results ◽  
Large Amplitude Motion ◽  
Excitation Waveform ◽  
Sinusoidal Excitation

This article models the dynamics of cilia-based devices (soft cantilever-type, vibrating devices that are excited by external vibrations) for mixing and manipulating liquids in microfluidic applications. The main contribution of this article is to develop a model, which shows that liquid sloshing and the added mass effect play substantial roles in generating large-amplitude motion of the cilia. Additionally, experimental results are presented to show that (i) mixing is substantially improved with the use of cilia when compared to the case without cilia and (ii) mixing with cilia can be further enhanced by using an asymmetric excitation waveform when compared to sinusoidal excitation.

Parker-Type Acoustic Resonances in the Return Guide Vane Cascade of a Centrifugal Compressor – Theoretical Modeling and Experimental Verification

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Sven König ◽  
Nico Petry
Keyword(s):  
High Pressure ◽  
Centrifugal Compressor ◽  
Vortex Shedding ◽  
Guide Vane ◽  
Experimental Results ◽  
Simplified Model ◽  
Centrifugal Compressors ◽  
Acoustic Modes ◽  
Trailing Edges ◽  
Acoustic Resonances

The potential of acoustic resonances within vane arrays of turbomachinery has been known since the fundamental investigations of Parker back in the sixties and seventies. In his basic studies on flat plate arrays (and later on for an axial compressor) he could show that vortex shedding from the respective trailing edges may excite acoustic resonances that are localized to the vaned flow region. In principle, such phenomena are conceivable for any kind of turbomachinery; however, no such investigations are publicly available for the centrifugal type. The current investigation is one part of an extended research program to gain a better understanding of excitation and noise generating mechanism in centrifugal compressors, and focuses on Parker-type acoustic resonances within the return guide vane cascade of a high-pressure centrifugal compressor. A simplified model to calculate the respective acoustic eigenfrequencies is presented, and the results are compared with finite element analyses. Furthermore, the calculated mode shapes and frequencies are compared with experimental results. It is shown that for high-pressure centrifugal compressors, according to the nomenclature of Parker, acoustic modes of the α, β, γ, and δ type exist over a wide operating range within the return guide vane cascade. For engine representative Reynolds numbers, the experimental results indicate that the vortex shedding frequencies from the vane trailing edges cannot be characterized by a definite Strouhal number; the excitation of the Parker-type acoustic modes is mostly broadband due to the flow turbulence. No lock-in phenomenon between vortex shedding and acoustic modes takes place, and the amplitudes of the acoustic resonances are too small to cause machines failures or excessive noise levels. The simplified model presented in the current paper has been successfully validated for the return guide vane cascade of a centrifugal compressor but can also be applied for arbitrary blade and vane arrays, given that the chord-to-pitch ratio is sufficiently high. With this model, frequency components in measured pressure signals, that were left unexplained in the past, can be easily inspected for possible Parker-type resonances.

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