Numerical Characterization of Swirl Brakes for High Pressure Centrifugal Compressors

2013 ◽  
Author(s):  
Riccardo Da Soghe ◽  
Mirko Micio ◽  
Antonio Andreini ◽  
Bruno Facchini ◽  
Luca Innocenti ◽  
...  
Keyword(s):  
High Pressure ◽  
Tangential Velocity ◽  
Operating Conditions ◽  
Design Parameters ◽  
Centrifugal Compressors ◽  
Labyrinth Seals ◽  
Numerical Characterization ◽  
Lean Angle ◽  
The Stability ◽  
The Many

High pressure centrifugal compressors continue to experience vibrations due to rotordynamic stability. The main cause for aero-induced exciting forces that affects the stability, is the tangential velocity component of the gas entering the many labyrinth seals throughout the machine. In order to control or limit these swirling flows, swirl brakes are generally implemented both at the impeller eye seals and at the balance piston or division wall seal of a centrifugal compressor. This paper deals with the aerodynamic characterization, by means of CFD, of such kind of devices. Several design parameters, such as teeth lean, angle of attack and pitch-to-chord ratio have been considered and also the operating conditions (pressure level and swirl at the swirl brake inlet) are accounted for. This paper aims to improve the physical understanding of the fluid flow of centrifugal compressors swirl brakes allowing an optimization of such systems.

Roles of vanes in diffuser on stability of centrifugal compressor

2019 ◽  
Vol 233 (14) ◽  
pp. 5380-5392
Author(s):  
Wangzhi Zou ◽  
Xiao He ◽  
Wenchao Zhang ◽  
Zitian Niu ◽  
Xinqian Zheng
Keyword(s):  
High Pressure ◽  
Centrifugal Compressor ◽  
Dynamic Pressure ◽  
Pressure Ratio ◽  
Pressure Rise ◽  
Rotating Stall ◽  
Centrifugal Compressors ◽  
Compression System ◽  
The Stability ◽  
Rotating Instability

The stability considerations of centrifugal compressors become increasingly severe with the high pressure ratios, especially in aero-engines. Diffuser is the major subcomponent of centrifugal compressor, and its performance greatly influences the stability of compressor. This paper experimentally investigates the roles of vanes in diffuser on component instability and compression system instability. High pressure ratio centrifugal compressors with and without vanes in diffuser are tested and analyzed. Rig tests are carried out to obtain the compressor performance map. Dynamic pressure measurements and relevant Fourier analysis are performed to identify complex instability phenomena in the time domain and frequency domain, including rotating instability, stall, and surge. For component instability, vanes in diffuser are capable of suppressing the emergence of rotating stall in the diffuser at full speeds, but barely affect the characteristics of rotating instability in the impeller at low and middle speeds. For compression system instability, it is shown that the use of vanes in diffuser can effectively postpone the occurrence of compression system surge at full speeds. According to the experimental results and the one-dimensional flow theory, vanes in diffuser turn the diffuser pressure rise slope more negative and thus improve the stability of compressor stage, which means lower surge mass flow rate.

Some Guidelines for the Experimental Characterization of Vaneless Diffuser Rotating Stall in Stages of Industrial Centrifugal Compressors

2014 ◽  
Author(s):  
Alessandro Bianchini ◽  
Davide Biliotti ◽  
Marco Giachi ◽  
Elisabetta Belardini ◽  
Libero Tapinassi ◽  
...  
Keyword(s):  
Dynamic Pressure ◽  
Industrial Test ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Design Parameters ◽  
Accurate Estimation ◽  
Pressure Measurements ◽  
Vaneless Diffuser ◽  
Centrifugal Compressors ◽  
Test Models

An accurate estimation of rotating stall is one of the key technologies for high-pressure centrifugal compressors, as it is often connected with the onset of detrimental subsynchronous vibrations which can prevent the machine from operating beyond this limit. With particular reference to the vaneless diffuser stall, much research has been directed at investigating the physics of the phenomenon, the influence of the main design parameters and the prediction of the stall inception. Few of them, however, focused attention on the evaluation of the aerodynamic unbalance due to the induced pressure field in the diffuser, which, however, could provide a valuable contribution to both the identification of the actual operating conditions and the enhancement of the compressor operating range by a suitable choice of the control strategy. Although advanced experimental techniques have been successfully applied to the recognition of the stall pattern in a vaneless diffuser, the most suitable solution for a wider application in industrial test-models is based on dynamic pressure measurements by means of a reduced number of probes. Within this context, a procedure to transpose pressure measurements into the spatial pressure distribution was developed and validated on a wide set of industrial test-models. In this work, the main guidelines of the procedure are presented and discussed, with particular reference to signals analysis and manipulation as well as sensors positioning. Moreover, the prospects of using a higher number of sensors is analyzed and compared to standard solutions using a limited probes number.

Unshrouded Rotor Tip Clearance Effects in Expander Cycle Turbines

2002 ◽  
Author(s):  
Lennard Helmers ◽  
Jens Klingmann
Keyword(s):  
Laser Doppler Anemometry ◽  
Tangential Velocity ◽  
Operating Conditions ◽  
Tip Clearance ◽  
Axial Position ◽  
Design Parameters ◽  
Channel Measurements ◽  
Velocity Mapping ◽  
Blade Row ◽  
The Impact

Steady flow in axial one-stage turbines is assessed numerically and experimentally. The simulations are performed on coarse meshes using a standard numerical approach (3D, steady state, kε-turbulence model, wall function at solid boundaries). In order to allow for conclusions drawn from these rapid numerical studies, the approach was compared with an explicit LDA (Laser Doppler anemometry) mapping of the velocity field downstream the rotor on a representative turbine stage. A two-component LDA system allowed for measurements of axial and tangential velocity components at varying depth (radius) in the flow channel, Measurements thus correspond to a full plane at constant axial position in the rotating frame of reference of the rotor. Comparison between LDA velocity mapping and CFD results shows good agreement. A series of subsequent simulations is thus used to judge the impact of varied blade/stage design parameters. Two turbine layouts are defined for identical operating conditions and shaft power. The flow in the unshrouded rotor blade row is analyzed for the influence of varying tip clearance size and the dependency on stage velocity triangles. – Known correlations for tip clearance losses (typically used in mean line predictions) are used, though the blade row geometry considered is beyond the limits the correlations are intended for. The absolute loss level found in CFD simulations differs significantly from what is expected when using loss correlations. Still the variation with tip gap size is predicted well by some of the investigated models. As dependency of tip clearance losses on stage velocity triangles is considered, none of the tested correlations gives results consistent with the numerical simulations. The use of standard correlations ‘beyond the limits’ is thus considered to introduce high uncertainty. Due to the good consistency between LDA and numerical results, the conclusions are considered to be valid for stage designs similar to the ones analyzed.

Generalized Model for the Approximation of Coupled Acousto-Mechanical Natural Frequencies in High-Pressure Centrifugal Compressors

2020 ◽  
Author(s):  
Christoph Rocky Heinrich ◽  
Arnold Kühhorn ◽  
Klaus Steff ◽  
Nico Petry
Keyword(s):  
Finite Element ◽  
High Pressure ◽  
Cylindrical Cavity ◽  
Natural Frequencies ◽  
Annular Plate ◽  
Computational Effort ◽  
Operating Conditions ◽  
Centrifugal Compressors ◽  
Generalized Model ◽  
The Impact

Abstract The oil and gas, chemical, and process industries employ centrifugal compressors for a wide range of applications. Due to this, the conditions under which centrifugal compressors have to operate, vary significantly from case to case. Gas pipeline compressors, for example, may feature discharge pressures well over 100 bar. In other fields of application, like gas injection, which is used to enhance oil recovery, this quantity can reach considerably higher values. Here, discharge pressures over 600 bar and gas densities over 300 kg/m3 are not uncommon. During the last several decades, comprehensive research was conducted on the impact of high pressure operating conditions on the vibrational behavior of centrifugal compressor wheels. Nowadays, it is well-known that an increase in gas pressure levels leads to a more pronounced interaction between the side cavities and the impeller, which results in a frequency shift of the acoustic and structural modes. For the safe operation of compressors, it is necessary to predict these coupled natural frequencies accurately. The state-of-the-art approach to achieve this objective is the finite element method. While this technique provides high-quality results, the simulation of acousto-mechanical systems is still a time-consuming process that incurs high computational costs. Therefore, finite element models are, in this case, not suitable for probabilistic studies, sensitivity analyses, and comprehensive simulations of the full operating range of the compressor. In 2013, Magara proposed a simplified model based on an annular plate between two cylindrical cavities to solve this problem. While this method reduces the required computational effort significantly, its use is limited to platelike impellers. The authors of the current paper propose a more generalized method to overcome the challenges mentioned above. It uses the uncoupled structural and acoustic modes of the actual impeller and side cavities in a modal superposition to approximate the natural frequencies of the coupled acousto-mechanical system. In this way, the intended design geometries of the impeller and side cavities are considered while maintaining the advantages of Magara’s model regarding the computational effort. In a numerical study, Magara’s method and the generalized model are applied to different systems of increasing complexity. The investigation starts with a simple annular plate in a cylindrical cavity and ends with an actual compressor impeller. At every complexity level, the results of both approaches are compared to a finite element analysis. Moreover, measurement data of a simplified rotor in a cylindrical cavity is used to validate the numerical models. Finally, the paper concludes with a discussion of the limitations and benefits of all employed numerical methods.

Structural Design Considerations for Tubular Power Tower Receivers Operating at 650°C

2014 ◽  
Author(s):  
Ty W. Neises ◽  
Michael J. Wagner ◽  
Allison K. Gray
Keyword(s):  
Carbon Dioxide ◽  
High Pressure ◽  
Supercritical Carbon Dioxide ◽  
Performance Metrics ◽  
Operating Conditions ◽  
Design Parameters ◽  
Outlet Temperature ◽  
Power Cycles ◽  
The Impact ◽  
Supercritical Carbon

Research of advanced power cycles has shown supercritical carbon dioxide power cycles may have thermal efficiency benefits relative to steam cycles at temperatures around 500–700°C. To realize these benefits for CSP, it is necessary to increase the maximum outlet temperature of current tower designs. Research at NREL is investigating a concept that uses high-pressure supercritical carbon dioxide as the heat transfer fluid to achieve a 650°C receiver outlet temperature. At these operating conditions, creep becomes an important factor in the design of a tubular receiver and contemporary design assumptions for both solar and traditional boiler applications must be revisited and revised. This paper discusses lessons learned for high-pressure, high-temperature tubular receiver design. An analysis of a simplified receiver tube is discussed, and the results show the limiting stress mechanisms in the tube and the impact on the maximum allowable flux as design parameters vary. Results of this preliminary analysis indicate an underlying trade-off between tube thickness and the maximum allowable flux on the tube. Future work will expand the scope of design variables considered and attempt to optimize the design based on cost and performance metrics.

scholarly journals Rail Track with Rail Compression

2021 ◽  
Vol 20 (3) ◽  
pp. 234-242
Author(s):  
V. N. Sukhodoev
Keyword(s):  
Effective Property ◽  
Operating Conditions ◽  
Design Parameters ◽  
Labor Costs ◽  
Term Operation ◽  
Rail Track ◽  
Loading And Unloading ◽  
The Stability ◽  
The Cost

The problem of damping the noise on the track, arising from the movement of the train, is solved sufficiently but it is simple, if the rail with spacers is laid inside the longitudinally located band sleeper-mechanism. The result is a layered rail thread, consisting of belts: a rail tape with elastic spacers on three sides, a tie-mechanism tape and a ballast layer. The unity of the layers is carried out due to their own mass. This is the static track without external load. Rail compression is an effective property of rail tracks. It is formed in the sleeper mechanism under the influence of vertical forces with displacements and their horizontal derivatives. When loading the track, the compression is carried out repeatedly with subsequent unloading.n this case, each previous changes in the conditions in work of the track are taken into account in the subsequent cycle of loading and unloading. A rail track with a rail compression is a kind of self-adapting linear system, which is necessary with frequent changes in load and operating conditions for silent performance of a functional purpose. The specificity of this path is that the movement of the wheel creates rail vibration and noise, which are immediately damped by compression with damping. The balance between the occurrence of noise and its suppression is achieved by the ratio of the lengths of half-sleeper shoulders as a lever. The condition for the appearance of a shift of the compression forces in the direction from vertical shoulder of the half-sleepers is the unequal settlements of the horizontal shoulder of the L-shaped half-sleepers and its eccentric loading. As a result of the research, the advantages of a rail track with rail compression have been revealed, which is a guarantor of the stability of the design parameters during long-term operation of the track. The cost of a rail track with rail reduction is halved as a result of steel savings, lower labor costs and operational needs.

The Impact of Adding a Labyrinth Surface to an Optimal Helical Seal Design

2018 ◽  
Author(s):  
Wisher Paudel ◽  
Cori Watson ◽  
Houston G. Wood
Keyword(s):  
High Pressure ◽  
Kinetic Energy ◽  
Labyrinth Seal ◽  
Groove Width ◽  
Design Parameters ◽  
Labyrinth Seals ◽  
Pressure Application ◽  
Helical Groove ◽  
Helical Grooves ◽  
Annular Seals

Non-contacting annular seals are used in rotating machinery to reduce the flow of working fluid across a pressure differential. Helical and labyrinth grooved seals are two types of non-contacting annular seals frequently used between the impeller stages in a pump and at the balance drum. Labyrinth seals have circumferential grooves cut into the surface of the rotor, the stator, or both. They function to reduce leakage by dissipating kinetic energy as fluid expands in the grooves and then is forced to contract in the jet stream region. Helical groove seals have continuously cut grooves on either or both the rotor and stator surfaces. Like labyrinth seals, they reduce leakage through dissipation of kinetic energy, but have the added mechanism of functioning as a pump to push the fluid back towards the high-pressure region. Previous work has shown that mixed helical-labyrinth seals with labyrinth grooves on stator and helical grooves on rotor or labyrinth grooves on rotor and helical grooves on stator have an approximately 45% lower leakage than an optimized helical groove seal with grooves just on the stator in a high pressure application. The primary objective of this study is to determine whether the same performance gains can also be achieved in a low pressure application. Simulations were run in ANSYS CFX for seal designs with a helical stator and labyrinth rotor. Several labyrinth design parameters including the number of grooves and the groove width and depth are varied while the helical variables such as the groove width and depth as well as helix angle are kept constant. The data obtained are analyzed using backward regression methods and various response plots to determine the relationship between the design parameters and mass flow and power loss. The optimized helical design was simulated and the axial pressure profiles of the designs were compared to analyze the mechanism of the mixed helical-labyrinth seal. Then, the same labyrinth seal designs were simulated for a labyrinth rotor and a smooth stator to determine whether the optimal number of grooves, groove width and groove depth change due to the helical stator. The findings of this study show the effectiveness of mixed helical labyrinth grooved seals for both low and high pressure cases, and thus their efficiency and reliability for numerous industrial applications.

Rotor Stability Criteria for Multi-Stage Centrifugal Compressors

2003 ◽  
Author(s):  
John W. Fulton
Keyword(s):  
Tangential Force ◽  
Centrifugal Compressors ◽  
Labyrinth Seals ◽  
Gas Density ◽  
7Th Edition ◽  
Multi Stage ◽  
Bending Mode ◽  
Tooth Type ◽  
The Stability ◽  
Threshold Line

The American Petroleum Standard 617, 7th edition [1], screens new designs of centrifugal compressors using its Figure 1.2-5, which plots mean gas density versus rotor flexibility ratio. The purpose is to avoid rotor instability from causing unacceptable vibrations, typically whirling of the first-forward bending mode. The API figure is based on a plot by Fulton [2,3] of the same variables showing a number of compressors tested near the threshold of instability, thus forming an empirical basis for a Stability Map. This paper develops a method to derive a threshold line, using a set of typical industrial rotors varying in flexibility and running on tilt pad bearings. Instability requires a tangential force (normal to the bending displacement) to act on the rotor in the direction of whirl. The source of this force is taken to be the (tooth type) labyrinth seals inside the compressor. This tangential force is represented as linear function of whirl/spin scaled by gas density. This function is applied to the set of rotors to produce a threshold line. The derivation thus forms a basis for understanding the Stability Map.

Improving the Design of a High Pressure Casing With the Help of Finite Element Analysis to Ensure the Rotor Dynamic Stability of a High Pressure Centrifugal Compressor Equipped With a Hole Pattern Seal

2011 ◽  
Vol 133 (7) ◽  
Author(s):  
Yves Bidaut ◽  
Urs Baumann
Keyword(s):  
High Pressure ◽  
Dynamic Instability ◽  
Operating Conditions ◽  
Element Analysis ◽  
History Of ◽  
The Stability ◽  
Discharge Pressure ◽  
Rotor Dynamic ◽  
Full Pressure ◽  
Stability Measurements

This paper focuses on the casing geometry of high pressure compressors. It is common practice to use damper seals, typically the hole pattern type, at the balance piston to ensure the stability of the compressor when compressing fluids with high density levels. Special attention must be paid to the clearance of the hole pattern seal, which must be kept convergent at all operating conditions because a clearance divergence can lead to a rotor dynamic instability of the compressor. Furthermore, the clearance must be kept as low as possible to reduce the leakage losses through the balance piston. Therefore, extensive fine element analyses are performed to determine the mechanical casing deflections in operation and hence, the correct clearance behavior of such damper seals. This paper discusses the history of the casing design during the last 10 years and compares the configurations with respect to the clearance distribution along the damper seal length. To validate the analytical predictions, leakage and stability measurements (using a magnetic shaker) are performed for these high pressure compressors during the full-load, full-pressure testing. This paper presents the stability measurements carried out on two compressors (390 bars and 655 bars discharge pressure) and compares the results.

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