Non-Axisymmetric Flows and Rotordynamic Forces in an Eccentric Shrouded Centrifugal Compressor—Part 2: Analysis

2019 ◽  
Vol 141 (11) ◽  
Author(s):  
Jieun Song ◽  
Seung Jin Song
Keyword(s):  
Pressure Distribution ◽  
Centrifugal Compressor ◽  
Axisymmetric Flow ◽  
Mass Conservation ◽  
Labyrinth Seal ◽  
Operating Conditions ◽  
New Model ◽  
Flow Coupling ◽  
Order Of Magnitude ◽  
Rotordynamic Forces

AbstractAn integrated analytical model to predict non-axisymmetric flow fields and rotordynamic forces in a shrouded centrifugal compressor has been newly developed and validated. The model is composed of coupled, conservation law-based, bulk-flow submodels, and the model takes into account the flow coupling among the blades, labyrinth seals, and shroud cavity. Thus, the model predicts the entire flow field in the shrouded compressor when given compressor geometry, operating conditions, and eccentricity. When compared against the experimental data from part 1, the new model accurately predicts the evolution of the pressure perturbations along the shroud and labyrinth seal cavities as well as the corresponding rotordynamic stiffness coefficients. For the test compressor, the cross-coupled stiffness rotordynamic excitation is positive; the contribution of the shroud is the highest; the contribution of the seals is less than but on the same order of magnitude as that of the shroud; and contribution of impeller blades is insignificant. The new model also enables insight into the physical mechanism for pressure perturbation development. The labyrinth seal pressure distribution becomes non-axisymmetric to satisfy mass conservation in the seal cavity, and this non-axisymmetry, in turn, serves as the influential boundary condition for the pressure distribution in the shroud cavity. Therefore, for accurate flow and rotordynamic force predictions, it is important to model the flow coupling among the components (e.g., impeller, shroud, labyrinth seal, etc.), which determines the non-axisymmetric boundary conditions for the components.

Non-Axisymmetric Flows and Rotordynamic Forces in an Eccentric Shrouded Centrifugal Compressor: Part 2 — Analysis

2019 ◽  
Author(s):  
Jieun Song ◽  
Seung Jin Song
Keyword(s):  
Pressure Distribution ◽  
Centrifugal Compressor ◽  
Axisymmetric Flow ◽  
Mass Conservation ◽  
Labyrinth Seal ◽  
Operating Conditions ◽  
New Model ◽  
Order Of Magnitude ◽  
Entire Flow ◽  
Rotordynamic Forces

Abstract An integrated analytical model to predict non-axisymmetric flow fields and rotordynamic forces in a shrouded centrifugal compressor has been newly developed and validated. The model is composed of coupled, conservation law-based, bulk-flow sub-models, and the model takes into account the flow coupling among the blades, labyrinth seals, and shroud cavity. Thus, the model predicts the entire flow field in the shrouded compressor when given compressor geometry, operating conditions, and eccentricity. When compared against the experimental data from Part 1, the new model accurately predicts the evolution of the pressure perturbations along the shroud and labyrinth seal cavities as well as the corresponding rotordynamic stiffness coefficients. For the test compressor, the cross stiffness rotordynamic excitation is positive — the contribution of the shroud is the highest; the contribution of the seals is less than but on the same order of magnitude as that of the shroud; and contribution of impeller blades is insignificant. For accurate flow and rotordynamic force predictions, it is critical to model the coupling among the components (e.g., impeller, shroud, labyrinth seal, etc.) which determines the non-axisymmetric boundary conditions for the components. The new model also enables insight into the physical mechanism for pressure perturbation development. The labyrinth seal pressure distribution becomes non-axisymmetric to satisfy mass conservation in the seal cavity, and this non-axisymmetry, in turn, serves as the influential boundary condition for the pressure distribution in the shroud cavity.

Non-Axisymmetric Flows and Rotordynamic Forces in an Eccentric Shrouded Centrifugal Compressor: Part 1 — Measurement

2019 ◽  
Author(s):  
Jieun Song ◽  
Suyong Kim ◽  
Tae Choon Park ◽  
Bong-Jun Cha ◽  
Dong Hun Lim ◽  
...  
Keyword(s):  
Centrifugal Compressor ◽  
System Level ◽  
Labyrinth Seals ◽  
Stiffness Coefficients ◽  
Pressure Distributions ◽  
Order Of Magnitude ◽  
Direct Stiffness ◽  
The Cross ◽  
Rotordynamic Forces ◽  
Pressure Perturbations

Abstract Centrifugal compressors can suffer from rotordynamic instability. While individual components (e.g., seals, shrouds) have been previously investigated, an integrated experimental or analytical study at the compressor system level is scarce. For the first time, non-axisymmetric pressure distributions in a statically eccentric shrouded centrifugal compressor with eye-labyrinth seals have been measured for various eccentricities. From the pressure measurements, direct and cross-coupled stiffness coefficients in the shrouded centrifugal compressor have been determined. Thus, the contributions of the pressure perturbations in the shroud cavity and labyrinth seals have been simultaneously investigated. The cross-coupled stiffness coefficients in the shroud and labyrinth seals are both positive and one order of magnitude larger than the direct stiffness coefficients. Furthermore, in the tested compressor, contrary to the common assumption, the cross-coupled stiffness in the shroud is 2.5 times larger than that in the labyrinth seals. Thus, the shroud contributes more to rotordynamic instability than the eye-labyrinth seals.

An analysis method of pressure characteristic for cylindrical intershaft gas film seal considering centrifugal expansion, rotor misalignment, and precession

2021 ◽  
pp. 135065012110397
Author(s):  
Guoqiang Hou ◽  
Hua Su ◽  
Yuhui Huang ◽  
Congcong Chen
Keyword(s):  
Pressure Distribution ◽  
Labyrinth Seal ◽  
Operating Conditions ◽  
Distribution Area ◽  
Maximum Pressure ◽  
Analysis Method ◽  
Film Pressure ◽  
Rotating Speed ◽  
Expansion Effect ◽  
Rotational Direction

To improve the weaknesses of large leakage and wear of dual-rotor intershaft labyrinth seal in aero-engines, the cylindrical gas film seal of metal rubber with a compliant feature is proposed to substitute this conventional seal. According to the dual-rotor operating condition, an analysis method of gas film pressure is presented considering the complex condition of rotor tilt, centrifugal expansion effect, and rotor circular precession. The characteristics of gas film pressure distribution are computed and comparisons are conducted in a complex operating state that the tilt rotor is in forward/backward circular precession under a homodromous/counter-rotating condition with/without the influence of centrifugal expansion. Besides, the formation mechanism of the gas film pressure caused by rotor rotational direction and circular precession direction is revealed. Also, the influence of rotor speed and seal ring speed on gas film pressure is analyzed when the rotor is tilted. The results indicate that for the dual-rotor cylindrical gas film seal with high rotating speed, the rotor tilt and centrifugal expansion effect have significant influence on the gas film pressure distribution, and the rotors’ rotational direction as well as rotor circular precession direction determines the maximum gas film pressure distribution area. The maximum pressure under a homodromous condition with backward precession is the highest; the maximum pressure under a homodromous condition with forward precession is the lowest. The former is 1.33% and 1.68% higher than the latter, respectively, with/without consideration of centrifugal expansion. The study method, which is generally suitable for the cylindrical gas film seal with single-rotor/dual-rotor, lays the foundation of performance analysis under complex operating conditions.

Experimental and Numerical Analysis of the Secondary Flow Across the Interphase Balance Drum of a High Pressure Back-to-Back Centrifugal Compressor

2017 ◽  
Author(s):  
Carmine Carmicino ◽  
Francesco Maiuolo ◽  
Emanuele Rizzo
Keyword(s):  
Experimental Data ◽  
High Pressure ◽  
Numerical Analysis ◽  
Pressure Distribution ◽  
Centrifugal Compressor ◽  
Operating Conditions ◽  
Local Pressure ◽  
Flow Angle ◽  
One Dimensional ◽  
Honeycomb Seal

With the major aim of gathering information on the machine lateral stability in high pressure-high density conditions, and of assessing the prediction capabilities of the in-house design tools and overall process, a back-to-back centrifugal compressor has been instrumented and tested in several operating conditions. The present paper focuses on the secondary flows across the interphase balance drum of the back-to-back compressor, where the sealing is accomplished with a honeycomb seal. The compressor interphase section has been instrumented with dedicated special probes for the clearance measurement associated to pressure and flow angle probes in order to characterize pressure distributions and swirl variations depending on the specific operating range. The experimental data acquired over the machine operation have been compared with a three-dimensional steady-state numerical analysis results obtained from the simulation, carried out with a Reynolds averaged Navier-Stokes (RANS) approach, of the flowfield in the complex interphase secondary system composed by the impeller cavities and the honeycomb seal. This paper addresses the comparison between numerical results and experimental data, which allowed the matching of models with experiments in terms of pressure distribution and the complex flowfield. Finally, all the data have been used to validate an in-house one-dimensional flow network solver for pressure distribution and leakage flow calculations along cavities and seals. Results have shown a general good agreement between measured data and calculation output. In particular, computational fluid dynamic analysis provided detailed pressure and velocity distributions that allowed gaining insight in the physics of such a complex region. The one-dimensional model has been demonstrated to be a fast and reliable tool to well predict local pressure variations inside cavities and seals and, consequently, the residual axial thrust.

scholarly journals DEVELOPMENT A MATHEMATICAL MODEL FOR RESEARCHING DYNAMIC PROCESSES IN THE LABYRINTH SEAL OF CENTRIFUGAL COMPRESSOR STAGE

2021 ◽  
pp. 115-124
Author(s):  
Anton Mikryukov ◽  
◽  
Vladimir Modorskii ◽  
Ivan Cherepanov ◽  
◽  
...  
Keyword(s):  
Centrifugal Compressor ◽  
Labyrinth Seal ◽  
Operating Conditions ◽  
Dynamic Processes ◽  
Computational Domain ◽  
Compressor Stage ◽  
Centrifugal Compressor Stage ◽  
Interdisciplinary Approaches ◽  
Physical Features ◽  
Oscillatory Processes

Research of dynamic processes occurring under real operating conditions of centrifugal compressors often require the use of interdisciplinary approaches. This is determined by the character of the processes, which significantly affect each other during the compressor operation. However, when using interdisciplinary approaches, there are difficulties in the numerical implementation. They are associated with the need to take into account all the geometric and physical features of the processes under research, which leads to significant time and computational costs. At this article discusses issues related to the causes of oscillatory processes in the centrifugal compressor stage, in particular, in the labyrinth seal channel. In the article using 2FSI approach allowing to take into account the bilateral interaction of physical process on another. The article discusses issues related to the causes of oscillatory processes in the centrifugal compressor stage, in particular, in the labyrinth seal channel. The computational domain of research is presented, conceptual and mathematical statements are performed, which allow describing, among other things, self-oscillatory processes using the 2FSI approach.

scholarly journals Effect of Vaneless Diffuser Shape on Performance of Centrifugal Compressor

2020 ◽  
Vol 10 (6) ◽  
pp. 1936
Author(s):  
Qian Zhang ◽  
Qiuhong Huo ◽  
Lei Zhang ◽  
Lei Song ◽  
Jianmeng Yang
Keyword(s):  
Numerical Simulation ◽  
Energy Loss ◽  
Pressure Distribution ◽  
Centrifugal Compressor ◽  
Aerodynamic Performance ◽  
Operating Conditions ◽  
Vaneless Diffuser ◽  
Centrifugal Compressors ◽  
Parallel Wall

The influence of four different vaneless diffuser shapes on the performance of centrifugal compressors is numerically studied in this paper. One of the studied shapes was a parallel wall diffuser. Two others had the width reduced only from hub and shroud and the rest had the width reduced from hub and shroud divided evenly. Then the numerical simulation was employed and the overall compressor aerodynamic performance was studied. The detailed velocity and pressure distribution and energy loss within the centrifugal compressor with different diffuser geometries and different operating conditions were analyzed. The results revealed that shroud pinch significantly improved the overall compressor aerodynamic performance more than any other pinch types, and the best performance can be achieved by pinched diffusers under the design condition compared with pinched diffusers under the near surge condition or choking condition. The range of energy loss, namely the static entropy area in the compressor, become reduced with the above three pinches diffusers.

An Analytical Model of Flow-Induced Rotordynamic Forces in Shrouded Centrifugal Pump Impellers

2016 ◽  
Author(s):  
Jieun Song ◽  
Seung Jin Song
Keyword(s):  
Flow Model ◽  
Axisymmetric Flow ◽  
Flow Fields ◽  
Industrial Applications ◽  
Operating Conditions ◽  
Centrifugal Pumps ◽  
Impeller Blade ◽  
Inlet Flow ◽  
Pump Test ◽  
Rotordynamic Forces

Shrouded centrifugal pumps are widely used in industrial applications such as process machines, and they can suffer from rotordynamic instability. Eccentric shrouded impellers induce non-axisymmetric flow fields which, in turn, lead to rotordynamic forces. Therefore, a new analytical flow model for shrouded pump impellers (which considers non-axisymmetric flow fields in the upstream inlet duct, shrouded impeller, and downstream) has been developed using an actuator disk approach. The model can predict impeller rotordynamic stiffness values from pump geometry and operating conditions. When compared to the available pump test data [1], the new model’s predicted stiffness coefficients agree well with the measured data. The new model’s predictions show the strong influence of the non-axisymmetric shroud inlet flow on the rotordynamic stiffness forces. The shroud inlet flow non-axisymmetry, in turn, results from the non-axisymmetric flows upstream of and inside the impeller blade passage induced by impeller eccentricity.

Clearance Effects on the Onset of Instability in a Centrifugal Compressor

2006 ◽  
Author(s):  
Matthias Schleer ◽  
Seung Jin Song ◽  
Reza S. Abhari
Keyword(s):  
Pressure Distribution ◽  
Mass Flow ◽  
Flow Rate ◽  
Centrifugal Compressor ◽  
Leading Edge ◽  
Operating Conditions ◽  
High Mass ◽  
Time Resolved ◽  
Flow Rates ◽  
Blade Loading

This report intends to shed an insight into the effect of large relative tip clearances on the onset of instability in a highly loaded centrifugal compressor. Time-resolved pressure measurements have been performed along the casing of a scaled-up model of a small compressor for two clearances at a wide range of operating conditions. Based on these time-resolved measurements the pressure distribution along the meridional length and the blade loading distribution are calculated for each operating condition. In addition, the phase locked pressure fluctuation and its deviation are computed. The results show the behavior of each sub-component of the compressor at different flow conditions and explain the role of the relative tip clearance on the onset of instability. For high mass flow rates the steady pressure distribution along the casing reveals that the inducer acts as an accelerating nozzle. Pressure is only built up in the radial part due to the centrifugal forces and in the subsequent diffuser due to area change. For off-design conditions incidence effects are seen in the blade loading distribution at the leading edge while the inducer is unloaded. A region of high pressure deviation originates at the leading edge of the main blade and convects downstream. This feature is interpreted as the trajectory of the leakage vortex. The trajectory of these vortices is strongly affected by the mass flow coefficient. If the mass flow rate is sufficiently small the trajectory of the leakage vortex becomes perpendicular to the axis of rotation, the leakage vortex interacts with the adjacent blade, and inlet tip recirculation is triggered. If the flow rate is further reduced, the leakage vortex vanishes and rotating stall is initiated in the diffuser. For larger clearances, stronger vortices are formed, stall is triggered at higher flow rates and the overall compressor performance deteriorates.

The Rotordynamic Forces on an Open-Type Centrifugal Compressor Impeller in Whirling Motion

1999 ◽  
Vol 121 (2) ◽  
pp. 259-265 ◽  
Author(s):  
Yoshiki Yoshida ◽  
Yoshinobu Tsujimoto ◽  
Nobuhiro Ishii ◽  
Hideo Ohashi ◽  
Fumitaka Kano
Keyword(s):  
Pressure Distribution ◽  
Centrifugal Compressor ◽  
Speed Ratio ◽  
Fluid Force ◽  
Open Type ◽  
Fluid Forces ◽  
Whirling Motion ◽  
Compressor Impeller ◽  
Whirl Speed ◽  
Rotordynamic Forces

In recent years, increasing interest has been given to the rotordynamic forces on impellers, from the view point of the shaft vibration analysis. Previous experimental and analytical results have shown that the fluid-induced forces on closed-type (with shroud) centrifugal impellers in whirling motion contribute substantially to the potential destabilization of subsynchronous shaft vibrations. However, to date nothing is known of the rotordynamic forces on open-type (without shroud) centrifugal impellers. This paper examines the rotordynamic fluid forces on an open-type centrifugal compressor impeller in whirling motion. For an open-type impeller, the variation of the tip clearance due to the whirling motion is the main contribute to the rotordynamic forces. Experiments were performed to investigate the rotordynamic forces by direct measurements using a force balance device, and indirectly from the unsteady pressure on the casing wall over a range of whirl speed ratio (Ω/ω) for several flow rates. In this paper, the following results were obtained: (1) Destabilizing forces occur at small positive whirl speed ratio (0 ≤ Ω/ω ≤ 0.3) throughout the flow range of normal operation; (2) At smaller flow rate with inlet backflow, the magnitude of the fluid force changes dramatically at a whirl speed ratio close to Ω/ω = 0.8, resulting in destabilizing rotordynamic forces. From the measurement of unsteady inlet pressure, it was shown that the drastic changes in the fluid force are related to the coupling of the whirling motion with a rotating flow instability, similar to “rotating stall”; (3) The forces estimated from the unsteady pressure distribution on the casing wall and those estimated from the pressure difference across the impeller blades were compared with the results from the direct fluid force measurements. The direct fluid forces correlate better with the forces due to the pressure distribution on the casing wall.

Non-Axisymmetric Flows and Rotordynamic Forces in an Eccentric Shrouded Centrifugal Compressor—Part 1: Measurement

2019 ◽  
Vol 141 (11) ◽  
Author(s):  
Jieun Song ◽  
Suyong Kim ◽  
Tae Choon Park ◽  
Bong-Jun Cha ◽  
Dong Hun Lim ◽  
...  
Keyword(s):  
Centrifugal Compressor ◽  
System Level ◽  
Labyrinth Seals ◽  
Stiffness Coefficients ◽  
Pressure Distributions ◽  
Order Of Magnitude ◽  
Direct Stiffness ◽  
The Cross ◽  
Rotordynamic Forces ◽  
Pressure Perturbations

Abstract Centrifugal compressors can suffer from rotordynamic instability. While individual components (e.g., seals, shrouds) have been previously investigated, an integrated experimental or analytical study at the compressor system level is scarce. For the first time, non-axisymmetric pressure distributions in a statically eccentric shrouded centrifugal compressor with eye-labyrinth seals have been measured for various eccentricities. From the pressure measurements, direct and cross-coupled stiffness coefficients have been determined. Thus, the contributions of the pressure perturbations in the shroud cavity and labyrinth seals have been simultaneously investigated. The cross-coupled stiffness coefficients in the shroud and labyrinth seals are both positive and one order of magnitude larger than the direct stiffness coefficients. Furthermore, in the tested compressor, contrary to the common assumption, the cross-coupled stiffness in the shroud is 2.5 times larger than that in the labyrinth seals. Thus, not only eye-labyrinth seals but also shrouds need to be considered in rotordynamic analysis.

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