Research

14 pages, 6489 KiB

Open AccessArticle

Exploration of Flow Instability Characteristics in a Two-Stage Axial-Flow Compressor via Numerical Simulation Method

by Tong Wang, Xiangyuan Dou and Yongwen Liu

Machines 2023, 11(3), 401; https://doi.org/10.3390/machines11030401 - 20 Mar 2023

Cited by 1 | Viewed by 1060

A four-blade-passage numerical model was developed for a two-stage axial-flow compressor with an inlet guide vane (IGV) for the purpose of studying the steady and dynamic characteristics of the compressor approaching its stability limit. The flow-field information indicated that the tip-leakage flow decreased [...] Read more.

A four-blade-passage numerical model was developed for a two-stage axial-flow compressor with an inlet guide vane (IGV) for the purpose of studying the steady and dynamic characteristics of the compressor approaching its stability limit. The flow-field information indicated that the tip-leakage flow decreased more rapidly from the blade’s leading edge to the trailing edge, with a decreasing flow rate. The leakage flow was verified to be driven via the blade load over the whole operating range. Further research on the blade load was carried out. The magnitude of the highest blade load in the leading-edge portion of the first-stage rotor determined the lowest flow rate with steady-simulation analysis. The circumferential grooves on the rotor improved the rotor’s stable range via reducing the blade load. Unsteady-simulation results showed that the extreme blade load appeared first at the front of the first stage, with a decreasing flow rate. The second stage played a positive compensative role through releasing some of the load from the first stage. It can be generalized that the lowest flow rate at a specific speed is determined via not only any single stage but also other stages in a multistage axial-flow compressor. Full article

(This article belongs to the Special Issue Selected Papers from CITC2022)

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12 pages, 5416 KiB

Open AccessArticle

Study on the Service Performance of a Two-Stage Floating-Ring Isolation Seal for a High-Speed Turbopump with a Cryogenic Medium

by Zifeng Song, Shuangxi Li, Xiaozhu Chen, Zhiyuan Liu, Tan Zhao and Baiqi Huang

Machines 2023, 11(3), 373; https://doi.org/10.3390/machines11030373 - 10 Mar 2023

Viewed by 1408

Abstract

The reliability and stability of the seal at the fuel-supply end of a rocket-engine turbopump are important factors in determining safety. Conventional single-stage floating rings used for the isolation-sealing of cryogenic media are highly susceptible to operational instability during startup and shutdown, which [...] Read more.

The reliability and stability of the seal at the fuel-supply end of a rocket-engine turbopump are important factors in determining safety. Conventional single-stage floating rings used for the isolation-sealing of cryogenic media are highly susceptible to operational instability during startup and shutdown, which places demands on the seals’ structure, size, and material properties. In this study, a two-stage floating-ring isolation seal with a non-slotted main sealing surface was designed using a tangential air-intake mode. Based on the full-size three-dimensional finite-volume model, the leakage characteristics of the floating ring during operation were calculated, taking into account the effect of the “inlet effect” on the seal’s performance. Combining the temperature and pressure distributions of the sealing system under cryogenic operating conditions, calculated using a numerical simulation, a reliability analysis of various inlet directions and two kinds of floating-ring schemes was carried out on a self-constructed service-performance test bench. The results indicate that the main wear location of the non-slotted floating ring occurs on the auxiliary sealing surface, with stable working performance. When the inlet direction and spindle-rotation direction are the same, this is more conducive to ensuring the stability of seal performance in practical applications. The results of the current research are instructive for designing floating-ring isolation seals for turbine pumps. Full article

(This article belongs to the Special Issue Selected Papers from CITC2022)

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12 pages, 3760 KiB

Open AccessArticle

Experimental Investigation of Vibration Reduction Effect of High-Pressure Air Compressor Using Composite Damping Base

by Feng Zhao, He Li, Hui Li and Duo Liu

Machines 2023, 11(2), 229; https://doi.org/10.3390/machines11020229 - 04 Feb 2023

Viewed by 1332

Abstract

High-pressure air compressor is one of the most important pieces of equipment for ships, which is one of the main sources of vibration on board. There are a lot of welded plate structures in the installation base of the compressor, which have weak [...] Read more.

High-pressure air compressor is one of the most important pieces of equipment for ships, which is one of the main sources of vibration on board. There are a lot of welded plate structures in the installation base of the compressor, which have weak stiffness and low damping and are prone to vibration radiation due to excitation. In this paper, a section of the base is taken as the test object. Through the analysis of the working principle, the vibration characteristics of the air compressor and the corresponding transmission path are mastered. In addition, it is tested and screened by filling different kinds of damping materials. Finally, it is concluded that the super-damping rubber has a better damping effect on the specimen of the base. According to the vibration characteristics of the plate structure, the sandwich structure, which is fixed by a restraint layer with super-damping rubber, is bonded to the plate. When the base is excited, the restraint layer moves in relative slippage, and the damping rubber can consume part of the vibration energy so that the vibration of the plate structure is reduced. Moreover, the technology has the characteristics of small additional mass and a good damping effect. It has been proved that the feet acceleration is reduced by 6 dB or above through experiments. Full article

(This article belongs to the Special Issue Selected Papers from CITC2022)

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16 pages, 10453 KiB

Open AccessEditor’s ChoiceArticle

Experimental Study on Tribological and Leakage Characteristics of a Rotating Spring-Energized Seal under High and Low Temperature

by Dengyu Liu, Jun Zhao, Shuangxi Li, Xinni Zhao and Lele Huang

Machines 2023, 11(2), 221; https://doi.org/10.3390/machines11020221 - 03 Feb 2023

Cited by 1 | Viewed by 1631

Abstract

A spring-energized seal, whose PTFE plastic shell has excellent self-lubrication and a low temperature stability, is used widely in liquid fuel valves’ rotating end-face seals. However, in practical application, temperature has a larger effect on not only the physical and tribological properties of [...] Read more.

A spring-energized seal, whose PTFE plastic shell has excellent self-lubrication and a low temperature stability, is used widely in liquid fuel valves’ rotating end-face seals. However, in practical application, temperature has a larger effect on not only the physical and tribological properties of materials, but also on the leakage performance of spring-energized rings. Thus, a high and low temperature sealing test of the spring-energized seal that applies to an engine was carried out. In this paper, the leakage characteristics, friction torque and wear characteristics of a spring-energized ring under different temperatures were studied. The friction torque at high temperature was less than that at normal temperature, and a low temperature could effectively reduce the wear amount of PTFE material. In order to study the influence of temperature on PTFE filled with graphite, the friction and wear test of PTFE-2 was carried out. The results showed that the amount of wear of PTFE-2 was only 27.8% of that at the normal temperature but the friction coefficient was three times larger when the temperature was −45 °C. Full article

(This article belongs to the Special Issue Selected Papers from CITC2022)

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23 pages, 7535 KiB

Open AccessArticle

Study of Parallel Compressor System and Real-Time Simulation Based on Modular Dynamic System Greitzer Modeling

by Yang Su, Xuejiang Chen, Xiaoming Liu, Xin Wang and Xiaodong Li

Machines 2023, 11(2), 213; https://doi.org/10.3390/machines11020213 - 02 Feb 2023

Viewed by 1426

Abstract

The compressor system is widely used in aerospace, chemical industry, and other industrial fields. Modeling a compressor system is of great significance to the study of hydrodynamics and surge characteristics. Modular Dynamic System Greitzer (MDSG) modeling is a real-time model to simulate the [...] Read more.

The compressor system is widely used in aerospace, chemical industry, and other industrial fields. Modeling a compressor system is of great significance to the study of hydrodynamics and surge characteristics. Modular Dynamic System Greitzer (MDSG) modeling is a real-time model to simulate the dynamic response of complex compressor systems. An industrial air suction parallel compressor system with three compressors is modeled and simulated by the MDSG model, and the results are compared with the experimental results; the average error is less than 3%, which demonstrates that the MDSG model for the parallel compressor systems is reliable and accurate. Finally, a compression system with one valve and two valves is developed by the MDSG model, and the typical surge phenomena of two compression systems are dynamically simulated and discussed. The dynamic performance of the single compressor and parallel compressor systems can be described by the MDSG model. Full article

(This article belongs to the Special Issue Selected Papers from CITC2022)

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15 pages, 10318 KiB

Open AccessEditor’s ChoiceArticle

Rejection of Synchronous Vibrations of AMB System Using Nonlinear Adaptive Control Algorithm with a Novel Frequency Estimator

by Xiaoyu Bian, Zhengang Shi, Ni Mo, Lei Shi, Yangbo Zheng and Xingnan Liu

Machines 2023, 11(2), 188; https://doi.org/10.3390/machines11020188 - 31 Jan 2023

Cited by 2 | Viewed by 978

Abstract

This paper focuses on the synchronous vibration suppression of an active magnetic bearing (AMB) system without a rotating speed sensor. One of the most intractable problems with AMB systems is the synchronous vibration caused by the mass imbalance of the rotor. Moreover, practically [...] Read more.

This paper focuses on the synchronous vibration suppression of an active magnetic bearing (AMB) system without a rotating speed sensor. One of the most intractable problems with AMB systems is the synchronous vibration caused by the mass imbalance of the rotor. Moreover, practically all existing unbalance control algorithms require the rotating speed sensor to determine rotation speed. However, in some unique applications, it is impossible to install and use the rotating speed sensor as intended. This study provided a nonlinear adaptive control (NAC) algorithm and a modified frequency estimator to address the above issues. The proposed approach can suppress current and displacement vibrations by regulating the control structure. The frequency estimator calculates the rotating speed based on the position of the rotor at different moments, which has a quick response time, high precision, and effective tracking. The NAC algorithm can achieve unbalanced control based on the period iteration strategy. Additionally, the Lyapunov method is used to demonstrate the stability of the NAC algorithm. Finally, the experimental and simulation results also confirm the effectiveness and reliability of the overall control scheme. The results from simulations and experiments indicate that the novel frequency estimator can track the speed accurately and that its error can be regulated to within

\pm

0.05 Hz. The overall control schema can reduce the displacement vibration’s amplitude by 72.2% and the current vibration’s amplitude by 65.6%. Full article

(This article belongs to the Special Issue Selected Papers from CITC2022)

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18 pages, 7729 KiB

Open AccessEditor’s ChoiceArticle

Numerical and Experimental Investigations of Axial Flow Fan with Bionic Forked Trailing Edge

by Zhong Liang, Jun Wang, Wei Wang, Boyan Jiang, Yanyan Ding and Wanxiang Qin

Machines 2023, 11(2), 155; https://doi.org/10.3390/machines11020155 - 23 Jan 2023

Cited by 2 | Viewed by 2319

Abstract

To improve the performance of the aerodynamic properties and reduce the aerodynamic noise of an axial flow fan in the outdoor unit of an air conditioner, this study proposed a bionic forked trailing-edge structure inspired by the forked fish caudal fin and implemented [...] Read more.

To improve the performance of the aerodynamic properties and reduce the aerodynamic noise of an axial flow fan in the outdoor unit of an air conditioner, this study proposed a bionic forked trailing-edge structure inspired by the forked fish caudal fin and implemented by modifying the trailing edge of the prototype fan. The effect of the bionic forked trailing edge on the aerodynamic and aeroacoustic performance was investigated experimentally, and detailed analyses of the blade load and internal vortex structures were performed based on large-eddy simulations (LES). It is shown that the bionic forked trailing edge could effectively adjust the blade load distribution, reduce the pressure difference between the pressure side and suction side near the trailing edge of the blade tip region, and weaken the intensity and influence range of the inlet vortex (IV) and the tip leakage vortex (TLV). The discrete noise caused by the vortices in the rotor tip area was also reduced, particularly at the blade passing frequency (BPF) and its harmonic frequency. The experimental results confirmed the existence of an optimal bionic forked trailing-edge structure, resulting in the maximum power-saving rate γ of 7.5% and the reduction of 0.3 ~ 0.8 dB of aerodynamic noise, with an included angle θ_t of 13.5°. The detailed analysis of the internal vortex structures provides a good reference for the efficiency improvement and noise reduction of axial flow fans. Full article

(This article belongs to the Special Issue Selected Papers from CITC2022)

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15 pages, 5920 KiB

Open AccessArticle

Investigation of Flow and Heat Transfer Characteristics in Microchannels with Fins

by Murun Li, Xuan Gao, Haiwang Li, Jichang Sang, Pengpeng Nie, Weidong Fang and Tiantong Xu

Machines 2023, 11(2), 154; https://doi.org/10.3390/machines11020154 - 22 Jan 2023

Cited by 1 | Viewed by 1177

Abstract

A highly efficient thermal management is imperative to overcome the main challenges associated with heat extraction requirements in electronics. In this study, the flow and heat transfer characteristics of microchannels with various types of fins were numerically analyzed for Re = 0–500 (Re: [...] Read more.

A highly efficient thermal management is imperative to overcome the main challenges associated with heat extraction requirements in electronics. In this study, the flow and heat transfer characteristics of microchannels with various types of fins were numerically analyzed for Re = 0–500 (Re: Reynolds number). Investigation of the aspect ratio, incident angle, and smoothness as well as the flow and heat transfer behaviors revealed the exceptional performance of the optimized fin structure, up to a performance evaluation criterion of 1.53. At large Re values, the fin with a high aspect ratio, small incidence angle, and high smoothness showed the best performance, as it avoids stagnation zones because of flares and sharp corners and simultaneously leads to boundary layer destruction and redevelopment. Interestingly, the microchannel without internal microstructures performed well at small Re values. Among all the designed variables, the influence of the incident angle was superior owing to its ability to generate significant vortices by periodically changing the channel cross-sectional area and flow direction. The conclusions can be innovatively generalized to other microchannels with fins. Full article

(This article belongs to the Special Issue Selected Papers from CITC2022)

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15 pages, 11547 KiB

Open AccessArticle

Effects of Matching between the Inducer and the Impeller of a Centrifugal Pump on Its Cavitation Performance

by Daocheng Wang, Bingwen Gao, Yunzhang Chen, Yufan Pan, Jinping Luo, Lei Liu, Qingxi Wei and Lijun Liu

Machines 2023, 11(2), 142; https://doi.org/10.3390/machines11020142 - 20 Jan 2023

Cited by 1 | Viewed by 1616

Abstract

The inducer is often used to prevent cavitation in a centrifugal pump. However, it may lead to deterioration of the cavitation performance of the pump when poorly matched with the impeller. Numerical simulations are employed to study the effects of the matching, specifically, [...] Read more.

The inducer is often used to prevent cavitation in a centrifugal pump. However, it may lead to deterioration of the cavitation performance of the pump when poorly matched with the impeller. Numerical simulations are employed to study the effects of the matching, specifically, the axial space and the circumferential deflection between the inducer and the impeller, on the cavitation performance. The results show that the inducer destroys the rotational symmetry of the velocity distribution at the inlet of the impeller, resulting in the influence of cavitation on the part of the channels in advance, which explains why the inducer cannot improve the cavitation performance even though it improves the inlet energy of the impeller. On the basis of not changing the geometric shape of the inducer and the impeller, the suction-specific speed is increased by nearly 300 by only adjusting the axial space and by nearly 100 by only adjusting the circumferential deflection. The cavitation performance is better with a larger axial space. There is an optimal value of the circumferential deflection at which the pump works at the best cavitation performance. The effect of the axial space on the overall cavitation performance is more significant than that of the circumferential deflection. The results provide a useful reference for the design and installation of a centrifugal pump inducer. Full article

(This article belongs to the Special Issue Selected Papers from CITC2022)

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16 pages, 9712 KiB

Open AccessArticle

Effect of Slot Jet Flow on Non-Axisymmetric Endwall Cooling Performance of High-Load Turbines

by Kun Du, Yihao Jia, Hui Song, Lei Chen, Qian Zhang, Tingting Cui and Cunliang Liu

Machines 2023, 11(2), 134; https://doi.org/10.3390/machines11020134 - 18 Jan 2023

Cited by 2 | Viewed by 1230

Abstract

As vane inlet temperatures and turbine loadings are increasing, the aerodynamic and thermal management for the endwalls of gas turbines have received increased attention. Non-axisymmetric endwalls are becoming popular due to their proficient capabilities to modify the secondary flow fields and to change [...] Read more.

As vane inlet temperatures and turbine loadings are increasing, the aerodynamic and thermal management for the endwalls of gas turbines have received increased attention. Non-axisymmetric endwalls are becoming popular due to their proficient capabilities to modify the secondary flow fields and to change the film cooling performance on the endwalls. In this study, by considering the interaction between mainstream and purge flow based on non-axisymmetric endwall contouring, the numerical research model used in the present research was established. Based on the validated numerical method, the influence of the non-axisymmetric endwall contouring on the film-cooling effectiveness and aerodynamic characteristics was studied. Furthermore, the effect of different inclination angles on the film-cooling performance of the contoured endwalls was also investigated. The results indicate that for the high-load turbine vane used in this research, various types of non-axisymmetric endwall contouring can alter the aero-dynamic characteristics and cooling performance simultaneously. By inhibiting the secondary flows, non-axisymmetric endwall contouring can reduce the total cascade pressure loss coefficient by 0.305%. In addition, non-axisymmetric endwall contouring can significantly enhance the effective coverage area of purge flow up to 28.29%, and the endwall near the suction side can achieve better cooling performance. Finally, non-axisymmetric endwall contouring can improve the protective effect of large-angle purge flow. Full article

(This article belongs to the Special Issue Selected Papers from CITC2022)

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17 pages, 4701 KiB

Open AccessArticle

Study on Nonlinear Correlation in Modal Coefficients of the Bionic Airfoil

by Qianhao Xiao, Jun Wang, Boyan Jiang, Yanyan Ding and Xiaopei Yang

Machines 2023, 11(1), 88; https://doi.org/10.3390/machines11010088 - 10 Jan 2023

Cited by 3 | Viewed by 1350

Abstract

Applying bionic airfoils is essential in enlightening the design of rotating machinery and flow control. Dynamic mode decomposition was used to reveal the low dimensional flow structure of Riblets, Seagull, and Teal bionic airfoils at low Reynolds numbers 1 × 10⁵ and [...] Read more.

Applying bionic airfoils is essential in enlightening the design of rotating machinery and flow control. Dynamic mode decomposition was used to reveal the low dimensional flow structure of Riblets, Seagull, and Teal bionic airfoils at low Reynolds numbers 1 × 10⁵ and is compared with NACA4412 airfoils. The attack angle of the two-dimensional airfoil is 19°, and the SST k-ω turbulence model and ANSYS fluent were used to obtain the transient flow field data. The sparse identification of nonlinear dynamics reveals the nonlinear correlation between modal coefficients and establishes manifold dynamics. The results show that the bionic airfoil and NACA4412 airfoil have the same type of nonlinear correlation, and the dimension and form of the minimum reduced-order model are consistent. The modal coefficients always appear in the manifold equation in pairs with a phase difference of 90°. The dimension of the manifold equation is two-dimensional, and the absolute value of the coefficient corresponds to the fundamental frequency of airfoil vortex shedding. The reconstructed flow field based on the manifold equation is highly consistent with the numerical simulation flow field, which reveals the accuracy of the manifold equation. The relevant conclusions of this study emphasize the unity of the nonlinear correlation of bionic airfoils. Full article

(This article belongs to the Special Issue Selected Papers from CITC2022)

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21 pages, 6106 KiB

Open AccessArticle

Numerical Examination of the Dynamic Evolution of Fluctuations in Cavitation and Pressure in a Centrifugal Pump during Startup

by Shaofeng Liu, Haifeng Cao, Yuxuan Chen, Shiwei Ni, Guofeng Zhao and Chenxing Jiang

Machines 2023, 11(1), 67; https://doi.org/10.3390/machines11010067 - 05 Jan 2023

Cited by 1 | Viewed by 1218

Abstract

Rapid changes in the performance-related parameters of a pump during its startup operation lead to large pressure fluctuations and structural vibrations in it. In view of these problems, this study investigates the evolution of cavitation and the characteristics of fluctuations under pressure in [...] Read more.

Rapid changes in the performance-related parameters of a pump during its startup operation lead to large pressure fluctuations and structural vibrations in it. In view of these problems, this study investigates the evolution of cavitation and the characteristics of fluctuations under pressure in a centrifugal pump during startup. We use the finite volume method to simulate this dynamic process. To characterize the acceleration, we assume that the rotational speed and rate of flow of the pump are not constant but vary with time. A steady-state numerical simulation is performed to examine the external characteristics of the pump to verify the accuracy of the numerical procedure. The evolution of fluctuations in the cavity and pressure over time is then analyzed in detail. We use the short-term Fourier transform for post-processing in light of its advantage in treating non-stationary signals. The results indicate that both the frequency and the amplitude of the fluctuations in pressure increase with the speed of the impeller. The transient operation causes the average pressure at the inlet of the impeller to decrease to the evaporation pressure, and this leads to an increase in the volume fraction of vapor. Moreover, both the impeller–tongue interaction and the impeller–diffuser interaction influence the fluctuations in cavitation. Full article

(This article belongs to the Special Issue Selected Papers from CITC2022)

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14 pages, 4518 KiB

Open AccessArticle

Investigating the Flow Characteristics of Superhydrophobic U-Shaped Microchannels

by Zhi Tao, Weidong Fang, Haiwang Li, Tiantong Xu, Yi Huang, Hanxiao Wu and Murun Li

Machines 2023, 11(1), 51; https://doi.org/10.3390/machines11010051 - 01 Jan 2023

Viewed by 1723

Abstract

Hydrophobicity has been widely reported for its superior behavior in drag reduction, self-cleaning, and anti-corrosion in many areas. Especially in engineering design, the research of the unique property of the slip flow with complex flow patterns is essential for practical applications. In this [...] Read more.

Hydrophobicity has been widely reported for its superior behavior in drag reduction, self-cleaning, and anti-corrosion in many areas. Especially in engineering design, the research of the unique property of the slip flow with complex flow patterns is essential for practical applications. In this paper, the flow characteristics of a superhydrophobic U-shaped microchannel are systematically investigated, as the curved part is a fundamental component in microfluids. A slip model is established based on theoretical and experimental solutions. Various types of U-shaped microchannels, radii of curvature, and contact angles are studied with a wide range of Reynolds numbers from 0 to 300. We propose a velocity distribution to examine the non-uniformity of slip velocity on the cross-section. This imbalance is improved with an increase in the apparent contact angle and flow rate, and a decrease in the radius of curvature. The secondary flow and vortices generated by the centrifugal force are enhanced, and their positions are changed due to the slippery boundary. The results show a considerable drag reduction from 10% to 40% with different contact angles. The variation of curvature does not have a decisive impact on the final performance when the surface wettability maintains a steady state. Our research elucidates the physical principle of the slip model in curved channels, showing extensive applications of hydrophobicity in the design of complex microchips and the optimization strategy of heat transfer systems. Full article

(This article belongs to the Special Issue Selected Papers from CITC2022)

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20 pages, 9353 KiB

Open AccessArticle

Nonlinear Analysis of Rotor-Bearing-Seal System with Varying Parameters Muszynska Model Based on CFD and RBF

by Rui Wang, Yuefang Wang, Xiaojian Cao, Shuhua Yang and Xinglin Guo

Machines 2022, 10(12), 1238; https://doi.org/10.3390/machines10121238 - 18 Dec 2022

Viewed by 1118

Abstract

The computational fluid dynamics (CFD) combined with radial basis function (RBF) method were adopted to obtain the response surface of the Muszynska nonlinear seal force model coefficient with two variables: eccentricity and rotation speed. During the implementation of the simulation, three coefficients of [...] Read more.

The computational fluid dynamics (CFD) combined with radial basis function (RBF) method were adopted to obtain the response surface of the Muszynska nonlinear seal force model coefficient with two variables: eccentricity and rotation speed. During the implementation of the simulation, three coefficients of the seal force model were calculated in each sub-step according to the current state of the rotor-bearing seal system; following which the rotor dynamics analysis with varying parameters was realized. As with the traditional constant coefficient method, the first-order critical speed of the system was obtained, and the bifurcation point and oil film whirl of the system response were identified. The difference is that the coefficients of the traditional method ordinarily do not change with the state of the system. Comparing the results of the varying parameter method with those of the traditional method, it can be seen that the speeds of the system corresponding to the bifurcation and oil film whirl are different. The varying parameter rotor dynamics simulation method proposed in this paper provides a new way of analyzing the nonlinear characteristics of rotor-bearing-seal systems. Full article

(This article belongs to the Special Issue Selected Papers from CITC2022)

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