Numerical Modeling of Static and Rotordynamic Characteristics for Three Types of Helically Grooved Liquid Annular Seals

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
Zhigang Li ◽  
Zhi Fang ◽  
Jun Li ◽  
Zhenping Feng
Keyword(s):  
Perturbation Method ◽  
Navier Stokes ◽  
Force Coefficients ◽  
Numerical Predictions ◽  
Curve Fit ◽  
Annular Seal ◽  
Frequency Independent ◽  
Computational Fluid Dynamics Cfd ◽  
Multiple Reference ◽  
Annular Seals

Abstract This paper deals with numerical predictions of the leakage flowrates, drag power, and rotordynamic force coefficients for three types of helically grooved liquid annular seals, which include a liquid annular seal with helically grooved stator (GS/SR seal), one with helically grooved rotor (SS/GR seal), and one with helical grooves on stator and rotor (GS/GR seal). A novel transient computational fluid dynamics (CFD)-based perturbation method was proposed for the predictions of the leakage flowrates, drag power, and rotordynamic force coefficients of helically grooved liquid annular seals. This method is based on the unsteady Reynolds-averaged Navier–Stokes (RANS) solution with the mesh-deformation technique and the multiple reference frame theory. The time-varying fluid-induced forces acting on the rotor/stator surface were obtained as a response to the time-dependent perturbation of the seal stator surface with the periodic motion, based on the multiple-frequency elliptical-orbit stator whirling model. The frequency-independent rotordynamic force coefficients were determined using curve fit and fast Fourier transform (FFT) in the frequency domain. The CFD-based method was adequately validated by comparisons with the published experiment data of leakage flowrates and fluid response forces for three types of helically grooved liquid annular seals. Based on the transient CFD-based perturbation method, numerical results of the leakage flowrates, drag powers, and rotordynamic force coefficients were presented and compared for three types of helically grooved liquid annular seals at five rotational speeds (n = 0.5 krpm, 1.0 krpm, 2.0 krpm, 3.0 krpm, and 4.0 krpm), paying special attention to the effective stiffness coefficient and effective damping coefficient.

Numerical Modeling of Static and Rotordynamic Characteristics for Three Types of Helically-Grooved Liquid Annular Seals

2019 ◽  
Author(s):  
Zhigang Li ◽  
Zhi Fang ◽  
Jun Li ◽  
Zhenping Feng
Keyword(s):  
Perturbation Method ◽  
Leakage Flow ◽  
Centrifugal Pumps ◽  
Flow Rates ◽  
Force Coefficients ◽  
Numerical Predictions ◽  
Multi Stage ◽  
Annular Seal ◽  
Helical Grooves ◽  
Annular Seals

Abstract This paper deals with numerical predictions of the leakage flow rates, drag power and rotordynamic force coefficients for three types of helically-grooved liquid annular seals, which include a liquid annular seal with helically-grooved stator (GS/SR seal), one with helically-grooved rotor (SS/GR seal), and one with helical grooves on stator and rotor (GS/GR seal). These seals are frequently used for multiple-stage centrifugal pumps as they have the advantage of low leakage (even to zero) due to the “pumping effect” of the helical grooves. However, the static and rotordynamic characteristics of helically-grooved liquid annular seals still are not fully understood, and even more pronounced is the lack of effective numerical models in the literature. A novel transient CFD-based perturbation method was proposed for the predictions of the leakage flow rates, drag power and rotordynamic force coefficients of helically-grooved liquid annular seals. This method is based on the unsteady Reynolds-Averaged Navier–Stokes (RANS) solution with the mesh deformation technique and the multiple reference frame theory. The time-varying fluid-induced forces acting on the rotor/stator surface were obtained as a response to the time-dependent perturbation of the seal stator surface with the periodic motion, based on the multiple-frequency elliptical-orbit stator whirling model. The frequency-independent rotordynamic force coefficients were determined using curve fit and Fast Fourier Transform (FFT) in the frequency domain. The CFD-based method was adequately validated by comparisons to the published experiment data of leakage flow rates and fluid response forces for three types of helically-grooved liquid annular seals. Based on the transient CFD-based perturbation method, numerical results of the leakage flow rates, drag powers and rotordynamic force coefficients were presented and compared for three types of helically-grooved liquid annular seals at five rotational speeds (n = 0.5 krpm, 1.0 krpm, 2.0 krpm, 3.0 krpm and 4.0 krpm), paying special attention to the effective stiffness coefficient and effective damping coefficient. Results show that the GS/GR seal has the best sealing capability, followed by the GS/SR seal and then the SS/GR seal. The leakage flow rate of all three helically-grooved seals monotonically decreases with the increasing rotational speed. The GS/SR seal possesses the best stiffness and damping capability, followed by the SS/GR seal and then the GS/GR seal. Rotordynamic instability problems are more likely caused by the GS/GR seal in multi-stage centrifugal pumps. From a rotordynamic viewpoint, the GS/SR helically-grooved liquid annular seal is a better seal concept for multi-stage centrifugal pumps.

scholarly journals Transient CFD Simulation on Dynamic Characteristics of Annular Seal under Large Eccentricities and Disturbances

Energies ◽  
2020 ◽  
Vol 13 (16) ◽  
pp. 4056
Author(s):  
Kai Zhang ◽  
Xinkuo Jiang ◽  
Shiyang Li ◽  
Bin Huang ◽  
Shuai Yang ◽  
...  
Keyword(s):  
Dynamic Model ◽  
Dynamic Characteristics ◽  
Nonlinear Dynamic ◽  
Cfd Simulation ◽  
Resonance Region ◽  
Nonlinear Dynamic Model ◽  
Annular Seal ◽  
Transient Simulations ◽  
Computational Fluid Dynamics Cfd ◽  
Annular Seals

Annular seals of turbomachinery usually suffer from various degrees of eccentricities and disturbances due to the rotor–stator misalignment and radial loads, while the discussion of annular seal under both large static eccentricities and dynamic disturbances is relatively limited. In this paper, the applicability of linear assumption and reliability of nonlinear dynamic model for eccentric annular seals under large eccentricities and disturbances is discussed based on the investigation of seals with various rotor motions through computational fluid dynamics (CFD). After the validation of transient CFD methods by comparison with experimental and bulk theory results, the dynamic behaviors of annular seal are analyzed by adopting both direct transient simulations and the nonlinear Muszynska model. The results show that the nonlinear dynamic model based on rotor circular whirls around seal center can predict the fluid excitations of different types of rotor motions well under small static eccentricities, while it is limited severely with large static eccentricities, which indicates that the dynamic characteristics of annular seal under large eccentricities are related with the rotor’s motion ways. The paper provides a reference for studies of rotor–seal system with complex rotor motions considering radial loads or running across the resonance region.

A Comparison of Static and Rotordynamic Characteristics for Two Types of Liquid Annular Seals With Parallelly Grooved Stator/Rotor

2020 ◽  
Vol 142 (9) ◽  
Author(s):  
Zhigang Li ◽  
Zhi Fang ◽  
Jun Li
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Leakage Flow ◽  
Frequency Range ◽  
Flow Rates ◽  
Pressure Drops ◽  
Force Coefficients ◽  
Operation Conditions ◽  
Annular Seal ◽  
Annular Seals

Abstract Liquid annular seals with parallelly grooved stator or rotor are used as replacements for smooth plain seals in centrifugal pumps to reduce leakage and break up contaminants within the working fluid. Parallelly grooved liquid annular seals have advantages of less leakage and smaller possibility of abrasion when the seal rotor–stator rubs in comparison to smooth plain seals. This paper deals with the static and rotordynamic characteristics of parallelly grooved liquid annular seals, which are limited in the literature. Numerical results of leakage flow rates, drag powers, and rotordynamic force coefficients were presented and compared for a grooved-stator/smooth-rotor (GS-SR) liquid annular seal and a smooth-stator/grooved-rotor (SS-GR) liquid annular seal, utilizing a modified transient computational fluid dynamics-based perturbation approach based on the multiple-frequency elliptical-orbit rotor whirling model. Both liquid annular seals have identical seal axial length, rotor diameter, sealing clearance, groove number, and geometry. The present transient computational fluid dynamics-based perturbation method was adequately validated based on the published experiment data of leakage flow rates and frequency-independent rotordynamic force coefficients for the GS-SR and SS-GR liquid annular seals at various pressure drops with differential inlet preswirl ratios. Simulations were performed at three pressure drops (4.14 bar, 6.21 bar, and 8.27 bar), three rotational speeds (2 krpm, 4 krpm, and 6 krpm) and three inlet preswirl ratios (0, 0.5, and 1.0), applying a wide rotor whirling frequency range up to 200 Hz, to analyze and compare the influences of operation conditions on the static and rotordynamic characteristics for both the GS-SR and SS-GR liquid annular seals. Results show that the present two liquid annular seals possess similar sealing capability, and the SS-GR seal produces a slightly larger (∼2–10%) drag power loss than the GS-SR seal. For small rotor whirling motion around a centered position, both seals have the identical direct force coefficients and the equal-magnitude opposite-sign cross-coupling force coefficients in the orthogonal directions x and y. For all operation conditions, both the GS-SR and SS-GR liquid annular seals possess negative direct stiffness K and positive direct damping C. The GS-SR seal produces purely positive Ceff throughout the whirling frequency range for all operation conditions, while Ceff for the SS-GR seal shows a significant decrease and transitions to negative value at the crossover frequency fco with increasing rotational speed and inlet preswirl. From a rotordynamic viewpoint, the GS-SR liquid annular seal is a better seal concept for pumps.

Numerical Comparison of Static and Rotordynamic Characteristics for a Grooved-Stator/Smooth-Rotor and a Smooth-Stator/Grooved-Rotor Liquid Annular Seals

2019 ◽  
Author(s):  
Zhigang Li ◽  
Zhi Fang ◽  
Jun Li ◽  
Zhenping Feng
Keyword(s):  
Working Fluid ◽  
Leakage Flow ◽  
Frequency Range ◽  
Flow Rates ◽  
Pressure Drops ◽  
Force Coefficients ◽  
Operation Conditions ◽  
Annular Seal ◽  
Positive Direct ◽  
Annular Seals

Abstract Liquid annular seals with parallelly-grooved stator or rotor are used as replacements for smooth plain seals in centrifugal pumps to reduce leakage and break up contaminants within the working fluid. Parallelly-grooved liquid annular seals have advantages of less leakage and smaller possibility of abrasion when the seal rotor-stator rubs in comparison to smooth plain seals. This paper deals with the static and rotordynamic characteristics of parallelly-grooved liquid annular seals, which are limited in the literature. Numerical results of leakage flow rates, drag powers and rotordynamic force coefficients were presented and compared for a grooved-stator/smooth-rotor (GS-SR) liquid annular seal and a smooth-stator/grooved-rotor (SS-GR) liquid annular seal, utilizing a modified transient CFD-based perturbation approach based on the multiple-frequency elliptical-orbit rotor whirling model. Both liquid annular seals have identical seal axial length, rotor diameter, sealing clearance, groove number and geometry. The present transient CFD-based perturbation method was adequately validated based on the published experiment data of leakage flow rates and frequency-independent rotordynamic force coefficients for the GS-SR and SS-GR liquid annular seals at various pressure drops with differential inlet preswirl ratios. Simulations were performed at three pressure drops (4.14 bar, 6.21 bar, 8.27 bar), three rotational speeds (2 krpm, 4 krpm, 6 krpm) and three inlet preswirl ratios (0, 0.5, 1.0), applying a wide rotor whirling frequency range up to 200 Hz, to analyze and compare the influences of operation conditions on the static and rotordynamic characteristics for both the GS-SR and SS-GR liquid annular seals. Results show that the present two liquid annular seals possess similar sealing capability, and the SS-GR seal produces a slightly larger (∼ 2–10%) drag power loss than the GS-SR seal. For small rotor whirling motion around a centered position, both seals have the identical direct force coefficients and the equal-magnitude opposite-sign cross-coupling force coefficients in the orthogonal directions x and y. For all operation conditions, both the GS-SR and SS-GR liquid annular seals possess negative direct stiffness K and positive direct damping C. The GS-SR seal produces purely positive Ceff throughout the whirling frequency range for all operation conditions, while Ceff for the SS-GR seal shows a significant decrease and transitions to negative value at the crossover frequency fco with increasing rotational speed and inlet preswirl. From a rotordynamic viewpoint, the GS-SR liquid annular seal is a better seal concept for pumps.

Clearance Effects on Corresponding Annular and Labyrinth Seal Flow Leakage Characteristics

1993 ◽  
Vol 115 (4) ◽  
pp. 699-704 ◽  
Author(s):  
D. L. Rhode ◽  
R. I. Hibbs
Keyword(s):  
Computer Code ◽  
Labyrinth Seal ◽  
Momentum Conservation ◽  
Navier Stokes ◽  
Unexpected Finding ◽  
Labyrinth Seals ◽  
Swirl Velocity ◽  
Small Clearance ◽  
Annular Seal ◽  
Annular Seals

A previous Navier-Stokes finite difference computer code is extended in order to compute seal leakage directly from given upstream and downstream reservoir pressures. The numerical results are in excellent agreement with previous measurements, the discrepancy being less than eight percent. Annular seals are found to leak approximately twenty percent more than corresponding labyrinths over the entire range of realistic clearance. A rather unexpected finding is that a dramatic increase of swirl velocity occurs near the discharge of small-clearance annular seals, which does not arise in corresponding labyrinth seals. The results, which are used to explain this finding, show that a large density drop occurs near the small-clearance annular seal exit, which provides the swirl velocity increase in accordance with angular momentum conservation.

scholarly journals Research on Rotordynamic Characteristics of Pump Annular Seals Based on a New Transient CFD Method

Processes ◽  
2020 ◽  
Vol 8 (2) ◽  
pp. 227 ◽  
Author(s):  
Fengqin Li ◽  
Baoling Cui ◽  
Lulu Zhai
Keyword(s):  
Pump System ◽  
Pump Rotor ◽  
Annular Seal ◽  
Reaction Forces ◽  
Rotor Surface ◽  
Computational Fluid Dynamics Cfd ◽  
The Stability ◽  
Cfd Method ◽  
Supporting Condition ◽  
Annular Seals

Pump annular seals can cause fluid reaction forces that have great effects on the vibration characteristic and stability of a pump system. For this reason, it is important to study rotordynamic characteristics of annular seals. In this paper, a new transient computational fluid dynamics (CFD) method with dynamic mesh is proposed to investigate rotordynamic characteristics of the pump annular seal. The reliability of the transient CFD method is validated by comparison with the results from the experiment and the bulk-flow method, and the relationship between the seal length and rotordynamic characteristics is investigated by the transient CFD method. The results indicate that direct stiffness decreases sharply even turns to negative as the seal length increases, this phenomenon may change the direction of fluid force on the rotor surface and affect supporting condition of the pump rotor. With the increasing seal length, the whirl frequency ratio gradually increases, which would weaken the stability of the pump rotor system.

Acoustoelastic Interaction in Combustion Chambers: Modeling and Experiments

2008 ◽  
Vol 130 (5) ◽  
Author(s):  
R. A. Huls ◽  
J. F. van Kampen ◽  
P. J. M. van der Hoogt ◽  
J. B. W. Kok ◽  
A. de Boer
Keyword(s):  
Cfd Simulation ◽  
Pressure Sensors ◽  
Structural Vibration ◽  
Navier Stokes ◽  
Laser Vibrometer ◽  
Combustion Chambers ◽  
Lean Premixed Combustion ◽  
Frequency Independent ◽  
Modeling And Experiments ◽  
Computational Fluid Dynamics Cfd

To decrease NOx emissions from combustion systems, lean premixed combustion is used. A disadvantage is the higher sensitivity to combustion instabilities, leading to increased sound pressure levels in the combustor and resulting in an increased excitation of the surrounding structure: the liner. This causes fatigue, which limits the lifetime of the combustor. This paper presents a joint experimental and numerical investigation of this acoustoelastic interaction problem for frequencies up to 1kHz. To study this problem experimentally, a test setup has been built consisting of a single burner, 500kW, 5bar combustion system. The thin structure (liner) is contained in a thick pressure vessel with optical access for a traversing laser vibrometer system to measure the vibration levels of the liner. The acoustic excitation of the liner is measured using pressure sensors measuring the acoustic pressures inside the combustion chamber. For the numerical model, the finite element method with full coupling between structural vibration and acoustics is used. The flame is modeled as an acoustic volume source corresponding to a heat release rate that is frequency independent. The temperature distribution is taken from a Reynolds averaged Navier Stokes (RaNS) computational fluid dynamics (CFD) simulation. Results show very good agreement between predicted and measured acoustic pressure levels. The predicted and measured vibration levels also match fairly well.

Recent Developments in Computational Methods for the Analysis of Ducted Propellers in Open Water

2019 ◽  
Vol 63 (4) ◽  
pp. 219-234
Author(s):  
João Baltazar ◽  
José A. C. Falcão de Campos ◽  
Johan Bosschers ◽  
Douwe Rijpkema
Keyword(s):  
Computational Methods ◽  
Open Water ◽  
Boundary Element Methods ◽  
Navier Stokes ◽  
Hydrodynamic Analysis ◽  
Numerical Predictions ◽  
Ducted Propeller ◽  
Recent Developments ◽  
Propeller Performance ◽  
Ducted Propellers

This article presents an overview of the recent developments at Instituto Superior Técnico and Maritime Research Institute Netherlands in applying computational methods for the hydrodynamic analysis of ducted propellers. The developments focus on the propeller performance prediction in open water conditions using boundary element methods and Reynolds-averaged Navier-Stokes solvers. The article starts with an estimation of the numerical errors involved in both methods. Then, the different viscous mechanisms involved in the ducted propeller flow are discussed and numerical procedures for the potential flow solution proposed. Finally, the numerical predictions are compared with experimental measurements.

Computational Fluid Dynamic Using Parallel Loop of Multi-Cores Processor

2014 ◽  
Vol 493 ◽  
pp. 80-85 ◽  
Author(s):  
C.L Siow ◽  
Jaswar ◽  
Efi Afrizal
Keyword(s):  
Fluid Flow ◽  
Early Stage ◽  
Fluid Dynamic ◽  
Visual Basic ◽  
Computer Hardware ◽  
Navier Stokes ◽  
Computer Memory ◽  
Large Size ◽  
Computational Fluid Dynamics Cfd ◽  
Reynolds Average

Computational Fluid Dynamics (CFD) software is often used to study fluid flow and structures motion in fluids. The CFD normally requires large size of arrays and computer memory and then caused long execution time. However, Innovation of computer hardware such as multi-cores processor provides an alternative solution to improve this programming performance. This paper discussed loop parallelize multi-cores processor for optimization of sequential looping CFD code. This loop parallelize CFD was achieved by applying multi-tasking or multi-threading code into the original CFD code which was developed by one of the authors. The CFD code was developed based on Reynolds Average Navier-Stokes (RANS) method. The new CFD code program was developed using Microsoft Visual Basic (VB) programming language. In the early stage, the whole CFD code was constructed in a sequential flow before it is modified to parallel flow by using VBs multi-threading library. In the comparison, fluid flow around the hull of round-shaped FPSO was selected to compare the performance of both the programming codes. Besides, executed results of this self-developed code such as pressure distribution around the hull were also presented in this paper.

Reynolds-averaged Navier–Stokes simulation of hydrofoil effects on hydrodynamic coefficients of a catamaran in forced oscillation

2016 ◽  
Vol 231 (2) ◽  
pp. 364-383
Author(s):  
Amin Najafi ◽  
Mohammad Saeed Seif
Keyword(s):  
High Speed ◽  
Experimental Approach ◽  
Navier Stokes ◽  
Hydrodynamic Coefficients ◽  
Laboratory Equipment ◽  
Factors Affecting ◽  
High Frequencies ◽  
Frequency Independent ◽  
Reynolds Averaged Navier Stokes

Determination of high-speed crafts’ hydrodynamic coefficients will help to analyze the dynamics of these kinds of vessels and the factors affecting their dynamic stabilities. Also, it can be useful and effective in controlling the vessel instabilities. The main purpose of this study is to determine the coefficients of longitudinal motions of a planing catamaran with and without a hydrofoil using Reynolds-averaged Navier–Stokes method to evaluate the foil effects on them. Determination of hydrodynamic coefficients by experimental approach is costly and requires meticulous laboratory equipment; therefore, utilizing the numerical methods and developing a virtual laboratory seem highly efficient. In this study, the numerical results for hydrodynamic coefficients of a high-speed craft are verified against Troesch’s experimental results. In the following, after determination of hydrodynamic coefficients of a planing catamaran with and without foil, the foil effects on its hydrodynamic coefficients are evaluated. The results indicate that most of the coefficients are frequency-independent especially at high frequencies.

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