Numerical and Experimental Analyses of Dynamic Characteristics for Liquid Annular Seals With Helical Grooves in Seal Stator

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
K. Nagai ◽  
S. Kaneko ◽  
H. Taura ◽  
Y. Watanabe
Keyword(s):  
Numerical Analysis ◽  
Dynamic Characteristics ◽  
Operating Conditions ◽  
Fluid Film ◽  
Fluid Inertia ◽  
Governing Equations ◽  
Whirling Motion ◽  
Experimental Analyses ◽  
Helical Grooves ◽  
Annular Seals

Numerical and experimental analyses were carried out to investigate the dynamic characteristics of liquid annular seals with helical grooves in the seal stator. In the numerical analysis, the governing equations were the momentum equations with turbulent coefficients and the continuity equation, all averaged across the film thickness and expressed using an oblique coordinate system in which the directions of coordinate axes coincided with the circumferential direction and the direction along the helical grooves. These governing equations were solved numerically to obtain the dynamic characteristics, such as the dynamic fluid-film forces, dynamic coefficients, and whirl-frequency ratio (WFR). The numerical analysis included the effect of both fluid inertia and energy loss at the steps between the helical groove and the land sections. In the experiments, the dynamic fluid-film pressure distributions, which were induced by a small whirling motion of the rotor about the seal center, were measured to obtain the dynamic characteristics. The equivalent numerical results reasonably agree with the experimental results, demonstrating the validity of the numerical analysis. The value of the tangential dynamic fluid force induced by the rotor whirling motion decreased with increasing the helix angle γ. Consequently, the values of the cross-coupled stiffness coefficient and WFR decreased with increasing γ and became negative for large γ. In general, pump rotors rotate with a forward whirling motion under normal operating conditions. Hence, the negative value of WFR for helically grooved seals contributes to rotor stability by suppressing the forward whirling motion of the rotor.

scholarly journals Dynamic analysis of liquid annular seals with herringbone grooves on the rotor based on the perturbation method

2018 ◽  
Vol 5 (6) ◽  
pp. 180101 ◽  
Author(s):  
Lulu Zhai ◽  
Zhang Zhenjie ◽  
Chi Zhonghuang ◽  
Guo Jia
Keyword(s):  
Dynamic Characteristics ◽  
Operating Conditions ◽  
Geometric Parameters ◽  
Leakage Flow ◽  
Flow Rates ◽  
Rotordynamic Coefficients ◽  
Sealing Performance ◽  
Spiral Angle ◽  
Herringbone Grooves ◽  
Annular Seals

Annular seals have significant effects on the hydraulic and rotordynamic performances of turbomachinery. In this paper, an analysis method for calculating the leakage flow rates and dynamic characteristics of liquid annular seals with herringbone grooves on the rotor is proposed and verified. Leakage flow rates and dynamic characteristics of the model seals under different operating conditions are theoretically analysed and compared with those of plain and spiral-grooved seals of the same size. In addition, the influence of geometric parameters such as spiral angle and the lengths of the constituent parts on the sealing and rotordynamic coefficients of seals with herringbone grooves are also discussed. The results show that seals with herringbone grooves have better sealing performance, while providing better support actions and damping characteristics than the other two seal types under the same operating conditions. The seal geometric parameters including spiral angle, the lengths of the constituent parts and the clearance value have a significant influence on the dynamic characteristics of seals with herringbone grooves.

Numerical and Experimental Analyses of Static and Dynamic Characteristics for Partially Helically Grooved Liquid Annular Seals

2018 ◽  
Vol 141 (2) ◽  
Author(s):  
Keisuke Nagai ◽  
Kazuki Koiso ◽  
Satoru Kaneko ◽  
Hiroo Taura ◽  
Yusuke Watanabe
Keyword(s):  
Flow Rate ◽  
Dynamic Characteristics ◽  
Smooth Surface ◽  
Reaction Force ◽  
Leakage Flow ◽  
Dynamic Reaction ◽  
Static And Dynamic Characteristics ◽  
Whirling Motion ◽  
Leakage Flow Rate ◽  
Experimental Analyses

Numerical and experimental analyses of the static and dynamic characteristics of the liquid annular seals with axially partial helical grooves were conducted to investigate the effects of the axial length gal of a helically grooved section in a seal stator. The numerical solution and experimental procedures were applied in the same manner as in previous studies on through-helically grooved seals, wherein the grooves extend across the seal length. The numerical results qualitatively agreed with the experimental results, demonstrating the validity of the numerical analysis. The leakage flow rate Q was lower in the partially helically grooved seals than that of conventional through-helically grooved seals across a small range of rotor spinning velocities. In contrast, the reduction in Q due to the pumping effect caused by the spin of the rotor diminished with the decrease in gal. For a small concentric whirling motion of the rotor, the radial dynamic reaction force Fr and magnitude of variation in the tangential dynamic reaction force Ft with the whirling angular velocity increased with the decrease in gal, and their values approached the corresponding values for the smooth-surface seal. Under the same rotor whirling velocity, the Ft for the partially helically grooved seals became lower than that for the smooth-surface seal (similar to the case for the through-helically grooved seal), although decreasing gal tended to increase Ft. These results suggest that partially helically grooved seals can improve the efficiency and stability margin of the pumps because of the reduction in leakage flow rate and suppression of the rotor forward whirling motion (with large radial and tangential dynamic reaction forces) as compared to conventional through-helically grooved seals.

scholarly journals Theoretical Solutions for Dynamic Characteristics of Liquid Annular Seals with Herringbone Grooves on the Stator Based on Bulk-Flow Theory

2018 ◽  
Vol 2018 ◽  
pp. 1-13
Author(s):  
Lulu Zhai ◽  
Zhonghuang Chi ◽  
Jia Guo ◽  
Zhenjie Zhang ◽  
Zuchao Zhu
Keyword(s):  
Dynamic Characteristics ◽  
High Speed ◽  
Flow Theory ◽  
Operating Conditions ◽  
Bulk Flow ◽  
Analysis Method ◽  
The Stability ◽  
Herringbone Grooves ◽  
Better Than ◽  
Annular Seals

Liquid annular seals are primarily used to control the leakage in high-speed turbomachinery, especially in nuclear and petrochemical pumps. In this paper, a theoretical analysis method for dynamic characteristics of liquid seals with herringbone grooves on the stator is proposed based on bulk-flow theory. Steady-state velocities and leakage rates within the upstream and downstream spiral parts and the middle plain part taking account of the pumping effects are figured out first with the inertia term of the fluid within the whole seal. Then, the dynamic characteristics of the whole seal are solved based on Childs’ finite-length solutions and verified by comparing with experimental hydraulic forces. Moreover, characteristic coefficients and instability parameters of the herringbone-grooved teeth-on-stator (TOS) seals and teeth-on-rotor (TOR) seals of the same size under different pressure differences are predicted and compared in detail. The influences of the lengths of constituent parts on the dynamic characteristics and instability parameters of the model seals are theoretically investigated. The results show that the stability of the TOS seal is much better than that of the TOR seal under most operating conditions. And the lengths of the middle plain part significantly affect the dynamic characteristics and the stability parameter.

Numerical and Experimental Analyses of the Dynamic Characteristics of Journal Bearings With Square Dimples

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
Hiroyuki Yamada ◽  
Hiroo Taura ◽  
Satoru Kaneko
Keyword(s):  
Numerical Analysis ◽  
Dynamic Characteristics ◽  
Journal Bearings ◽  
Friction Torque ◽  
Operating Conditions ◽  
Shaft Speed ◽  
Static Characteristics ◽  
Stability Threshold ◽  
Dynamic Coefficients ◽  
Stiffness Coefficients

Numerous previous numerical studies have investigated the effect of surface texturing upon the static characteristics of journal bearings, including their load-carrying capacity and friction torque. In general, the dynamic characteristics of journal bearings are also important, since they are essential factors in predicting the vibration behavior of actual rotors supported by journal bearings. However, the effects of surface texture upon these dynamic characteristics have not been investigated through either numerical or experimental analysis. Thus, in the present study, such analyses were conducted to investigate the dynamic characteristics of textured journal bearings, such as their dynamic coefficients of oil film and the stability-threshold shaft speed supported by the bearings. Numerical analysis was done using a model that included inertial effects and energy loss; this model agreed well with experimental results concerning static characteristics from our previous study. Dynamic testing based on a sinusoidal-excitation method was also performed using textured journal bearings with uniform square dimples to verify the numerical results, which agreed qualitatively with those of experiment, confirming the validity of the numerical analysis. These results suggest that under the same operating conditions, the main effect of texturing upon the dynamic coefficients is to yield the cross-coupled stiffness coefficients with lower absolute values than the conventional ones with a smooth surface. The linear stability-threshold shaft speed of the rotor supported by the textured journal bearings became higher than that of a smooth bearing, mainly due to the reduction of cross-coupled stiffness coefficients. This tendency became more pronounced for high Reynolds number operating conditions and textured bearings with a large number of dimples.

Numerical and experimental characterization of singularities of a six-wire parallel architecture

Robotica ◽  
2006 ◽  
Vol 25 (3) ◽  
pp. 315-324 ◽  
Author(s):  
Erika Ottaviano ◽  
Marco Ceccarelli
Keyword(s):  
Numerical Analysis ◽  
Tracking System ◽  
Parallel Architecture ◽  
Operating Conditions ◽  
Experimental Results ◽  
Experimental Characterization ◽  
Singular Configurations ◽  
Experimental Analyses ◽  
The Wire

SUMMARYA characterization of singularities for a six-wire parallel architecture is presented as a result of numerical and experimental analyses. Numerical analysis has been developed through geometrical and analytical considerations. The study is based on a classification that has been derived on the basis of the geometry of tetrahedra, and singular configurations have been classified as a function of the tetrahedron volume. Experimental characterization has been carried out by considering the wire parallel architecture Cassino tracking system (CATRASYS). Experimental results are reported to characterize the performance of the CATRASYS chain in different operating conditions as an illustrative practical example.

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