Characteristics Of Liquid Annular Seals Research Articles

Numerical Analyses of Static Characteristics of Liquid Annular Seals Based on 2D LBM-LES Model

Static characteristics and leakage flow rates of liquid annular seals have great influences on the hydraulic efficiency of turbomachinery. In this paper, a two-dimensional (2D) mathematical model for predicting the leakage flow rates and static characteristics of liquid seal is established, based on the lattice Boltzmann method (LBM) combined with the D2G9 velocity model for incompressible fluid and large eddy simulation (LES) turbulence model, in which the transformation equation of reference pressure is developed with the Bernoulli equation. Moreover, the proposed model is validated by comparing with the experimental results, calculation results based on the finite volume method (FVM), and the results based on the empirical method of three seals under different operating conditions. The comparisons show that the maximum deviation in leakage prediction of the calculating model based on 2D LBM is 4%, and this calculating model will effectively improve the leakage prediction accuracy of the seals compared with the FVM and theoretical method.

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

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.

A transient CFD research on the dynamic characteristics of liquid annular seals

In this paper, a transient CFD method has been proposed in predicting the dynamic characteristics of liquid annular seals and the reliability of the method is validated by comparing with the experiments of Kanemori and Iwatsubo. Dynamic characteristics of the liquid annular seals with different length have also been calculated. The results indicate that the principal stiffness of the annular seal can turn into negative from positive as the length of the seal increases, this phenomenon may change the force direction of the annular seal and affect the supporting conditions of the pump rotor.

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

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 Dynamic Characteristics for Liquid Annular Seals With Helical Grooves in Seal Stator

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.

Experimental Analysis on Static and Dynamic Characteristics of Liquid Annular Seals with Axially Partial Helical Grooves in Seal Stator

Experimental Analysis on Static and Dynamic Characteristics of Liquid Annular Seals with Axially Partial Helical Grooves in Seal Stator

Numerical Analysis on Static and Dynamic Characteristics of Liquid Annular Seals with Hole Pattern in Seal Stator

Numerical Analysis on Static and Dynamic Characteristics of Liquid Annular Seals with Hole Pattern in Seal Stator

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

Numerical and experimental analyses were carried out to investigate the static characteristics of liquid annular seals with helical grooves in a seal stator. In the numerical analysis, the momentum equations with turbulent coefficients and the continuity equation, which were averaged across the film thickness, were numerically solved to obtain the leakage flow rate and the pressure distributions in the seal clearance. To accurately define the location of the step between the groove and the land regions in the calculation domain, these governing equations were 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. The numerical analysis included the effects of both fluid inertia and energy loss due to expansion during the passage of fluid from the land region to the helical groove region and that due to contraction from the groove region to the land region. In the experimental analysis, the leakage flow rate and the fluid-film pressure distributions in the seal clearance were measured for the helically grooved seals with different helix angles of the helical groove. The numerical results of leakage flow rate and pressure distributions agree reasonably with the experimental results, which demonstrates the validity of the numerical analysis. The leakage flow rate of the helically grooved seals was influenced by two factors: fluid energy loss during passage through the step between the groove and the land, and the pumping effect by which the spinning motion of the rotor pushes the flow back upstream along the helical grooves. Under a low range of rotor spinning velocity, the leakage flow rate decreased with helix angle because the effect of fluid energy loss in the steps was significant. By contrast, under a high range of spinning velocity, the quantitative difference in the leakage flow rate due to the helix angle decreased compared to that under a low range because the reduction in the leakage flow rate due to the pumping effect was pronounced for a larger helix angle. The effects of helix angle and rotor spinning velocity on the leakage flow rate are explained qualitatively using a simplified model.

Numerical Analysis on Static and Dynamic Characteristics of Liquid Annular Seals With Partial Helical Grooves in Axial Direction

Numerical Analysis on Static and Dynamic Characteristics of Liquid Annular Seals With Partial Helical Grooves in Axial Direction

Static Characteristics of Liquid Annular Seals with Square-Hole Pattern

The theoretical and experimental study is carried out to investigate the static characteristics of the liquid annular seals with a square-hole pattern in seal stator. The momentum equations with turbulent coefficients and the continuity equation, which are averaged across the film thickness, are numerically solved to obtain the pressure distributions in the seal clearance and the leakage flow rate. Semi-empirical pressure jump coefficients are used for evaluation of both pressure jumps due to the expansion at the passage of the fluid from the land to the square-hole region and the contraction from the square-hole to the land region. The numerical results of the pressure distribution and the leakage flow rate agree well with the experimental results, which proves the validity of the numerical analysis. The pressures decrease in the axial direction and their distribution has periodical unevenness due to the square-hole pattern in the seal stator. The square-hole pattern seal as well as the parallel-grooved annular seal yields a lower leakage flow rate than conventional seals with smooth surfaces. This reduction of the leakage flow rate is attributed to the pressure jump phenomena with energy loss induced by the axial flow passage across each step between the land and the square-hole region.

Dynamic Characteristics of Liquid Annular Seals with Square-Hole Pattern

Dynamic Characteristics of Liquid Annular Seals with Square-Hole Pattern

Experimental Study on Static and Dynamic Characteristics of Liquid Annular Convergent-Tapered Damper Seals With Honeycomb Roughness Pattern

Honeycomb damper seals with convergent-tapered clearance have been proposed to improve static and dynamic characteristics of liquid annular seals employed in pumps. Their characteristics are experimentally investigated and compared to those for a conventional straight (no taper) annular seal with smooth surface and a straight damper seal with identical honeycomb pattern in seal stator. Three convergent-tapered honeycomb damper seals are used in the test, and have different inlet clearance (maximum clearance) and almost the same outlet clearance (minimum clearance). Their outlet clearance is almost the same as the clearance of the straight smooth seal and is slightly smaller than the clearance of the straight damper seal. Experimental results show that the convergent-tapered damper seals as well as the straight damper seal have lower leakage flow rate and cross-coupled stiffness coefficients, and larger main damping coefficients than the straight smooth seal, resulting in larger effective damping coefficients. These results are mainly due to surface roughness in the seal stator such as a honeycomb pattern used in the present analysis. The convergent-tapered damper seals also have larger main stiffness coefficients than the straight smooth and damper seals, which is mainly due to the convergent-tapered clearance and yields larger radial reaction force for a small concentric whirling motion. Consequently, the convergent-tapered damper seals have better seal characteristics than the conventional straight smooth seal and the straight damper seal with the same roughness pattern from the viewpoints of decreasing the leakage and improving the rotor stability capacity.