Radial Seals Research Articles

Effect of Rim Seal Geometry on Rotationally-Driven Ingestion

Abstract This study investigates turbine rim seal geometry effects within the rotationally-driven ingestion regime. Computations were performed with a wall-resolved unsteady Reynolds-averaged Navier–Stokes (URANS) model and a large-eddy simulation (LES) model including near-wall boundary layer modeling, that is, wall-modeled LES (WMLES). Use of simplified rim sealing models is proposed as an efficient method of ranking seal designs and investigating sensitivity to seal geometry. Four rim seal configurations, two chute seals, an axial seal and a radial seal which are representative of those used in gas turbines and in previous research were investigated. Furthermore, hybrid seals combining geometric characteristics from both the chute and radial seal were considered. Significant sensitivities of sealing performance to turbulence modeling are identified, but URANS and WMLES show similar trends in ranking of seal performance, and these are consistent with previous experimental work. The addition of an outer radial clearance section to a chute seal is effective in reducing ingestion levels.

Calculation and experimental studies for the spent nuclear fuel shipping cask sealing assembly

One of the safety requirements regarding the shipping cask for spent nuclear fuel is that its leak-tightness should be maintained by preserving the cask body structural integrity and the sealing system tightness under normal and accident transportation conditions. The cask under design has a cylindrical process penetration (port) in its bottomб which is sealed using a plug with a radial seal composed of two rubber O-rings. The cask sealing assembly design was justified by the ANSYS LS-DYNA code calculation results. In particular, the strains of the cask components were calculated when dropped from a height of 1 m with the sealing assembly hitting a vertical bar. The cask was concluded to be leak-tight or leaky based on the strain nature and amount. To verify the adequacy of the results, computer-aided and realistic simulations were undertaken with a 1/2.5 scale mockup cask dropped on a bar from a height of 1 m. The computational and experimental results show a good agreement in terms of the impact response accelerations (overloads) for the mockup cask and bar collision and in terms of the plastic strains for the key components of the mockup bottom port sealing assembly. This proves the adequacy of the numerical cask model that has been developed and the efficiency of the LS-DYNA simulations. The inner rubber O ring compression is reduced by the plastic strains in the cask’s bottom port area, leading to a loose inner radial seal, as shown by the calculations. But the outer seal remains leak-tight, ensuring so the mockup cask tightness. The physical test results have also confirmed that the mockup cask remains leak-tight.

Semi-Analytical Methods for the Joint Strength and Sealing Performance in the Failure Process of the Subsea Pipeline Compression Connector

Radial seals are sensitive to axial overload failure and may cause leaks. This paper presents two semi-analytical methods for the joint strength and sealing performance of the subsea pipeline compression connector under axial overload failure. The method for the joint strength consists of two parts: One is the analytical model for the joint strength of the connection and seal under axial tension and compression conditions. The models are based on membrane theory, considering the hardening and bending effects. The other is a two-dimensional, axisymmetric finite element model for the joint strength of the radial metal seal. The semi-analytical method for the overload sealing performance is derived using a finite element model and the Reynolds equation of the laminar flow. The effects of critical parameters on the joint strength and the overload sealing performance are analyzed. The experiments are carried out with specimens and prototypes to evaluate the evolution of the sealing interface and the joint strength. The results show that both the internally turned sealing surface and the deflection of the pipe can improve the joint strength. In addition, the compression-type connector can remain sealed under the maximum axial overload. The proposed methods allow the prediction and identification of the overload joint strength and the sealing condition of the compression-type connector and provide a better understanding of the radial metal seal under the axial overload condition.

Перспективы совершенствования центробежных насосов

The application of modern software systems and the exclusion of technological restrictions on the shape complexity can improve the energy, cavitation and mass characteristics of pumps. Plastic casings and wheels with metal frames provide increased rigidity and versatility of the units. Special coatings improve the smoothness and wear resistance of working surfaces. New shapes of axial and radial dynamic seals reduce volume losses during stabilization and the forces transmitted to the supports. The range of sensors built into the pump adjusting the mode and determining the continuous diagnostics of the pump condition increases.

Sealing Behavior Research on the Radial Ferrofluid Seal Structure with Oblique Teeth

Considering various unstable factors when the large-diameter spindle operates at a high speed, such as eccentricity, centrifugal force, etc., the ordinary ferrofluid seal structures will show poor sealing performance. This paper proposes an axial-radial bidirectional ferrofluid seal structure with radial oblique teeth to improve the sealing performance. The pressure resistance of the radial ferrofluid seal structure in the magnetic circuit is theoretically analyzed. The magnetic flux distribution characteristic in the gap of the oblique teeth is studied by magnetic field simulation. According to the analysis results of the magnetic induction intensity, to obtain the larger theoretical pressure resistance, the optimal angle of oblique teeth is 77.87°, 64.28° and 62.81° under the radial seal structure with different gaps of 0.1 mm, 0.15 mm and 0.2 mm, respectively. In addition, simulation analysis is carried out to obtain the fluid pressure and velocity distribution of the radial ferrofluid seal structure with different oblique teeth angles. When the oblique teeth angle is small, the pressure drops and gas flow speeds in the ferrofluid area are all lower, and the pressure resistance is higher.

Development of a test-rig for advanced rotor–stator seals used in jet engines: Part II

Advanced rotor–stator seals are becoming more and more common in the latest generation of jet engines. In order to develop new radial seals and fully understand existing ones, testing needs to be done under full-scale conditions. It is necessary to be able to evaluate a new seal concept at “scale one”, under representative operating temperatures, pressure and rotational speed. This article – published in two instalments – presents details of an advanced new test-rig that is able to achieve this goal. It describes many facets of its design, construction, commissioning and use, and the challenges associated with its development.

Development of a test-rig for advanced rotor–stator seals used in jet engines: Part I

Advanced rotor–stator seals are becoming more and more common in the latest generation of jet engines. In order to develop new radial seals and fully understand existing ones, testing needs to be done under full-scale conditions. It is necessary to be able to evaluate a new seal concept at “scale one”, under representative operating temperatures, pressure and rotational speed. This article – published in two instalments – presents details of an advanced new test-rig that is able to achieve this goal. It describes many facets of its design, construction, commissioning and use, and the challenges associated with its development. The first instalment, which appears here, looks at key characteristics of the test-rig, provides an overview of its mechanical design and airflow loop, and lists associated references. The second instalment will be published in the January 2022 issue of Sealing Technology.

Numerical and experimental study of the embedded magnetic fluid seal with a small gap

To improve the pressure capability of the ordinary magnetic fluid (MF) seal (MFS) with a small gap, a device of the embedded MFS is designed according to the theory of embedded MFS. The magnetic field distribution in the seal gaps of the embedded MFS was studied by employing the finite-element method, and the theoretical pressure capability of the seal are calculated. A seal experimental platform was designed and built. The effects of MF injection volume, radial seal gap height, axial seal gap width, number of radial pole teeth (PT), number of axial PT, and the ratio of PT length to its width on the pressure capability of embedded MFS device was investigated, and compared to the experimental pressure capability of the ordinary MFS. The results show that the experimental and theoretical pressure capabilities of the embedded MFS are in good agreement. When the MF injection volume is 1.5 ml, the pressure capability has reached the maximum and tends to be stable. The pressure capability of the embedded MFS is better than that of the ordinary MFS. The pressure capability of the embedded MFS is not only related to the size of the seal gap and the number of PT but also related to the ratio of PT length to its width.

Experimental Studies of the Discharge Characteristics of Variable-Pitch Multifinned Seals

Variable-pitch multifinned seals (VPMS) have not hitherto found wide use in the steam turbines produced in Russia, although they are quite often used outside of Russia. In modernizing the existing and designing new steam turbines, rotor blades with an integrally machined shroud are used, which opens the possibility to manufacture multirow peripheral seals. In this connection, the question about selecting the optimal VPMS configuration becomes of important practical significance. The results obtained in this study made it possible to experimentally estimate the extent to which different combination of fin pitches on the rotor and stator influence the VPMS discharge characteristics and to elaborate practical recommendations on using them. The minimal leak flow was recorded for the VPMS models with a 2-mm-wide pitch on the rotor. Comparative experimental investigations of VPMS models with 3- and 4-mm-wide spacers on the rotor and 4- and 5-mm-wide spacers on the stator were carried out as applied to the shroud seals of large-capacity steam turbines. The model pair with the 4- and 5-mm-wide spacers on the rotor and stator, i.e., with the pitches equal to 4.8 and 5.8 mm on the rotor and stator, respectively, can be regarded as the most optimal of those investigated in this work. It has been shown experimentally that, with all other things being equal, the leak in VPMSs is by 22–25% smaller than it is in straight-flow seals. By using VPMS, it becomes possible to avoid rubbing of the rotor against the stator under the conditions of relative radial and axial rotor displacements in transient modes of operation. In addition, the aerodynamic forces in VPMS able to excite a low-frequency shaft line self-oscillation are approximately equal to 60% of the similar forces occurring in the conventional radial clearance seals. In view of this circumstance, VPMS can be recommended for use instead of the standard tip shroud seals in the high- and intermediate-pressure cylinders in new and modernized steam turbines.

Investigation of thermal mechanical coupling numerical simulation and theoretical study of k-shaped combined metal seal of downhole flow control valve

The K-shaped seal assembly is composed of K-shaped metal seal, high temperature nickel base alloy (GH4169). Its sealing performance directly affects the reliability and stability of flow control system. The 2-D axisymmetric K-shaped metal seal is abstracted as the combination of interference fit model and cantilever beam model. Considering the influence of temperature on the seal, based on the 2-D constitutive relation of elastic medium and heat conduction theory, the theoretical model between contact stress and self variation of K-shaped metal seal ring is deduced by using inverse method. Using ABAQUS thermal structure coupling analysis method, the thermal mechanical coupling finite element model of K-shaped seal assembly is established. The theoretical analytical solution proposed in this paper can be used to calculate the approximate solution of contact stress of radial metal seal under current oilfield conditions, and provides theoretical support for the numerical calculation of thermal stress of radial metal seal.

Influence of radial labyrinth seal on the several specific speed pumps

Influence of radial labyrinth seal on the several specific speed pumps

Analysis of sealing performance of a kind of profiled rubber gasket used in the radial contact seal structure

Sealing performance of standard rubber gaskets in the radial contact seal structure are observed through the experiment. A kind of profiled rubber gasket is proposed to replace the standard gasket. Leakage experiment and numerical simulation are carried out to study the sealing performance and failure mode of the profiled gasket. Several equations are presented to help analyze the failure reason. Results show that sealing performance of the profiled rubber gasket is more reliable than that of the standard rubber gasket. The failure reason of the profiled rubber gasket is that the friction force between the gasket external face and tube wall cannot balance the tube internal pressure. Dimension precision of the metal compressive ring has a great effect on the failure pressure.

Effect of the protrusion shape on gas ingestion of two sealing structures

The windage loss caused by protrusion in a rotor–stator cavity has been studied in detail, and there are abundant fitting formulas that have been summarized to calculate the moment coefficients. Some other theorists have emphasized its effect on the sealing efficiency, proposing that installation of protrusion could alleviate gas ingestion. However, the protrusion shape which is an influential factor on the sealing efficiency has not been focused in previous research. Using the experimental method of measuring CO2 volume fraction, cavity pressure, and power consumption, we investigated the effects of several typical protrusion shapes on various parameters for two sealing structures, in order to obtain the optimal shape. Results showed that a variation of the protrusion shape had little impact on the static pressure, but the total pressure and the sealing efficiency increased in different degrees. Furthermore, even though the hexagon shape resulted in the highest sealing efficiency, we observed that the drop shape had the best overall performance in all of the eight models, which could result in higher efficiency of the turbine cavity. The combination of a radial seal structure and protrusion could improve sealing efficiency better.

Inertial waves in turbine rim seal flows

Unsteady flow modes with intrinsic frequencies unrelated to that of the turbine blades are found to be dominated by inertial waves. In the presence of these waves, rim sealing is less efficient, and conventional Reynolds-averaged Navier-Stokes methods fail to predict the sealing effectiveness. The radial seal, which limits the radial flow motion and, in turn, the circumferential Coriolis force, can suppress inertial waves (unsteady flow modes).

Magnetic Circuit Design and Magnetic Field Finite Element Analysis of Converging Stepped Magnetofluid Seal with Small Clearance

The stepped magnetofluid seal is an effective method for improving the pressure ability of ordinary magnetofluid seals (OMS) with large clearance. At present, the research on stepped magnetofluid seal with less than 0.4 mm small clearance has not been carried out yet. The equivalent magnetic circuit design of converging stepped magnetofluid seal (CSMS) with small clearance has been carried out and verified by magnetic field finite element method based on the CSMS theory and magnetic circuit theory. The effects of the width of the axial seal position, the height of the radial seal position, the number of the pole tooth in the axial seal position, and the number of the pole tooth in the radial seal position on the theoretical pressure ability of the CSMS are investigated by numerical simulation. The calculation results are analyzed and discussed. The results show that the magnetic flux leakage at the junction of the permanent magnet and pole piece causes the higher pressure ability of the CSMS structure designed by the equivalent magnetic circuit method than that calculated by the magnetic field finite element method. When the width of the axial seal position is greater than the height of the radial seal position and the number of pole teeth in the axial seal position is less than the number of pole teeth in the radial seal position, the CSMS has the best effect. Compared with OMS with small clearance, CSMS has greater advantages.

Arteztutako gainazaletan diamantatze prozesuko patroiak karakterizatzeko metodologiaren garapena

Diamantatze prozesuaren eragin nabarmenetako bat da prozesuak pieza arteztuaren gainazalaren akabera baldintzatzen duela. Hain zuzen, aitzinapen transbertsaldun diamantatze prozesuen eraginez, arteztutako piezen gainazalean helize itxurako markak agertu ohi dira. Gisa horretako markak agertzeak eragin kaltegarriak izan ditzake zenbait aplikazioren errendimenduan, piezen funtzio nagusia zigilatzea edo koipeztatzea bada. Horren aplikazio nabarmenetako bat zigilu erradialak daramatzaten ardatz birakariak dira, non ezinbestekoa gertatzen den zigiluaren bizitza ahalik eta gehien luzatzea betiere zigilatzea bermatuaz. Horretarako, ezinbestekoa gertatzen da piezaren gainazala neurtu eta helize itxurako patroiak era egoki batean karakterizatzea. Artikulu honetan, patroi horiek ebaluatzeko erabiltzen diren ohiko metodoen berrikusketa sakon bat egiteaz gain, metodologia berri baten berri emango da, IK4-Ideko garatzen ari dena arteztutako gainazalak neurtzeko eta dressing-leada karakterizatzeko.

Harmonisation of Coolant Flow Pattern with Wake of Stator Vane to Improve Sealing Effectiveness Using a Wave-Shaped Rim Seal

The rim seal of the gas turbine is intended to protect the material of the turbine disk from hot combustion gases. The study of the rim seal structure is important to minimise the coolant flow and maximise the sealing effect. In this paper, a wave-shaped rim seal for stator disks is proposed and its effect is confirmed by numerical analysis. To characterise the flow phenomena near the wave-shaped rim seal, a simplified model of the wave-shaped rim seal (Type 1 model), which excludes the rotor blade and stator vane, is analysed and compared with the conventional rim seal. Then, through analysis of the wave-shaped rim seal geometry (Type 2 model), which includes the rotor blade and stator vane, a reduction in egress and ingress flow was observed owing to the wave-shaped rim seal, and the sealing effectiveness on the stator disk of turbine was increased by up to 3.8%. Implementation of the wave-shape geometry in the radial seal is a novel choice for turbine designers to consider in future for better-performing and more-efficient turbines.

Influence of radial labyrinth seal on pump performance

Influence of radial labyrinth seal on pump performance

Study of the Impact of Wear of Movable Interfaces on Failures of an Immersible Electrically Operated Vane Pump for Oil Extraction

This article considers the conditions for wear-induced operating and parametric failure of electrically operated vane pump installations for oil extraction. It is shown that the wear of radial interfaces intensifies the vibration of the installation body by 10 to 15 times. It is found that the amount of leakage through radial seals of different radial stages hardly depends on the capacity of these stages. It is recommended to use wearproof bearings and reduce axial interface gaps.

Effect of rotor-mounted protrusion on sealing performance and flow structure in rotor-stator cavity

This paper presents an experimental investigation on the effect of protrusion radial position and height on the sealing performance and flow structure in the rotor-stator cavity. The rotor-mounted protrusions are assembled at three radial positions and are set to three heights. The cavity is equipped with three rim seals: a radial seal, an axial seal and a seal with double fins on the stator. The annulus Reynolds number is set at 4.39×105 and the rotational Reynolds number ranges from 7.51×105 to 1.20×106. Heat and mass transfer analogy is applied. Pressure and CO2 concentration are measured. The experimental results show that in cavities with different rim seals, radial distributions of the sealing efficiency, pressure and swirl ratio are basically the same. The sealing performance is improved by protrusions compared with the cavity without protrusion and improves with the increase of protrusion radial position and height. The effect of protrusion increases with the increase of the rotational Reynolds number. The windage loss and the flow resistance introduced by protrusions are investigated. It is found that induced windage loss and flow resistance decrease with the increase of protrusion radial position but increase with the protrusion height.