Shuangfu Suo

An Acoustic Emission Study on the Starting and Stopping Processes of a Dry Gas Seal for Pumps

The starting process and the stopping process of a double dry gas seal for pumps were investigated by acoustic emission (AE) testing. The characteristic frequency band of contact of the seal faces was distinguished from noises in three different comparative experiments. The root mean square (RMS) of the AE signals after band-pass filtering was determined to effectively reflect the contact condition of the seal faces. Based on the characteristics of the AE RMS, both the starting process and the stopping process could be divided into three periods, and a lift-off rotational speed and a touch-down rotational speed were defined. The lift-off speed varied non-monotonically with the inlet pressure. The lift-off speed was smallest at a certain pressure, which meant that at that speed the seal faces lift-off most easily. The behavior of the touch-down speed was similar to that of the lift-off speed, but was a little smaller than the latter. These results reveal the potential of AE technology for monitoring the contact condition of dry gas seals during the starting and stopping processes and may help in the design and operation of the dry gas seals.

Fluid-solid Interaction Model for Hydraulic Reciprocating O-ring Seals

Elastohydrodynamic lubrication characteristics of hydraulic reciprocating seals have significant effects on sealing and tribology performances of hydraulic actuators, especially in high parameter hydraulic systems. Only elastic deformations of hydraulic reciprocating seals were discussed, and hydrodynamic effects were neglected in many studies. The physical process of the fluid-solid interaction effect did not be clearly presented in the existing fluid-solid interaction models for hydraulic reciprocating O-ring seals, and few of these models had been simultaneously validated through experiments. By exploring the physical process of the fluid-solid interaction effect of the hydraulic reciprocating O-ring seal, a numerical fluid-solid interaction model consisting of fluid lubrication, contact mechanics, asperity contact and elastic deformation analyses is constructed with an iterative procedure. With the SRV friction and wear tester, the experiments are performed to investigate the elastohydrodynamic lubrication characteristics of the O-ring seal. The regularity of the friction coefficient varying with the speed of reciprocating motion is obtained in the mixed lubrication condition. The experimental result is used to validate the fluid-solid interaction model. Based on the model, The elastohydrodynamic lubrication characteristics of the hydraulic reciprocating O-ring seal are presented respectively in the dry friction, mixed lubrication and full film lubrication conditions, including of the contact pressure, film thickness, friction coefficient, liquid film pressure and viscous shear stress in the sealing zone. The proposed numerical fluid-solid interaction model can be effectively used to analyze the operation characteristics of the hydraulic reciprocating O-ring seal, and can also be widely used to study other hydraulic reciprocating seals.

Dynamic Leakage Analysis of Noncontacting Finger Seals Based on Dynamic Model

Noncontacting finger seals are new compliant seal in gas turbine engine sealing technology. Their potential hydrodynamic and hydrostatic lifting capabilities make them preferable to brush seals and contacting finger seals. The work concerns the mechanism of dynamic leakage of noncontacting finger seal, and a novel dynamic leakage analysis model is proposed. The model combines seal dynamic analysis and seal leakage analysis together to estimate seal dynamic performance through seal leakage. The nature of dynamic leakage performance affected by the change of seal–rotor clearance is revealed. Dynamic leakage increasing is mainly affected by ratio of friction force to finger stiffness, finger mass natural frequency, and rotor excitation amplitude. Results show that the leakage increasing caused by the rotor eccentricity is inevitable. In the design optimization of the noncontacting finger seal, the ratio of friction force to finger stiffness and the rotor excitation should be as small as possible, and the finger natural frequency should be as large as possible. [DOI: 10.1115/1.4029776]

Semi-Analytical Dynamic Analysis of Noncontacting Finger Seals

Noncontacting finger seals represent a new noncontacting and compliant seal in gas turbine sealing technology. The compliance and noncontacting nature make this kind of seals fully adaptive to rotor excursions in the radial direction without damaging the seal performance. A new semi-analytical method is developed for characterizing the linearized dynamic performance of noncontacting finger seals. The linearized dynamic characteristics of the gas film are numerically computed using the step jump method and then approximated analytically in the equations of motion using a Prony series. By combining the gas film analytical dynamic characterization with the constitutive model for the dynamic properties of noncontacting finger seals, the dynamic equation of motion for the system is derived in analytical form. The results are presented of the gas film properties, natural transient response to initial conditions, steady-state response to rotor excursion, transmissibility ratios and dynamic stability analysis using the analytical model. It is demonstrated that the steady-state responses from the closed-form solutions agree well with those by the numerical simulation, and the analytical solutions can be used as the benchmark for calibrating the results from numerical analysis.

Theoretical and Experimental Investigation on Tip Forces and Temperature Distributions of the Brush Seal Coupled Aerodynamic Force

Based on a type of three-dimensional slice model of a brush seal combined with the commercial CFD software FLUENT, the study calculated the leakage flow of the brush seal. The aerodynamic forces applied on upstream and downstream bristles are analyzed and reduced to a smaller amount of point forces for analysis convenience. The frictional coefficient between the bristle material Haynes 25 and rotor material 1Cr14Mn14Ni are tested. Tip forces including normal reaction and frictional forces caused by aerodynamic forces are quantitatively investigated under conditions with and without frictions using the torque balance principle and nonlinear beam theory (by ANSYS simulations), respectively. Torques, frictional heats, and the temperature distributions of the rotor and bristle pack are studied further. Details and characteristics of the flow and temperature distributions inside the bristle pack are presented. In the experiments, besides traditional tests, such as leakage and torque tests, an infrared camera is employed to capture temperature distributions at the interface of the rotor, bristle pack and nearby zones under various pressure differentials and rotation speeds. The three-dimensional slice model is firstly verified by calculating the leakages, torques and temperature distributions of the brush seal and confirmed via experimentation. The influence of various frictional coefficients and pressure differentials on tip forces, torque and temperature distributions are also examined.

Study on Stick–Slip Friction of Reciprocating O-Ring Seals Using Acoustic Emission Techniques

The stick–slip friction of the reciprocating O-ring seal in reactor coolant pumps (RCPs) has significant effects on the characteristic of the stationary ring and dynamic behaviors of the entire sealing system and has always been somewhat difficult to study due to the fact that entrance into the contact area is almost impossible and only indirect measurements can be used. The acoustic emission (AE) technique is a direct measurement method and is sensitive to the microstructural changes within the material and is used in this article to study the four typical states of the stick–slip friction of the reciprocating O-ring seal, including standstill, partial slip, transition from static to dynamic friction, and slip of low amplitude. Experiments investigating the stick–slip friction of the specimens of the O-ring seal were performed using an SRV friction and wear tester and an AE device. From the experimental results, the following relationships were discovered: the frequency-domain characteristic of the AE signals of the O-ring seals of ordinary materials, the correlations of the AE root-mean-square (RMS) voltage with the friction coefficient and the stick–slip friction, and the influence of the normal load and precompression ratio of the specimen on the AE activities. The article focuses on how the AE activities associated with the different friction states could be connected with the tribological behaviors of the frictional pair. The AE technique is proven to be effective in characterizing the various states of stick–slip friction and helpful in monitoring the conditions of the reciprocating O-ring seal in operation.

Mechanical Seal Face Texturing by the Acousto-Optic Q-Switched Pulsed Nd:YAG Laser

Mechanical seal face texturing has the advantage of improving mechanical seal performance, such as improving opening force, reducing friction coefficient and minimizing wear and so on. In this paper, mechanical seal face, composed of sintered silicon carbon(S-SiC), is textured by the acoustic-optic Q-switched pulsed Nd:YAG laser in multi-mode. The micro-dimples are produced in mechanical seal face, and the profiles are measured by scanning electron microscopy (SEM) and 3D white light interference surface morphology apparatus. Results show that it is in the focus plane that maximal depth and minimum diameter appear and the circular profile of the micro-dimple can be acquired. And the diameter of micro-dimple increases with the increasing of single pulse energy reaching a saturation value at about 3.8mJ, but the increasing of single pulsed energy will reduce the depth of micro-dimple in a small range.

Experimental Investigation on Fiber Thermocouples Used in Brush Seals for Temperature Measurements

A type of fiber thermocouple is applied to a brush seal in order to obtain the temperature of the bristle-rotor friction zone. Using a brush seal test rig, the temperature measurements utilizing a fiber thermocouple, infrared thermometer, and common thermocouple are compared and studied. The fiber thermocouple is studied under various operational conditions consisting of different pressure and speed variations, rotor-bristle interferences, and eccentricities. Some interesting phenomena and characteristics of brush seals are revealed during these experiments. Some preliminary wear results of a fiber thermocouple are also presented. The results demonstrate the superiority of fiber thermocouples when used in narrow spaces, high temperature, and pressure environments within the heart of an aero-engine.

Thermal Fluid-Solid Interaction Model and Experimental Validation for Hydrostatic Mechanical Face Seals

Hydrostatic mechanical face seals for reactor coolant pumps are very important for the safety and reliability of pressurized-water reactor power plants. More accurate models on the operating mechanism of the seals are needed to help improve their performance. The thermal fluid-solid interaction (TFSI) mechanism of the hydrostatic seal is investigated in this study. Numerical models of the flow field and seal assembly are developed. Based on the mechanism for the continuity condition of the physical quantities at the fluid-solid interface, an on-line numerical TFSI model for the hydrostatic mechanical seal is proposed using an iterative coupling method. Dynamic mesh technology is adopted to adapt to the changing boundary shape. Experiments were performed on a test rig using a full-size test seal to obtain the leakage rate as a function of the differential pressure. The effectiveness and accuracy of the TFSI model were verified by comparing the simulation results and experimental data. Using the TFSI model, the behavior of the seal is presented, including mechanical and thermal deformation, and the temperature field. The influences of the rotating speed and differential pressure of the sealing device on the temperature field, which occur widely in the actual use of the seal, are studied. This research proposes an on-line and assembly-based TFSI model for hydrostatic mechanical face seals, and the model is validated by full-sized experiments.

Gas Sealing Performance Study of Metal W Shaped Seal Ring

Gas sealing performance of metal seal ring directly affects the security and reliability of equipment operation. Gas static seals of W-ring is taken as a study object, based on the theory of rough surface contact model and the theory of gas average flow model in the rough surface gap, the gas sealing leakage model is established to analyze the relationship between the leakage and the sealing load and surface roughness parameters.