Finger Seal Research Articles

Impact dynamic analysis of C/C composite finger seal

With the development of science and technology, the performance of an aero-engine has been given more rigorous requirements. Seal device is an important component part of an aero-engine, and the improvement in its performance may be an efficient way to further improve the performance of an aero-engine. Finger seal is a flexible seal and has higher performance price ratio, therefore it gets more attention and research recently. The phenomenon of noncontact state converting to contact state will occur in every working cycle of finger seal that inevitably lead to the finger seal bearing the impact effect of rotor. But so far, the influence of impact on the finger seal performance has not been discussed and researched. To overcome this shortcoming, the stress–strain curves of C/C composite under different impact velocities are obtained by the Gleeble3500 thermo-simulator system in the paper, and then the elastic modulus of C/C composite in three directions is calculated by experimental data. The effects of impact velocity and impact damping on the impact force are analyzed by means of the impact theory. The new structural stiffness of finger seal and the impact displacement excitation of the rotor are built through impact effect analysis. On this basis, the equivalent dynamic model of C/C composite finger seal with distributed mass is established to evaluate the impact effect. By the model, the difference of calculated results is analyzed under whether considering the impact effect or not. And the effect of impact velocity and coefficient of restitution on the dynamic performance of the finger seal is also analyzed under considering the impact effect, respectively. The above results show that the impact effect has significant influence on the leakage and wear of finger seal, therefore when the performance of the finger seal was analyzed, it is necessary to consider the impact effect.

Effect of temperature on the dynamic performance of C/C composite finger seal

The designs of sealing device have prominent influence on the performance of aero-engine. The high temperature environment during the working process of aero-engine also has important influence on the performance of sealing device which is located in the aero-engine. Finger seal has a flexible characteristic and high price performance compared with the other seal devices, thus it gets more attention, and lots of researchers have studied about finger seal’s performance recently. But so far the dynamic performance of finger seal considering temperature effect is not yet analyzed and discussed. Based on this, an equivalent dynamic model based on distributed mass considering temperature effect is proposed in the paper. The effects of environment temperature and heat through friction on the equivalent structural stiffness of finger stick and contact pressure between finger stick and rotor are discussed. Moreover, the data exchange between the dynamic and thermal analysis is confirmed based on the movement relationship between the rotor excitation and finger stick response. Therefore, the dynamic performance analysis of finger seal including thermal-structure coupling is obtained based on an equivalent dynamic method. The effect of temperature on the dynamic performance of finger seal using this model is analyzed, and the effect of C/C composite structural parameters on the finger seal performance is investigated considering the temperature effect. The above results show that the temperature effect has important influence on the performance of finger seal, so it is necessary to consider the temperature effect when the performance of finger seal is analyzed. The current work further improves the theoretical system about finger seal equivalent dynamic research, and has higher academic significance and engineering value.

Study on 2.5D C/C composite finger seal integrate optimization combined with microstructural parameters of material and macro geometry of finger seal

The current study focuses on performance analysis and structural optimization of the 2.5 D C/C composite finger seal. A micro/macrostructural integrated optimization method of 2.5D C/C composite finger seal is presented. Based on uniform strain assumption the stiffness average method is used to predict the elastic properties of 2.5D C/C composite material. In order to achieve the advantage of the designability of composite material, the microstructure parameters are also as design variables together with the macro structure of finger seal. Considering the two optimization objectives, leakage and contact pressure, are both implicit functions of the structure parameters of finger seal which obtained by finite element method, a Krige model is established to replace the finite element method analysis in each optimization iteration, which could improve the optimization calculating efficiency obviously. By using the multi objective genetic algorithm NSGA-II the 2.5D C/C composite finger seal optimization is implemented availably. An example is given which indicates the leakage and contact pressure of finger seal decrease significantly through the integration optimization of 2.5D C/C composite finger seal which develop a new approach to design finger seal with high performances.

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.

Non-contacting finger seal dynamic model

Dynamic response of the finger seal compliant elements to rotor motion is investigated. It is shown that radial adjustment of the fingers with respect to rotor surface displacements requires convergent (in rotor rotation direction) operating clearance under the pads. Due to arising gasdynamic lifting force appropriate seal gasdynamic balancing and non-contacting operating mode can be achieved. The results are numerically obtained on the basis of the aeroelastic dynamics analysis.

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.

Numerical Analysis of Finger Seal with Grooves on Lifting Pads

Numerical research on lifting and sealing performance of a whole ring finger seal with grooved pad structures is presented in this paper. Different groove structures on the bottom of a lifting pad, such as one and two straight grooves, or two herringbone grooves with different gradients, etc., will be simulated. For discussing interaction between the rotor and finger seal, the vibration trajectory of the rotor is taken into account in the numerical computation. Numerical simulation results indicate that the complete ring model is more suitable than an individual finger model to simulate the fluid–solid interactions of the finger seal. Deformation of the finger seal is changed by vibration of the rotor, and it should adapt the clearance in a uniform way according to the rotor position. The grooved pad structures have effects on the leakage flows and the lifting force on the finger. Analytical data revealed that the self-adaptive performance of the finger seal to rotor vibration is subsistent. The self-adaptive performance will be helpful to make the finger seal processes lower wear and with smaller leakage in a rotor–seal system.

Design approach for maximising contacting filament seal performance retention

Good sealing is a key requirement for modern efficient turbomachinery such as steam and gas turbines. A class of seals that promise better performance, compared to conventional labyrinth seals, are contacting filament seals such as brush, leaf, or finger seal. When new, these filament seals offer better performance; however, if poorly designed they wear excessively, resulting in leakages higher than a comparable labyrinth seal. This paper outlines a design methodology for selecting ideal contacting filament seal properties for a given operating cycle or set of operating cycles. Following this approach ensures the seal performs well, the seal retains its performance, and performance is retained if the operating cycle is altered. In the approach, the seals are described by four generic properties (stiffness, blow-down, cross-coupling, and build clearance), which are then used for a performance evaluation based on a number of test cycles. Once the ideal seal properties for a given operating cycle have been identified, a seal to match these can be designed. The approach is evaluated with a generic gas turbine cycle and recommendations for ideal contacting filament seal properties for this cycle are made.

Dynamic analysis of C/C composite finger seal

A seal device as an important component of aeroengines has decisive influence on performance, reliability, and working life of aeroengines. With the development of aeroengines, demands on the performance characteristics of seal devices are made strictly. Finger seal as a novel kind of sealing device, recently attracts more and more attentions in academic circles and engineering fields at home and abroad. Research on finger seals has been extensively developed, especially on leakage and wear performances under dynamic conditions. However, it is a pity that the work on finger seals has been limited with a single approach that is improving the performance by structural optimization; in addition, the technology of dynamic analysis on finger seals is weak. Aiming at the problems mentioned above, a distributed mass equivalent dynamic model of finger seals considering the coupling effect of overlaid laminates is established in the present paper, the dynamic performance of 2.5 dimension C/C composite finger seal is analyzed with the model, and then the effects of fiber bundle density and fiber bundle preparation direction on finger seal’s dynamic performance are discussed, as well as compared with those of Co-based alloy finger seal. The current work is about dynamic analysis of finger seals and application of C/C composite in this paper may have much academic significance and many engineering values for improving research level of finger seal dynamics and exploring feasibility of C/C composite being used for finger seals.

Dynamic analysis of finger seal using equivalent model based on distributed mass method

Dynamic analysis of finger seal can be performed by finite element method or equivalent model based on lumped mass method now available, which is difficult in meeting both the acceptable calculation time and accuracy simultaneously. For this reason, interactions between finger elements are considered and the equivalent dynamic model based on distributed mass method is proposed in this article. Seal dynamic performances are obtained by using this model to calculate the equivalent parameters, air leakage flow, and the contact behavior between finger seal and the rotor. The work to be presented here concerns the mapping of dynamic behavior of the finger seal with a stack of three finger elements, including the dynamic displacement responses of finger elements, the leakage clearances, and the contact pressures between the finger elements and the rotor, as well as the leakage flow rate and the wear rate. The results calculated by the equivalent model presented in this study are evaluated by comparison with the published experimental data and results from the model based on lumped mass method, which shows that the equivalent model based on distributed mass method is far superior to that based on lumped mass method because the calculations are in good agreement with the experimental results.

Dynamic Analysis of 2.5D C/C Composites Finger Seal

For the finger seal, leakage and wear are key factors to affect its sealing performance and service life. To reduce the wear of the finger seal, C/C composites are probably used for finger seal material preparation for its self-lubrication and light weight properties compared with the metal. The work to be presented here assessed the elastic properties of the 2.5D C/C composites by the volume average method and established a finite element model for finger seal dynamic analysis. The results show that increasing warp yarn density and using shallow direct-joint structure can notably improve sealing performance of the finger seal, but can also increase contact pressure between the finger seal and the rotor.

Structural Optimization Design of the Arc Finger Seal

According to the working condition of the finger seal, a geometric model applied to optimization of finger seal with arc curve (arc finger seal) is established based on mathematical relationship analysis of the finger seal structural parameters. Two performances, the hysteresis and contact pressure between finger pad and rotors surface, are put forward as the objectives for the structure optimization of the finger seal. The optimization model of C/C composites arc finger seal is presented and the multi-objective optimization process is carried out based on ANSYS software. An optimization design example is given which shows that comprehensive performance of finger seal can be obviously improved through the structure optimization. The performance comparison between a C/C composites and a metal material arc finger seal with the same structural and working conditions proves that the choice of C/C composites as the finger seal material, to a certain extent, may improve the sealing performance effectively. It provides a new choice for the design of the finger seal.

Analysis on Thermal-Fluid-Solid Interaction of Straight Pad Finger Seal Performance

Aimed at the structure and working condition analysis of the straight pad finger seal, an analysis model of the straight pad finger seal which contains three complete fingers is presented. And then the influence of heat effect to the seal structure body and fluid flow state is considered in the model. By using the thermal-fluid-solid interaction numerical calculation method, the working performance of the non-contacting finger seal and its change law with working condition is studied in the paper. The straight pad finger seal's leakage rate, gas film lift capacity and gas film flow field characteristics in different working conditions are analyzed. The results show that the gas film between finger foot and rotor has radial lift capacity, which can meet the requirement of reducing wear. And since the deformation of whole finger foot is relatively uniform, it is hard to have the appearance of circumferential warp. It is advantageous to adapt to the rotor radial runout and deflection. The performance of straight pad finger seal is influenced much more by the high-to low-pressure differential and the gas temperature of high pressure chamber. The work presented here provides helpful reference and theoretical basis to design the non-contacting finger seal with high performance.

Optimization Investigation on Contact Finger Seal Performances Based on a Fuzzy Game Approach

Optimization Investigation on Contact Finger Seal Performances Based on a Fuzzy Game Approach

Performance Analysis of Hydrodynamic Finger Seal with Herringbone-Grooved Structure

Three dimensional solid-fluid interaction numerical analysis models of both the finger seal with herringbone-grooved pad and the finger seal with herringbone-grooved rotor were established in order to study the performance of hydrodynamic finger seal. The models investigated fluid radial under pad force and fluid leakage as a function of both the rotor speed and the high- to low-pressure differential. It was shown that the finger seal with herringbone-grooved structure in pad or in rotor could bring lift force under the finger pad so as to keep the finger seal in non-contacting status. For the two types of finger seal, their load carrying ability and fluid leakage varying with the pressure differential were almost same. In the same velocity of rotor surface, the load carrying capacity of the finger seal with herringbone- grooved rotor was greater and the leakage was less than that of the finger seal with herringbone-grooved pad respectively. With the conditions of rotor structure allowing, it is suggested to select the finger seal with herringbone-grooved rotor first for designing the hydrodynamic finger seal with herringbone-grooved structure.

The Performances Optimization of Finger Seal Based on Fuzzy Game Theory

Leakage and abrasion are two key performances of finger seals (FS). They not only contradict each other in FS design but also relate to many design parameters. Moreover, in the multi-objective optimization progress, the problems of optimizing results decision and preference requirement for optimization objectives are still challenge to researcher. So far, they are still important influence factors for advanced FS design. Therefore, the current work presents a new multi-objective optimization method by introducing game theory and fuzzy comprehensive evaluation theory. The optimizing results are compared to that of the general optimization method and finite element method (FEM). The study show that the FS, which is obtained by presented optimization method, has good performances. Compared respectively with the general optimization method and FEM, the computational results indicate that the presented method can effectively reflect the different response requirements of optimization objectives. Furthermore, the decision-making difficulty for multi-objective optimization of FS performances is significantly reduced.

Optimization Design of Finger Seal Performances Based on Game Theory

To reach the expecting goal of lower leakage ratio and longer operation life(lower wear ratio) for finger seal, great efforts have been made continuously to obtain good structure of finger seal with advanced optimization design technology. A cooperation Nash equilibrium mathematical model of multi-objective optimization for finger seal is presented in current work based on Nash equilibrium of game theory. In this solution, the reciprocal of leakage ratio and the wear ratio value for finger seal are thought as the payoff functions and the game is solved by genetic algorithm. The numerical simulation in the paper shows that the finger seal with better performances can be achieved by using Nash equilibrium method. This means Nash equilibrium method can be used as a new multi-objective optimization method for finger seal performances optimization.

Dynamic Behavior Analysis of Finger Seal Based on Equivalent Dynamic Model

Finger seal is a new technology developed for gas path sealing in gas turbine engine.It has been paid attention to its good sealing performance and lower manufacture cost.The vibration behavior of finger seal is not be considered in performance analysis for the contact finger seal with compliant geometric configuration,then this will influence the reliability of the performance analysis and the parametric design of a finger seal.According to the dynamic character of finger seal,the harmonic vibration and free vibration models of a repetitive section of a two-layer finger seal that contains one high and one low finger seal are established separately.The dynamic behavior of finger seal in different working conditions is obtained based on the dynamic response analysis of finger's vibrations.The dynamic low hysteresis and low wear terms based on the equivalent dynamic model of finger seal are put forward,which can be used to predict the dynamic behavior of finger seal.As an example,the dynamic behaviors of an 8-layer finger seal and a 10-layer finger seal were predicted,and the validity of the prediction was demonstrated by the leakage test results of these two finger seals.The work presented here not only could make the dynamic analysis of finger seal with complicated structure simple and easy especially for multi-layer finger seal system,but also suggest a useful method for designing the finger seal with good dynamic behavior by means of different seal layers assembly.

New Method for Performance Optimization of Finger Seals

Improving simultaneously the two desirable objectives — lower leakage and lower abrasion—is very difficult for designing finger seals.Using the existing multi-objective methods to solve this problem,the shortcoming is the necessity of selecting the best design out of many possible ones.Therefore,a new method based on the Nash equilibrium game theory is presented to achieve a better design of finger seal in current study.In this method,there are two key techniques:① the BP neural network technology is used for establishing the mapping relations between optimization variables and the two objectives of leakage and abrasion respectively;② the genetic algorithm is introduced to Nash equilibrium game theory for solving the optimization process.The optimization result is compared with that of the weighted average optimization method with a numerical example.And the numerical results are validated from physical test.The results show preliminarily that:① comparing with the weighted average optimization method,the presented optimization method has only one set of optimized result,which reduces the difficulty of decision-making;② the numerical and test results all indicate that the optimized finger seal through the presented method has lower leakage and lower abrasion than other finger seals.The presented method is very significant to the design of better finger seal.

Analysis on Hysteresis Charcteristics of Finger Seal

The hysteresis phenomena of finger seal is studied by using the finite element method. It is concluded that there is no hysteresis for the finger seal working in static conditions. But the hysteresis of the finger seal working in dynamic situations is an inevitable phenomenon when the radial force on the finger changes in a cycle, which influences the leakage obviously. The hysteresis characteristics are analyzed from the viewpoint of energy. It is found that the hysteresis is caused by the different friction work at a cycle of force applied to the finger which generates the hysteresis energy. Under a certain condition, the characteristic of hysteresis depends on whether there is hysteresis energy or not, and the hysteresis degree is determined by the value of hysteresis energy. It is presented that the lower hysteresis finger seal can be obtained through the reasonable structure design of finger seal to increase the finger seal’s stiffness or decrease the pressure on the upside seal. It is a good way to reduce the hysteresis energy so as to weaken the hysteresis by decreasing the friction coefficient of finger and aft plate. The basis for the further reasonable design of finger seal with low hysteresis and high performance is also established.