Eaton Char-Lynn Motor , Sealing Technology Affects Aero Motor Performance


       The    Eaton Char-lynn Motor     states that the fluid dynamic seal of an aerospace motor generally refers to the dynamic seal of the airflow leaving the main flow path into the second flow path. It mainly includes: sealing of different parts of the rotor internal flow system (such as stator tip, interstage, compressor outlet, turbine inlet, bearing chamber, etc.) to control leakage; the rotor tip is sealed to prevent backflow or leakage. They have a significant impact on the overall performance of aircraft motors (work efficiency, thrust-to-weight ratio, fuel consumption, reliability and economy), but they are easily overlooked in motorering applications, so attention should be paid to improving the seal design to improve overall performance. . There are many predictive assessments of the benefits and potential of improved seal designs.

  (1) The study believes that improving the seal design of the second runner system can increase the efficiency by 4.4% at the high pressure compressor. This efficiency improvement can extend the life of the relevant components by reducing the turbine inlet temperature of 85 °F (47 °C). The net thrust is 7.6%; improving the seal design at the high pressure turbine increases the efficiency by 4.2%, or extends the component life by reducing the turbine inlet temperature by 93°F (52°C), or increasing the thrust by 9.7%.

  (2) At the end of the 20th century, Chinese motor researchers have clearly realized that under the current technical level, the improvement of motor design can greatly reduce the fuel consumption of the motor by 0.1% to 0.2%, but if the air seal is improved. The design is designed to improve the sealing effect, which can reduce the fuel consumption rate by 1% to 2%.

  (3) The capital investment for compressor and turbine design to improve performance is at least 4 to 5 times higher than the cost of improving the seal design by receiving the same effect.

  (4) A gas/gas non-contact gas film sealing device that is currently being developed for a high-pressure compressor can increase the thrust of the motor by 2% to 2.5%.

  With the improvement of the performance of the aero-motor, the requirements for sealing are also increasing, and the traditional sealing method is difficult to meet the requirements. The gas film sealing technology is based on the principle of gas dynamic and static pressure, which forms a certain thin pressure film at the sealing position to produce a sealing effect. Its outstanding feature is that the non-contact and small gap of the sealing interface are realized by a very thin pressure gas film, thereby exhibiting superior anti-leakage characteristics, long life and low maintenance characteristics, which has made it an advanced sealing technology field. An important research direction.

  Since the air gap is small and suitable for operation at high interface slip speed and high ambient temperature, it is particularly suitable as a fluid dynamic seal of a high speed rotor system under high pressure difference. The research has achieved phased results. In the high-speed fluid machinery such as blowers and compressors for ground industries, a large number of end face film seals have been successfully applied. However, there have been no successful applications on aero motors. The key to the constraint is that the displacement of the sealing sub-surface caused by the severe vibration and thermal and mechanical deformation of the aero-motor rotor system is much greater than the thickness of the sealing film. Based on the analysis of relevant main research data, this paper will introduce in more detail the progress of research on the application of gas film sealing structure and the main points of further research.

  Research on Application of Gas Film Sealing in Rotor System

  The application of gas film sealing technology to the inflow system of the second runner of the aeromotor rotor has been carried out for quite some time, and the types of seals involved are various. The focus here is on the research progress of typical structural forms with a certain experimental or practical background.

  1 Research progress on gas seals on the end face

  In the 1980s, the focus of the application of the face film seal on the motor was to reverse the inter-shaft seal. NASA and Pratt & Whitney have conducted pioneering research on reversing the spiral groove film seal between the shafts and accumulated a lot of experience. Later, further research was carried out to increase the film thickness by static pressure, to improve the film stiffness and sealing performance by opposing gas film, and to test the new end face structure to solve the problems caused by vibration and deformation at high temperature, at high strength. Great progress has been made in the research of carbon graphite materials.

  Since the end of the 20th century, research on end face film seals has focused on high temperature, high speed and large diameter conditions. EG&G Company proposed a double-spiral static pressure gas film sealing structure, and it is hoped that the double-helical structure generates a certain motion to compensate the deformation of the sealing interface, so that the sealing has a certain flexibility. The structure was tested for high temperature, high speed and large diameter ground tests, resulting in a large leak. These new structures are currently in the research and exploration phase. Domestically, the end face gas film sealing technology has been studied in depth and made some progress.

  2 Research progress of cylindrical gas film sealing

  Since the mid-1990s, with the deepening of research on the rotor inflow system sealing technology, the research of gas film sealing began to turn from the end face film seal to the study of cylindrical gas film seal. The author believes that the advantage of the latter is that it is easy to achieve greater flexibility in the radial direction to cope with severe vibration and heat and force deformation, and the structure size can be more compact.

  3 Application of gas film sealing for rotor tip

  The application research of gas film sealing is mostly concentrated in the internal flow system. In recent years, foreign countries have begun to pay attention to the application of the gas film sealing type at the tip of the aviation gas turbine rotor. It is considered that the improvement of the sealing performance of the tip position is more important. A 0.01 in. (0.025 cm) gap at the tip means a typical fuel consumption of 1% reduction and an exit temperature of 10 °C. Tip sealing studies will be an important direction.

  From the requirements of aero-motor sealing technology, the research progress of gas film sealing and the analysis of typical gas film sealing system characteristics, the following enlightenment can be obtained.

  1 The core pursuit of the evolution of research progress – sealed large flexible floating support and rigid air film

  (1) Special working conditions.

  The operating conditions of the aeromotor high-speed flexible rotor system seal can be summarized as static “three high” (high interface slip speed of the seal pair, high ambient temperature and high boundary pressure difference) and dynamic large displacement deformation. High sliding speed and high circulating temperature are favorable for forming a dynamic pressure sealing gas film with a film thickness of about 10 μm or even a thinner gas film, so that even under high pressure difference, leakage can be made small; at the same time, contact can be avoided. The high friction heat, high wear and high leakage of the fluid dynamic seal not only reduce the fuel consumption of the whole machine, but also improve the reliability of the whole machine. Compared with the static “three high” working conditions, the dynamic condition of the aero-motor has a more prominent influence on the sealing state. Compared with the ground equipment, its structure is thin and easy to deform, frequent starting and stopping and changing speed state, as well as being subjected to high maneuvering load and centrifugal load, etc., will cause the rotor to have large eccentric vibration displacement. The research shows that the radial displacement of the rotor precession can reach 0.2-0.5mm, the axial displacement of the nutation is 0.125mm or even larger, and the value is much larger than the film thickness. It is guaranteed that the sealing film has a reliable minimum film thickness and avoids direct metal contact during the working process, which is a major obstacle to be overcome in the gas film sealing technology.

  (2) The core of the evolution of research progress.

  The research on the application of gas film seals in the rotor internal flow system (whether end face or cylinder surface), although overcoming the above main obstacles, although each has different specific physical forms of structure, it can adopt a class for the form of large displacement. The same method: the relevant components in the gas film sealing system have large flexibility or floating characteristics, and the film stiffness is high; the dynamic displacement is taken by the flexible member to ensure the necessary film thickness. The pursuit of sealing systems with large flexible floating supports and rigid air films to avoid contact friction and wear on the sealing sub-surface is the core of a series of research and development of gas film sealing.

  2 cylindrical gas film potential

  (1) Limitations of the end face film seal.

  The fact that the end face film seal is successfully applied on the relatively smooth ground large-scale fluid machine shows that the flexibility of the end face gas film seal structure can meet the requirements in the fluid machine with small axial displacement of the seal sub-rotating surface. In special fluid machines such as aero-motors, many endeavors in end-face gas film sealing research (including tilting of the face seal pair, sharp step dynamic pressure, spiral groove dynamic pressure, increased static pressure of film thickness, and increased stiffness) Static pressure, etc., are caused by severe vibration and thermal deformation of the rotor system, or contact wear and excessive leakage. It shows that there are major limitations in the conditions of adapting to large displacement.

  (2) The potential of cylindrical gas film sealing.

  In a typical fluid dynamic seal, it is possible to deal with the large vibration displacement of the aeromotor. Only the brush seal has greater flexibility and has been tested by a large number of successful application practices; however, the contact type brush seal is difficult to form. Fluid-powered gas films have inherent metal contact friction and wear.

  The above research on the application of cylindrical gas film sealing for the aeromotor rotor internal flow system shows that the cylindrical seal can have a strong flexible floating support structure, and maintain a certain film lubrication under the severe vibration and thermal deformation of the rotor. Tests of compliant foil seals and thin blade seals on simulated testers and surface gas turbines have shown that they can form a hydrodynamic gas film seal at the journal, avoiding the intense friction and wear that occurs with direct metal contact. Although this seal is still insufficient, it has a strong flexibility to adapt, making it more potential to overcome the obstacles of large displacement.

  (3) The force characteristics of the cylindrical gas film seal provide the possibility of structural design of the flexible floating bearing.

  The seals of the aero-motor rotor internal flow system and the rotor tip do not withstand the rotor counterforce during operation, which provides the possibility of designing a large flexible floating support structure for these parts with a cylindrical gas-sealed sealing sub-member. .

  The key to cylindrical gas film sealing research

  Adapted to the sealing requirements of the aeromotor flexible rotor system under special working conditions, the key to the research of advanced cylindrical gas film sealing lies in the following two aspects.

  1 Sealing system structure

  The basis of the research on cylindrical gas film sealing is to propose a new type of sealing system structure, which should meet two basic points:

  (1) Considering the overall structure of the system, the system has sufficient flexible support by the elastic members and the floating members, and the large vibration displacement from the rotor is mainly absorbed by the flexible support, and the system is adaptive to ensure sufficient air film. The thickness forms a non-contact friction film seal.

  (2) Structural design should fully consider that the large flexible support structure with adaptability should be easy to quantitatively design and analyze.

  2 Complete quantitative design analysis method

  Establishing the quantitative analysis method of sealing system under certain working conditions, predicting and analyzing the sealing performance, and quantitatively designing the relevant parameters of the sealing system is the premise of the experimental research and application of the sealing system, which can achieve twice the result with half the effort. The main points of analysis include:

  (1) Establish a system model under the condition of large vibration displacement of the rotor, and perform mechanical analysis of the sealing film under the minimum film thickness and quantitative analysis of the sealing characteristics of the system;

  (2) Performing a macro-micro-combination design analysis of the gas film sealing system designed to test the above-mentioned sealing system analysis, including the effects of high-speed turbulence effect of the gas film, film slipstream effect and surface roughness effect, and correcting the aforementioned calculation and analysis;

  (3) Perform stability analysis of the sealing system.

  The impact of advanced sealing technology on the performance improvement of aero-motors has become increasingly prominent, and the development of gas-film sealing technology is of great significance. Research and analysis on aero-motor sealing conditions and research progress show that cylindrical gas film sealing research has great potential.

  The key to the study of air-jet gas cylinder rotor seal is to explore the flexible support structure with sufficient “adaptive” and easy to quantitative design analysis; establish a complete quantitative design analysis method for the seal system. In order to carry out further experimental research and application.