Leakage reduction by optimization of hole-pattern damping seal with inclined hole cavity

Annular-shaped gas seals are essential in turbomachinery to satisfy their sealing requirements. These annular gas seals are employed in many compressors, aerospace-related engines, and other critical applications virtue of their good feasibility to enhance the performance of turbomachinery and controlling the leakage mainly. There are different types of seals employed such as labyrinth seals (LS), honeycomb seals (HS), brush seals, etc. however these seals fail to give a good leakage reduction and stability and provide consistency and cost-effectiveness. This paper discusses the hole-pattern damping seals (HPDS) developed with the help of an electrical discharge machine or a CNC machine. HDPS allows for customization of the geometrical configurations of the cavities that can help solve problems such as unstable vibrations and damaging of the shafts that are encountered in other types of competitive seals. The idea is to keep an eye on the main geometrical parameters (hole depth and diameter, seal clearance) that can affect the leakage characteristics of the HDPS. This paper helps in revealing the effect of the axial inclined angle for the HDPS and the LS seals, at which the inclined holes are situated with respect to the shaft axis, hence allowing for comparisons of the leakage characteristics under different working conditions.

In a new research published in International Journal of Heat and Mass Transfer , Miss Xuan Zhang, Dr. Jinbo Jiang, Professor Xudong Peng, Dr. Wenjing Zhao, and Professor Jiyun from the Zhejiang University of Technology investigated the influence of the geometrical parameters such as hole diameter, seal clearance, and spacing on the axially inclined HDPS’s leakage properties which lead to the identification of the best possible parameters for a good sealing performance. These tests were also carried out on LS to prepare an argument on how the HDPS performs better than the LS with an inclined hole. The numerical calculations of the fluid field were conducted with the help of computational fluid dynamics (CFD), and it also helped in gaining results for leakage patterns of the HDPS. It should be noticed that the operating conditions were kept steady to determine and analyze the changes that happen due to differences in the geometrical parameters. These conditions included angular speed, inlet, and outlet pressure and temperatures, hole, and rotor diameters.

The authors’ findings were based on several factors, including the axial angle, the influence of hole diameter, and seal clearance on leakage reduction. In comparison to the straight hole seal, the axial inclined angle exhibited a better leakage reduction. Furthermore, the HDPS with an inclined angle reduces leakage far better than the LS seal. Any reduction in this angle reduces the leakage rate of the sloped HDPS in the windward direction. The HDPS’ capacity to reduce leakage was also influenced by the seal clearance and other geometrical factors. The research team established a practical aspect to the testing by utilizing a range of 0.05 mm to 0.9 mm that has been used mostly in many practical applications. Any increase in the seal clearance for different inclined angles in the axial direction led to a decrease in the increment ratio of the leakage rate followed by an increase in the trend. This means that there is an optimum dimension of the seal clearance that leads to the best attainable leakage reduction capability.

Conclusively, to sum up, the results, the windward inclined HDPS leads to a reduction in the leakage as compared to the leeward inclined HDPS with the traditional HDPS being a reference point. Results show that the leakage is reduced by a maximum of 25% in the windward inclined HDPS. Other reasons for the leakage reduction are the production of low, weak high speed, and a violent vortex in the outlet, inlet, and inside the cavity respectively. Geometrical parameters also dictate how much leakage reduction is attained, the best being a large-large or a small-small seal clearance and hole diameter. In a statement to Advances in Engineering Series, the authors said these advancements achieved in their study will allow better control over the leakage rate as it provides an avenue for further research and a better chance for maintaining the leakage characteristics.