Abstract
Hydrodynamic pressure finger seal1 is a kind of flexible noncontact dynamic sealing device with good application potential. It relies on the ultrathin dynamic pressure film effect produced by the rotation of finger boot and rotor to realize the design of noncontact and low leakage and is suitable for high-speed dynamic sealing parts. However, under the high-speed condition, there is a wall slip effect when the gas flows in the microchannel with a thickness of about 10 μm between the finger boot and rotor, which affects the stability of the dynamic pressure air film and also affects the change of the air film bearing capacity and the leakage rate of the finger seal. Therefore, based on the theory of microflow, the interstitial flow field model of finger seal under fluid dynamic pressure is established, and its slip effect under high speed is analyzed. The results show that the slip ratio of the sealing medium temperature of 500°C and 0.1 MPa conditions reached 27.28%. When considering the slip effect of the wall surface generated by the gas under shear driving, the gas film bearing capacity decreased and the leakage rate increased. When the pressure difference between the upper and lower reaches of the seal is 0.1 MPa, and the rotor line speed is 400 m/s, the gas film bearing capacity decreases by 17.39% after considering the slip effect of the wall surface, and the leakage rate increases by 14.06%. The results provide an important reference for the structural design and leakage control of hydrodynamic finger seal.
Highlights
Yan-chao Zhang,1 Ting Wang,1 Dong-ya Zhang,1 Ming-hu Yin,1 Ya-hui Cui,1 Ling-ping Chen,1 Peng-fei Du,2 and Rui Wang3
Under the high-speed condition, there is a wall slip effect when the gas flows in the microchannel with a thickness of about 10 μm between the finger boot and rotor, which affects the stability of the dynamic pressure air film and affects the change of the air film bearing capacity and the leakage rate of the finger seal. erefore, based on the theory of microflow, the interstitial flow field model of finger seal under fluid dynamic pressure is established, and its slip effect under high speed is analyzed. e results show that the slip ratio of the sealing medium temperature of 500°C and 0.1 MPa conditions reached 27.28%
The flow field model of hydrodynamic pressure finger seal gap is established based on the theory of microflow, and the slip effect of fluid seal is analyzed by CFX simulation; the key conclusions are summarized as follows
Summary
Many physical quantities in the macroscopic state will change, and the flow speed on the surface of the channel will show a slip phenomenon, and the surface viscous shear stress will be reduced At this point, the effect of the wall slip on the flow of gas sealed by the hydrodynamic pressure finger cannot be ignored. Combined with the actual working conditions of the hydrodynamic pressure finger seal, the minimum characteristic scale of the flow field is 0.00635 mm, and the average free path calculation of the gas molecule is shown in the following formula:. E slip boundary condition of the wall surface becomes an unnegligible factor affecting the leakage flow characteristics, which affects the overall working stability and reliability of the hydrodynamic pressure finger seal system. E slip rate can be calculated as s 27.28%. e calculated slip rate can be used as the boundary condition for hydrodynamic pressure finger seal leakage calculation
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