Abstract: A new theory to reduce fluid induced force in seal is presented. The main idea is to change fluid field by the automatic tilting motion of seal pad. Using ANSYS CFX, the fluid-solid coupling model is set up. The tilting motion of seal pads are realized by mesh deformation method. Calculation results of seal force under different rotation speed, eccentric ratio and pressure are given. Comparison between the two kinds of seal shows that force increase with the increase of three parameters. In total cases, force of the tilting pad seal is smaller then force of the fixed pad seal. The difference becomes larger in case of large pressure, rotation speed and eccentric ratio. The test rig is set up. Seal force is identified by using transfer function method. Influence of seal force is enlarged to improve accuracy by test near the resonance region. The calculation results are verified by experiment. The seal force difference between the two kinds of seal may be large for the modern super critical turbines due to the large inlet pressure.

Key words: Fluid induced vibration, Fluid-solid coupling vibration, Seal