Abstract
Air-induced force generated in seals is one key factor on the stability of the rotor system. In this paper, a novel negative dislocated seal (NDS) was developed in respect of dislocated bearing theory, to reduce hydrodynamic pressure effect and air-induced force and improve rotor stability as well. A test rig was built to test rotordynamic characteristics and rotor stability of the NDS. The rotordynamic characteristics of seals were investigated based on the unbalanced synchronous excitation method, and seal-rotor system stability was evaluated by the identification method with an electromagnetic bearing exciter. The effects of both rotating speed and inlet/outlet pressure ratio on the rotordynamic characteristics and rotor stability of both NDS and conventional cylindrical labyrinth seal were experimentally investigated. The results show that with the increasing rotating speed, inlet/outlet pressure ratio is promising to reduce the direct stiffness coefficients of seals and the logarithmic decrement rate of seal-rotor system and enhance both cross stiffness and damping coefficient as well. Besides, the developed NDS effectively reduces cross-stiffness coefficients and increases direct damping coefficients and the logarithmic decrement rate of the seal-rotor system, relative to the conventional cylindrical seal. The proposed seal can effectively improve seal stability of turbomachinery.
Highlights
For turbomachinery such as steam turbine, centrifugal compressor, and aeroengine, seals are one critical component and play the key role of preventing working medium leakage, reducing energy consumption, and improving work efficiency [1,2,3]
As for anti-preswirl seal, the anti-preswirl idea was developed by Muszynska in the 1980s [4]. e anti-preswirl seal can be divided into swirl brake seal and antiswirl seal. e swirl brake seal is commonly installed at the sealed inlet, to stop vortex and resistance to swirl [5]
Shunt injection is revealed an effective approach to improve the rotordynamic characteristics of labyrinth seal [9,10,11]. erefore, the stability of rotor system is commonly disturbed by inappropriate anti-prewhirl seal structure
Summary
For turbomachinery such as steam turbine, centrifugal compressor, and aeroengine, seals are one critical component and play the key role of preventing working medium leakage, reducing energy consumption, and improving work efficiency [1,2,3]. Catering for the problem of the increasing hydrodynamic pressure effect of sealed fluid under high parameters and the increase of airflow exciting force, this paper proposes a negative dislocated seal (NDS) structure by considering the dislocated bearing theory. In contrast to the improvement of hydrodynamic pressure effects with the positive-dislocated bearings, a divergent flow field gap can form in the circumferential wedge gap of the NDS, while the conditions to form hydrodynamic pressure effects do not exist, and the seal airflow force is reduced In this paper, both the rotordynamic characteristics and rotor stability of the NDS and the traditional circular seal are experimentally studied by using seal rotordynamic characteristic identification methods based on unbalanced common-frequency excitation and rotor stability experiment identification method based on the electromagnetic bearing exciter.
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