Measurement Versus Predictions of Rotordynamic Coefficients of a Hole-Pattern Gas Seal With Negative Preswirl

Brown, P.; Childs, Dara W.

doi:10.1115/1.4007331

Cited by 32 publications

(3 citation statements)

References 7 publications

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“…The reversed-swirl brakes are intended to induce fluid rotation against shaft rotation and reduce the destabilizing effects of a combined labyrinth-brush seal. In 2012, Brown and Childs [24] investigated the rotordynamic coefficients for a hole-pattern seal with negative preswirl. Results show that the negative preswirl could reverse the sign of cross-coupled stiffness coefficients and significantly increase the effective damping coefficient.…”

Section: Introductionmentioning

confidence: 99%

Improving the rotordynamic stability of short labyrinth seals using positive preswirl

Zhang¹,

Gu²,

Cao³

et al. 2020

J. vibroeng.

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Introducing a negative preswirl at the upstream of annular gas seals has been considered as an effective way to improve the system stability. This paper demonstrates a stability enhancement approach for a short labyrinth seal using positive preswirls. The static and dynamic characteristics of the labyrinth seal with various blade numbers (5, 10, 15), inlet preswirl ratios (-0.3,-0.15, 0, 0.15, 0.3) were studied. Results show that the inlet preswirl ratio has a dramatic effect on the circumferential location of the high-pressure spot for each seal cavity, particularly for the first cavity. The inlet preswirl ratio has opposite effects on the system stability due to the difference of high-pressure spot locations between the first cavity and the others. An increasing positive inlet preswirl could improve the system stability for the labyrinth seal with fewer blades (e.g. 5 blades). Its characteristics is mainly dominated by the first seal cavity. For the labyrinth seal with 10 blades, the system characteristics shows slight dependency on the inlet preswirl ratio. For the labyrinth seal with more blades (e.g. 15 blades), the negative inlet preswirl still increases the system stability, which agrees with the conventional conclusion. The paper provides a deeper understanding on the stability improvement of the labyrinth seal.

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Section: Introductionmentioning

confidence: 99%

Improving the rotordynamic stability of short labyrinth seals using positive preswirl

Zhang¹,

Gu²,

Cao³

et al. 2020

J. vibroeng.

View full text Add to dashboard Cite

show abstract

“…erefore, the stability of rotor system is commonly disturbed by inappropriate anti-prewhirl seal structure. Some investigations showed that setting anti-prewhirl structure has a certain effect, but it has a difficult design and complicated structure and may lead to instability of the rotor system [12]. e concept of damping seal was first proposed by Pragenau in 1982 [13].…”

Section: Introductionmentioning

confidence: 99%

Experimental Investigation on Rotordynamic Characteristics and Rotor System Stability of a Novel Negative Dislocated Seal

Sun

Wang²,

Fei

et al. 2019

Shock and Vibration

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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.

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“…The flow was seen to be strongly three-dimensional from identifying the vortex flow structures within the vanes responsible for swirl brake performance. Brown [13] presented the test results for the rotordynamic coefficients of a hole-pattern annular gas seal with negative preswirl. Results showed that changes in the pressure ratio had only small effects on most rotordynamic coefficients, while increasing rotor speed significantly increased the cross-coupled stiffness and cross-coupled damping.…”

Section: Introductionmentioning

confidence: 99%

Research on characteristics of fluid-induced vibration for short labyrinth seals

Zhang¹,

Yang²,

Li³

et al. 2016

J. vibroeng.

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Short seal (e.g. shroud seal) is a key component for the safe and reliable operation of a turbine unit. This paper sets up the three dimensional numerical model of a short labyrinth seal and analyzes its characteristics of the fluid-induced force. Results show that the tangential fluid-induced force increases almost linearly as the rotational speed increases. The sign of the radial fluid-induced force changes as the rotational speed increases. For higher inlet pressure, a more dramatic increase can be found for both the tangential and radial fluid-induced force. A transition speed range was found that the magnitude of the radial fluid-induced force at higher inlet pressure became less than that at lower inlet pressure. For each seal cavity, the peak pressure location had a shift away from the minimum clearance location as the rotational speed increased. This shift also existed in the axial direction. The effect of the rotational speed on the fluid-induced force became more remarkable for the longer seal with many cavities. Both the radial and tangential fluid-induced force increased with the increasing preswirl ratio. However, the two forces decreased with the increasing preswirl ratio when the inlet total pressure was kept as a constant value. In the end, the critical preswirl ratio which corresponds to zero tangential fluidinduced force was calculated, and results show that a smaller magnitude of the preswirl ratio will be needed to offset the effect of rotational speeds at higher inlet pressures. The inlet preswirl generated a majority of the tangential force for short seals.

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Measurement Versus Predictions of Rotordynamic Coefficients of a Hole-Pattern Gas Seal With Negative Preswirl

Cited by 32 publications

References 7 publications

Improving the rotordynamic stability of short labyrinth seals using positive preswirl

Improving the rotordynamic stability of short labyrinth seals using positive preswirl

Experimental Investigation on Rotordynamic Characteristics and Rotor System Stability of a Novel Negative Dislocated Seal

Research on characteristics of fluid-induced vibration for short labyrinth seals

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