Abstract
A new type of stepped seal with a ribbed casing is proposed to efficiently reduce the leakage at the tips of turbine blades. The leakage characteristics of two different types of labyrinth seals (conventional seal vs. ribbed seal) were compared and analyzed through computational fluid dynamics (CFD) in a wide operating range of pressure ratios and clearances. The analysis showed that the ribbed seal has superior leakage performance to the conventional seal at all clearance sizes. With the same clearance size (S/H = 1.0), the flow function of the ribbed seal was approximately 21.5–42.6% less than that of the conventional seal. Also, different trends of variation in the flow function according to the increase of the clearance were found between the conventional and ribbed seals. The leakage flow inside the labyrinth seal was analyzed to explain the cause of this difference in tendency, and it was confirmed that the added ribs cause collision between the leakage flow and the tooth wall, even with the increase of the clearance. Also, the ribbed seal enables operation at a larger clearance with the same leakage performance when comparing the absolute leakage flow rate of the two seals. In addition, a parametric study on the influence of the rib height and rib inclination angle revealed that the flow function generally decreases as both parameters increase.
Highlights
As the performance requirements for gas turbines steadily increase, sealing technology is becoming essential for efficiency enhancement of turbomachinery such as compressors and turbines
After confirming the substantial leakage reduction effect at the reference clearance size, we extended the investigation to a wider step height (S/H) range and identified a significant difference in the trend of the flow function change with clearance between the ribbed and conventional seals
After confirming the substantialtoleakage effect the reference clearancedifsize, ference in the trend of the flow function change with clearance between the ribbed andin we extended the investigation to a wider S/H range and identified a significant difference conventional seals
Summary
As the performance requirements for gas turbines steadily increase, sealing technology is becoming essential for efficiency enhancement of turbomachinery such as compressors and turbines. Wittig et al [2,3,4] conducted experimental and computational studies on the leakage flow characteristics and heat transfer of straight and stepped seals. They conducted experiments with scale variations to analyze the effect of the scale of the experiment on the flow coefficient and the friction factor. With the development of computational fluid dynamics (CFD), research has been conducted on the internal flow phenomena inside a labyrinth seal according to the change of design parameters. Kang et al [14] conducted an experiment and numerical analysis on a stepped seal with changes in the number of teeth and clearance They compared the leakage characteristics of solid and honeycomb seals.
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