Large-scale experimental investigation of flow characteristics in labyrinth seal geometries

Abstract

order to determine the flow characteristics and leakage resistance properties of advanced labyrinth seals. A unique water test facility is used to acquire leakage resistance measurements for two-dimensional, planar models of multi-cavity, stepped seal geometries. The test-section includes a series of 100: I scale, acrylic models of actual rotor and stator elements. Adjustable external controls allow individual positioning of the seal elements to the desired radial and axial position. Flow-visualization techniques are also used to assist in identification and understanding of the turbulence generating flow patterns which promote improved leakage resistance. Seal geometries are examined over a range of flow Reynolds numbers, and axial rotor positions, for fixed restrictor clearance and stator step height values. Four separate flow path regions of interest, within the seal cavity, are identified. Each region of interest is comprised of a series of acrylic components which can be interchanged to construct a wide range of advanced seal geometries. The effects of isolated, geometric alterations in each region of interest are investigated and used in conjunction with flow-visuahzation studies to obtain a better understanding of the labyrinth flow field and seal performance. Additionally, complicated coupling mechanisms goveming the relationship between seal leakage resistance and seal geometry are identified and the influence of axial distance-tocontact is addressed. Experimental results imply that leakage resistance can be improved through the development of opposing flow recirculation zones in the upsmm portion of the seal cavity. Also, contoured surfaces and restrictor leading-edge extensions of proper dimensions can be introduced in the seal cavity to reduce ovemu seal leakage. Addition of annular grooves to the geometries provided no improvement in leakage resistance, and in some instances proved detrimental to seal performance. The leakage resistance coefficient for a given geometry improves considerably when the distance-to-contact value approaches that of the seal restrictor clearance. The relationship between seal distance-tocontact, cavity penetration and mainstream flow path length plays a significant role in determining seal performance.