Validation of Flow Coefficients Measurement by Laser Velocimeter in Straight-Through Labyrinth Seal Models With Full Size Test Rig Results

In the computation of overall efficiency in turbomachines the increase of performance in high pressure centrifugal compressors renders of great importance the role of leakage in straight-through labyrinth seals.A test rig for labyrinth seals used in process compressors was built in order to carry out a systematic study of the fluidodynamic phenomena characteristic of flow in these devices.Full size seals were tested under different working conditions and the results were utilized for a quantitative definition of the experimental coefficients introduced in previsional methods which were shown the best ones on the basis of previous investigation (1).The coefficients consider the principal fluidodynamic phenomena existent in the seals: fluid flow contraction in the throttlings and kinetic energy carry-over, which have contrasting effects on the leakage of a straight-through labyrinth seal.The results were used to find elements of correct design in these seals. They point out besides the geometric parameters which optimize seal performance, minimizing the leakage on a fixed length of the labyrinth.Larger scale models of the same seals tested on the above mentioned test rig were studied in a smoke tunnel under conditions which satisfied the Reynolds similarity.This experimental set-up permitted the measurement of the velocity distributions within the straight through labyrinth seal models by means of a laser Doppler velocimeter.Particular attention was dedicated to the definition of uncertainty of the experimental coefficients. The information obtained was satisfactory.The results showed promising correlations between real seals and larger models. These relations could be very useful when designing labyrinth seals for centrifugal compressors, as a large part of long, costly tests on real seals could be substituted by faster and more economical measurements on models.© 1984 ASME