An Experimental and Numerical Investigation of the Rotordynamic Coefficients of a Gas Labyrinth Seal: Part 1 – Experimental Results

Abstract This paper is the first of a two-part series investigating the rotordynamic behavior of a six-tooth gas labyrinth seal. Part 1 focuses on the experimental work, presenting a detailed description of the test rig, rotordynamic coefficients, and leakage values obtained at various operating conditions. The seal was tested at three pressure ratios (0.2, 0.3, and 0.4) and three rotor speeds (5, 10, and 15 kRPM). The supply pressure was maintained at 13.1 bars, with the discharge pressure adjusted through a back pressure valve to achieve the desired ratios. The rotordynamic coefficients were obtained by pseudo-random excitation of the seal at subsynchronous frequencies with different waveforms. Five waveforms were used: three individual frequency waveforms — 50, 100, and 150 Hz — and two multi-frequency waveforms — 50–150 Hz and 10–350 Hz. Frequency independence of the rotordynamic coefficients was observed at low and medium frequencies, while at high frequencies the direct stiffness increased with increasing frequency. The rotordynamic coefficients were compared using the individual and multi-frequency waveforms values for 50, 100, and 150 Hz at the specified pressure ratios. The rotordynamic coefficients showed good agreement between measurements using different waveforms. Additionally, the influence of the cross-coupled stiffness on effective damping was analyzed. Part 2 of this series explores the computational aspects, including a grid independence study and comparison between experimental and numerical results.