The design and experimental activity presented in this paper is related to a novel hybrid seal which is intended to work as a balance piston seal in an AMBs levitated high-pressure motor-compressor. Due to the project case operating conditions (about 300bar delivery pressure) the rotordynamic stability is a primary focus in the compressor design. The typical solution adopted for a high-pressure centrifugal compressor balance piston is a damper seal (e.g. honeycomb seal). However, due to the concurrent AMBs presence, the aforementioned selection is not so straightforward because the seal high stiffness level might lead to unexpected interactions with the AMB controller and cause a lack of stability. Based on these assumptions, an optimum trade-off between high damping performance and low stiffness requirements is needed, together with a proper leakage reduction.After a review of the state of the art it was found that a combination of some conventional geometries (e.g. labyrinth and honeycomb) can be adopted to achieve the desired target [1]. Based on this approach and upon several design iterations a final design was found which is based on a mix of multiple honeycomb seal and labyrinth seal portions. The design was done using a novel tool joining two validated bulk flow codes for both labyrinth [2] and honeycomb seal [3] portion. Moreover, a CFD analysis (both stationary and unsteady) was carried out as a final verification of the design and to provide a calibration tool for the 1D code. CFD analysis was based on some literature references [4] which provide relevant guidelines.The experimental activity was then performed at the Authors’ internal seal test rig [5]. The seal was initially tested at the exact project design conditions (310bar inlet, 200bar outlet, 11500rpm rotational speed). Moreover, an extensive test campaign was carried out in order to collect data and validate the design tools. As typical in rotordynamic seal testing activity, the operating parameters to explore performance sensitivity are rotational speed, inlet pressure, pressure ratio and inlet swirl level. The outcome was satisfactory both in terms of leakage and rotordynamic coefficients.Major feedback from the test:-&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Measured damping higher than predicted-&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Measured stiffness negative and lower than predicted-&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; CFD matching experimental data more closely than 1D codeAt the moment, 1D code needs further development before using it as a design tool while CFD resulted to be a reliable predictor. Furthermore hybrid seal is a valid technology for the intended application.References[1] R. De Noronha, L. Tapajoz, G. Grosso, D. Yoshikazu, R. Moreira, "Applying CFD To Solve A Vibration Problem Of A Compressor", Proceedings of the 44th Turbomachinery and 31st Pump Symposia, Houston, Texas, US, September &nbsp;14–17, 2015.[2] F. Cangioli, P. Pennacchi, G. Vannini, L. Ciuchicchi, A. Vania, S. Chatterton e P. V. Dang, On the Thermodynamic Process in the Bulk-Flow Model for the Estimation of the Dynamic Coefficients of Labyrinth Seals, ASME Journal of Engineering for Gas Turbines and Power, vol. 140, n. 3, 2018.[3] G. Kleynhans, D. Childs, The acoustic Influence of Cell Depth on the Rotordynamic Characteristics of Smooth Rotor/Honeycomb Stator Annular Gas Seals, ASME Journal of Engineering for Gas Turbines and Power, October 1997, Vol. 119 (4), pp. 949-957.[4] K.K. Nielsen., K. Jønck, H. Underbakke, Hole-Pattern and Honeycomb Seal Rotordynamic Forces: Validation of CFD-Based Prediction Techniques, Proceedings of ASME Turbo Expo 2012, GT2012-69878, June 11-15 2012, Copenhagen, Denmark[5] G. Vannini, S. Cioncolini, V. Calicchio e F. &amp; Tedone, Development of a High Pressure Rotordynamic Test Rig for Centrifugal Compressors Internal Seals Characterization, in Proceedings of the 40th Turbomachinery Symposium, Texas A&amp;M University - Turbomachinery Laboratories., 2011

A Novel Hybrid Seal: Design and Experimental Validation on a High Pressure Rotordynamic Test Rig

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2021/volume/84898

Turbo Expo 2021

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