General presentation > Keynote speaker

Dr. Luis San Andrés

Luis San Andrés is the Mast-Childs Chair Professor of Mechanical Engineering at Texas A & M University (TAMU). Through 32 years conducting funded research at the TAMU Turbomachinery Laboratory, professor San Andrés and students have produced experimentally verified predictive tools modeling squeeze film dampers for aircraft engines, hybrid bearings for cryogenic turbopumps, the nonlinear dynamics of turbochargers, gas foil bearings for oil-free machinery, lubricated bearings for high performance turbomachinery, and multiple-phase flow seals for wet gas compressors. Luis is a Fellow of ASME, STLE, and GPPS, a member of the Industrial Advisory Committees for the TAMU Turbomachinery and Pump Symposia, and a US member for IFToMM Technical Committee in Rotordynamics. Dr. San Andrés and students have authored over 200 papers in refereed journals, with over a dozen recognized as best. Dr. San Andrés received the ASME-IGTI 2022 Aircraft Engine Technology Award for sustained personal creative contributions to aircraft engine technology

Annular Gas Seals in the 21^st century: Leakage, Force Coefficients and Rotor DYNAMIC Stability.

Turbomachinery seals are engineered to maintain efficiency and power delivery by minimizing leakage. Seals also appreciably affect the system rotordynamic behaviour due to their relative position within a turbomachine. The lecture reviews the published experimental record on gas seals and gives insight into the physical models predicting leakage and dynamic force coefficients. The review includes uniform clearance seals, various types of labyrinth seals (LS), and damper seals (honeycomb seals and pocket damper seals). LS with teeth on the rotor surface are notorious for producing large cross-coupled stiffnesses (k). Poorly designed LS are the cause of many rotordynamic instability fiascos. Damper seals produce direct stiffness (K) and damping (C) coefficients, orders of magnitude larger than those from conventional LS. Textured surface seals in conjunction with a swirl brake also produce very small k; hence, effectively removing a concern on rotordynamic instability.

Past are the days for known bad actors, such as LS, being the sole choice for effectively sealing the stages in a turbomachine. Incidentally, damper seals, honeycomb and hole-pattern seals in particular, can produce a large centering stiffness (K>>0 ) that makes a balance piston seal act as a third bearing, hence rising the first natural frequency of the rotor system.

 Although both bulk flow and computational fluid dynamics (BFM & CFD) models are very good at predicting seal leakage, they fall short to replicate the experimental force coefficients of seals, those with complex geometry in particular. The predictive methods still need improvement, hence the need of constant and continuous experimental verification. In the 21^st century, damper seals offer a remarkable opportunity to control the leakage and tailor the rotordynamic performance and stability of modern rotating machinery.