Browsing by Author "Venkataraman, Balaji"

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    CST14 - Design and Implementation of Swirl Brakes for Enhanced Rotordynamic Stability in an Off?shore Centrifugal Compressor
    (Turbomachinery Laboratory, [2019]) Cave, Michael; Moulton, David; Eldridge, Thom; Wilkes, Jason; Clarke, Chris; Venkataraman, Balaji; Moore, Jeff
    Rotordynamic stability of gas compressors at high speeds and operating pressures is a significant technical challenge. Dynamic instability must be avoided for the sake of safe, reliable and continuous operation of turbomachinery. During the last few decades, the industry has successfully used swirl-brakes in a Teeth-on-Stator configuration for many applications. This case study presents the design, testing and successful implementation of swirl-brakes for a Teeth-on-Rotor configuration to improve rotordynamic stability.
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    Design and Implementation of Swirl Brakes for Enhanced Rotordynamic Stability in an Off-shore Centrifugal Compressor
    (Turbomachinery Laboratory, Texas A&M Engineering Experiment Station, 2018) Venkataraman, Balaji; Moulton, David; Cave, Mike; Clarke, Chris; Moore, Jeff; Wilkes, Jason; Eldridge, Thom
    Rotordynamic stability of gas compressors at high speeds and operating pressures is a significant technical challenge. Dynamic instability must be avoided for the sake of safe, reliable and continuous operation of turbomachinery. Experience and literature have shown that one of the main sources of instability is the swirl within the secondary leakage path in shrouded impellers, especially the swirl entering the shroud seals. The technical brief presents the design and implementation of swirl brakes for centrifugal compressors with Teeth-on-Rotor seal configurations for shrouded impellers. Discussion includes (a) aerodynamic design of swirl brakes with the help of Computational Fluid Dynamics (CFD), (b) sub-scale testing of the swirl brake design in an instrumented single-stage test rig to measure the inlet swirl ratio in a shrouded impeller, (c) full-scale prototype shop-testing and qualification, with and without the swirl brakes in a closedloop test facility, and (d) results of incorporating the swirl brakes at an off-shore compressor installation to improve rotordynamic stability.
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    Electric-Motor-Driven Gas Compressor Packages: Starting Methods for Large Electrical Motors and Torsional Integrity
    (Turbomachinery Laboratory, Texas A&M Engineering Experiment Station, 2017) Cole, Ge'Juan; Glasbrenner, Michael; Venkataraman, Balaji; Kurz, Rainer; Turbomachinery Symposium (46th : 2017)
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    Stability Analysis of a Multi-stage Gas Compressor With Swirl-brakes Using Three Dimensional Transient CFD Model
    (Turbomachinery Laboratory, Texas A&M Engineering Experiment Station, 2021) Kim, Eunseok; Venkataraman, Balaji
    Minimizing fluid induced forces through the secondary leakage flow paths in shrouded centrifugal impellers is crucial to improve the rotordynamic stability of high-pressure centrifugal gas compressors. Swirl brakes (SBs) are widely used in turbomachinery to reduce the fluid induced forces and enhance the system rotordynamic behavior. Prior to the present study, swirl-brakes of a high-pressure multistage compressor were designed using 3D steady-state computational fluid dynamics (CFD) analysis and verified through multiple fullscale closed loop tests for a compressor, operating with and without the SBs. In the present study, a 3D transient CFD analysis is conducted to calculate the fluid induced rotordynamic coefficients of a Teethon- Rotor (TOR) seal and the impeller shroud cavity. Full 360o fluid domains including the impeller, the shroud cavity, and TOR seals with either a swirl-brake or without it are numerically modeled. A mesh deformation technique is employed to follow the whirling rotor motion of the impeller. To evaluate the capability of the transient CFD model, comparisons are made between the prior test results and predictions from the current numerical study. The cross-coupled destabilizing forces as calculated from CFD are then compared with the methodologies recommended by API 617 and a few other researchers in the literature. In addition, the destabilizing forces calculated through the CFD methodology are used in rotordynamic simulations of the rotor, with and without SBs. Comparisons of simulation results to test results and field performance show good qualitative correlation. CFD predicts forces in the secondary flow path (without SBs) that cause early signs of instability observed in the compressor. The same methodology with SBs predicts cross-coupling forces that are benign, which is also confirmed by stable operation of the same compressor when rebuilt with SBs. These results are included in the paper.
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    Thermo-Hydrodynamic analysis of turbulent cryogenic eccentric annular seals and effects of seal flexibility
    (Texas A&M University, 1995) Venkataraman, Balaji
    High performance turbomachines such as the Space Shuttle Main Engine Turbopumps (SSME-HPOTP and HPFTP) are prone to experience severe vibration problems due to high operating pressures and speeds. The stability and response characteristics of these pumps depend significantly on the rotordynamic features of hardware elements such as the seals and bearings. The focus of this research effort is to develop a comprehensive thermo-elasto-hydrodynamic analysis of turbulent liquid annular seals and to understand the effects of annular seals on the pump rotordynamics. Seal eccentricity has been included for rigid seals. The eccentric seal analysis is based on the work of Nelson and Nguyen (1988), but a much simpler and effective method, namely the cubic spline interpolation method, is adapted to obtain the circumferential derivatives of the primitive variables. The bulk flow continuity, axial and circumferential momentum and the energy transport equations are utilized to model the flow field while Moody's friction factor model is adapted to account for the wall shear stresses. Wall flexibility of the seal can significantly impact rotordynamic coefficients of the turbopumps due to high pressures and low clearances. Linings of interstage annular seals in the SSME-HPOTP are made up of soft Silver alloys which can deform easily under the high pressures that are usually encountered. This study analyzes the effects of flexibility on the dynamic characteristics of concentric seals. The wall deformations are obtained using an iso-parametric, axi-symmetric Finite Element formulation of the seal wall. Numerical solution obtained by the current analysis compares wen with those of earlier researchers for the rigid as well as the flexible cases.
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    TL09 - Dynamics of Modular Rotors in High Speed Centrifugal Compressors: Design, Operational Performance and Field Serviceability
    (Turbomachinery Laboratory, Texas A&M Engineering Experiment Station, [2019]) Venkataraman, Balaji; Kurz, Rainer; Gonzalez, Francisco; Rajagopalan, Vinayaka; Favela, Beatriz; Hodgson, Lance; Turbomachinary Symposium (48th : 2019)
    Turbomachinery depends on optimal rotor-bearing systems for reliable operation. One type of rotor construction is the concept of modular rotors. While gas turbines have implemented this concept extensively, there has been a steady acceptance of modular rotors in gas compressors in the recent past. End-users have experienced the mechanical reliability, ease of re-staging and high operational availability of compressors with modular rotors for their mission-critical operations. This lecture presents key rotordynamic attributes of centrifugal compressors with modular rotors. Mechanical performance, sensitivity to unbalance, balance repeatability and rotordynamic stability are shown. Historical data on vibration from compressors operating in the field have been presented to validate the design, construction and operation.