Investigation of a Rotordynamic Instability in a High Pressure Centrifugal Compressor Due to Damper Seal Clearance Divergence
01 Jan 2006-
TL;DR: In this article, the potential for excess distortion of a honeycomb damper seal under high differential pressure in a centrifugal compressor, the problems this can cause, and options for solution are discussed.
Abstract: This paper documents the potential for excess distortion of a honeycomb damper seal under high differential pressure in a centrifugal compressor, the problems this can cause, and options for solution. A strong negative stiffness can result, dropping the first natural frequency into a region of negative effective damping. The paper shows the need to manage seal clearance profile and inlet swirl to avoid this condition, and to optimize damper seal contribution to stability. The paper presents predicted seal distortion, resulting dynamic characteristics, and their influence on rotor stability. Field vibration data confirm seal distortion under pressure can cause damaging, self-excited sub-synchronous vibrations, and that an appropriate seal clearance profile predictably corrects this condition. The paper shows that optimum stability requires uniquely different clearance profiles for low and high-pressure compressors.
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TL;DR: In this paper, the authors describe the design, construction, and modeling process for a high performance active magnetic bearing (AMB) test rig which typifies a small industrial super-critical centrifugal compressor.
Abstract: A successful industrial application of flexible rotors supported on active magnetic bearings (AMBs) requires careful attention not only to rotordynamic design aspects but also to electromagnetic and feedback control design aspects. Model-based control design provides the framework to ensure efficient, reliable, and safe operation of turbomachinery on AMBs. This paper describes in detail the design, construction, and modeling process for a high performance AMB test rig which typifies a small industrial super-critical centrifugal compressor. A unique aspect of the design are the two additional radial AMBs to allow the application of simulated destabilizing fluid or electromagnetic forces to the rotor. These forces are difficult to predict and can lead to rotordynamic instability of industrial machinery if not properly accounted for. This test rig provides a realistic platform to evaluate stabilizing control algorithms for high performance turbomachinery. A complete model of rotor, AMB actuators and accompanying electronics, is constructed from individually verified component models. Model validation is confirmed through the successful design and implementation of a μ-synthesis controller.
127 citations
Cites background from "Investigation of a Rotordynamic Ins..."
...As compressors operate at higher speeds and pressures and as rotor designs become slender to accommodate multiple impellers, instability due to aerodynamic CCS will become more of a concern [5]....
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...Cascade plot of vibration spectra during start-up of a high pressure centrifugal compressor showing the subsynchronous vibrations (SSV) leading to instability [5]....
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DOI•
01 Jan 2009
TL;DR: In this article, the development and analysis of the components of the centrifugal compressors for oil and gas application is discussed, with the aim of providing technical support in rotordynamics and stress analysis.
Abstract: Mechanical Development department of MAN Turbo, in Zürich, Switzerland. His job function includes the development and analysis of the components of centrifugal compressors for oil and gas application. He is responsible for providing technical support in rotordynamics and stress analysis. Before joining the site in Switzerland in 2003, he was employed for six years in MAN Turbo, Berlin, where he was involved in the design, finite element analysis, rotordynamic analysis, testing, and development of centrifugal compressors. Mr. Bidaut received his diploma (Mechanical Engineering, 1995) from the University of Valenciennes (France).
17 citations
8 citations
TL;DR: In this paper, the authors present a case study in which a high speed gas lift centrifugal compressor experienced significant vibration problems associated with start-up and operation of a two-stage 8-impeller unit.
8 citations
DOI•
01 Jan 2014
TL;DR: In this paper, a CFD study was carried out in order to evaluate the impact of each geometrical parameter on swirl brake performance, starting from a baseline and varying it over a possible design range, identifying an optimum design that could achieve a strong preswirl reduction over the widest range of compressor applications, sizes and operating conditions.
Abstract: The rotordynamic stability of high pressure compressors is strongly affected by the aerodynamic effects induced by the gas flow through rotor-stator seals. In particular the tangential velocity (swirl) of the gas flowing through the seals is a main destabilizing factor (Childs, 1993) and therefore needs to be minimized. Swirl brakes are well-known devices to reduce the swirl of the leakage at seal inlet, or preswirl. Their effectiveness is function of several geometrical parameters (swirl brake vane dimensions and shape, clearance gap between rotor and stator, seal diameter) and operating parameters (such as rotating speed, gas pressure, temperature, molecular weight, gas swirl upstream of the seal). A CFD study was carried out in order to evaluate the impact of each geometrical parameter on swirl brake performance, starting from a baseline and varying it over a possible design range. The purpose was to identify an optimum design that could achieve a strong preswirl reduction over the widest range of compressor applications, sizes and operating conditions. Swirl brakes developed according to this optimization study were used in a high pressure centrifugal compressor. The full load test performed in 2013 included a direct measurement of the logarithmic decrement, thus providing useful information to validate the outcome of the analysis. A comparison between calculation and test results allowed to verify the effectiveness of swirl brakes, by quantifying the actual preswirl value obtained from the labyrinth seals.
7 citations
Cites result from "Investigation of a Rotordynamic Ins..."
...This is also in good agreement with the results of CFD analysis, and is not far from some SR values suggested in literature, usually ranging between 0 and 0.25 (e.g. Camatti et al., 2006; Baumann, 1999; API684, 2005)....
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References
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01 Jan 2002
119 citations
TL;DR: In this paper, a two-control-volume model is employed for honeycomb-stator/smooth-rotor seals, with a conventional control-volume used for the throughflow and a capacitance-accumulator model for the honeycomb cells.
Abstract: A two-control-volume model is employed for honeycomb-stator/smooth-rotor seals, with a conventional control-volume used for the throughflow and a capacitance-accumulator model for the honeycomb cells. The control volume for the honeycomb cells is shown to cause a dramatic reduction in the effective acoustic velocity of the main flow, dropping the lowest acoustic frequency into the frequency range of interest for rotordynamics. In these circumstances, the impedance functions for the seals cannot be modeled with conventional (frequency-independent) stiffness, damping, and mass coefficients. More general transform functions are required to account for the reaction forces, and the transfer functions calculated here are a lead-lag term for the direct force function and a lag term for the cross-coupled function. Experimental measurements verify the magnitude and phase trends of the proposed transfer functions. These first-order functions are simple, compared to transfer functions for magnetic bearings or foundations. For synchronous response due to imbalance, they can be approximated by running-speed-dependent stiffness and damping coefficients in conventional rotordynamics codes. Correct predictions for stability and transient response will require more general algorithms, presumably using a state-space format.
91 citations
TL;DR: In this paper, hole pattern gas damper seal stators are used to reduce the number of holes in honeycomb annular annular seal and achieve higher effective damping, especially under high speeds and low inlet pressure ratio conditions.
Abstract: Honeycomb annular seals are an attractive design alternative due to their superior static and dynamic performance. However, their implementation in industrial practice has been delayed by the following characteristics: a) manufacturing time can be appreciable, and b) they can seriously damage the shaft if rubbing occurs. To minimize these problems, hole-pattern gas damper seals, which are formed by simply drilling holes into an annular smooth seal, were manufactured and tested. The hole-pattern damper seal stator can be made of high-strength plastic materials which are less likely to damage a shaft during rubbing. The experimental results presented demonstrate that, compared to a honeycomb seal, a hole-pattern damper seal with 3.18 mm hole diameters and a high percentage of hole surface has achieved: (a) an average of 12 percent reduction in leakage rate, and (b) considerably higher effective damping, especially under high speeds and low inlet pressure ratio conditions.
51 citations
DOI•
01 Jan 2002
TL;DR: In this article, the rotordynamic stability of a 7-stage back-to-back centrifugal compressor was measured using a magnetic bearing attached to the free end of the rotor, which injected an asynchronous force into the rotor system to excite the first forward whirling mode.
Abstract: Full-load, full-pressure rotordynamic stability measurements were conducted on a seven-stage, back-to-back centrifugal compressor. To validate rotordynamic predictions, the rotor was excited while operating at full load and full pressure during factory testing. This was accomplished through means of a magnetic bearing, which was attached to the free end of the rotor. This device injected an asynchronous force into the rotor system to excite the first forward whirling mode. This technique measures the rotor’s logarithmic decrement (log dec), which indicates the level of stability, or damping, in the rotor. The device is designed to be nonintrusive to the original dynamics of the rotor and may be easily installed/removed on the test stand. This paper discusses the techniques used to measure the rotordynamic stability from a fullload, full-pressure test of a 6000 psi reinjection compressor. The results demonstrate the effectiveness of swirl brakes and damper seals in producing a compressor that becomes more stable as discharge pressure increases. This approach to compressor design is in stark contrast to traditional designs in which the stability degrades with increasing pressure, ultimately leading to rotordynamic instability. This technology ensures trouble-free startup and operation of these compressors in the field, minimizing risk for the end-user.
33 citations
19 Sep 1993
30 citations