Abstract:The current centrifugal compressor design for the oil & gas market is more and more challenging, and the presence of many competitors is pushing technology towards both a casing size reduction and a rotational speed increase. The first point is leading to an increase in the number of wheels per rotor (to do the same service), and the second point is forcing to cross two or even three rotor modes (hence a higher control of rotor damping is necessary). The two points together are leading to increase the roto… Show more
“…To further validate the orbit decomposition method, its prediction results are compared with the experimental data tested on the high-pressure seal test rig owned by GE Oil & Gas [17]. The test object is the labyrinth seal.…”
Section: Comparison With Experimental Datamentioning
confidence: 99%
“…Five whirl frequencies are measured with a 10,000 rpm running speed. The detailed test conditions can be found in [17].…”
Section: Comparison With Experimental Datamentioning
confidence: 99%
“…With this method, the obtained rotordynamic coefficients are frequency independent [13,14]. The latest research results show that many annular seals possess frequency-dependent rotordynamic coefficients, including the labyrinth seal [16,17], pocket damper seal [17], hole-pattern seal [18,19], etc. Interaction between the acoustic waves in a circumferential annulus and the rotor excitation frequency is the cause of the frequency dependency [20].…”
The elliptical orbit whirl model is widely used to identify the frequency-dependent rotordynamic coefficients of annular seals. The existing solution technique of an elliptical orbit whirl model is the transient computational fluid dynamics (CFD) method. Its computational time is very long. For rapid computation, this paper proposes the orbit decomposition method. The elliptical whirl orbit is decomposed into the forward and backward circular whirl orbits. Under small perturbation circumstances, the fluid-induced forces of the elliptical orbit model can be obtained by the linear superposition of the fluid-induced forces arising from the two decomposed circular orbit models. Due to that the fluid-induced forces of circular orbit, the model can be calculated with the steady CFD method, and the transient computations can be replaced with steady ones when calculating the elliptical orbit whirl model. The computational time is significantly reduced. To validate the present method, its rotordynamic results are compared with those of the transient CFD method and experimental data. Comparisons show that the present method can accurately calculate the rotordynamic coefficients. Elliptical orbit parameter analysis reveals that the present method is valid when the whirl amplitude is less than 20% of seal clearance. The effect of ellipticity on rotordynamic coefficients can be ignored.
“…To further validate the orbit decomposition method, its prediction results are compared with the experimental data tested on the high-pressure seal test rig owned by GE Oil & Gas [17]. The test object is the labyrinth seal.…”
Section: Comparison With Experimental Datamentioning
confidence: 99%
“…Five whirl frequencies are measured with a 10,000 rpm running speed. The detailed test conditions can be found in [17].…”
Section: Comparison With Experimental Datamentioning
confidence: 99%
“…With this method, the obtained rotordynamic coefficients are frequency independent [13,14]. The latest research results show that many annular seals possess frequency-dependent rotordynamic coefficients, including the labyrinth seal [16,17], pocket damper seal [17], hole-pattern seal [18,19], etc. Interaction between the acoustic waves in a circumferential annulus and the rotor excitation frequency is the cause of the frequency dependency [20].…”
The elliptical orbit whirl model is widely used to identify the frequency-dependent rotordynamic coefficients of annular seals. The existing solution technique of an elliptical orbit whirl model is the transient computational fluid dynamics (CFD) method. Its computational time is very long. For rapid computation, this paper proposes the orbit decomposition method. The elliptical whirl orbit is decomposed into the forward and backward circular whirl orbits. Under small perturbation circumstances, the fluid-induced forces of the elliptical orbit model can be obtained by the linear superposition of the fluid-induced forces arising from the two decomposed circular orbit models. Due to that the fluid-induced forces of circular orbit, the model can be calculated with the steady CFD method, and the transient computations can be replaced with steady ones when calculating the elliptical orbit whirl model. The computational time is significantly reduced. To validate the present method, its rotordynamic results are compared with those of the transient CFD method and experimental data. Comparisons show that the present method can accurately calculate the rotordynamic coefficients. Elliptical orbit parameter analysis reveals that the present method is valid when the whirl amplitude is less than 20% of seal clearance. The effect of ellipticity on rotordynamic coefficients can be ignored.
“…Relative to the labyrinth seal, the stator surface of this seal has larger roughness and bigger damping coefficient, which contribute to reduce circumferential flow velocity in the seal, decrease seal cross stiffness, and improve rotor system stability. At present, existing damping seals include honeycomb seal [14,15], hole-pattern seal [16], and pocket damper seal [17].…”
Air-induced force generated in seals is one key factor on the stability of the rotor system. In this paper, a novel negative dislocated seal (NDS) was developed in respect of dislocated bearing theory, to reduce hydrodynamic pressure effect and air-induced force and improve rotor stability as well. A test rig was built to test rotordynamic characteristics and rotor stability of the NDS. The rotordynamic characteristics of seals were investigated based on the unbalanced synchronous excitation method, and seal-rotor system stability was evaluated by the identification method with an electromagnetic bearing exciter. The effects of both rotating speed and inlet/outlet pressure ratio on the rotordynamic characteristics and rotor stability of both NDS and conventional cylindrical labyrinth seal were experimentally investigated. The results show that with the increasing rotating speed, inlet/outlet pressure ratio is promising to reduce the direct stiffness coefficients of seals and the logarithmic decrement rate of seal-rotor system and enhance both cross stiffness and damping coefficient as well. Besides, the developed NDS effectively reduces cross-stiffness coefficients and increases direct damping coefficients and the logarithmic decrement rate of the seal-rotor system, relative to the conventional cylindrical seal. The proposed seal can effectively improve seal stability of turbomachinery.
“…The above experimental and numerical results of rotordynamic coefficients for the labyrinth seal are all assumed to be frequency-independent. However, the latest test results of Ertas et al 22 and Vannini et al 23 have demonstrated that the labyrinth seal possesses strongly frequency-dependent rotordynamic coefficients, especially for the direct stiffness and effective damping coefficients. The numerical results presented by Thorat and Childs 24 show frequency dependence of stiffness and damping coefficients of labyrinth seals when rotor speed approaching to Mach 1.…”
Numerical results of frequency-dependent rotordynamic force coefficients and leakage flow rates are presented and compared with three types of labyrinth gas seals, which include a tooth-on-stator (TOS) labyrinth seal, a tooth-on-rotor (TOR) labyrinth seal, and an interlocking-tooth (INT) labyrinth seal. These three labyrinth seals represent the typical labyrinth seal designs used in rotating machinery as shaft seals to limit leakage and ensure a robust rotordynamic design. The three labyrinth seals have the identical rotor diameter, sealing clearance, tooth number, and profile. Using a proposed transient computational fluid dynamics (CFD) method based on the multi-frequency elliptical orbit whirling model, transient CFD solutions were conducted at rotational speed of 7000 r/min, inlet pressure of 6.9 bar, ambient out pressure, and three inlet preswirl ratios up to 1.0. The accuracy and availability of the present transient CFD method were demonstrated with the experiment data of frequency-dependent rotordynamic coefficients of the TOS labyrinth seal with different rotational speeds and inlet preswirl ratios. The rotordynamic coefficients were generally well-predicted by the present numerical method, with direct stiffness and direct damping modestly under predicted ($67% and $34%, respectively). Numerical results compared leakage flow rates and rotordynamic coefficients for three labyrinth seals, while paying special attention to the cross-coupling stiffness, effective damping, crossover frequency, and swirl velocity development along the flow direction in seal. The INT and TOS labyrinth seals consistently leaks less than the TOR labyrinth seal across all preswirl ratios, respectively, by factors of 27% and 5%. The TOS labyrinth seal is relatively most stable, followed by the INT labyrinth seal and then the TOR labyrinth seal. The stability of labyrinth seals can be improved by reducing the swirl velocity at the seal entrance (installing anti-swirl devices) and in the seal cavity (applying ''textured'' or ''pocket'' stator surfaces).
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