Abstract
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.
Highlights
Annular seals are widely used in turbomachinery to control the leakage flow through rotor–stator clearances from high-pressure regions to low-pressure regions [1,2]
The present method cannot be used to identify the frequency-dependent rotordynamic coefficients according to Equation (6)
The orbit decomposition method based on small perturbation and linear superposition theory is proposed for the rapid identification of frequency-dependent rotordynamic coefficients for annular seals
Summary
Annular seals are widely used in turbomachinery to control the leakage flow through rotor–stator clearances from high-pressure regions to low-pressure regions [1,2]. The average values of variables are used force Ftθ is divided by the rotor whirl velocity Ωr to yield the direct damping C. The numerical accuracy of the bulk-flow model largely relies on these corrections [11,12 seal cavity is represented one control volume. When a large number of control volumes are employed to fill the seal flow domain, the analysis results tend to reach the real flow field This led to the development of the CFD method [13]. The elliptical orbit model is widely used to predict the frequency-dependent rotordynamic coefficients of annular seals [24,25,26]. As the fluid-induced forces of the circular orbit model can be calculated with the steady CFD method, the transient computations can be replaced with the steady ones in the solution process of the elliptical orbit whirl model. To study the effects of elliptical orbit parameters on the results of the present method, two major parameters are investigated, whirl amplitude and ellipticity
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