CFD Based Impeller Rotordynamic Force Coefficients

TRC CONTINUATION PROPOSAL 2014- 2015
CFD Based Centrifugal Pump/Compressor Rotordynamic Force Coefficients
by Dr. Palazzolo [email protected] and Mr. Eunseok Kim
INTRODUCTION AND JUSTIFICATION
API 617 level-II analysis requires detailed computed rotordynamic coefficients if level-I criteria fails.
Thus, calculating more accurate rotordynamic coefficients is crucial to analyze rotordynamic stability.
In the proposed work, CFD approach will be utilized to develop stand-alone code to evaluate
impedances caused by whirling of a shrouded impeller of a Centrifugal Pump/Compressor and the
corresponding stiffness, damping and inertia coefficients associated with translation and tilt motions.
DELIVERABLES
(a) Detailed Worked Examples on transient analysis of impeller and various perturbation
models utilizing commercial CFD software, ANSYS CFX.
(b) Parametric study for effect of dynamic eccentricity and misalignment.
(c) With EXCEL based GUI, stand-alone Matlab code for evaluating the rotordynamic
coefficients of Seal and Centrifugal Pump/Compressor impeller problems
(d) Modified XLTRC2 that utilizes general impedance curves for stability and imbalance
response predictions
COSTS
1 PhD Student, 12 months $2,200/mo. Salary, $197/mo. Insurance,
0.6% Fringe on salary, approx. $9000 Tuition and Fees., Supplies $1, 000
Total: $39,000
STATUS OF CURRENT WORK
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A full set of rotordynamic coefficients for a pump impeller were successfully
determined and analyzed to explain the influence of coupled motion(cylindrical and
conical) on the rotordynamic stability of the shrouded pump impeller problem.
Curve-fit approach has been developed to calculate a more accurate description of
impeller forces than the standard dynamic coefficient model
PROPOSED WORK
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Determine rotordynamic coefficients for dynamic and static perturbation with transient
analysis with mesh deformation
Determine effect of translational and rotational whirl amplitudes and parallel and tilt static
eccentricity on dynamic coefficients
Develop an alternative approach to the Wachel kxy formula in API617
Develop user friendly TRC software to determine translational and rotational mass, damping
and stiffness coefficients for a centrifugal impeller utilizing a CFD based approach. This will
be accomplished in a graduated manner by first using the generic CFD code CFX and then
developing a stand-alone code The model includes the primary and secondary (leakage) flow
paths, inlet region, swirl brakes and outlet region (diffuser)
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DISCUSSION
(1) Transient analysis for rotordynamic problems
Force Impedance for oscillation in y-direction at 200Hz
x 10
y(m)
1
0
-1
-2
0
50
100
150
200
250
Timestep #
300
350
400
450
0
50
100
150
200
250
Timestep #
300
350
400
450
400
200
y
F (N)
Frequency-dependent rotordynamic coefficients can be calculated by
constructing a virtual experiment model in the CFD code CFX. This
can be done by employing a transient analysis. In addition, the
transient analysis facilitates to model a static eccentricity problem
with elliptical orbit. This approach will be applied on the centrifugal
pump/ compressor impeller problem.
-5
2
0
-200
-400
(2) Effect of Static eccentricity
Calculating the impedance forces and dynamic coefficients are
crucial because the stability of a centrifugal pump/compressor is
highly influenced by those parameters. Past studies on the shrouded
impeller have been focused on the effect of the centered whirling
motion. We will evaluate the influences of the dynamic eccentricity
with misalignment of the rotor.
(3) Effect of dynamic eccentricity and tilting
Tilting would typically occur in a pump/compressor due to the
classical rotor bending line. Through tilting, the pressure distribution
along the impeller shroud is changed, causing mainly the
rotordynamic coefficients to be influenced. The results will be
analyzed and compared with a full set of coefficients for tilting and
lateral displacement.
(3) Developing Stand-alone code
To determine the rotordynamic coefficients utilizing commercial software, generating mesh, set up
domains and boundary conditions, and post processing for calculating need user’s a lot of efforts.
Thus, developing stand-alone code including, 3D mesh generator, solver, post processor is proposed
to facilitate these complicated procedures. Pre and Post Processor codes utilized with CFX will be
completed in May 2015. Completely stand – alone code (CFX not required) to be completed by May
2016.
RELATED REFERENCES
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J. J. Moore, A. B. Palazzolo, 2001, “ Rotordynamic Force Prediction of Whirling
Centrifugal Impeller Shroud Passages Using Computational Fluid Dynamic Techniques”,
ASME Journal of Engineering for Gas Turbines and Power, Vol. 123, pp 910-918.
CHILDS, D., 1989, “Fluid-Structure Interaction Forces at Pump-Impeller-Shroud
Surfaces for Rotordynamic Calculations”, ASME Journal of Vibration Acoustics Stress
and Reliability in Design, Vol 111, pp 216-225.
Chochua, Gocha., Soulas, A. Thomas., “Numerical Modeling of Rotordynamic
Coefficients for deliberately Roughened Stator Gas Annular Seals. “ ASME Journal of
Tribology, Vol. 129, April 2007, pp 424-429.
J. Jeffery Moore, David L. Ransom, Flavia Viana, “Rotordynamic Force Prediction of
Centrifugal Compressor Impellers Using Computational Fluid Dynamics” ASME
Journal of Engineering for Gas Turbine and Power, Vol. 133, 042504
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