Abstract
Unsteady Reynolds-averaged Navier-Stokes (URANS) simulation has been conducted to investigate how the flow coefficient affects unsteady impeller loading. Simulations have been carried out at three flow coefficients — near stall, design, and near choke conditions — for a centrifugal compressor with a radial gap of 1.04. For computational efficiency, the unsteady simulation has been conducted for two impeller and diffuser passages via the Fourier transformation method. Unsteady loading is the largest at the near stall condition; second largest at the near choke condition; and smallest at the design condition. Relative to the design condition, the near stall condition shows lower minimum loading, and the near choke condition shows higher maximum loading. Thus, both off-design conditions result in higher unsteady loading than at the design condition. Such increases at off-design conditions stem from the variations in the pitch-wise static pressure at the diffuser vane inlet caused by the diffuser vane incidence.
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Abbreviations
- b :
-
Diffuser vane height, mm
- C :
-
Absolute velocity, m/s
- C p :
-
Static pressure coefficient
- DV :
-
Diffuser vane
- L DVPS :
-
Length of vane pressure side, mm
- L DVSS :
-
Length of vane suction side, mm
- N :
-
Shaft speed, RPM
- N D :
-
Diffuser vane number
- N I :
-
Impeller blade number
- P :
-
Pressure, Pa
- PS :
-
Pressure side
- P T :
-
Total pressure, Pa
- Q :
-
Volume flow rate, m3/sec
- r :
-
Radial coordinate (= radius)
- s :
-
Stream-wise coordinate (= chord-wise coordinate)
- SS :
-
Suction side
- T :
-
Diffuser vane passing period, sec
- t :
-
Time, sec
- T t :
-
Total temperature, K
- U tip :
-
Impeller tip speed, m/s
- W :
-
Relative velocity, m/s
- Z :
-
Axial coordinate
- α 4SS :
-
Diffuser vane angle, deg
- α DV :
-
Diffuser vane wedge angle, deg
- β b :
-
Impeller back-sweep angle at the exit, deg
- Y :
-
Specific heat ratio
- ∆P :
-
Loading (= PPS-PSS), Pa
- η c :
-
Isentropic efficiency
- θ :
-
Circumferential coordinate
- θ d :
-
Diffuser vane pitch, deg
- π tc :
-
Total pressure ratio
- ρ :
-
Density, kg/m3
- T tc :
-
Total temperature ratio
- φ :
-
Flow coefficient (= Q/(Ω r23))
- Ω :
-
Angular speed, rad/s
- 2 :
-
Impeller exit
- 4 :
-
Diffuser vane inlet
- 4M :
-
4M measurement location
- 8M :
-
8M measurement location
- max :
-
Maximum
- min :
-
Minimum
- -:
-
Time average
- ’:
-
Fluctuation
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Acknowledgments
Financial support from Hanwha Power Systems Co., Ltd. and the Seoul National University Institute of Advanced Machines and Design (SNU-IAMD) are gratefully acknowledged by the authors. The authors are also grateful to Dr. Hönen and the Institute of Jet Propulsion and Turbomachinery at RWTH Aachen, Germany, for making available the “Radiver” test data.
Parts of this paper have been presented at ASME Turbo Expo 2018 (GT2018-75584), entitled “Influence of flow coefficient on the unsteady impeller loading induced by the impeller-diffuser interaction”.
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Dongjae Kong is a Ph.D. student at the Department of Mechanical Engineering, Stanford University. He received his B.S. and M.S. in Mechanical Engineering from Seoul National University. Before joining Stanford University, he was a fulltime lecturer at the Department of Aerospace Engineering, Korea Air Force Academy. His research interest now covers thermochemistry, electrochemistry, and nanomaterials for energy applications.
Seung Jin Song is a Professor at the School of Mechanical and Aerospace Engineering, Seoul National University. He received S.M. and Sc.D. in Aeronautics and Astronautics from MIT. His current research interests include aerodynamics and fluid-structure interactions in turbomachinery, cavitation in rocket turbopumps, analysis of propulsion/power generation systems, and related areas of fluid mechanics.
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Kong, D., Song, S.J. Influence of flow coefficient on unsteady impeller loading induced by impeller-diffuser interaction. J Mech Sci Technol 36, 2403–2413 (2022). https://doi.org/10.1007/s12206-022-0423-0
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DOI: https://doi.org/10.1007/s12206-022-0423-0