Abstract
Three-dimensional vortex dynamics in the wake behind a flat plate at 20○ angle of attack are explored by means of the Hilbert–Huang transform. While a completely regular vortex shedding is observed at Reynolds number Re = 500 with a distinct shedding frequency and only a single subharmonic frequency, a complex shedding behavior is observed at Re = 525 and above. The low-frequency variations of the energy content and frequency in time are deduced from the Hilbert spectra. The low-frequency modulations along the span of the plate are substantially increased from Re = 525 to Re = 800. The mean marginal spectra reveal that the energy in the low-frequency band increases with increasing Re. A corresponding reduction of the energy content in the high-frequency band is observed at the highest Reynolds number.
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Abbreviations
- A(T):
-
Correlation function
- A i (t):
-
Instantaneous amplitude of each IMF (intrinsic mode functions) component
- C i (t):
-
ith Intrinsic mode functions component
- \({\tilde {C}_i (t)}\) :
-
Hilbert transforms of the ith intrinsic mode function component
- \({\mathbb{C}_i \left(t\right)}\) :
-
Complex analytic signal
- d :
-
Flat plate width (m)
- e max (t):
-
Upper envelope for a given time series
- e min (t):
-
Lower envelope for a given time series
- E j :
-
Local energy of the different frequency bands
- E :
-
Total energy
- f :
-
Frequency (1/s)
- h ij (t):
-
The ith intrinsic mode function component after j times sifting process
- H j :
-
Relative energy distribution of the different frequency bands
- H (ω, t):
-
Hilbert spectrum
- h (ω):
-
Marginal spectrum
- IE (t):
-
Instantaneous energy
- m i (t):
-
Mean of the upper envelope and the lower envelope
- r i (t):
-
Residual obtained by separating the intrinsic mode functions from the original data
- Re :
-
Reynolds number
- RP:
-
Real part
- SD:
-
The standard deviation defined by two successive sifting processes
- t :
-
Running time (s)
- T :
-
Time lag (s)
- u′:
-
Velocity fluctuations (m/s)
- U 0 :
-
Uniform bulk velocity (m/s)
- τ :
-
Total length of data analyzed
- ν :
-
Kinematic viscosity (m2/s)
- φ i (t):
-
Instantaneous phase
- ω i (t):
-
Instantaneous frequency
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Yang, D., Pettersen, B., Andersson, H.I. et al. Analysis of vortex splitting characteristics in the wake of an inclined flat plate using Hilbert–Huang transform. Acta Mech 226, 1085–1104 (2015). https://doi.org/10.1007/s00707-014-1222-1
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DOI: https://doi.org/10.1007/s00707-014-1222-1