Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Hybrid POD-FFT analysis of nonlinear evolving coherent structures of DNS
  wavepacket in laminar-turbulent transition   This paper concerns the study of direct numerical simulation (DNS) data of a
wavepacket in laminar turbulent transition in a Blasius boundary layer. The
decomposition of this wavepacket into a set of "modes" (a basis that spans an
approximate solution space) can be achieved in a wide variety of ways. Two
well-known tools are the fast Fourier transform (FFT) and the proper orthogonal
decomposition (POD). To synergize the strengths of both methods, a hybrid
POD-FFT is pioneered, using the FFT as a tool for interpreting the POD modes.
The POD-FFT automatically identifies well-known fundamental, subharmonic and
Klebanoff modes in the flow, even though it is blind to the underlying physics.
Moreover, the POD-FFT further separates the subharmonic content of the
wavepacket into three fairly distinct parts: a positively detuned mode
resembling a Lambda-vortex, a Craik-type tuned mode and a Herbert-type
positive-negative detuned mode pair, in decreasing order of energy. This
distinction is less widely recognized, but it provides a possible explanation
for the slightly positively detuned subharmonic mode often observed in previous
experiments and simulations.

5
The categories of this paper are: gr-qc
10
The categories of this paper are: q-bio
37
The categories of this paper are: supr-con
19
The categories of this paper are: eess
24
The categories of this paper are: dg-ga
21
The categories of this paper are: adap-org
0
The categories of this paper are: hep-ph
4
The categories of this paper are: cond-mat
7
The categories of this paper are: hep-th
28
The categories of this paper are: alg-geom
11
The categories of this paper are: hep-lat
22
The categories of this paper are: chao-dyn
20
The categories of this paper are: acc-phys
30
The categories of this paper are: q-alg
26
The categories of this paper are: bayes-an
13
The categories of this paper are: quant-ph