Instabilities of flows in helical pipes

Disturbance modes and animations


 


mode

 e


Range of 

Mode characteristics

Perturbation animation

Flow animation

1

0.01

0≤l2.87


Antisymmetry-breaking

Dean vortices oscillate in counter phase

Zero pseudo streamline is strongly perturbed

An increase of through flow intensifies the Dean vortices, which slow down the through flow and consequently weaken by themselves

Perturbation_e=0p01_l=0.avi

Perturbation_e=0p01_l=2.avi

Flow_e=0p01_l=0.avi

Flow_e=0p01_l=2.avi

 

 

 

 

 

 

2

0.01

2.87l5


Perturbations are located inside

Perturbation_e=0p01_l=4.avi

Flow_e=0p01_l=4.avi

 

0.03

1.1≤l5

a weaker vortex and are advected

Perturbation_e=0p05_l=4.avi

Flow_e=0p05_l=4.avi

 

0.05

 1≤l5



along the streamlines

Perturbation_e=0p1_l=3p5.avi

Flow_e=0p1_l=3p5.avi

 

0.075

1.9≤l5


Zero pseudo streamline is strongly

 

 

 

0.1

2.8≤l5

 


perturbed

Instability of   boundary layer is assumed

 

 

3

0.03

 

0≤l1.1

Antisymmetry-preserving

Perturbation_e=0p03_l=0.avi

Flow_e=0p03_l=0.avi

 

0.05

 

0≤l1

Zero pseudo streamline is not perturbed

Perturbation_e=0p03_l=1.avi

Flow_e=0p03_l=1.avi

 

0.075

0.1

0≤l0.9

0≤l0.6

 


Dean vortices oscillate in phase and do not interact

Perturbation_e=0p05_l=0.avi

Perturbation_e=0p075_l=0.avi

Flow_e=0p05_l=0.avi

Flow_e=0p075_l=0.avi

 

 

 

Instability of   boundary layer is assumed

Perturbation_e=0p1_l=0.avi

Flow_e=0p1_l=0.avi

 

 

 

 

 

 

4

0.075

0.9≤l1.9


Small circumferential wavenumber

 

 

 

0.1

0.6≤l2.8


downstream cross-flow wave located inside

Perturbation_e=0p1_l=1p5.avi

Flow_e=0p1_l=1p5.avi

 

0.2

 

0.4≤l2.55

a weaker vortex

Zero pseudo streamline is strongly perturbed

Perturbation_e=0p2_l=1p5.avi

Flow_e=0p2_l=1p5.avi

5

0.1

0.2

0.3

0.4

4.2≤l5

 2.55≤l5

 2.6≤l2.88

 2.2≤l2.35


Large circumferential wavenumber

upstream cross-flow wave

Zero pseudo streamline, if exists, is strongly perturbed

Perturbation_e=0p1_l=4p5.avi

Perturbation_e=0p2_l=3.avi

Perturbation_e=0p2_l=4.avi

Perturbation_e=0p2_l=5.avi

Perturbation_e=0p3_l=2p7.avi

 Perturbation_e=0p4_l=2p3.avi

Flow_e=0p1_l=4p5.avi

Flow_e=0p2_l=3.avi

Flow_e=0p2_l=4.avi

Flow_e=0p2_l=5.avi

Flow_e=0p3_l=2p7.avi

Flow_e=0p4_l=2p3.avi

6

0.2

0≤l0.4


Antisymmetry-breaking

Perturbation_e=0p2_l=0.avi

Flow_e=0p2_l=0.avi

 

0.3

0≤l≤1.37


Dean vortices do not interact

Perturbation_e=0p3_l=0.avi

Flow_e=0p3_l=0.avi

 

0.4

0≤l0.7


Zero pseudo streamline is weakly perturbed

Perturbation_e=0p3_l=1.avi

Flow_e=0p3_l=1.avi

 

0.5

0≤l0.81


At larger  perturbations are located

Perturbation_e=0p4_l=0.avi

Flow_e=0p4_l=0.avi

 

0.6

0≤l0.3


inside a stronger vortex

An inviscid instability of through flow is assumed

Perturbation_e=0p5_l=0.avi

Perturbation_e=0p6_l=0.avi

Flow_e=0p5_l=0.avi

Flow_e=0p6_l=0.avi

 

 

 

 

 

 

7

0.3

2.9≤l5


The disturbance propagates upstream the mean through flow

Perturbation_e=0p3_l=4.avi

Flow_e=0p3_l=4.avi

 

0.4

0.5

0.6

 2.45≤l5

 2.05≤l5

1.75≤l5


Large circumferential wavenumber downstream cross-flow wave developing in a single Dean vortex flow

 

Perturbation_e=0p4_l=4.avi

Perturbation_e=0p5_l=4.avi

Perturbation_e=0p6_l=4.avi

 

Flow_e=0p4_l=4.avi

Flow_e=0p5_l=4.avi

Flow_e=0p6_l=4.avi

 

8

0.3

 1.37≤l2


Oscillations in the bulk of

Perturbation_e=0p3_l=1p55.avi

Flow_e=0p3_l=1p55.avi

 

0.4

1.33≤l1.7


the counter clockwise vortex that cause

Perturbation_e=0p4_l=1p4.avi

Flow_e=0p4_l=1p4.avi

 

 

 

oscillations in the whole flow.

 

 

 

 

 

Instability of a locally developing mixing layer is assumed

 

 

9

0.4

1.17≤l1.34


Small circumferential wavenumber

Perturbation_e=0p4_l=1p1.avi

Flow_e=0p4_l=1p1.avi

 

0.5

0.81≤l1.24


downstream cross-flow wave

Perturbation_e=0p5_l=1.avi

Flow_e=0p5_l=1.avi

 

0.6

 

0.57≤l1.2

Zero pseudo streamline is strongly perturbed

Instability of a locally developing mixing layer is assumed

Perturbation_e=0p6_l=0p6.avi

Flow_e=0p6_l=0p6.avi

10

0.3

 2≤l2.6


The disturbance propagates upstream the mean through flow

Perturbation_e=0p3_l=2p4.avi

Flow_e=0p3_l=2p4.avi

 

0.4

1.7l2.2

 


Large circumferential wavenumber downstream cross-flow wave

Perturbation_e=0p4_l=1p8.avi

Flow_e=0p4_l=1p8.avi

 

0.5

1.24l1.88

 


An inviscid instability of through flow is

Perturbation_e=0p5_l=1p5.avi

Flow_e=0p5_l=1p5.avi

 

0.6

1.2l≤1.6

 


assumed

Perturbation_e=0p6_l=1p3.avi

Flow_e=0p6_l=1p3.avi

11

0.4

2.27≤l2.45

s – independent (k=0)

 

 

 

0.5

1.88≤l2.05

large circumferential wavenumber

Perturbation_e=0p4_l=2p3_k=0.avi

Flow_ e=0p4_l=2p3_k=0.avi

 

0.6

1.6≤l1.75


downstream cross-flow wave

Perturbation_e=0p6_l=1p7_k=0.avi

Flow_ e=0p6_l=1p7_k=0.avi

 

 

 

Zero pseudo streamline is slightly perturbed

 

 

 

12

0.4

0.6

 0.7≤l1.16

0.47≤l≤0.55


large circumferential wavenumber upstream wave

Instability of a locally developing mixing layer is assumed

Zero pseudo streamline is slightly perturbed

Perturbation_e=0p4_l=1p1avi

Perturbation_e=0p6_l=0p5avi

Flow_ e=0p4_l=1p1.avi

Flow_ e=0p6_l=0p5.avi

 

 

 

 

 

 

 

13

0.6

0.3≤l0.47


Small circumferential wavenumber

Perturbation_e=0p6_l=0p4avi

Flow_ e=0p6_l=0p4.avi

 

 

 

downstream waves developing

 

 

 

 

 

in both vortices

 Instability of a locally developing mixing layer is assumed

 Zero pseudo streamline is strongly perturbed

 

 

 

 


 


 


 


 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


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