Similarity and decay laws of momentumless wakes

1980 ◽  
Vol 23 (2) ◽  
pp. 404 ◽  
Author(s):  
Samuel Hassid
Keyword(s):  
Momentumless Wakes

Contribution to the theory of laminar momentumless wakes

1986 ◽  
Vol 21 (2) ◽  
pp. 195-199 ◽  
Author(s):  
V. I. Korobko ◽  
V. K. Shashmin ◽  
Z. P. Shul'man
Keyword(s):  
Momentumless Wakes

Stability of momentumless wakes

2016 ◽  
Vol 808 ◽  
pp. 316-336 ◽  
Author(s):  
M. Rizqie Arbie ◽  
Uwe Ehrenstein ◽  
Christophe Eloy
Keyword(s):  
Base Flow ◽  
Navier Stokes ◽  
Upstream Region ◽  
Propulsion Efficiency ◽  
Aquatic Locomotion ◽  
Moderate Reynolds Number ◽  
Oseen Approximation ◽  
The Stability ◽  
Momentumless Wake ◽  
Momentumless Wakes

The caudal fin of swimming animals can be modelled as a thrust-producing flapping foil. When considered alone, such a foil produces on average a jet wake with a positive net momentum. It has been argued that the instability characteristics of these averaged wakes are linked to the propulsion efficiency of swimming animals. Here, we reconsider this question by taking into account both the thrust and the drag exerted on a self-propelled swimming body. To do so, we study the stability of a family of momentumless wakes, constructed as the Oseen approximation of a force doublet moving at constant velocity. By performing a local stability analysis, we first show that these wakes undergo a transition from absolute to convective instability. Then, using the time stepper approach by integrating the linearised Navier–Stokes system, we investigate the global stability and reveal the influence of a non-parallel base flow as well as the role of the locally absolutely unstable upstream region in the wake. Finally, to complete the global scenario, we address the nonlinear evolution of the wake disturbance. These results are then discussed in the context of aquatic locomotion. According to the present stability results, and assuming the Oseen approximation whose validity has been assessed only for moderate Reynolds number, the momentumless wake of aquatic animals is generally stable, whereas the corresponding thrust part is unstable. It is therefore essential to consider all forces exerted on a self-propelled animal when discussing its wake stability and its propulsion efficiency.

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