A vortex pair in ground effect, dynamics and optimal control

2019 ◽  
Vol 885 ◽  
Author(s):  
Arnold Wakim ◽  
Vincent Brion ◽  
Agnès Dolfi-Bouteyre ◽  
Laurent Jacquin

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Chao Xia ◽  
Xizhuang Shan ◽  
Zhigang Yang

The influence of ground effect on the wake of a high-speed train (HST) is investigated by an improved delayed detached-eddy simulation. Aerodynamic forces, the time-averaged and instantaneous flow structure of the wake are explored for both the stationary ground and the moving ground. It shows that the lift force of the trailing car is overestimated, and the fluctuation of the lift and side force is much greater under the stationary ground, especially for the side force. The coexistence of multiscale vortex structures can be observed in the wake along with vortex stretching and pairing. Furthermore, the out-of-phase vortex shedding and oscillation of the longitudinal vortex pair in the wake are identified for both ground configurations. However, the dominant Strouhal number of the vortex shedding for the stationary and moving ground is 0.196 and 0.111, respectively, due to the different vorticity accumulation beneath the train. A conceptual model is proposed to interpret the mechanism of the interaction between the longitudinal vortex pair and the ground. Under the stationary ground, the vortex pair embedded in a turbulent boundary layer causes more rapid diffusion of the vorticity, leading to more intensive oscillation of the longitudinal vortex pair.


1988 ◽  
Vol 108 (3-4) ◽  
pp. 269-290 ◽  
Author(s):  
G. R. Burton

SynopsisWe prove an existence theorem for a steady planar flow of an ideal fluid, containing a bounded symmetric pair of vortices, and approaching a uniform flow at infinity. The data prescribed are the rearrangement class of the vorticity field, and either the momentum impulse of the vortex pair, or the velocity of the vortex pair relative to the fluid at infinity. The stream function ψ for the flow satisfies the semilinear elliptic equationin a half-plane bounded by the line of symmetry, where φ is an increasing function that is unknown a priori. The results are proved by maximising the kinetic energy over all flows whose vorticity fields are rearrangements of a specified function.


2002 ◽  
Vol 1 (2) ◽  
pp. 97-114 ◽  
Author(s):  
S.S. Collis ◽  
K. Ghayour ◽  
M. Heinkenschloss

This paper presents an optimal control formulation and solution for an idealized Blade Vortex Interaction (BVI) problem. This problem consists of the interaction of an inviscid vortex pair with a circular cylinder in a steady Mach 0.3 uniform flow with wall-normal velocity used as control on the cylinder surface. This model problem captures the fundamental noise generation process of the BVI phenomena while mitigating many of the complexities of the full rotorcraft problem. The optimal control problem is solved using a gradient based method where gradient information is computed from a continuous adjoint analysis of the governing unsteady Euler equations. The BVI wave packet is targeted by defining an objective function that measures the square amplitude of pressure fluctuations in an observation region over a time interval of interest. When the observation region encloses the entire flow a 6 dB reduction in overall BVI noise is obtained. When the observation region is limited to the region of greatest BVI noise, a 13dB reduction is obtained. The optimal control, unlike most common mitigation methods, does not target the interaction directly — instead, the computed boundary control modulates the potential flow about the cylinder, producing a wave packet of the correct amplitude and phase to approximately cancel the BVI noise in the observation region.


Author(s):  
Gerhard-W. Weber

AbstractWe will study one-parameter families of differentiable optimal control problems given by:Here, at given times t the inequality constraint functions are of semi-infinite nature, the objective functional may also be of max-type. For each s ∈ ℝ the problem is equivalent to a one-parameter family (Ps (t))t∈[a,b] of differentiable optimization problems. From these the consideration of generalized critical trajectories, such as a local minimum trajectory, comes into our investigation. According to a concept introduced by Hettich, Jongen and Stein in optimization, we distinguish eight types of generalized critical trajectories. Under suitable continuity, compactness and integrability assumptions, those problems, which exclusively have generalized critical points being of one of these eight types, are generic. We study normal forms and characteristic examples, locally around these trajectories.Moreover, we indicate the related concept of structural stability of optimal control problems due to the topological behaviour of the lower level sets under small data perturbations. Finally, we discuss the numerical consequences of our investigations for pathfollowing techniques with jumps.


1983 ◽  
Vol 129 (-1) ◽  
pp. 409 ◽  
Author(s):  
A. J. Peace ◽  
N. Riley
Keyword(s):  

2020 ◽  
Vol 891 ◽  
Author(s):  
Peter J. Baddoo ◽  
Melike Kurt ◽  
Lorna J. Ayton ◽  
Keith W. Moored


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