Please click on one of the items to get more info.
close
close
Numerical tools for the simulation of helical vortices
In the framework of a collaboration between LIMSI (CNRS) and the d'Alembert lab (Sorbonne Université), significant advances in the numerical simulation of helical vortex systems have been done. This kind of flow is encountered in rotor wakes such as propeller, helicopter, wind turbine wakes...
Experiment by Leweke et al. (IRPHE, Marseilles)
Helical rotor-wake vortices
Whether operating in propulsive mode such as in marine and aircraft propellers or helicopters, or in energy-production mode as in wind and water turbines, rotor blades produce multiple helical vortices in their wake, strongly linked to the interacting forces between the blades and the surrounding fluid.
Why study them?
In helicopters, these vortices sometimes cause the dramatic VRS (vortex ring state) in descent flight, causing the lift to strongly decrease and potentially leading to a crash. In wind farms, the dynamics of these vortices is of great interest as they influence power generation, particularly when the wind blows parallel to a direction of aligned wind turbines and thus brings the vortex wake from one turbine onto the next one.
Improved modelling
In the framework of the LIMSI-d'Alembert collaboration, several numerical codes have been implemented. In order to gain some fundamental knowledge on such complex three-dimensional situations, we have incorporated the locally helical nature of the flow into the numerical solvers. Only one plane is being simulated, the neighbouring ones being deduced by screw symmetry. There is a gain of memory and CPU time, and we can thus reach higher Reynolds numbers. In some cases, this also allows to filter out some instabilities that would prevent a simulation of long times dynamics.
Many results and perspectives
We could characterize the aging of a helical vortex, for which there is no analytical model available, as a function of the helical pitch. We were also able to study the interaction between two or three vortices, to describe several scenarii for their merging together. We also characterized large wavelength instability modes that grow in such systems. The investigation of short wavelength modes (elliptic and curvature instabilities), hitherto inaccessible numerically and experimentally, is currently under progress.
More on this topic...
- I. Delbende, M. Rossi, O. Daube, DNS of flows with helical symmetry, Theoretical and Computational Fluid Dynamics, 2012, vol. 26, n°1, 141-160, DOI : 10.1007/s00162-011-0241-y
- I. Delbende, M. Rossi, B. Piton, Direct numerical simulation of helical vortices, International Journal of Engineering Systems Modelling and Simulation, 2012, vol. 4, n°1/2, 94-101, DOI : 10.1504/IJESMS.2012.044847
- I. Delbende, B. Piton, M. Rossi, Merging of two helical vortices, European Journal of Mechanics - B/Fluids, 2015, vol. 49, 363-372, DOI : 10.1016/j.euromechflu.2014.04.005
- C. Selcuk, I. Delbende, M. Rossi, Helical vortices: Quasiequilibrium states and their time evolution, Physical Review Fluids, 2017, 2, 084701, URL : https://link.aps.org/doi/10.1103/PhysRevFluids.2.084701, DOI : 10.1103/PhysRevFluids.2.084701
- C. Selcuk, I. Delbende, M. Rossi, Helical vortices: linear stability analysis and nonlinear dynamics, Fluid Dynamics Research, 2018, 011411, URL : https://doi.org/10.1088/1873-7005/aa73e3, DOI : 10.1088/1873-7005/aa73e3
- I. Delbende, C. Selcuk, M. Rossi, Nonlinear dynamics of two helical vortices: a dynamical system approach, Physical Review Fluids, 2021, 6(8), 084701, DOI : 10.1103/PhysRevFluids.6.084701
