Simulation of Moving Objects on an Cartesian Mesh Using an Improved Alternating Direction Forcing Immersed Boundary Method

Lead Research Organisation: Imperial College London
Department Name: Dept of Aeronautics


The main aim of this PhD project is to develop an improved alternating direction forcing immersed boundary method (AFD IBM) for turbulence-resolving simulations of moving objects on a fixed Cartesian mesh. Most of the immersed boundary methods suffer from spurious force oscillations (SFOs) when moving boundaries are simulated. One of the main sources of SFOs has been identified as the velocity discontinuity that occurs at the immersed boundary interface. The proposed method is based on a cubic spline interpolation to obtain an artificial internal flow within the solid domain while ensuring the continuity of the velocity field at the wall of the solid object. Even though the proposed method is intended for moving objects, it also provides significant improvements for static objects. The ADF IBM will be implemented in the high-order, finite-difference flow solver Incompact3D, which is a powerful tool to simulate turbulent flows using the most powerful supercomputers in the world. Once the ADF IBM is implemented and validated, it will be used to study energy efficient swimming by multiple fish through deep reinforcement learning. By combining state-of-the-art turbulence-resolving simulations of the 3D Navier-Stokes equations with reinforcement learning, this project will demonstrate that fish can reduce their energy expenditure by harnessing turbulence.


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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509486/1 01/10/2016 31/03/2022
2091216 Studentship EP/N509486/1 01/10/2017 30/09/2021 Athanasios Emmanouil Giannenas
Description We developed an original method to simulate turbulent flows with moving objects immersed in the flow. This method will allow the study of the performance of vertical tidal turbines.
Exploitation Route All our methods are open source so the scientific community can use them. We are also open to collaborations. The details of the method are currently under review in a manuscript.
Sectors Aerospace, Defence and Marine,Energy

Description Immersed Boundary Method for moving objects 
Organisation University of Poitiers
Country France 
Sector Academic/University 
PI Contribution Contribution from Imperial: Numerical data and expertise in high-fidelity simulations
Collaborator Contribution Contribution from Poitiers: expertise in immersed boundary methods
Impact publication under review.
Start Year 2019
Title Incompact3d 
Description Incompact3d is a powerful high-order flow solver for academic research. Dedicated to Direct and Large Eddy Simulations (DNS/LES), it can combine the versatility of industrial codes with the accuracy of spectral codes. It scales with up to one million cores. The incompressible Navier-Stokes equations are discretized with finite-difference sixth-order schemes on a Cartesian mesh. Explicit or semi-implicit temporal schemes can be used for the time advancement depending on the flow configuration. To treat the incompressibility condition, a fractional step method requires to solve a Poisson equation. This equation is fully solved in spectral space via the use of relevant 3D Fast Fourier transforms(FFTs), allowing any kind of boundary conditions for the velocity field in each spatial direction. Using the concept of the modified wavenumber, the divergence free condition is ensured up to machine accuracy. The pressure field is staggered from the velocity field by half a mesh to avoid spurious oscillations. The modelling of a solid body inside the computational domain is performed with a customised Immersed Boundary Method. It is based on a direct forcing to ensure a no-slip boundary condition at the wall of the solid body while imposing non-zero velocities inside the solid body to avoid discontinuities on the velocity field. This customised IBM, fully compatible with the 2D domain decomposition and with a possible mesh refinement at the wall, is based on a 1D expansion of the velocity field from fluid regions into solid regions using Lagrange polynomials. To reach realistic Reynolds numbers, an implicit LES strategy can be implemented to solve the Navier-Stokes equations without any extra explicit modelling. In order to mimic a subgrid-scale model, artificial dissipation can be added via the viscous term thanks to the artificial dissipative features of the high-order compact schemes. 
Type Of Technology Software 
Year Produced 2019 
Open Source License? Yes  
Impact see list of publications