AuthorElaine Bohr
TitleInflow Generation Technique for Large Eddy Simulation of Turbulent Boundary Layers
SchoolSchool of Engineering
InstitutionRensselaer Polytechnic Institute

When simulating turbulent flows using Large-Eddy Simulations (LES) or Direct Numerical Simulations (DNS), imposing correct instantaneous flow quantities at the inflow boundary is a challenge. Indeed, inflow fluctuations need to preserve the turbulent characteristics of the upstream flow that is not simulated. In this thesis, the rescaling recycling method for imposing boundary conditions at the inflow of turbulent boundary layer simulations is developed. The inflow conditions are rendered more physically meaningful by rescaling the instantaneous solution from an internal plane normal to the wall located inside the computational domain using self-similarity of the boundary layer velocity profile at each time step of the simulation. Thus the fluctuations at the inflow incorporate correct turbulent structures. This operation enables a reduction of the needed computational domain.

In addition, the rescaling recycling method was implemented in a finite element software using unstructured meshes to expand its application to curved domains (pipes, contracting or expanding nozzles). The important issue when using unstructured meshes is that the recycle plane from which the solution is rescaled is virtual and as such the solution must first be interpolated on that plane before the method can be applied.

In this thesis, the LES solutions are presented for zero pressure gradient flat plate turbulent boundary layer using two different scaling laws. First the scaling law developed by Lund, Wu and Squires (LWS) is used. An alternative scaling is also developed based on the theory by George and Castillo that incorporates the local Reynolds number dependence. It was found that the alternative scaling gives statistically similar flow profiles to those obtained by the LWS scaling, but the Reynolds number based on momentum thickness was 3% higher. The numerical results were found to be in good agreement with experimental data.

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