2,347 research outputs found
Calculation of two-dimensional turbulent flow fields
Navier-Stokes equation solutions for two- dimensional turbulent flow fields of compressible viscous flui
Hydrodynamic/acoustic splitting approach with flow-acoustic feedback for universal subsonic noise computation
A generalized approach to decompose the compressible Navier-Stokes equations
into an equivalent set of coupled equations for flow and acoustics is
introduced. As a significant extension to standard hydrodynamic/acoustic
splitting methods, the approach provides the essential coupling terms, which
account for the feedback from the acoustics to the flow. A unique simplified
version of the split equation system with feedback is derived that conforms to
the compressible Navier-Stokes equations in the subsonic flow regime, where the
feedback reduces to one additional term in the flow momentum equation. Subsonic
simulations are conducted for flow-acoustic feedback cases using a
scale-resolving run-time coupled hierarchical Cartesian mesh solver, which
operates with different explicit time step sizes for incompressible flow and
acoustics. The first simulation case focuses on the tone of a generic flute.
With the major flow-acoustic feedback term included, the simulation yields the
tone characteristics in agreement with reference results from K\"uhnelt based
on Lattice-Boltzmann simulation. On the contrary, the standard hybrid
hydrodynamic/acoustic method with the feedback-term switched off lacks the
proper tone. As the second simulation case, a thick plate in a duct is studied
at various low Mach numbers around the Parker-beta-mode resonance. The
simulations reveal the flow-acoustic feedback mechanism in very good agreement
with experimental data of Welsh et al. Simulations and theoretical
considerations reveal that the feedback term does not reduce the stable
convective flow based time step size of the flow equations.Comment: Submitted to Journal of Computational Physic
Turbulent jet simulation using high-order DG methods for aeroacoustics analysis
In this work, a high-order discontinuous Galerkin (DG) method is used to
perform a large-eddy simulation (LES) of a subsonic isothermal jet at high
Reynolds number Re D = 10^6 on a fully un-structured mesh. Its radiated
acoustic field is computed using the Ffowcs Williams and Hawkings formulation.
In order to assess the accuracy of the DG method, the simulation results are
compared to experimental measurements and a reference simulation based on a
finite volume method. The comparisons are made on the flow quantities (mean,
rms and spectra) and pressure far field (rms and spectra)
Numerical solution of the Navier-Stokes equations about three-dimensional configurations: A survey
The numerical solution of the Navier-Stokes equations about three-dimensional configurations is reviewed. Formulational and computational requirements for the various Navier-Stokes approaches are examined for typical problems including the viscous flow field solution about a complete aerospace vehicle. Recent computed results, with experimental comparisons when available, are presented to highlight the presentation. The future of Navier-Stokes applications in three-dimensions is seen to be rapidly expanding across a broad front including internal and external flows, and flows across the entire speed regime from incompressible to hypersonic applications. Prospects for the future are described and recommendations for areas of concentrated research are indicated
Improvement in Computational Fluid Dynamics Through Boundary Verification and Preconditioning
This thesis provides improvements to computational fluid dynamics accuracy and ef- ficiency through two main methods: a new boundary condition verification procedure and preconditioning techniques. First, a new verification approach that addresses boundary conditions was developed. In order to apply the verification approach to a large range of arbitrary boundary condi- tions, it was necessary to develop unifying mathematical formulation. A framework was developed that allows for the application of Dirichlet, Neumann, and extrapolation bound- ary condition, or in some cases the equations of motion directly. Verification of boundary condition techniques was performed using exact solutions from canonical fluid dynamic test cases. Second, to reduce computation time and improve accuracy, preconditioning algorithms were applied via artificial dissipation schemes. A new convective upwind and split pressure (CUSP) scheme was devised and was shown to be more effective than traditional precon- ditioning schemes in certain scenarios. The new scheme was compared with traditional schemes for unsteady flows for which both convective and acoustic effects dominated. Both boundary conditions and preconditioning algorithms were implemented in the context of a strand grid solver. While not the focus of this thesis, strand grids provide automatic viscous quality meshing and are suitable for moving mesh overset problems
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