6,168 research outputs found
Direct Numerical Simulation of Turbulent Katabatic Slope Flows with an Immersed-Boundary Method
We investigate a Cartesian-mesh immersed-boundary formulation within an incompressible flow solver to simulate laminar and turbulent katabatic slope flows. As a proof-of-concept study, we consider four different immersed-boundary reconstruction schemes for imposing a Neumann-type boundary condition on the buoyancy field. Prandtl’s laminar solution is used to demonstrate the second-order accuracy of the numerical solutions globally. Direct numerical simulation of a turbulent katabatic flow is then performed to investigate the applicability of the proposed schemes in the turbulent regime by analyzing both first- and second-order statistics of turbulence. First-order statistics show that turbulent katabatic flow simulations are noticeably sensitive to the specifics of the immersed-boundary formulation. We find that reconstruction schemes that work well in the laminar regime may not perform as well when applied to a turbulent regime. Our proposed immersed-boundary reconstruction scheme agrees closely with the terrain-fitted reference solutions in both flow regimes
Analysis of heating rates and forces on bodies subject to rocket exhaust plume impingement
Computer programs and engineering methods for calculating heating rates and forces in jet plume impingement problem
The tetrahedral finite cell method for fluids: Immersogeometric analysis of turbulent flow around complex geometries
We present a tetrahedral finite cell method for the simulation of incompressible flow around geometrically complex objects. The method immerses such objects into non-boundary-fitted meshes of tetrahedral finite elements and weakly enforces Dirichlet boundary conditions on the objects’ surfaces. Adaptively-refined quadrature rules faithfully capture the flow domain geometry in the discrete problem without modifying the non-boundary-fitted finite element mesh. A variational multiscale formulation provides accuracy and robustness in both laminar and turbulent flow conditions. We assess the accuracy of the method by analyzing the flow around an immersed sphere for a wide range of Reynolds numbers. We show that quantities of interest such as the drag coefficient, Strouhal number and pressure distribution over the sphere are in very good agreement with reference values obtained from standard boundary-fitted approaches. We place particular emphasis on studying the importance of the geometry resolution in intersected elements. Aligning with the immersogeometric concept, our results show that the faithful representation of the geometry in intersected elements is critical for accurate flow analysis. We demonstrate the potential of our proposed method for high-fidelity industrial scale simulations by performing an aerodynamic analysis of an agricultural tractor
Arbitrary Lagrangian-Eulerian form of flowfield dependent variation (ALE-FDV) method for moving boundary problems
Flowfield Dependent Variation (FDV) method is a mixed explicit-implicit numerical
scheme that was originally developed to solve complex flow problems through the use
of so-called implicitness parameters. These parameters determine the implicitness of
FDV method by evaluating local gradients of physical flow parameters, hence vary
across the computational domain. The method has been used successfully in solving
wide range of flow problems. However it has only been applied to problems where the
objects or obstacles are static relative to the flow. Since FDV method has been proved
to be able to solve many complex flow problems, there is a need to extend FDV
method into the application of moving boundary problems where an object
experiences motion and deformation in the flow. With the main objective to develop a
robust numerical scheme that is applicable for wide range of flow problems involving
moving boundaries, in this study, FDV method was combined with a body
interpolation technique called Arbitrary Lagrangian-Eulerian (ALE) method. The
ALE method is a technique that combines Lagrangian and Eulerian descriptions of a
continuum in one numerical scheme, which then enables a computational mesh to
follow the moving structures in an arbitrary movement while the fluid is still seen in a
Eulerian manner. The new scheme, which is named as ALE-FDV method, is
formulated using finite volume method in order to give flexibility in dealing with
complicated geometries and freedom of choice of either structured or unstructured
mesh. The method is found to be conditionally stable because its stability is dependent
on the FDV parameters. The formulation yields a sparse matrix that can be solved by
using any iterative algorithm. Several benchmark stationary and moving body
problems in one, two and three-dimensional inviscid and viscous flows have been
selected to validate the method. Good agreement with available experimental and
numerical results from the published literature has been obtained. This shows that the
ALE-FDV has great potential for solving a wide range of complex flow problems
involving moving bodies
Analysis of the trajectory, loads and heating experienced by a body passing through a supersonic flow field
Analytical methods for determination of trajectories, loads, and heating experienced by spacecraft passing through rocket exhaust fiel
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