8,830 research outputs found
The study on adaptive Cartesian grid methods for compressible flow and their applications
This research is mainly focused on the development of the adaptive Cartesian grid methods for compressibl  e
flow. At first, the ghost cell method and its applications for inviscid compressible flow on adaptive tree Cartesian
grid are developed. The proposed method is successfully used to evaluate various inviscid compressible flows
around complex bodies. The mass conservation of the method is also studied by numerical analysis. The
extension to three-dimensional flow is presented.
Then, an h-adaptive Runge–Kutta discontinuous Galerkin (RKDG) method is presented in detail for the
development of high accuracy numerical method under Cartesian grid. This method combined with the ghost
cell immersed boundary method is also validated by well documented test problems involving both steady and
unsteady compressible flows over complex bodies in a wide range of Mach numbers. In addition, in order to
suppress the failure of preserving positivity of density or pressure, which may cause blow-ups of the high order
numerical algorithms, a positivity-preserving limiter technique coupled with h-adaptive RKDG method is
developed. Such a method has been successfully implemented to study flows with the large Mach number,
strong shock/obstacle interactions and shock diffraction.
The extension of the method to viscous flow under the adaptive Cartesian grid with hybrid overlapping bodyfitted
grid is developed. The method is validated by benchmark problems and has been successfully
implemented to study airfoil with ice accretion.
Finally, based on an open source code, the detached eddy simulation (DES) is developed for massive separation flow, and it is used to perform the research on aerodynamic performance analysis over the wing with ice
accretion
Computing the force distribution on the surface of complex, deforming geometries using vortex methods and Brinkman penalization
The distribution of forces on the surface of complex, deforming geometries is
an invaluable output of flow simulations. One particular example of such
geometries involves self-propelled swimmers. Surface forces can provide
significant information about the flow field sensed by the swimmers, and are
difficult to obtain experimentally. At the same time, simulations of flow
around complex, deforming shapes can be computationally prohibitive when
body-fitted grids are used. Alternatively, such simulations may employ
penalization techniques. Penalization methods rely on simple Cartesian grids to
discretize the governing equations, which are enhanced by a penalty term to
account for the boundary conditions. They have been shown to provide a robust
estimation of mean quantities, such as drag and propulsion velocity, but the
computation of surface force distribution remains a challenge. We present a
method for determining flow- induced forces on the surface of both rigid and
deforming bodies, in simulations using re-meshed vortex methods and Brinkman
penalization. The pressure field is recovered from the velocity by solving a
Poisson's equation using the Green's function approach, augmented with a fast
multipole expansion and a tree- code algorithm. The viscous forces are
determined by evaluating the strain-rate tensor on the surface of deforming
bodies, and on a 'lifted' surface in simulations involving rigid objects. We
present results for benchmark flows demonstrating that we can obtain an
accurate distribution of flow-induced surface-forces. The capabilities of our
method are demonstrated using simulations of self-propelled swimmers, where we
obtain the pressure and shear distribution on their deforming surfaces
Downstream and soaring interfaces and vortices in 2-D stratified wakes and their impact on transport of contaminants
The flow of continuously stratified fluids past obstacles was studied analytically, numerically, and experimentally. The obstacles discussed here include a flat strip, aligned with the flow, inclined or transverse to the flow and a horizontal cylinder. In the flow pattern, transient and attached (lee) internal waves, downstream wakes with submerged interfaces and vortices, soaring singular interfaces, soaring vortices and vortex systems are distinguished. New components of laminar flow past a horizontally towed strip are presented. Fine transverse streaky structures on the strip in the downstream wake were visualized. Soaring isolated interfaces, which are internal boundary layers forming inside the downstream attached wave field past bluff bodies were observed. With increasing of the body velocity a vortex pair was formed directly at the leading edge of this interface
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