15 research outputs found
A high-order semi-explicit discontinuous Galerkin solver for 3D incompressible flow with application to DNS and LES of turbulent channel flow
We present an efficient discontinuous Galerkin scheme for simulation of the
incompressible Navier-Stokes equations including laminar and turbulent flow. We
consider a semi-explicit high-order velocity-correction method for time
integration as well as nodal equal-order discretizations for velocity and
pressure. The non-linear convective term is treated explicitly while a linear
system is solved for the pressure Poisson equation and the viscous term. The
key feature of our solver is a consistent penalty term reducing the local
divergence error in order to overcome recently reported instabilities in
spatially under-resolved high-Reynolds-number flows as well as small time
steps. This penalty method is similar to the grad-div stabilization widely used
in continuous finite elements. We further review and compare our method to
several other techniques recently proposed in literature to stabilize the
method for such flow configurations. The solver is specifically designed for
large-scale computations through matrix-free linear solvers including efficient
preconditioning strategies and tensor-product elements, which have allowed us
to scale this code up to 34.4 billion degrees of freedom and 147,456 CPU cores.
We validate our code and demonstrate optimal convergence rates with laminar
flows present in a vortex problem and flow past a cylinder and show
applicability of our solver to direct numerical simulation as well as implicit
large-eddy simulation of turbulent channel flow at as well as
.Comment: 28 pages, in preparation for submission to Journal of Computational
Physic
Improvement of finite element spot weld models for structural dynamics
The ACM 2 spot weld model is the currently most widely used spot weld model in industry. It is designed to be tuned using parameters to represent the stiffness characteristics of a spot weld in a suitable way. The choice of these parameters is however often associated with uncertainties. Therefore, the set of parameters with best performance is determined by employing an updating algorithm. Further, the result is compared to a new category of models, the so called Spider models, which intend to overcome mesh dependence in the spot weld area by re-meshing the structures locally. The results are formulated as guidelines for the optimum implementation of these spot weld models for structural dynamics. The studies are performed using two cut-out parts from a Volvo FH truck cabin. In addition, a new analytical approach for updating material data of isotropic shell structures is derived and the equations are verified using the same test pieces
Wall modeling via function enrichment within a high-order DG method for RANS simulations of incompressible flow
We present a novel approach to wall modeling for RANS within the
discontinuous Galerkin method. Wall functions are not used to prescribe
boundary conditions as usual but they are built into the function space of the
numerical method as a local enrichment, in addition to the standard polynomial
component. The Galerkin method then automatically finds the optimal solution
among all shape functions available. This idea is fully consistent and gives
the wall model vast flexibility in separated boundary layers or high adverse
pressure gradients. The wall model is implemented in a high-order discontinuous
Galerkin solver for incompressible flow complemented by the Spalart-Allmaras
closure model. As benchmark examples we present turbulent channel flow starting
from and up to as well as flow past
periodic hills at Reynolds numbers based on the hill height of
and