1,720,995 research outputs found
Numerical simulation of flows with shocks through an unstructured shock-fitting solver
No full textA new floating shock-fitting technique featuring the explicit computation of shocks by means of the Rankine-Hugoniot relations has been implemented in an unstructured solver. This paper briefly illustrates the algorithmic features of this orginal technique and the results obtained in the computation of the hypersonic flow past a circular cylinder
RANS simulations of a junction flow
No full textThe ERCOFTAC junction flow is numerically simulated with both a structured and an unstructured RANS solver for incompressible flows. The structured code adopts a finite volume, cell-centered formulation while the unstructured code uses residual distribution schemes and a vertex centered storage of the unknowns. Two differential eddy viscosity models, based on local quantities, are considered in the computations: the one-equation Spalart Allmaras model and the two equations k-e model proposed by Lam and Bremhorst. The grid dependence of the numerical solutions is evaluated by means of a convergence analysis based on computation of the GCI and a code-to-code comparison. The numerical results provided by both turbulence models are compared with the experimental measurements of the pressure and velocity fields
Numerical simulation of shock/shock interactions with an unstructured shock-fitting technique
No full textA new shock-fitting technique has been recently proposed and implemented by
the authors in conjunction with an unstructured shock-capturing solver.
In the present paper, the attention is addressed towards
the computation of shock-shock interactions by means of
this novel computing technique.
Different computing approaches are considered and their performances
are assessed through the computation of a type IV shock-shock interaction
Comparative study of stagnation point anomalies by means of shock-capturing and shock-fitting unstructured codes
No full textThe two-dimensional, hypersonic (M?=17.605), laminar flow (Re?=376930) past the forebody of a circular cylinder has been simulated by means of a vertex-centred CFD code using linear triangular elements. Two different approaches have been used to simulate the strong detached bow shock: shock-capturing on anisotropically refined meshes and shock-fitting. Concerning the boundary layer mesh, the distribution of gridpoints has been kept constant, while three different connectivity patterns have been examined. When looking at wall quantities such as pressure, skin friction and heat transfer these appear to be more heavily affected by the boundary layer mesh than by the numerical model used to simulate the detached shock wave
A shock-fitting technique for 2D unstructured grids
No full textA new floating shock-fitting technique featuring the explicit computation of shocks by means of the Rankine-Hugoniot relations has been implemented on two-dimensional unstructured grids. This paper illustrates the algorithmic features of this original technique and the results obtained in the computation of the hypersonic flow past a circular cylinder and a steady Mach reflection. (C) 2008 Elsevier Ltd. All rights reserved
An unstructured Shock-Fitting solver for two-dimensional flows
No full textThe computation of flows with shocks by means of the shock-fitting technique
was proposed by Moretti since the late sixties and used
by several researchers in the seventies and eighties. In those years the use
of this technique along with numerical schemes based on
the quasi-linear equations allowed the accurate
computation of flows characterized by strong discontinues with limited
computational resources. In the nineties, however, the increased
computing power along with the availability of modern general-purpose codes based on the
integral conservation equations produced a loss of interest in the shock fitting
technique.
Despite the widespread use of shock-capturing codes, shock solutions obtained by means of
shock-capturing schemes are plagued by a number of problems pertaining to accuracy,
stability and, more in general, solution quality.
Despite the continuous efforts made over the last 20 years,
these shortcomings have not been completely overcome and
appear to be particulary severe when unstructured-grids are used.
The complex and difficult implementation of the floating shock-fitting
technique in structured-grid solvers has largely contributed to discourage the
interest in this type of technique. Indeed, the motion of the shocks
throughout the flow-field is obtained by means of floating shock gridpoints which
can appear and disappear. This requires the implementation of algorithms
which are un-natural in a structured grid setting.
As a matter of principle, the management of shock points appears to be simpler
within an unstructured grid context. Indeed, the addition, motion and cancellation of
shock points and the mesh modifications which are necessary in the
neighbourhood of the shock front are operations which are less problematic inside an
unstructured solver rather than in a structured one.
To our knowledge, only a few attempts have been made
to incorporate shock-fitting ideas within shock-capturing, unstructured-grid solvers. These
include the work by Van Rosendale , Parpia and Parikh,
Tr\'epanier and co-workers and, more recently, Hanel and co-workers.
In the present work, a new floating shock-fitting technique featuring the explicit computation of shocks
by means of the Rankine-Hugoniot relations has been implemented in an unstructured
solver based on Roe's fluctuation splitting schemes .
This original technique will be presented
along with some numerical simulations of two-dimensional flows characterized by a single strong shock and
by interacting shocks
Shock interaction computations on unstructured, two-dimensional grids using a shock-fitting technique
No full textA new shock-fitting technique has been recently proposed and implemented by the authors in conjunction with an unstructured shock-capturing solver. In the present paper, the attention is addressed towards the computation of shock-shock and shock-wall interactions by means of this novel computational technique. (C) 2011 Elsevier Inc. All rights reserved
Convergence analysis of shock-capturing and shock-fitting solutions on unstructured grids
No full textA new shock-fitting technique for unstructured two- and three-dimensional meshes has been recently proposed and developed by the authors. In the present paper, both global and local a posteriori grid-convergence analysis is used to quantitatively measure the discretization error and order of convergence of the numerical solutions obtained using this new unstructured shock-fitting technique. Specifically, the analysis has considered the numerical solutions of two different flows characterized by the presence of strong shocks: a transonic source flow and an hypersonic flow past a circular cylinder. It is shown that the shock-fitting technique allows to compute numerical solutions that converge, both pointwise and in a global sense, with an observed order of accuracy that is very close to the design order of the spatial discretization scheme and with very small discretization errors
A selfconsistent unstructured solver for weakly ionized gases
No full textA selfconsistent unstructured solver for weakly ionized gases modeling inviscid multi-species
conservation equations coupled with a reduced state-to-state kinetics model is presented.
Mathematical model have been implemented in EulFS, a CFD unstructured solver using Residual
Distribution Schemes, to discretize convective fluxes and chemical source terms.
A simple model which couples the weakly ionized gas with an electric field controlled by
considering a power supply and an external circuit resistence Rc is considered.
Preliminary results will be shown for an argon plasma considering different 2D and 3D
geometrical configurations
A mass-matrix formulation of unsteady fluctuation splitting schemes consistent with Roe's parameter vector
No full textA mass-matrix formulation of the fluctuation splitting schemes for solving compressible, unsteady flows is proposed. This formulation is consistent with the conservative linearisation based on parameter vector and allows to extend to unsteady flows the invariance under similarity transformations' property that had been shown to hold for the steady version of the schemes. Second-order time accuracy is achieved using a Petrov-Galerkin finite element interpretation of the fluctuation splitting schemes. The approach may however be readily applicable to all other time-accurate fluctuation splitting formulations that have been so far proposed in the literature. Applications of the proposed methodology to two- and three-dimensional, inviscid and viscous compressible flows are reported and discussed in the paper
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