Araz Banaeizadeh

Compressible Scalar Filtered Mass Density Function Model for High-Speed Turbulent Flows

The scalar filtered mass density function model is further extended and employed for large-eddy simulations of high-speed turbulent mixing and reacting flows. The model is implemented through a hybrid mathematical/ computationalmethodology. In thismethodology, the filtered compressible Navier–Stokes equations in a curvilinear coordinate system are solved with a generalized, high-order, multiblock, finite difference scheme for the turbulent velocity and pressure. However, the scalar mixing and combustion are computed with the compressible scalar filteredmass density function. The pressure effect in the energy equation, as needed in high-speedflows, is included in the filtered mass density function formulation. The new compressible large-eddy simulation/filtered mass density function model is used for the simulations of flows in a rapid compression machine, in a shock tube and in a supersonic coaxial jet. The numerical results indicate that the model is able to correctly capture the scalar mixing in compressible subsonic and supersonic turbulent flows.

Parallel Computation of a Mixed Convection Problem Using Fully-Coupled and Segregated Algorithms

In this work, parallel solution of the Navier-Stokes equations for a mixed convection heat problem is achieved using a finite-element-based finite-volume method in fully coupled and semi coupled algorithms. A major drawback with the implicit methods is the need for solving the huge set of linear algebraic equations in large scale problems. The current parallel computation is developed on distributed memory machines. The matrix decomposition and solution are carried out using PETSc library. In the fully coupled algorithm, there is a 36-diagonal global matrix for the two-dimensional governing equations. In order to reduce the computational time, the matrix is suitably broken in several sub-matrices and they are subsequently solved in a segregated manner. This approach results in four 9-diagonal matrices. Different sparse solver algorithms are utilized to solve a mixed natural-forced convection problem using either fully-coupled or semi-coupled algorithms. The performance of the solvers are then investigated in solving on a distributed computing environment. The study shows that the iteration run time considerably decreases although the overall run time of the fully coupled algorithm still looks better.© 2004 ASME

Large eddy simulations of turbulent flows in ic engines

A new computational methodology is developed and tested for large eddy simulation (LES) of turbulent flows in internal combustion (IC) engines. In this methodology, the filtered compressible Navier-Stokes equations in curvilinear coordinate systems are solved via a generalized, high-order, multi-block, compact differencing scheme and various subgrid-scale (SGS) stress closures. Both reacting and nonreacting flows with and without spray are considered. The LES models have been applied to a piston-cylinder assembly with a stationary open valve and harmonically moving flat piston. The flow in a direct-injection spark-ignition (DISI) engine is also considered. It is observed that during the intake stroke of the engine operation, large-scale unsteady turbulent flow motions are developed behind the intake valves. The physical features of these turbulent motions and the ability of LES to capture them are studied and tested by simulating the flow in a simple configuration involving a stationary valve. The flow statistics predicted by LES are shown to compare well with the available experimental data. The DISI configuration includes all the complexities involved in a realistic single-cylinder IC engine, such as the complex geometry, moving valves, moving piston, spray and combustion. The spray combustion is simulated with the recently developed two-phase filtered mass density (FMDF) model.Copyright

Implicit Finite Volume Method to Simulate Reacting Flow

In this work, an efficient bi-implicit strategy is suitably developed within the context of a finite volume element approach in order to solve turbulent reactive flow governing equations. Based on the essence of control-volume-based finite-element methods, the formulation retains the geometrical flexibility of the pure finite element methods while derives the discrete alj;ebraic governing equations through using the conservation balance applied to discrete control volumes distributed all over the solution domain. The physical influence upwindinc scheme is used to approximate the advection fluxes at all cell faces. While respecting the physics of flow, this scheme also provides the necessary coupling of velocity and pressure fields. The two-equation I;-€ turbulence model and one step mixture fraction chemistry equation are simultaneously solved in a semi-coupled manner in order to achieve a better prediction of both the transport of turbulent species and the transport of mass fraction specie::. The validation of the current numerical results is fulfilled by comparing them with explerimental data and other available numerical results.

Large Eddy Simulation of Turbulent Combustion via Filtered Mass Density Function

This paper provides a brief review of the scalar filtered mass density function (FMDF) model. The FMDF is a subgrid-scale probability density function (PDF) model for large eddy simulation (LES) of turbulent combustion and is obtained by the solution of a set of stochastic differential equations by a Lagrangian Monte Carlo method. The applicability and the validity of the LES/FMDF are established by simulating various low and high speed, single- and two-phase turbulent reacting flows. The LES/FMDF results are found to be consistent and comparable to DNS and experimental results for different flows.