NISA Software - Compressible

Compressible

FLOW SPEED RANGE

Gas flow from the low Mach number up to hypersonic speed can be easily analyzed using NISA/3D-FLUID. Problems involving hypersonic flows should be solved using multiple component gas flow equations to account for the real gas effect.

Compressible flow through a convergent - divergent nozel

ANALYSIS CAPABILITIES AND DOMAIN

Inviscid and viscous flow problems with or without chemical reactions can be simulated in 2D, axisymmetric and 3D arbitrary geometries. Quadrilateral and triangular elements can be combined in a planar domain whereas 3D domain can consist of a combination of hexahedron and wedge elements.

BOUNDARY CONDITIONS

NISA/3D-FLUID allows specification of two types of boundary conditions. The zero normal velocities at solid boundary are enforced internally for inviscid flow and for viscous, multicomponent flow problems, non-slip, non-catalytic boundary conditions at solid surface are imposed. The user can also specify flow variables such as density, temperature and its derivative, species mass fractions, and x, y, z momentums at any location in the computational domain.

SOLUTION TECHNIQUE

A two step Taylor Galerkin finite element method is employed. Matrix lumping technique is used to shift the numerical scheme into explicit form such that no matrix operations are involved during calculations. A local time step method is utilized for solving steady state problems.

HEAT TRANSFER ANALYSIS

The solution of compressible flow equations always contains temperature as a variable and its value is obtained through the equation of state for gas or gas mixtures. Three sets of equations previously described solve convective heat transfer problems whereas the solution of heat conduction problems is obtained through Navier-Stokes equations.

Supersonic flow past a conical flying body with cavity at clyndrical section

STEADY STATE AND TRANSIENT ANALYSIS

The compressible flow program always solves the unsteady state governing equations. A constant time step size is used during numerical calculations for transient problems. A local time step technique can be used to accelerate convergence for steady state processes in which only the final steady state solutions have physical meaning.

MULTICOMPONENT MIXING AND CHEMICAL REACTION/ COMBUSTION

Mixing and combustion problems with multicomponents, multiple elementary reversible or irreversible chemical reactions are simulated by solving full Navier-Stokes equations and species continuity equations. The individual species mass fractions are determined in addition to the velocity, pressure and density of gas mixture to describe the flow field completely. A chemical kinetics program, CHEMKIN, and a transport property program, TRANSPORT, are used to assemble the chemical reaction mechanism and to evaluate the thermodynamic and transport properties of individual species and gas mixture accurately. Besides the solution for the standard Arrhenius form reaction, the solution for third body reactions, pressure-dependent fall-off reactions, and Landan-Teller reactions are also possible.

EQUATIONS SOLVED

The compressible flow program solves three sets of equations:

The Navier Stokes equation plus species continuity equations with or without chemical reactions for the mixing or the combustion of multiple species gas problems
The compressible Navier Stokes equations for single component gas flow problems with viscous effects
The Compressible Euler equations for single component inviscid gas flow problems