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What is QnS?

QUICK 'n SIMPLE, or QnS, allows users to set up and solve two-dimensional, laminar, incompressible flow problems using the Apple Macintosh(TM). QnS is intended primarily as a tool for teaching fluid mechanics and computational fluid dynamics (CFD). Without at least some training in these areas you will not fully understand how to accurately specify a problem and interpret the results.

On the other hand, QnS, as its name also implies, can be used to quickly and simply set up and solve fluid dynamics problems that are impossible to solve analytically. We have designed QnS to work in the natural way that fluid dynamicists describe the physical aspects of the problems they are attempting to solve.

To solve a flow problem you

1. Specify the size of the computational domain.
2. Assign boundary conditions: inflow, outflow.
3. Generate a grid that is consistent with the boundary conditions
4. Tell QnS to solve the flow field

Unlike many other CFD programs, QnS generates the grid after the physical problem is specified. We believe this is more intuitive, since the grid, after all, is merely an artifact of the solution method.

The name of the program is derived from the QUICK algorithm of B.P.Leonard [1] and the SIMPLE algorithm of S.V. Patankar and D.B.Spalding [2]. QnS incorporates both the SIMPLE and SIMPLER algorithms for the pressure-velocity coupling. QnS allows the user to select one of QUICK, pure upwinding, or the Power-Law difference method for modeling the convective transport.

QUICK 'n SIMPLE is an interactive educational tool for studying the behavior of typical fluid flows. It is not intended to compete with complex and expensive industrial strength CFD codes. In keeping with this purpose, we have only incorporated features which maintain the "quick" and "simple" nature of the user interface.

We are working on adding more features, however, this project competes with having fun (away from computers, that is!) and other projects that pay bills.

Features

• QnS is capable of solving the Navier-Stokes equations for laminar, incompressible flow in two-dimensional Cartesian or axisymmetric coordinate systems
• The user can easily chose from the following convection modeling schemes: QUICK, pure upwind, or Power-Law differencing
• Grid generation is easy and flexible. Nonuniform grids can be prescribed in a number of ways.
• Inflow, outflow, moving, and symmetry boundary conditions are selected by clicking and dragging with the mouse.
• Inflow velocity profiles can be uniform, linear, parabolic, or custom
• Internal obstacles in the flow field can be added by drawing them with the mouse
• Transport of a passive scalar, e.g., smoke or pollutant can also be modelled with a single source anywhere in the domain.
• Convergence is displayed graphically while calculations are under way.
• Solution to the flow field may be displayed graphically as velocity vectors, streamlines along with contours of pressure, vorticity, velocity magnitude, and pollutant concentration.
• The user can choose fluid properties of air or water at any temperature, or custom fluid properties can be used.

Limitations

The graphical user interface of QnS has allowed us to simplify the problem specification and hide the complexity of the solution algorithm. However, you must still understand enough about fluid mechanics to specify a meaningful problem and to interpret the results. Though QnS may solve your problem, it is no substitute for common sense and engineering experience. QnS merely permits you to spend less time on the tedious details of the problem solution and concentrate on the more important aspects of the fluid mechanics. We hope that by working with QnS you will develop your intuition of fluid behavior.

Availability

QnS version 1.1 is available as freeware. You can download the application and (skimpy) documentation from the QnS directory of the anonymous ftp server in the Mechanical Engineering Department of Portland State University.

You are ree to copy and distribute it in an unmodified form. If you find it useful, (or if you find bugs) please send us an email message. We will keep your address on file and send notices about updates and new versions.

References

1. Leonard, B.P., (1979), "A stable and accurate convective modelling procedure based on quadratic upstream interpolation" , Comp. Meth. in Appl. Mech. and Engrng., vol. 19, pp. 59-98.
2. Patankar, S.V. and D.B. Spalding, (1972), "A calculation procedure for heat, mass and momentum transfer in three-dimensional parabolic flows", Int. J. Heat Mass Transfer, vol. 15, p. 1787.

The Authors