2D HVAC problem
In my line of business, plant facilities, I have little need for CFD, but a couple of years ago, I wrote a small bit of code based on the StreamFunction/Vorticity Formulation. This worked well enough, and have not needed and CFD since. However, I would like to simulate a problem where pressure is taken into account. Specifically, I need to simulate air flow in a long, pressurized, ceiling plenum for a cleanroom. From what I have read, introducing a pressurization function into my current code is not reccommended. I'm a rankamateur at CFD, and my company wont pay $ thousands a year for a commercial program that will seldom be used. I'm not interested in heat transfer, just the fluid dynamics. I guess what I'm looking for is some advice on how to formulate the algorithm. I using a PC, and writing in powerbasic. What method would be best for a novice like me?

Re: 2D HVAC problem
Check out "Numerical Heat Transfer and Fluid Flow" by Patankar. It's got a layman's description of how the method is derived and works.

Re: 2D HVAC problem
(1). I think you are happy with your 2D incompressible world. The real world is too complicated and there is no real interest from the company side. So, the solution has to be simple. (2). The solution is: you can still use your 2D stream function/ vorticity formulation. All you need to do is to integrate the momentum equation to get the pressure distribution. (3). After you have obtained the converged solution from the stream function/vorticity equations, you should have the velocity distribution (u and v are related to the stream function through the definition). The next step to do is to integrate the momentum equation, say xmomentum equation, from the inlet (where the pressure is specified) to the exit. This can be done along the grid line in the middle of the channel, or through every grid lines. (4). At the end of the integration process, you should have the pressure distribution from the inlet to the exit.

Re: 2D HVAC problem
It seems like you are working on viscous incompressible flows. The solution of the NavierStokes equations for a viscous incompressible fluid in terms of pressure is given below.
C = (1/density of air)(kinematic viscosity/r)**2 Re = Radial Reynolds Number S = Swirl Reynolds Number P  Pinfinity =  C(Re**2 + S**2) + Z dP/dZ Reference : " Modeling Flow and Heat Transfer in Vortex Burners " Anatoly Borissov, Vladimir Shtern and Fazle Hussain, University of Houston, Mechanical Engineering Department, Houston, Texas 772044792 AIAA Journal, Vol. 36, No.9, September 1998 Although, the authors in this journal worked on gas turbine, still the generalized equations can be applied to solve fluid dynamics problems in HVAC and other fields of widespread technological importance. Good Luck!! 
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