A general-purpose computational steering system (POSSE) which can be coupled to any C/C++ simulation code, has been developed and tested with a 3-D Navier-Stokes flow solver (PUMA2). This paper illustrates how to use "computational steering" with PUMA2 to visualize CFD solutions while they are being computed, and even change the input data while it is running. In addition, the visualizations can be displayed using virtual reality facilities (such as CAVEs and RAVEs) to better understand the 3-D nature of the flowfields. The simulations can be run on parallel computers or Beowulf clusters, while the visualization is performed on other computers, through a clientserver approach. A key advantage of our system is its scalability. The visualization is performed using a parallel approach. This is essential for large-scale simulations, since it is often not possible to postprocess the entire flowfield on a single computer due to memory and speed constraints. Example solutions from this solver are presented to show the usefulness of POSSE. The examples include unsteady ship airwake simulations, unsteady flow over a helicopter fuselage, and unsteady simulations of a helicopter rotor. The results of the rotor simulations in hover are compared with the experimental measurement and discussed in some detail. The advantages of using object-oriented programming are also discussed.