Computational fluid dynamics (CFD) data is obtained as a result of numerical analysis performed on a flow model. In order for this data to be accurately analyzed, it is necessary to be able to visualize it in 3-D space. While visualizing this data, engineers sometimes find it necessary to visualize changes in the characteristics of the flow with respect to changes in the value of certain input parameters. However, generating CFD data sets for several values of input parameters is a tedious procedure, and cannot be done interactively. This thesis proposes a method where approximations between data sets are used instead of resolving the entire CFD model so that interaction with the data can be performed interactively. There are three parts to this thesis. The first part describes the methodology and features of visualizing the data in a virtual environment through the interactive creation and manipulation of flow entities such as streamlines, cutting planes, and isosurfaces. The second part of the thesis analyzes two methods of approximation on large data sets. The third part describes the actual interactive implementation of the approximation methods in a full-scale application. The methods used here are the Virtual knot technique of B-spline curve fitting and basic linear interpolation. The input parameters, that are being varied, are the geometrical attributes of the data set. The application was developed using OpenGL and the Visualization Toolkit (VTK) libraries for the rendering and visualization calculations. In addition, the C2 interface libraries were used to create the Virtual Reality environment.