This investigation aims to prove the natural unsteadiness of the upwash flow of the twin jet of the V/STOL aircraft upon impingement  on the ground. A model of the for the V/STOL twin jet in a tandem position with respect to the flow is built. Flow field velocity measurement is done by PIV technique at the ESM Fluids Mechanics Laboratory. The central plane of the two gets were only considered during data collection and during further analysis. The data collected was in the form of images of the particles seeded into the flow. The images are in the tiff-image format. Three sets for two different geometrical arrangements were collected during the experiment. The two arrangements are for plate- height-to-jet-diameter (h/d) of 4 and of 2. The 3 sets of date for each case were taken for 3 different free stream velocity of: 0.0m/s, 0.1 m/s, and 0.15 m/s. Only the case of h/d=4 was presented here for free stream velocities of  0.0m/s and 0.15m/s for comparison. The bulk data were collected at a rate of 250 fps for 4 seconds for each set alone.

The collected images were first processed with the Visiflow software to extract the flow field velocity vectors. The Velocity vectors were saved to ASCII data files for each instance. This leaded to 1000 data files. Post processing of the ASCII data files is done by a C++ code to calculate fluid flow properties at each instance of time. The calculated flow properties are the mean velocity magnitude, vorticity magnitude, Turbulent Kinetic energy, U' rms, V' rms, and U'V'. The processing were outputted in three different categories of data files in ASCII type. The first stores flow field properties for all instance with each instance stored as an independent zone or layer.

The final results of this processing is presented in four elements. First, flow visualization is presented once as a digital video file showing the flow over about 3 seconds. Second is the presentation of the steady state  or flow averaging. Seven different plots were given for each parametric case presented (h/d=4 Free stream=0.0 m/s, and h/d=4 Free stream=0.15 m/s). Third, unsteady flow is presented by videos showing velocity vectors together with contour plot of vorticity. Extracted images were also provided at 3 different instances for each case. Finally, volume plot of vorticity magnitude during the test in the plane of view with time as the third dimension.