3. Data Reduction Procedures

• SPIV recordings are processed with LaVision DaVis v7.2 software in batch processes. 
• First, the raw images are rotated and mirrored. 
• Then the correlations are completed with one pass using 128´128 pixel interrogation windows followed by 64´64, and then finally 32´32 pixel interrogation windows. 
• Fifty percent overlap is used in the horizontal and vertical directions on all correlation passes. 
• Vectors are range filtered, and then a median filter follows, removing vectors if their magnitude is greater than two times the rms value of their neighboring vectors. 
• Spurious vectors are not replaced with interpolated values, and blank spots in the measurement area are not filled. 
• The vector fields and analog voltages (Sanshin sway and yaw and Krypton sway and yaw) are exported and organized according to zone number and carriage run. 
• Then, a FORTRAN program is used to complete the phase-averaging part of the data reduction. 
• Vectors from each carriage run are non-dimensionalized with the measured carriage speeds. 
• Then, the vector fields are sorted into their respective phase groups by analyzing the sway and yaw analog voltage levels associated with each SPIV recording. 
• When the phase-sorting is complete, the phase averaged velocities and Reynolds stresses are computed. 
• The solution for the complete region of interest is stitched together from the multiple zones at the x-station. 
• An averaging technique will be used in the overlapping regions of the multiple zones.