Data variance due to different testing techniques

A comparison of the boattail pressure distributions from data presented earlier shows that there is a significant variance in the data obtained in the various facilities, particularly at 0.9 and 0.95 Mach numbers. The analysis is concentrated on the 15 deg AGARD boattail tested in the 0.8 to 0.95 Mach number range. Differences in model support, model scale, tunnel blockage, tunnel buoyancy, wall type and porosity, and determination of tunnel reference flow conditions are examined in an attempt to understand the disagreement in the data. Model and wall static pressure distributions from various facilities are analyzed to try to isolate the reasons for these differences and to determine if there is a significant effect on the flow over the nozzle boattail. An indication of possible wall interference is obtained by comparing the measured wall static pressure distributions to those determined analytically with a far field boundary condition corresponding to free flight conditions.