Drag measurements for excrescence arrays of square section mounted on a smooth wall and subjected to two adverse pressure gradients in equilibrium are obtained. Differences in drag which arise when the excrescences are uniformly distributed and when tending to isolation are shown. Flow visualization photographs using the surface oil flow technique are presented to illustrate different flow patterns around arrays of varying spacing. A prediction model for the drag of excrescence arrays based on the results obtained was devised. Its range of application could be extended to excrescences of varying shape providing they are sufficiently small to be immersed in the logarithmic part of the boundary layer. Drag results are determined by both a momentum defect and a pressure distribution technique. These results are compared and the difference between them is partially attributed to the change in surface friction between the excrescences and partially to some lack of two-dimensionality in the test procedure. Corrections for the latter effect are made to the data obtained.

A drag study was conducted on an oblate ellipsoid body in the Virginia Tech Stability Wind Tunnel. Two-dimensional wake surveys were taken with a seven-hole probe and an integral momentum method was applied to the results to calculate the drag on the body. Several different model configurations were tested; these included the model oriented at a 0° and 10° angle of attack with respect to the oncoming flow. For both angles, the model was tested with and without flow trip strips. At the 0° angle of attack orientation, data were taken at a speed of 44 m/s. Data with the model at a 10° angle of attack were taken at 44 m/s and 16 m/s. The high speed flow corresponded to a length-based Reynolds number of about 4.3 million; the low speed flow gave a Reynolds number of about 1.6 million. The results indicated that the length-squared drag coefficients ranged from around 0.0026 for the 0° angle of attack test cases and 0.0035 for the 10° angle of attack test cases. The 10° angle of attack cases had higher drag due to the increase in the frontal profile area of the model and the addition of induced drag. The flow trip strips appeared to have a tiny effect on the drag; a slight increase in drag coefficient was seen by their application but it was not outside of the uncertainty in the calculation. At the lower speed, uncertainties in the calculation were so high that the drag results could not be considered with much confidence, but the drag coefficient did decrease from the higher Reynolds number cases. Uncertainty in the drag calculations derived primarily from spatial fluctuations of the mean velocity and total pressure in the wake profile; uncertainty was estimated to be about 16% or less for the 44 m/s test cases. / Master of Science