Boundary-layer transition on a body of revolution

Abstract

The laminar-to-turbulent transition region was measured over a body length Reynolds number range of 9.55- 47.7 million on a large, streamlined, axisymmetric body sting mounted in the Applied Research Laboratory's 1.22 m diameter water tunnel. Theoretical calculations of the transition Reynolds numbers for this body shape were carried out and the results were correlated with the experimental data. It is shown that good correlation can be achieved if en is chosen as the transition criterion in the linear stability calculations, where n is an empirical number, which depends on the freestream turbulence intensity. It was found that this number approached 9 for those test velocities where the freestream turbulence intensity is on the order of 0.1%. OUNDARY-layer transition on axisymmetric bodies is of practical importance because its location influences the total skin frictional drag of the body. It is well recognized that moving the transition point downstream to larger body arc length positions results in drag reduction. Consequently, much of the current research is dealing with boundary-layer control concepts such as temperature differentials at the wall and surface suction. The Applied Research Laboratory at The Pennsylvania State University is actively engaged in transition research from both the analytical and experimental points of view. Experiments are generally designed for the 1.22 m diameter water tunnel located at this laboratory. This facility is par- ticularly suited for such work because of the high water velocities that can be attained (up to 19.8 m/s), the ability to test large bodies ( — 0.50 m in diameter and -3.5 m long), and the fact that settling section turbulence management results in test section turbulence intensities that are quite low ( — 0.1 %). Under normal operating water temperatures (25 °C) this water tunnel has an upper unit Reynolds number of approximately 21 million/m. By way of preliminary preparation for planned experiments on bodies with various types of boundary-laye r control, the work described in this paper was carried out. After a can- didate body shape was selected and a test model fabricated, experiments were performed in the 1.22 m diameter water tunnel to acquire baseline transition data and in-tunnel body pressure distributions. Except for the hydrodynamic shape of this body, no boundary-laye r control was employed in these experiments. The results of the pressure distribution measurements are presented elsewhere.! In addition to the experimental results, theoretical calculations for the growth of linear disturbances in the laminar boundary layer are also described for the test body. These calculations were performed using the methods of Gentry and Wazzan,2 where the body pressure distribution (which is a required input) was calculated from potential flow theory and corrected for inviscid tunnel interference ef- fects.3'4 The transition location may be deduced from this