Skin Friction In Turbulent Boundary Layers Research Articles

Bubble friction drag reduction in a high-Reynolds-number flat-plate turbulent boundary layer

Turbulent boundary layer skin friction in liquid flows may be reduced when bubbles are present near the surface on which the boundary layer forms. Prior experimental studies of this phenomenon reached downstream-distance-based Reynolds numbers (m. At the lowest test speed and highest air injection rate, buoyancy pushed the air bubbles to the plate surface where they coalesced to form a nearly continuous gas film that persisted to the end of the plate with near-100% skin-friction drag reduction. At the higher two flow speeds, the bubbles generally remained distinct and skin-friction drag reduction was observed when the bubbly mixture was closer to the plate surface than 300 wall units of the boundary-layer flow without air injection, even when the bubble diameter was more than 100 of these wall units. Skin-friction drag reduction was lost when the near-wall shear induced the bubbles to migrate from the plate surface. This bubble-migration phenomenon limited the persistence of bubble-induced skin-friction drag reduction to the first few metres downstream of the air injector in the current experiments.

Influence of Free-Stream Turbulence on Turbulent Boundary Layer Heat Transfer and Mean Profile Development, Part II—Analysis of Results

An experimental research program was conducted to determine the influence of free-stream turbulence on zero pressure gradient, fully turbulent boundary layer flow. In Part I of this paper, convective heat transfer coefficients, boundary layer mean velocity and temperature profile data, as well as wall skin friction coefficient distribution data were presented for five flow conditions of constant free-stream velocity (30 m/s) and free-stream turbulence intensities ranging from approximately 1/4 to 7 percent. These data indicated that the turbulence had significant effects on both the turbulent boundary layer skin friction and heat transfer. In the current paper, these new data are compared to various independent experimental data and analytical correlations of free-stream turbulence effects. This analysis has shown that the effects documented in Part I were a function of the freestream turbulence intensity, the turbulence length scale, and the boundary layer momentum thickness Reynolds number. In addition, the Reynolds analogy factor (2St/cf) was shown to increase by just over 1 percent for each 1 percent increase in free-stream turbulence level. New correlations for the influence of free-stream turbulence on skin friction, heat transfer, and the Reynolds analogy factor are presented.

Effect of Frequency in Unsteady Transonic Flow

2x10 5x10 1x10 2x10 5x10 1 x 10 2x10 R 10 Wilson, R. E., Boundary-Layer Temperature Profiles and Reynolds Analogy, International Journal of Heat and Mass Transfer, Vol. 21, Aug. 1978, pp. 1167-1170. Harkness, J. L., The Effect of Heat Transfer on Turbulent Boundary Layer Skin Friction, Defense Research Laboratory, University of Texas, DRLRept. 436, CM-940, June 1959. Schoenherr, K. E., Resistance of Flat Surfaces Moving Through a Fluid, Transactions of the Society of Naval Architectures and Marine Engineering, Vol. 40, 1932, pp. 279-313.

Analysis of the sound field of a large span oscillating body of revolution

V. P. Motulevich, "The method of relative correspondence and its use in problems of heat and mass transfer," Inzh.-Fiz. Zh., 14, No. i (1968). S. S. Kutateladze and A. I. Leont'ev, Heat and Mass Transfer and Friction in a Turbulent Boundary Layer [in Russian], Energiya, Moscow (1972). R. L. Simpson, "A generalized correlation of roughness density effects on the turbulent boundary layer," AIAA J., II, No. 2 (1973). F. W. Fenter, "Analysis and direct measurement of the skin friction of uniformly rough surfaces at supersonic speeds," Inst. Aeronaut. Sci. Preprint No. 837 (1958). F. L. Young, "Experimental investigation of the effect of surface roughness on compressible turbulent boundary layer skin friction and heat transfer," Univ. Texas AD 621085 (1965). A. E. Perry and P. N. Joubert, "Rough-wall boundary layers in adverse pressure gradients," J. Fluid Mech., 17, Part 2 (1963). H. Schlichting, Boundary Layer Theory, 6th ed., McGraw-Hill (1968).