EFFECTS OF CONVEX TRANSVERSE CURVATURE ON WALL-BOUNDED TURBULENCE .1.THE VELOCITY AND VORTICITY

Convex transverse curvature effects in wall-bounded turbulent flows ar e significant if the boundary-layer thickness is large compared to the radius of curvature (large gamma = delta/a). The curvature affects th e inner part of the flow if a+, the cylinder radius in wall units, is small. Two direct numerical simulations of a model problem approximati ng axial flow boundary layers on long cylinders were performed for gam ma = 5 (a+ almost-equal-to 43) and gamma = 11 (a+ almost-equal-to 21). Statistical and structural data were extracted from the computed flow fields. The effects of the transverse curvature were identified by co mparing the present results with those of the plane channel simulation of Kim, Moin & Moser (1987), performed at a similar Reynolds number. As the curvature increases, the skin friction increases, the slope of the logarithmic region decreases and turbulence intensities are reduce d. Several turbulence statistics are found to scale with a curvature d ependent velocity scale derived from the mean momentum equation. Near the wall, the flow is more anisotropic than in the plane channel with a larger percentage of the turbulent kinetic energy resulting from the streamwise velocity fluctuations. As the curvature increases, regions of strong normal vorticity develop near the wall.