초록 ▼

To modify a turbulent boundary layer flow over a surface to reduce its drag, a series of streamwise riblet projections is provided on the surface arranged in a pattern consisting of spaced large height projections between which are a plurality of smaller height projections. The latter inhibit turbul

To modify a turbulent boundary layer flow over a surface to reduce its drag, a series of streamwise riblet projections is provided on the surface arranged in a pattern consisting of spaced large height projections between which are a plurality of smaller height projections. The latter inhibit turbulent eddy motions from penetrating deep into the grooves between them and so displace the turbulent motion away from the wall. The larger projections control the longitudinal vortices or streaks that are characteristic of turbulent boundary layer flow and promote energy transfer to the smaller scale secondary vortices associated with the smaller projections. In another configuration the projections are arranged in a repeated spanwise pattern in which the adjacent projections in each pattern repeat project to different heights, the different heights being so scaled in relation to each other and to the boundary layer thickness that the displacement of the turbulent motion away from the surface by the smaller height projections is extended further by the larger height projections. A further possibility lies in increasing the heights, and possibly also the pitches, of the projections progressively in the downstream direction to mitigate the self-limiting effect of the projections as they establish a raised virtual wall surface for the turbulent boundary layer, the increase being made, continuously or in one or more steps.

대표청구항 ▼

A fluid dynamic wall surface having a series of elongate projections on said surface extending in the direction of fluid flow relative to said surface for modification of a turbulent boundary layer on said surface, said projections comprising larger and smaller height projections, adjacent ones of s

A fluid dynamic wall surface having a series of elongate projections on said surface extending in the direction of fluid flow relative to said surface for modification of a turbulent boundary layer on said surface, said projections comprising larger and smaller height projections, adjacent ones of said larger height projections being spaced apart from each other and a plurality of said smaller height projections being disposed therebetween, said larger height projections and said smaller height projections being discreet, separate formations of said surface, said larger height projections projecting farther into said boundary layer in use than all said smaller height projections.