A THEORY FOR THE LAMINAR SUBLAYER OF A TURBULENT FLOW
ARMY BALLISTIC RESEARCH LAB ABERDEEN PROVING GROUND MD
Pagination or Media Count:
A simplified linearized form o the equations f motion for the turbulent fluctuations is used to describe the turbulent field between the wall and the fully turbulent part of the flow. The mean flow in the sublayer and the turbulence field outside the sublayer are assumed to be known from the experiments. The thickness of the sublayer arises naturally in the t eory and is directly analogous to the inner viscous region for the fluctuations in a laminar flow. It is shown that the large scale fluctuations containing most of the turbulent energy are convected downstream with a velocity characteristic of the middle of the boundary layer. thus Taylors hypothesis does not apply to these large scale fluctuations near the wall. The convective velocity found in the measurements of pressure fluctuations at the boundaries of turbulent flows is in accord with the theory. Calculations are given for the energy spectra and u fluctuation level in the sublayer and other aspects of the fluctuation field are discussed. It is shown that the production of turbulent energy is a maximum where the laminar shearing stress is equal to the turbulent shearing stress.
- Fluid Mechanics