Affiliation:
1. NASA Glenn Research Center, 2100 Brookpark Road, Cleveland, 44135 OH, USA
Abstract
This paper is concerned with the transition to turbulence in flat plate boundary layers due to moderately high levels of free-stream turbulence. The turbulence is assumed to be generated by an (idealized) grid and matched asymptotic expansions are used to analyse the resulting flow over a finite thickness flat plate located in the downstream region. The characteristic Reynolds number
R
λ
based on the mesh size λ and free-stream velocity is assumed to be large, and the turbulence intensity
ε
is assumed to be small. The asymptotic flow structure is discussed for the generic case where the turbulence Reynolds number
εR
λ
and the plate thickness and are held fixed (at
O
(1) and
O
(λ), respectively) in the limit as
and
ε
→0. But various limiting cases are considered in order to explain the relevant transition mechanisms. It is argued that there are two types of streak-like structures that can play a role in the transition process: (i) those that appear in the downstream region and are generated by streamwise vorticity in upstream flow and (ii) those that are concentrated near the leading edge and are generated by plate normal vorticity in upstream flow. The former are relatively unaffected by leading edge geometry and are usually referred to as Klebanoff modes while the latter are strongly affected by leading edge geometry and are more streamwise vortex-like in appearance.
Subject
General Physics and Astronomy,General Engineering,General Mathematics
Reference35 articles.
1. Dryden HL. 1936 Air flow in the boundary layer near a plate. NACA Report no. 562. See http://naca.central.cranfield.ac.uk/reports/1937/naca-report-562.pdf.
2. Effect of free stream turbulence on a laminar boundary layer;Klebanoff P;Bull. Am. Phys. Soc.,1971
3. The effect of wind-tunnel screens on nominally two-dimensional boundary layers
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