Journal of Fluid Mechanics

The structure of two-dimensional separation

Laura L.  Pauley a1, Parviz  Moin a2 and William C.  Reynolds a2
a1 The Pennsylvania State University, University Park, PA 16802, USA
a2 Stanford University, Stanford, CA 94305, USA and NASA/Ames Research Center, Moffett Field, CA 94035, USA

Article author query
pauley ll   [Google Scholar] 
moin p   [Google Scholar] 
reynolds wc   [Google Scholar] 


The separation of a two-dimensional laminar boundary layer under the influence of a suddenly imposed external adverse pressure gradient was studied by time-accurate numerical solutions of the Navier–Stokes equations. It was found that a strong adverse pressure gradient created periodic vortex shedding from the separation. The general features of the time-averaged results were similar to experimental results for laminar separation bubbles. Comparisons were made with the ‘steady’ separation experiments of Gaster (1966). It was found that his ‘bursting’ occurs under the same conditions as our periodic shedding, suggesting that bursting is actually periodic shedding which has been time-averaged. The Strouhal number based on the shedding frequency, local free-stream velocity, and boundary-layer momentum thickness at separation was independent of the Reynolds number and the pressure gradient. A criterion for onset of shedding was established. The shedding frequency was the same as that predicted for the most amplified linear inviscid instability of the separated shear layer.

(Published Online April 26 2006)
(Received June 19 1989)
(Revised April 17 1990)