Disturbance Growth in Boundary Layers Subjected to Free-stream Turbulence

Free-stream turbulence (FST) is perhaps the most important source inducing by-pass transition in boundary layer flows. The present study describes the initial energy growth of streamwise-oriented d ...

Transition induced by free-stream turbulence

A differential method is proposed to simulate bypass transition. The intermittency in the transition zone is taken into account by conditioned averages. These are averages taken during the fraction of time the flow is turbulent or laminar respectively. Starting from the Navier-Stokes equations, conditioned continuity, momentum and energy equations are derived for the larninar and turbulent parts of the intermittent flow. The turbulence is described by a classical k-e model. The supplementary parameter, the intermittency factor, is determined by a transport equation applicable for zero, favourable and adverse pressure gradients. Results for these pressure gradients are given.

Modelling of bypass transition with conditioned Navier-Stokes equations coupled to an intermittency transport equation

Evaluation of two-equation turbulence models for predicting transitional flows

An experimental study has been carried out to examine the effect of a sharp-edged step on boundary layer transition. The transition position and disturbance spectra in the boundary layer for different step heights and free-stream velocities were measured by hot-wire anemometry. A correlation between the transition Reynolds number and the relative step height has been established for both backward-facing and forward-facing steps. The transition position is associated with the “N-factor” that defines the integrated growth of instability waves at transition. The boundary layer over a step has an earlier transition position than that on a smooth plate, since the instability waves amplify more rapidly than those on a smooth surface. The transition N-factor for the flow containing a step, calculated using the amplification rates on a smooth plate, will, therefore, be smaller than that on surfaces without a step. The observed reduction of the N-factor occurring with a step has been shown to correlate with the height of the step, thus, providing an empirical tool that can be used to estimate the transition position when steps occur. An appropriate value of N can be determined from knowledge of the step height.

Effect of surface steps on boundary layer transition

Investigation of the intermittent behavior of transitional boundary layer using a conditional averaging technique

http://www.jidonline.org/article/S0022202X23016962/pdf

1504 Sequential release of immunomodulatory signaling molecules-laden polyelectrolyte complex nanoparticles from via bilayer alginate hydrogels promotes regenerative wound healing

C.L. Kuan

Papers

Investigation of the intermittent behavior of transitional boundary layer using a conditional averaging technique

1504 Sequential release of immunomodulatory signaling molecules-laden polyelectrolyte complex nanoparticles from via bilayer alginate hydrogels promotes regenerative wound healing