When a laminar boundary layer separates because of an adverse streamwise pressure gradient, the flow is subject to increased instability with respect to smallamplitude disturbances. Laminar–turbulent transition occurs under a rapid three-dimensional (3D) development within the separated shear layer. When the following turbulent boundary layer reattaches, a laminar separation bubble is formed. T...

Especially for large amplitude initial disturbances so called vortices de velop during the non linear late stages of laminar turbulent transition Once formed they may persist as so called hairpin vortices well into the ensuing turbulent boundary layer This makes their study important for under standing transition and turbulence in wall bounded shear ows In Direct Numerical Simulations DNS as we...

The evolution of co-rotating streamwise vortices in a canonical flat plate turbulent boundary layer ~thickness of the boundary layer d0.99525 mm) is studied. The vortices are produced by an array of inclined jets ~diameter D514 mm) with the same orientation ~skew angle b and pitch angle a of 45°!. The focus of the investigation is on the immediate vicinity of the jet exit and downstream locatio...

Numerical simulations of a model of plane Couette flow focusing on its in-plane spatio-temporal properties are used to study the dynamics of turbulent spots. While the core of a spot is filled with small scale velocity fluctuations, a large scale flow extending far away and occupying the full gap between the driving plates is revealed upon filtering out small scales. It is characterized by stre...

An experimental study was performed to analyze the stability of localized streaky structure in a Blasius boundary layer. An artificial streaky structure was created by using suction or blowing through a thin spanwise slot at the wall. The velocity gradient generated by the suction or blowing was controlled by a damper. The Reynolds number based on the displacement thickness d1 was Red1 =280 at ...

Energy and exergy characteristics of a square cylinder (SC) in confined flow are investigated computationally by numerically handling the steady-state continuity, Navier-Stokes and energy equations in the Reynolds number range of Re = 10–50, where the blockage ratio (β = B/H) is kept constant at the high level of β = 0.8. Computations indicated for the upstream region that, the mean non-dimensi...

Direct numerical simulations ~DNS! of a turbulent channel flow at low Reynolds number (Ret 5100,200,400, where Ret is the Reynolds number based on the wall-shear velocity and channel half-width! are carried out to examine the effectiveness of using the Lorentz force to reduce skin friction. The Lorentz force is created by embedding electrodes and permanent magnets in the flat surface over which...

The effect of finite dimensions of ∨and ×-probes is investigated for the measurement of mean and variances of streamwise and spanwise velocities in wall-turbulence. The probes are numerically simulated using a Direct Numerical Simulation database of channel flow at a friction Reynolds number (Reτ ) of 934 by varying the probe parameters, namely, the wire-lengths (l), the angle between the wires...

Direct numerical simulations at two friction Reynolds numbers (550 and 1000) have been performed to explore the statistical behaviors of wall-attached motions (WAMs) in open- closed-channel flows (OCFs CCFs). To fully capture largest energetic WAMs, superlarge domain sizes are employed (24–48 π h along streamwise direction with being height OCFs). Based on analysis linear coherence spectrum, bo...