L. Djenidi

Direct numerical simulations of turbulent channel flow with transverse square bars on one wall

Direct numerical simulations have been carried out for a fully developed turbulent channel flow with a smooth upper wall and a lower wall consisting of square bars separated by a rectangular cavity. A wide range of

The turbulent boundary layer over transverse square cavities

w/k

Effects of initial conditions in decaying turbulence generated by passive grids

, the cavity width to roughness height ratio, was considered. For

Simulation of gas flow in microchannels with a sudden expansion or contraction

w/k\,{\ge}\,7

Low-Reynolds-number effects in a turbulent boundary layer

, recirculation zones occur immediately upstream and downstream of each element while mean streamlines and spatial distributions of the skin frictional drag indicate that each element is virtually isolated. The maximum form drag occurs at

Lattice-Boltzmann simulation of grid-generated turbulence

w/k\,{=}\,7

Anisotropy of the dissipation tensor in a turbulent boundary layer

and coincides with the minimum skin frictional drag. The dependence on

LDA measurements in a turbulent boundary layer over a d-type rough wall

w/k

LDA measurements in low Reynolds number turbulent boundary layer

of the Clauser roughness function reflects that of the form drag.

Velocity and passive scalar characteristics in a round jet with grids at the nozzle exit

Laser-induced uorescence (LIF) and laser Doppler velocimetry (LDV) are used to explore the structure of a turbulent boundary layer over a wall made up of two-dimensional square cavities placed transversely to the flow direction. There is strong evidence of occurrence of outflows of fluid from the cavities as well as inflows into the cavities. These events occur in a pseudo-random manner and are closely associated with the passage of near-wall quasi-streamwise vortices. These vortices and the associated low-speed streaks are similar to those found in a turbulent boundary layer over a smooth wall. It is conjectured that outflows play an important role in maintaining the level of turbulent energy in the layer and enhancing the approach towards self-preservation. Relative to a smooth wall layer, there is a discernible increase in the magnitudes of all the Reynolds stresses and a smaller streamwise variation of the local skin friction coefficient. A local maximum in the Reynolds shear stress is observed in the shear layers over the cavities.