2 research outputs found
An experimental realisation of steady spanwise forcing for turbulent drag reduction
We present an experimental realisation of spatial spanwise forcing in a
turbulent boundary layer flow, aimed at reducing the frictional drag. The
forcing is achieved by a series of spanwise running belts, running in
alternating spanwise direction, thereby generating a steady spatial square-wave
forcing. Stereoscopic particle image velocimetry is used to investigate the
impact of actuation on the flow in terms of turbulence statistics, performance
characteristics, and spanwise velocity profiles, for a waveform of . An extension of the classical spatial Stokes layer theory is proposed
based on the linear superposition of Fourier modes to describe the
non-sinusoidal boundary condition. The experimentally obtained spanwise
profiles show good agreement with the extended theoretical model. In line with
reported numerical studies, we confirm that a significant flow control effect
can be realised with this type of forcing. The results reveal a maximum drag
reduction of 26% and a maximum net power savings of 8%. In view of the limited
spatial extent of the actuation surface in the current setup, the drag
reduction is expected to increase further as a result of its streamwise
transient. The second-order turbulence statistics are attenuated up to a
wall-normal height of , with a maximum streamwise stress
reduction of 44% and a reduction of integral turbulence kinetic energy
production of 39%