The paper reports on new oscillatory flow tunnel experiments in which detailed measurements have been made of boundary layer velocities for full-scale regular and irregular oscillatory flows over sand-rough and gravel-rough fixed beds. The irregular flows were generated by amplitude modulation of the corresponding regular flows, to give same free-stream urms and same velocity and acceleration skewness. The experimental setup is described and initial results relating to flow structure, turbulence and bed shear stress are presented. Results presented for boundary layer development, turbulence intensity, turbulent stress and log-law-based estimates of bed shear stress suggest that the hydrodynamics within a flow half-cycle are largely independent of the previous flow half-cycle, at least close to the bed where the presented results have focused. Time-history effects are not entirely absent however, especially higher up from the bed. More detailed analysis is needed to elucidate further.
Bibliographical noteThis research is part of the SINBAD project funded by EPSRC in the UK (EP/J00507X/1) and STW in The Netherlands (12058). Mahesa Bhawanin gratefully acknowledges receipt of a PhD Studentship from the University of Aberdeen.
- oscillatory flow
- boundary layer
- flow tunnel
- laboratory experiments