Fundamentally excited flow past a surface-mounted rib. Part I: Turbulent structure characterisation

Different data analysis techniques for characterisation of the turbulent flow past a surface-mounted rib are reviewed. Deficiencies of the existing techniques are explained and modified techniques for determination of coherent structure magnitude and phase jitter are suggested. The effect of fundamental excitation on the flow is studied by using these turbulent signal analysis techniques. The appropriate length scale for characterizing the large-scale structures present in the reattaching shear layer of the surface-mounted rib is found to be the momentum thickness at the downstream edge of the rib, and the corresponding Strouhal number is 0.013. This is in contrast to a rib in the free stream, where the rib height is the correct scaling parameter. The post reattachment region is observed to be dominated by large-scale structures contrary to the traditional belief that large eddies break into small scales at the reattachment location. Low magnitude of phase jitter in the near field region is observed, indicating coherence of the flow structures. Phase decorrelation begins to occur beyond three rib heights from the downstream edge of the rib. From the quadrant analysis results, the outer edge of the shear layer is observed to be dominated by large-scale ejection motions.