Abstract
In order to investigate the effect of gap size on the spanwise turbulence properties of a boundary layer flow through a gap in an isolated wall-mounted roughness element, the turbulence quantities and secondary velocity components have been measured. All measurements were made at a Reynolds number of 3 300, based on obstacle height and free-stream velocity. The three components of turbulence intensity, the Reynolds shear stress and the magnitudes of transverse and spanwise velocity components near the central region reach higher maximum values for smaller gaps. However, the present turbulence field can also be divided in the same way as mentioned in our previous paper. From the off-centerline turbulent quantities, the classification of the gap size proposed by Osaka et al., is definitely reasonable. Further downstream from the gap, it is shown that turbulent structures for 4 gap sizes flows are different from that of the undisturbed flow respectively but are identical to that of a two-dimensional fence flow. The downstream change of the spanwise averaged turbulent kinetic energy flux has been investigated for all gap sizes.
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