Structure Functions of Turbulence Through a Degraded Channel Bed

This investigation deals with the turbulence characteristics for flow through a degraded channel bed consisting of sand-gravel mixture of equal proportions. Three-dimensional velocity was measured throughout the depth at three different steamwise locations over a degraded bed. The velocity data were then processed to observe the vertical profiles of velocity distributions in vector form, turbulence indicator and length scales at different locations. The main intend of the present study was to observe the effect of bed degradation on the intermittency and anisotropy in the higher order scaling exponents using the structure functions methodology. The extended self-similarity (ESS) technique was employed to estimate the scaling exponents from higher-order structure functions of streamwise and vertical components which show that below the bed-level (level of the bed surface measured before the degradation started), the scaling exponents deviate from the theoretical values indicating intermittency of scaling exponents. Furthermore, data were analyzed to observe the scaling exponents from higher order mixed structure functions. To this end, the SO (3) symmetry decomposition was utilized to differentiate the isotropic and anisotropic parts of the scaling exponents. The anisotropic scaling exponents obtained from higher order mixed structure functions possess higher values than that of isotropic part. The experimental findings also specify that as one moves close to the degraded bed, the scaling exponents obtained from the higher order mixed structure functions deviate more significantly. Furthermore, the structure functions based anisotropy was observed by measuring the angle of anisotropy using second-order structure functions. The anisotropy angles show more anisotropy in the vicinity of the degraded bed than that above the bed-level. It is expected that the results of the present study will essentially lead to new contributions to the existing knowledge in the field of turbulence through a degraded channel bed.