چكيده به لاتين
Abstract
Planning and design in river engineering rely on bed deflections and its interactions with the flow, so it is essential to investigate the bed-flow interaction in more detail.
The main objective of this paper is to investigate the comparison between the Coles law in outer region of boundary layer and parabolic law method on riffle, finding the relation between Coles parameter and dimensionless pressure gradient β, determination of the Von Karman constant in riffle and application of double average methodology. Spectral analysis for recognition of validity or invalidity in known Kolmogorov law for both inner and outer boundary layer of riffle has also been inquired in the present thesis.
The gained data of Isfahan university of technology have been used to perform this survey. Three-dimensional water flow velocity measurement using ADV has been done. In order to simulate the river bed, grain size diameter of d50=10 mm is consumed. the results represent that outer boundary layer of riffle can be well parametrized using both Coles and parabolic laws, while the inner part of boundary layer does not follow these laws.
There is no strong relation between pressure gradient parameter and Coles parameter, but in the acceleration region, an equation with high correlation coefficient has been obtained. Von Karman constant is near to global constant of 0.4 according to shear velocity using boundary layer method and indicates a few variation alongside the bed.
To validate the Colmograf law, the results of both inner and outer regions demonstrate that the energy for decelerating flows in low-frequency regions in upper hand formation of the bed is less than the related amount lower hand. For accelerating flow, the above mentioned procedure is vice versa. Charts reveals that in the accelerating and quasi-uniform region profiles, it is clearly obvious that the Sub-layer is -5/3 and in other words the Colmograf law is established for all three dimensions. The balanced boundary layer is not established in any tests because Reynolds stress profiles do not have the same shapes unlike the velocity and its square root of the square average distribution of fluctuation profiles. The logarithmical law in inner double averaging region of flow velocity is run and the parabolic law can be well fit over the velocity of the outer region of double averaging velocity profile.
Keywords:riffle, Coles law, parabolic law, pressure gradient, , Von Karman constant, Colmogorove law,
