Study Of Hydraulic Factors's Influence On Roughness Coefficient Through 3D Numerical Simulation

N is called Manning roughness coefficient,but in essence it is a comprehensive hydraulic friction coefficient which reflects roughness condition of walls,sectional form of channels,hydraulic conditions and other factors.In hydraulic calculation of the open channel,roughness coefficient is a very important and sensitive parameter,comprehensive understanding of characteristics and variation of roughness will have great significance for determining reasonably values.Physical model tests and prototype observation methods are used in previous studies on roughness coefficient.Because these measures are high cost,and the data range is difficult to control,so the study of roughness coefficient is not sufficient.On account of this,based on the analysis on existing research achievements of the open channel roughness from home and abroad,standard k-? turbulence model in FLUENT is adopted to study the effects of hydraulic factors like Froude number,channel bottom slope and aspect ratio on roughness coefficient in uniform,and the change rule of the roughness coefficient with relative depth in non-uniform open channel flow in this paper.The main conclusions are as follows:(1)In the same rough bed and flow condition,variation of roughness coefficient with Fr-number relates to the flow states.In the subcritical flow,roughness coefficient increases with the increasing of Fr-number faster;In the critical flow,roughness coefficient increases with the increasing of Fr-number slower.Also,at the same flow rate,when the Fr-number is small,roughness coefficient changes mainly with the Fr-number,roughness height has little effect;when the Fr-number is greater,roughness coefficient changes mainly with roughness height,the Fr-number has less impacts on it.For a rough bed of open channel flow,roughness coefficient and Fr/(?) have the same relevance,also roughness coefficient decreases with decreasing of Fr/(?) in a Logarithmic function.For a fixed channel,roughness coefficient increases with the aspect ratio logarithmically.The calculation formula of roughness coefficient in uniform open channel flow is obtained by fitting.(2)It can be described by a power formula between the relative wall shear stress and the relative depth of non-uniform open channel flow,and the smooth and rough condition of the bed has no effect on this correlation.It can also be described by a power formula between relative roughness coefficient and relative water depth in non-uniform open channel flow.Under the backwater condition,roughness coefficient increases with the increase of water depth along the channel;Under the condition of drop water,roughness coefficient decreases with the decrease of water depth along the channel.The calculation formula of roughness coefficient in non-uniform open channel flow is obtained by fitting.The results show that,the standard k-? turbulence model can simulate the change rule of the roughness coefficient with hydraulic factors well.The research results can be applied to hydraulic calculation of open channel flows,also have certain guidance value to the engineering practice and application.