Experimental Study And Flow Field Numerical Simulation On Loss Of Pipe With Sudden Expansion Or Contraction

Hydraulics computer has extensive application range in environmental hydraulics, which flow pattern and energy consumption of pipeline flow are often encountered in hydraulic engineering. In actual engineering, hydraulics computer of pipeline is very important in designing of blown down pipeline, energy-saving and reducing cost. One of the major task of hydraulics is resistance calculation of pipeline. As a common application in engineering, it has representative meaning to discuss the turbulent state of pipe with sudden expansion or sudden contraction.In this paper, experimental study is performed on 4 different types of sudden-expansion ratio and 3 different types of sudden-contraction ratio.There exist differences between the measurement results and the traditional calculation results of the local resistance coefficient. Therefore, the traditional method applied in practical engineering will produce unneglectable error. The results show that, under the experiment conductions of this paper, local resistance coefficient of pipe with sudden expansion increases with the decreases of sudden-expansion ratio;local resistance coefficient of pipe with sudden contraction increases with the sudden-contraction ratio;local loss coefficient of circular pipe with sudden contraction and sudden expansion are functions of Reynolds number, they are well fitted by cubic polynomial equation.In view of its complexity and the difficulty of measuring, experiments can only give the parameters of total flow;they can not give details of the flow. While numerical simulation can provide specific messages on related fluid field.FLUENT is a good method in large numbers of numerical simulation methods.With its application to fluid simulation, we can get the total distribution of each fluid parameter. Computation with FLUENT is simple, fast and convenient and the precision is fine.It's not only can simulate laminar flow and turbulence but also can simulate incompressible viscous flows and compressible flows,so it has strong practicability.In this paper, large-scale fluid dynamics software FLUENT for computing platforms, using RNG k-εturbulence model, study on pipe with sudden expansion or sudden contraction under turbulent state, showing the contours of stream function, contours of vorticity magnitude and velocity vectors.In the considered range of Reynolds number, the calculation of the flow map has similarity. Obtained the corresponding numerical solutions,and compared with existing data, find that using FLUENT to simulate has better precision and it is effective to the calculation of sudden expansion, sudden contraction flow.In the same ratio of sudden expansion, the numerical simulation of the flow and the trend of flow both are similar, recirculation length and axial velocity are increasing with the Reynolds number increased.When the Reynolds number is constant, the recirculation length increases with sudden expansion ratio decreases.In the same ratio of sudden expansion, the numerical simulation of the flow and the trend of flow both are similar, vortex in the sudden contraction department and axial velocity increase with the increasing of Reynolds number.