Large Eddy Simulation Of Wall Jet Based On Downbursts Flow

The downburst is the strong winds near the ground, which is caused by the lash ofstrong downdraft. Downbursts have been caused a lot of damage of many engineeringstructures in the world, especially the collapse of the transmission towers. In the lastthree decades, downbursts are becoming the focus in the field of structural windengineering. The outlet of downbursts is similar to the wall jet, so the study of wall jet isof great importance to clarify downbursts well.In recent years, with the development of computer performance and numericalsimulation technique, Computational Fluid Dynamics (CFD) is becoming widely usedin the study of downbursts. The advantage of CFD is cheaper, more timesaving andconvenient. Reynolds Average Navier-Stokes (RANS) is the most popular numericalsimulation method, but the wind fluctuation cannot be obtained, and its accuracydepends on the turbulence model. The LES can take the wind fluctuation into accountand has high accuracy, so it is becoming more and more popular. In this paper, the walljet will be simulated with the use of LES method. The work is as below:①In order to study the influence of the various parameters on the numericalsimulation, including grid meshing, time step and the subgrid model, the experiment ofMclntyre is simulated. The result shows that the reasonable time step is1×10-5s, thesubgrid model is Smagorinsky model, and the y+should be less than10.②According to the parameter analysis, the experiment of wall jet with the co-flowis simulated with the use of LES method. The mean velocity profile and the Reynoldsstress profile of the numerical simulation are compared with the result of the windtunnel test, the mean velocity profiles match well with those of the experiment, but theReynolds stress profiles of the numerical simulation are bigger.③The wall jet has the universal laws independent of Reynolds numbers. From thecomparison of numerical simulation and wind tunnel test, the mean velocity profiles ofnumerical simulation can be collapsed onto a universal curve; other universal laws arealso match well with the experiment result.④In order to study the universal laws of wall jet without co-flow, the inletcondition of the model is modified to be the wall. Normalizing the mean velocity profilewith maximal velocity Umand normalizing height y with half-height y1/2, the result are similar to those from Eriksson; other universal laws are also fit well in the area wherethe length is more than20b.⑤The wall roughness will change the rules of the wall jet significantly, and thusaffect the entire flow. In order to study the influence of the wall roughness, the flow issimulated by setting the roughness elements. And the mean velocity profile and theturbulent intensity profile of roughness elements with different height are compared, theresults indicate that the roughness elements will reduce the velocity and increase theturbulent intensity, and the height of the roughness elements is proportional to theinfluence.