CFD Multi-scale Simulation Of Wind Flow Over Hilly Terrain

The output and economic benefit of wind farm depend to the site for windturbines. When wind farm is built in the mountain, to evaluate the field's windenergy distribution is so difficult only with limited data from observation. But CFDtechnology can help us to obtain the details of wind energy distribution. In thispaper, multi-scale simulation of wind field is investigated by wind tunnelexperiment and commercial CFD code FLUENT 6.3.In order to study wind field of typical hilly terrain, two-dimensional slopemodel, two-dimensional ridge model and three-dimensional axisymmetric hillmodel are manufactured, scaled 1:1000. A series of wind speed profiles, which areabove the model's different locations, have been measured in the atmosphericboundary layer wind tunnel and the wind field about various typical hilly terrainhave been obtained. Then the wind field of three-dimensional axisymmetric hill issimulated. Compared with the result from wind tunnel experiment, the results basedon the different wall functions, the different inlet turbulent profiles, the differentinlet velocity profiles and the different turbulent models is analyzed to understandimpact of these parameters. A group of good parameters is selected, and applied towind field simulation of two-dimensional slope and two-dimensional ridge to verifythe applicability of this group of parameters. This group of parameters will beapplied to wind field simulation of complex hilly terrain.Based on the current condition of computer hardware, calculating wind fieldwhose horizontal resolution is 5m costs too high. Multi-scale simulation of windfield is tested using two kinds of turbulent model, namely RNG turbulentmodel and SST turbulent model. The horizontal grid resolution of first-levelhilly model is 40m and the local horizontal grid resolution of second-level hillymodel can achieve 5m. The data transfer between grids ,whose resolutions aredifferent, is by way of interpolation. The connection between the two grids ofdifferent resolution is made use of interface. A strong wind event with stable winddirection from the record of a real hilly terrain is chosen to simulate. Comparedwith simulation results and the field records from various sites, the result of the second-level hilly model is more precision than the result of the first-level hillymodel. This indicates that multi-scale simulation of wind field is feasible.