| Gravel covering reduces the exposed surface area directly, increases the surface roughness height and weakens the wind strength in the near-surface region, especially below the gravel height. Current researches on the flow over gravel-covered surface are mainly through wind tunnel experiments. Reynolds stress equation model (RSM) is used to simulate the turbulent flow over surfaces covered with repeated transverse rod roughness and staggered arrays of cubic roughness elements respectively in this paper, the main contents are as follows:1. For repeated transverse rod roughened surface, a simulation of turbulent flow over repeated transverse rod roughened surface is taken at first, and the cross section of transverse rod is square. Streamlines and boundary layer velocity profile obtained from the simulation are compared with previous results, it shows well agreement and proves reliability of the simulation.2. The roughness element pitch ratio w/b, height to width ratio klb and pitch to height ratio w/k are chosen as characteristic parameters of transverse rod roughened surface, judge the key parameter of transverse rod roughened surface according to the effect of different w/b, klb and w/k on surface resistance.3. Based on the simulation of turbulent flow over transverse rod roughened surface, a simulation of surface covered with staggered arrays of cubic roughness elements is taken, to study the variation of turbulent characteristics, resistance and resistance partition, zero-plane displacement height and aerodynamic roughness height with the roughness elements density.4. The frictional velocity is determined by the simulation results of rough surface resistance, and then the aerodynamic roughness z0 is derived by the method of fitting velocity profile. A simple function formula is given to describe the variation of zo with λf, it fits well with experimental results of Hall et al. and empirical formulas raised by Macdonald and Shao et al. |
PDF Full Text Request