Study of the effects of translation and roughness on tornado-like vortices by large-eddy simulations

• Similarity law still works even tornado is translating or ground is rough.
• To reproduce tornado in nature effects from translation have to be considered.
• Effects from ground roughness are not same for different types of tornadoes.

The numerical simulation by LES turbulent model for translating tornadoes and those over roughness was carried out in a Ward type simulator. The tornado translation was modeled by providing a relative motion on the ground and the roughness was simulated through adding a momentum source in the Navier–Stokes equation. The effects of translation and roughness on the flow fields of three typical tornado-like vortices, i.e., vortex breakdown, vortex touching down and multi-vortex, were investigated and the detailed velocity distributions, Reynolds stresses and the pressure on the ground were examined. The similarity of the flow fields after the introduction of translation and ground roughness was also studied. It was found that, at the high elevation, Vc and rc shows the same trend versus the external swirl ratio for stationary and translating tornadoes. However, if the ground is rough, the core radius at high elevation changes greatly. The ground roughness will expand the size of the core. But for the very small swirl ratio cases, the ground roughness shows the effect reducing the core size. The explanation for the evolution of the flow fields due to translation and ground roughness is provided.