Taichi Maki

Three dimensional numerical simulation of the flow over complex terrain with windbreak hedge

Abstract In order to clarify the effects of windbreaks on flow and to determine where to set windbreaks for the optimum prevention of wind erosion in a complex terrain, a three-dimensional numerical model for simulating wind distribution over a real complex terrain with a variation of relative height less than 100 m is used. The three-dimensional, time-dependent Navier–Stokes equation written with generalized coordinates and the Smagorinsky-type scheme for turbulent parameterization are use in the model. Numerical simulations of windbreak effect on wind speed distribution over a sand dune are carried out by erecting windbreak hedges at different places. The influence of topography and windbreaks on wind distribution, for example the location of the maximum wind speed reduction, are well simulated. Thus, the best setting place of windbreaks for the prevention of wind erosion may be decided by simulating the wind distribution over real terrain using the model. An example, using a 2 m high windbreak hedge for preventing sand shifting around a barchan sand dune, which is 5 m high, 64 m wide and 96 m long, is given and the effect of the windbreak hedge is discussed. The simulation results show that the best place should be at 18–22 m in front of the top of the sand dune.

Agricultural Damage by Local Wind and Its Countermeasure

The airflow over mountains is formed on the Aso somma under conditions in stable stratification and the prevailing southeastly wind with a speed of over 10 m s^(-1) at 850 hPa pressure level. The wind converges in the valley of Aso somma, creating a strong easterly wind with a speed of over 20m s^(-1). This strong easterly wind is called as ”Matsubori Kaze”. ”Matsubori Kaze” is often generated in April and May. ”Matsubori Kaze” that blows at this period decreases the yield of wheat and barley. The yield of barley has decreased when the ”Matsubori Kaze” blows within 30 days after the heading time because ”Matsubori Kaze” removes the awn of barley, thus obstructing the ripening of the grain by eliminating photosynthesis by the awn. The awn of barley was removed at three years among investigations of four years, and the damage area was wide. On the other hand, the yield of wheat has decreased only when ”Matsubori Kaze” blows immediately before the harvest because ”Matsubori Kaze” causes the shedding of wheat. The shedding of wheat occurred only at one year, and the damage area was very limited. It is thought that wheat is more suitable for the cultivation in this region than barley.