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Field observations were performed to explore the variation of large-scale structure inclination angles in the high Reynolds number atmospheric surface layer (ASL). The high Reynolds number flow measurements [Reτ ∼ Ο (106)] were acquired at the Qingtu Lake observation array site. The structure inclination angles inferred from two-point correlations of the fluctuating streamwise velocity were obtained for different friction velocities in the neutral regime and different thermal stability conditions. Results indicate that, in addition to the Monin− Obukhov stability parameter, the structure inclination angle varies systematically with the friction velocity in the neutral surface layer. An empirical model is proposed to parametrize the variation of the inclination angle with the normalized friction velocity. The empirical formula agrees well with both the current ASL results and the previously documented results. Further analysis suggests that the inclination angle is dominated by the vertical velocity gradient (vertical wind shear) for both neutral and non-neutral regimes. The present work contributes to a better understanding of the inclination angle for the large-scale structures and may be used to improve the existing wall-models in the large-eddy simulation of the ASL.

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The electrification of sand particles plays an important role in aeolian events. In this paper, the charge-to-mass ratio vertical profiles of saltating particles in wind-blown sand were measured by a field experiments. By combining the results of field measurements with our previous wind-tunnel measurements, we discussed the factors affecting the charge-to-mass ratio of saltating particles. It reveals that the magnitude of the charge-to-mass ratio increases exponentially with height above the surface. In addition, the charge polarity of saltating particles depends on the relative size between saltating and creeping particles, and the magnitude of charge-to-mass ratio is determined by wind velocity and the relative size difference ratio between saltating and creeping particles.

This paper presents finite volume computations of turbulent flow through a square cross‐sectioned U‐bend of curvature strong enough (Rc/D =0.65) to cause separation. A zonal turbulence modelling approach is adopted, in which the high‐Re k‐ε model is used over most of the flow domain with the low‐Re, I‐equation model of k‐transport employed within the near‐wall regions. Computations with grids of different sizes and also with different discretization schemes, demonstrate that for this flow the solution of the k and ε equations is more sensitive to the scheme employed in their convective discretization than the solution of the mean flow equations. To avoid the use of extremely fine 3‐Dimensional grids, bounded high order schemes need to be used in the discretization of the turbulence transport equations. The predictions, while encouraging, displayed some deficiencies in the downstream region due to deficiencies in the turbulence model. Evidently, further refinements in the turbulence model are necessary. Initial computations of flow and heat transfer through a rotating U‐bend, indicate that at rotational numbers (Ro = ΩD/Wb) relevant to blade cooling passages, the Coriolis force can substantially modify the hydrodynamic and thermal behaviour.

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Recent observation results show that sand ripples and dunes are movable like those on Earth under current Martian climate. And the aeolian process on Mars therefore is re-attracting the eyes of scientific researchers in different fields. In this paper, the spatial and temporal evolution of wind-blown sand on Mars is simulated by the large-eddy simulation method. The simulations are conducted under the conditions of both friction wind speed higher and lower than the "fluid threshold", respectively. The fluid entrainment of the sand particles, the processes among saltation sand particles and sand bed, and the negative feedback of sand movement to flow field are considered. Our results show that the "overshoot" phenomenon also exists in the evolution of wind-blown sand on Mars both temporally and spatially; impact entrainment affects the sand transport rate on Mars when the wind speed is smaller or larger than the fluid threshold; and both the average saltation length and height are one order of magnitudes larger than those on Earth. Eventually, the formulas describing the sand transport rate, average saltation length and height on Mars are given, respectively.

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