Comprehensive windproof effects evaluation of low-coverage meadow paving layout forms based on numerical wind tunnel experiments

Abstract

The sustainability of the ecological system in Alpine regions is being increasingly threatened by grassland desertification under climate change conditions. In order to address this global issue, this study took the typical desertified grassland in the northeastern edge of the Tibetan Plateau, as a case, proposing a low-coverage meadow paving layout forms for mitigating wind and sand erosion. Six paving layout forms (“spacing strips” (SS-1, SS-1.5), “lattice-shaped” (LS-1, LS-2), checkerboard intervals“ (CI), “square intervals” (SI)) were designed and comprehensive analysis of their windproof effects were explored by numerical wind tunnel experiments. The patchy meadow is generalized as a porous medium and the porosity source terms were added to the RNG k-ε turbulence model to simulate the disturbance of the meadow on the airflow characteristics. The improved mathematical model was verified by the field experiments of Hesp et al. (2019). Following that, a series of numerical wind tunnel experiments were conducted on the 6 arrays, with the single meadow coverage of 40.00 %, at incoming wind speeds of 7 m/s (low), 11 m/s (medium) and 15 m/s (high) (wind speed is 2 m from the surface). In addition, this study uses flow field, windproof efficiency (E), downwind speed percentage (DSP), integrated cumulative distribution function of wind speeds below the threshold of 4.19 m/s in Maqu (P < 4.19 m/s) and economy to comprehensively evaluate the windproof effects based on the results of numerical wind tunnel experiments. Evaluation results based on individual index indicated that: (1) The meadow array significantly reduces the wind speed, and the meadow array pattern changes the airflow field around the meadow. (2) The E value in windproof areas for different meadow layouts ranking from largest to smallest is as follows: LS-1 > SS-1 > CI > SS-1.5 > LS-2 > SI. (3) Within the windproof area, the DSP of various meadow arrays revealed significant distribution differences, with significant reduction occurring especially for SS-1, SS-1.5, and LS. (4) As for the value of P_{<4.19 m/s}, the order from largest to smallest for the 6 layouts reveals a law of LS-1 > SS-1 > SS-1.5 > CI > LS-2 > SI. (5) The paving decrement compared to the full pavement ranking from largest to smallest is SS-1.5 > CI > SS-1 > SI > LS-2 > LS-1. Based on the comprehensive evaluation results, which consider ecological economic benefits, it can be concluded that SS-1 demonstrates superior effectiveness as a low-coverage wind and sand control mode for a single wind direction. On the other hand, LS is found to be more suitable for scenarios involving multiple wind directions or variable wind directions. The anticipated outcomes of this study are poised to offer a novel approach for managing wind and sand, as well as facilitating ecological restoration in the alpine desertified grassland in the future.