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Saltation transport rate in unsteady wind variations
1Key Laboratory of Mechanics on Disaster and Environment in Western China, Lanzhou University, 730000, Gansu, China, wping@lzu.edu.cn.
The European Physical Journal. E, Soft Matter
|May 24, 2014
Summary
Unsteady wind significantly impacts sand saltation, leading to higher transport rates than steady models predict. This research introduces a new formula for predicting sand transport under fluctuating wind conditions.
Area of Science:
- Earth and Atmospheric Sciences
- Geosciences
- Environmental Science
Background:
- Atmospheric boundary layer wind flow is typically turbulent.
- Gusty winds critically affect saltation transport, often simplified as equilibrium saltation.
- Existing models may inaccurately predict sand transport under unsteady wind conditions.
Purpose of the Study:
- To investigate the influence of periodical wind variations on sand saltation dynamics.
- To analyze the impact of wind fluctuation parameters on saltation response.
- To improve the prediction accuracy of sand transport rates under unsteady wind.
Main Methods:
- One-dimensional numerical simulations of unsteady sand saltation.
- Analysis of saltation response to varying wind parameters (amplitude, frequency).
- Comparison of unsteady and steady saltation transport rates.
Main Results:
- Unsteady transport rates consistently exceed those predicted by steady-state models for equivalent mean wind velocities.
- The ratio of unsteady to steady transport rates increases with wind fluctuation amplitude and frequency.
- Prediction errors for transport rates can exceed 200% for winds near the saltation threshold, compared to about 10% for higher velocities.
- Sand transport occurs even when average wind velocity is at or below the saltation threshold, unlike in steady models.
Conclusions:
- Periodical wind variations significantly alter sand saltation dynamics and transport rates.
- Steady-state models are inadequate for accurate sand transport prediction in gusty conditions, especially near the threshold.
- A novel unsteady transport rate prediction formula incorporating mean velocity, fluctuating intensity, and period is proposed.
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