Arctic observations and numerical simulations of surface wind effects on Multi-Angle Snowflake Camera measurements

Ground-based measurements of frozen precipitation are heavily influenced by interactions of surface winds with gauge-shield geometry. The Multi-Angle Snowflake Camera (MASC), which photographs hydrometeors in free-fall from three different angles while simultaneously measuring their fall speed, has been used in the field at multiple midlatitude and polar locations both with and without wind shielding. Here, we present an analysis of Arctic field observations – with and without a Belfort double Alter shield – and compare the results to computational fluid dynamics (CFD) simulations of the airflow and corresponding particle trajectories around the unshielded MASC. MASC-measured fall speeds compare well with Ka-band Atmospheric Radiation Measurement (ARM) Zenith Radar (KAZR) mean Doppler velocities only when winds are light (≤5ms-1) and the MASC is shielded. MASC-measured fall speeds that do not match KAZR-measured velocities tend to fall below a threshold value that increases approximately linearly with wind speed but is generally <0.5ms-1. For those events with wind speeds ≤1.5ms-1, hydrometeors fall with an orientation angle mode of 12∘ from the horizontal plane, and large, low-density aggregates are as much as 5 times more likely to be observed. Simulations in the absence of a wind shield show a separation of flow at the upstream side of the instrument, with an upward velocity component just above the aperture, which decreases the mean particle fall speed by 55 % (74 %) for a wind speed of 5 m s−1 (10 m s−1). We conclude that accurate MASC observations of the microphysical, orientation, and fall speed characteristics of snow particles require shielding by a double wind fence and restriction of analysis to events where winds are light (≤5ms-1). Hydrometeors do not generally fall in still air, so adjustments to these properties' distributions within natural turbulence remain to be determined.

A Study on the Effect of Wind Fences in Reducing Wind Velocity at Fruit Farms

Fruit growers install wind fences to prevent fruits from dropping. To examine the effect of wind fences in reducing wind velocity, this study conducted a performance experiment, a farmhouse model experiment, and analyzed how wind fences reduce wind velocity. Among the four types of wind fence with porosities ranging between 30% and 60%, the one with a porosity of 40% showed the highest performance. Findings from the reduced model experiment that used a wind tunnel showed that wind fences with a porosity of over 50% had a wind velocity reduction effect. In addition, the experiment found that the wind velocity reduction rate is affected by the installation distance of the wind fence.

Wind-Induced Vibration Analysis of Wind Fence Structure

As a new wind-break and dust-control technology, the wind fence is widely used at storage yards in factories and ports. The wind fence structure is a new high-rise wind-resistant structure with light damp and very heavy wind load, and the wind-induced vibration response is unknown and equivalent static wind load is hard to determine in design. Based on the Davenport spectrum, wind-induced vibration of the plane frame structure was analyzed with frequency domain method and the response spectrum of displacement and acceleration were obtained. The equivalent static wind load was studied and the wind-induced vibration coefficient and gust loading factor were gained. The results show that the wind-induced vibration response of the structure is significant, and it should be taken into consideration in structural design.