The Variations of Wind over the Valley Topography of Baihetan Hydropower Station
Baihetan Hydropower Station,the second largest in the world,is located in a canyon over downstream of the Jinsha River.Frequent windy weather has an important impact on the construction and operation of the hydropower station.Based on the meteorological observation data around the hydropower station and its surrounding areas,this paper analyzes the variation characteristics of windy weather in the dam area,and uses the Canyon Wind Index(CWI)to evaluate the impact of terrain effect on the wind.The conclusions of the paper are as follows:(1)The most frequent wind direction and the average wind direction of the maximum wind speed at all stations of the dam area are either southerly wind and northerly wind,both along the direction of the canyon.The frequency of the northerly wind is higher than that of the southerly wind,indicating that the canyon terrain locks the direction of air flows.(2)Gales occur most frequently in the dam area in the dry season from November to May.The CWI shows that the effect of valley wind is stronger in the dry season than that in the rainy season.July to September is a transitional season that witnesses the change of the wind field,and the canyon wind effect is much weakened.The canyon wind effect is an important factor for the gales in the dam area.The daily variation of gale shows that the velocity is higher during the night and in the early morning than that in the rest of the day,and the canyon wind effect is more significant from 19:00 at night to 08:00 of the next day in the dry season.(3)The wind velocities of the northerly wind at the sites of Mabozi station and Hulukou Bridge in the dam area is compared,and the effect of narrow valley topography of the dam area on the wind speed is evaluated.It shows that when the air flow passes through the canyon,the velocity can be magnified by 1.27 times.The effect of narrow canyon can be best fit by the velocities of Mabozi and Hulukou Bridge when the velocity is between 5.0 and 11.5 m·s-1.For high velocities that are more than 11.5 m·s-1,however,the polynormal fit can better reflects the relationship of the velocities between the two sites.
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