Wind turbine icing often occurs in winter, which changes the aerodynamic characteristics of the blades and reduces the work efficiency of the wind turbine. In this paper, the glaze ice model is established for horizontal-axis wind turbine in 3-D. The model contains the grid generation, two-phase simulation, heat and mass transfer. Results show that smaller wind turbine suffers from more serious icing problem, which reflects on a larger ice thickness. Both the collision efficiency and heat transfer coefficient increase under smaller size condition.
Blade profile changes lift and drag on the surface. So it is necessary to measure the power change of the wind turbine in the cold area by simulating the icing process. Computational fluid dynamics is considered as an effective method to predict ice accumulation. In this paper, the formation process of glaze ice was simulated by heat and mass transfer balance. The numerical calculation of 3-d blades was optimized by node interpolation and time step. Results show that the collision coefficient and ice shape would be changed by increasing the number of grid nodes. Through multi-step time iteration, it is easier to get the biangular ice in line with the actual situation.
With TC data from 1949 to 2005,we analyzes the situation of TC influence the waters around 200km of Dongsha Islands.The results indicated that in recent 56 years there were 288 TC affecting Dongsha Island seas,in frequency of 5 times per year.Since 2000,the affects tended to decrease.Secondly,the first TC influence occurred on April 9 and the latest December 27.The third,July,August and September were the seasons TC influenced the most,in approximately the rate 2/3 of the total.The ranks STS and TY were composed approximately 1/2 of the total.The last,there were 40 TC affected the areas in recent 10 years.The average wind power was about 22m/s with maximum wind speed at 55m/s.
In order to have better medium-range forecasts of flood-causing torrential rains in the Xijiang river valley,the characteristics of low-frequency oscillations of rainfall in the valley and wind field at 850 hPa are studied,with wavelet transform and Lanczos filter,for 13 cases of such rains since 1961.The effect is studied of low-frequency propagation of 850 hPa wind field on the rains in the region.Using composite analysis,an atmospheric circulation model is constructed of quasi-biweekly oscillation of the rains that are caused by westerly systems.Results show that the rainfall exhibits mainly quasi-biweekly oscillations with periods of 10 to 20 days,which correspond well with the positive phase of 8 to 35 day oscillations of the wind field at 850 hPa.The convergence over the valley between low-frequency zonal winds—either propagating northward from areas south of the valley or travelling southward from areas near 30 oN while strengthening—and those going westward from the northwest Pacific,is one of the possible causes of the quasi-biweekly oscillation of the flood-causing torrential rains in this region.When the rain begins and develops to its maximum intensity gradually,the high ridge east of the Balkhash Lake begins to rise and moves eastwards gradually,an apparent low trough in North China gradually controls an area from Northeast China to the lower reaches of the Yangtze River,while South China is controlled by a deep upper-level trough taking the place of a weak westerly trough east of Qinghai-Tibet Plateau.The subtropical high keeps enhancing and moving westwards,Southwest Monsoon coming from the Bay of Bengal and going through India-China Peninsula at 850 hPa continually strengthens,and a weak cyclonic curvature of streamlines west of a jet stream axis located over South China continually enhances,all at the same time.Sea level pressure appears to be higher in the east and lower in the west and its isobars exhibit significant meridionality.These are beneficial to medium-range forecast of flood-causing torrential rains in the Xijiang river valley.
Cu2O thin film was fabricated by electrochemical depositon using ITO and Cu strip as working electrode.The effect of temperatrue and pH value on the microstructure,surface morphology and current density of Cu2O thin films were studied by XRD and SEM,the growth mechanism was also discussed.The reults indicate that the temperature has little effect on the microstructure of Cu2O thin film,and the pH value has obvious influence on the preferential orientation.Under the action of double electrodeposition,the working current of as-prepared Cu2O thin film could reached 6 mA·cm-2,higher than the current by using a three-electrode system(1 mA·cm-2).
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)