旋流喷嘴作为造雪机关键部件,其雾化效果直接影响成雪效果。为进一步探索旋流喷嘴雾化特性,基于VOF to DPM模型,建立旋流喷嘴雾化的数值模型,对旋流喷嘴进行三维数值模拟。研究不同入口压力对液滴粒径、液滴速度等雾化特性的影响,并通...旋流喷嘴作为造雪机关键部件,其雾化效果直接影响成雪效果。为进一步探索旋流喷嘴雾化特性,基于VOF to DPM模型,建立旋流喷嘴雾化的数值模型,对旋流喷嘴进行三维数值模拟。研究不同入口压力对液滴粒径、液滴速度等雾化特性的影响,并通过实验验证了模型的准确性。结果表明,喷雾充分发展后,索特平均粒径随入口压力的增大而减小,入口压力增大,增强了液体和空气之间的气动不稳定性,促进了液体的破碎分解,缩短了液体所需破碎时间;液膜和液滴速度都随着入口压力的增大而增大,当入口压力由0.6 MPa增大到1.4 MPa时,出口液膜和液滴速度分别增加58.8%和52.2%;在破碎过程中,动能转化为表面能,会使液体速度发生削减。展开更多
Background： Pacing, defined as percentage changes of speed between successive splits, has been extensively studied in running and cycling endurance sports; however, less information about the trends in change of spee...Background： Pacing, defined as percentage changes of speed between successive splits, has been extensively studied in running and cycling endurance sports; however, less information about the trends in change of speed during cross-country （XC） ski racing is available. Therefore, the aim of the present study was to examine the effect of performance （quartiles of race time （Q）, with Q1 the fastest and Q4 the slowest） level on pacing in the Vasaloppet ski race, the largest XC skiing race in the world. Methods： For this purpose, we analyzed female （n = 19,465） and male （n = 164,454） finishers in the Vasaloppet ski race from 2004 to 2017 using a one-way （2 sexes） analysis of variance with repeated measures to examine percentage changes of speed between 2 successive splits. Overall, the race consisted of 8 splits. Results： The race speeds of Q1, Q2, Q3, and Q4 were 13.6 ± 1.8, 10.6 ± 0.5, 9.2 ± 0.3, and 8.1 ±- 0.4 km/h, respectively, among females and 16.7 ± 1.7, 13.1 ± 0.7, 10.9 ± 0.6, and 8.9 ± 0.7 km/h, respectively, among males. The overall pacing strategy of finishers was variable. A small sex × split interaction on speed was observed （η^2= 0.016, p 〈 0.001）, with speed difference between sexes ranging from 14.9% （Split 7） to 27.0% （Split 1） and larger changes in speed between 2 successive splits being shown for females （p 〈 0.001, η^2=0.004）. A large performance × split interaction on speed, with Q1 presenting the smallest changes of speed between splits, was shown for females （η^2= 0.149, p 〈 0.001） and males （η^2 = 0.169,p 〈 0.001）. Conclusion： Male and fast XC skiers are more even pacers. Coaches and athletes should develop tailored sex- and performance-level pacing strategies; for instance, they should advise fast XC skiers to start fast and maintain their speed, rather than starting slowly and trying to make up time by going faster at times during the race.2018 Published by Elsevier B.V. on behalf of Shanghai University of Sport. This is an open access article under the CC BY-NC-ND license. （http：//creativecommons.org/licenses/by-nc-nd/4.0/）.展开更多
文摘旋流喷嘴作为造雪机关键部件,其雾化效果直接影响成雪效果。为进一步探索旋流喷嘴雾化特性,基于VOF to DPM模型,建立旋流喷嘴雾化的数值模型,对旋流喷嘴进行三维数值模拟。研究不同入口压力对液滴粒径、液滴速度等雾化特性的影响,并通过实验验证了模型的准确性。结果表明,喷雾充分发展后,索特平均粒径随入口压力的增大而减小,入口压力增大,增强了液体和空气之间的气动不稳定性,促进了液体的破碎分解,缩短了液体所需破碎时间;液膜和液滴速度都随着入口压力的增大而增大,当入口压力由0.6 MPa增大到1.4 MPa时,出口液膜和液滴速度分别增加58.8%和52.2%;在破碎过程中,动能转化为表面能,会使液体速度发生削减。
文摘Background： Pacing, defined as percentage changes of speed between successive splits, has been extensively studied in running and cycling endurance sports; however, less information about the trends in change of speed during cross-country （XC） ski racing is available. Therefore, the aim of the present study was to examine the effect of performance （quartiles of race time （Q）, with Q1 the fastest and Q4 the slowest） level on pacing in the Vasaloppet ski race, the largest XC skiing race in the world. Methods： For this purpose, we analyzed female （n = 19,465） and male （n = 164,454） finishers in the Vasaloppet ski race from 2004 to 2017 using a one-way （2 sexes） analysis of variance with repeated measures to examine percentage changes of speed between 2 successive splits. Overall, the race consisted of 8 splits. Results： The race speeds of Q1, Q2, Q3, and Q4 were 13.6 ± 1.8, 10.6 ± 0.5, 9.2 ± 0.3, and 8.1 ±- 0.4 km/h, respectively, among females and 16.7 ± 1.7, 13.1 ± 0.7, 10.9 ± 0.6, and 8.9 ± 0.7 km/h, respectively, among males. The overall pacing strategy of finishers was variable. A small sex × split interaction on speed was observed （η^2= 0.016, p 〈 0.001）, with speed difference between sexes ranging from 14.9% （Split 7） to 27.0% （Split 1） and larger changes in speed between 2 successive splits being shown for females （p 〈 0.001, η^2=0.004）. A large performance × split interaction on speed, with Q1 presenting the smallest changes of speed between splits, was shown for females （η^2= 0.149, p 〈 0.001） and males （η^2 = 0.169,p 〈 0.001）. Conclusion： Male and fast XC skiers are more even pacers. Coaches and athletes should develop tailored sex- and performance-level pacing strategies; for instance, they should advise fast XC skiers to start fast and maintain their speed, rather than starting slowly and trying to make up time by going faster at times during the race.2018 Published by Elsevier B.V. on behalf of Shanghai University of Sport. This is an open access article under the CC BY-NC-ND license. （http：//creativecommons.org/licenses/by-nc-nd/4.0/）.
