In this work,the flow surrounding the train was obtained using a detached eddy simulation(DES)for slipstream analysis.Two different streamlined nose lengths were investigated:a short nose(4 m)and a long nose(9 m).The ...In this work,the flow surrounding the train was obtained using a detached eddy simulation(DES)for slipstream analysis.Two different streamlined nose lengths were investigated:a short nose(4 m)and a long nose(9 m).The time-average slipstream velocity and the time-average slipstream pressure along the car bodies were compared and explained in detail.In addition to the time-averaged values,the _(max)imum velocities and the pressure peak-to-peak values around the two trains were analyzed.The result showed that the nose length affected the slipstream velocity along the entire train length at the lower and upper regions of the side of the train.However,no significant effect was recognized at the middle height of the train along its length,except in the nose region.Moreover,within the train’s side regions(y=2.0-2.5 m and z=2-4 m)and(y=2.5-3.5 m and z=0.2-0.7 m),the ratio of slipstream velocity U_(max) between the short and long nose trains was notably higher.This occurrence also manifested at the train’s upper section,specifically where y=0-2.5 m and z=4.2-5.0 m.Similarly,regarding the ratio of _(max)imum pressure peak-to-peak values Cp-p_(max),significant regions were observed at the train’s side(y=1.8-2.6 m and z=1-4 m)and above the train(y=0-2 m and z=3.9-4.8 m).展开更多
Coalbed gas non-Darcy flow has been observed in high permeable fracture systems,and some mathematical and numerical models have been proposed to study the effects of non-Darcy flow using Forchheimer non-Darcy model.Ho...Coalbed gas non-Darcy flow has been observed in high permeable fracture systems,and some mathematical and numerical models have been proposed to study the effects of non-Darcy flow using Forchheimer non-Darcy model.However,experimental results show that the assumption of a constant Forchheimer factor may cause some limitations in using Forchheimer model to describe non-Darcy flow in porous media.In order to investigate the effects of non-Darcy flow on coalbed methane production,this work presents a more general coalbed gas non-Darcy flow model according to Barree-Conway equation,which could describe the entire range of relationships between flow velocity and pressure gradient from low to high flow velocity.An expanded mixed finite element method is introduced to solve the coalbed gas non-Darcy flow model,in which the gas pressure and velocity can be approximated simultaneously.Error estimate results indicate that pressure and velocity could achieve first-order convergence rate.Non-Darcy simulation results indicate that the non-Darcy effect is significant in the zone near the wellbore,and with the distance from the wellbore increasing,the non-Darcy effect becomes weak gradually.From simulation results,we have also found that the non-Darcy effect is more significant at a lower bottom-hole pressure,and the gas production from non-Darcy flow is lower than the production from Darcy flow under the same permeable condition.展开更多
基金Project(52202426)supported by the National Natural Science Foundation of ChinaProjects(15205723,15226424)supported by the Research Grants Council of the Hong Kong Special Administrative Region(SAR),China+1 种基金Project(K2021J041)supported by the Technology Research and Development Program of China RailwayProject(1-BD23)supported by The Hong Kong Polytechnic University,China。
文摘In this work,the flow surrounding the train was obtained using a detached eddy simulation(DES)for slipstream analysis.Two different streamlined nose lengths were investigated:a short nose(4 m)and a long nose(9 m).The time-average slipstream velocity and the time-average slipstream pressure along the car bodies were compared and explained in detail.In addition to the time-averaged values,the _(max)imum velocities and the pressure peak-to-peak values around the two trains were analyzed.The result showed that the nose length affected the slipstream velocity along the entire train length at the lower and upper regions of the side of the train.However,no significant effect was recognized at the middle height of the train along its length,except in the nose region.Moreover,within the train’s side regions(y=2.0-2.5 m and z=2-4 m)and(y=2.5-3.5 m and z=0.2-0.7 m),the ratio of slipstream velocity U_(max) between the short and long nose trains was notably higher.This occurrence also manifested at the train’s upper section,specifically where y=0-2.5 m and z=4.2-5.0 m.Similarly,regarding the ratio of _(max)imum pressure peak-to-peak values Cp-p_(max),significant regions were observed at the train’s side(y=1.8-2.6 m and z=1-4 m)and above the train(y=0-2 m and z=3.9-4.8 m).
基金Projects(91330106,11171190)supported by the National Natural Science Foundation of ChinaProjects(15CX05065A,15CX05003A)supported by the Fundamental Research Funds for the Central Universities,China
文摘Coalbed gas non-Darcy flow has been observed in high permeable fracture systems,and some mathematical and numerical models have been proposed to study the effects of non-Darcy flow using Forchheimer non-Darcy model.However,experimental results show that the assumption of a constant Forchheimer factor may cause some limitations in using Forchheimer model to describe non-Darcy flow in porous media.In order to investigate the effects of non-Darcy flow on coalbed methane production,this work presents a more general coalbed gas non-Darcy flow model according to Barree-Conway equation,which could describe the entire range of relationships between flow velocity and pressure gradient from low to high flow velocity.An expanded mixed finite element method is introduced to solve the coalbed gas non-Darcy flow model,in which the gas pressure and velocity can be approximated simultaneously.Error estimate results indicate that pressure and velocity could achieve first-order convergence rate.Non-Darcy simulation results indicate that the non-Darcy effect is significant in the zone near the wellbore,and with the distance from the wellbore increasing,the non-Darcy effect becomes weak gradually.From simulation results,we have also found that the non-Darcy effect is more significant at a lower bottom-hole pressure,and the gas production from non-Darcy flow is lower than the production from Darcy flow under the same permeable condition.
