flotran流体分析中，加了重力场，怎么计算不出流速？

lucky4231

即是想考虑在重力作用下，物体的流动状态。模型很简单，一弯管，进出口压力均设为0，边界施加无滑移约束，仅在重力作用下的流动。麻烦大家看看问题出在哪里啊？
ansys/flotran模块
命令流
finish
/clear
/prep7
et,1,fluid141
rectng,0,0.5,0,2
rectng,0,2,0,0.5
AOVLAP,1,2
/pnum,line,1
lplot
LFILLT,12,15,0.2, ,
al,2,4,5
aadd,all
esize,0.1
amesh,all
lplot
lsel,s,line,,12,15,1
lsel,a,line,,1,2,1
lsel,a,line,,9
nsll,s
d,all,vx
d,all,vy
allsel
lsel,s,line,,3,6,3
nsll,s
d,all,pres,0
allsel
acel,,9.81
FLDATA8,NOMI,DENS,1350
FLDATA8,NOMI,VISC,0.1
FLDATA2,ITER,EXEC,20
/solu
solve


查看结果时，什么也没有啊