[Arjun Jayakumar]

Hi...
I am new to openFoam, for the past week I am stuck with my problem. I am trying to simulate water falling on a circular tube surface. interFoam was selected as the base solver with dambreak as the base case.
slight modification were made with files of dambreak.

internalField was set as uniform 0. alpha.water for inlet as type fixedValue and value uniform 1. Wall B.C's as zeroGradient.

p_rgh B.C's
internalField uniform 0
walls as type fixedFluxPressure; value uniform 0;
inlet as type fixedValue; value uniform 0;

U B.C's
internalField uniform 0
wall as type fixedValue; value uniform (0 0 0);
inlet as type flowRateInletVelocity; massFlowRate constant 0.1; rhoInlet 1;

setFields as
defaultFieldValues
(
volScalarFieldValue alpha.water 0
);

After some time steps min(alpha1) deviates to too negative value. the terminal shows

Time = 0.000215

smoothSolver: Solving for alpha.water, Initial residual = 0.135945, Final residual = 4.85033e-09, No Iterations 6
Phase-1 volume fraction = -3.89404e-14 Min(alpha1) = -0.494288 Max(alpha1) = 1
MULES: Correcting alpha.water
MULES: Correcting alpha.water
Phase-1 volume fraction = -3.89404e-14 Min(alpha1) = -0.494288 Max(alpha1) = 1
DICPCG: Solving for p_rgh, Initial residual = 0.421282, Final residual = 0.0204154, No Iterations 6
time step continuity errors : sum local = 9.04479e-07, global = -1.89978e-07, cumulative = -5.23877e-07
DICPCG: Solving for p_rgh, Initial residual = 0.304169, Final residual = 0.0149129, No Iterations 5
time step continuity errors : sum local = 8.80687e-07, global = -1.71627e-07, cumulative = -6.95504e-07
DICPCG: Solving for p_rgh, Initial residual = 0.244908, Final residual = 9.59156e-08, No Iterations 462
time step continuity errors : sum local = 6.22699e-12, global = -1.30827e-14, cumulative = -6.95504e-07
ExecutionTime = 3316.69 s ClockTime = 4119 s

Courant Number mean: 5.63527e-05 max: 5.31579
Interface Courant Number mean: 2.13444e-06 max: 2.08533
Time = 0.00022

smoothSolver: Solving for alpha.water, Initial residual = 0.173116, Final residual = 5.69664e-09, No Iterations 14
Phase-1 volume fraction = -5.2177e-14 Min(alpha1) = -0.70481 Max(alpha1) = 1
MULES: Correcting alpha.water
MULES: Correcting alpha.water
Phase-1 volume fraction = -5.2177e-14 Min(alpha1) = -0.70481 Max(alpha1) = 1
DICPCG: Solving for p_rgh, Initial residual = 0.381394, Final residual = 0.0167599, No Iterations 10
time step continuity errors : sum local = 1.58839e-06, global = -2.25771e-07, cumulative = -9.21275e-07
DICPCG: Solving for p_rgh, Initial residual = 0.271973, Final residual = 0.0121764, No Iterations 5
time step continuity errors : sum local = 1.32254e-06, global = -6.32625e-08, cumulative = -9.84538e-07
DICPCG: Solving for p_rgh, Initial residual = 0.191749, Final residual = 9.99155e-08, No Iterations 469
time step continuity errors : sum local = 1.11654e-11, global = 9.08119e-14, cumulative = -9.84538e-07
ExecutionTime = 3398.03 s ClockTime = 4207 s

Courant Number mean: 8.40514e-05 max: 8.08132
Interface Courant Number mean: 4.53269e-06 max: 4.24642
Time = 0.000225

smoothSolver: Solving for alpha.water, Initial residual = 0.170608, Final residual = 3.34717e-09, No Iterations 10
Phase-1 volume fraction = -1.10859e-13 Min(alpha1) = -0.56912 Max(alpha1) = 1
MULES: Correcting alpha.water
MULES: Correcting alpha.water
Phase-1 volume fraction = -1.10859e-13 Min(alpha1) = -0.56912 Max(alpha1) = 1
DICPCG: Solving for p_rgh, Initial residual = 0.418703, Final residual = 0.0192012, No Iterations 5
time step continuity errors : sum local = 2.23831e-06, global = -6.45109e-08, cumulative = -1.04905e-06
DICPCG: Solving for p_rgh, Initial residual = 0.264399, Final residual = 0.0117227, No Iterations 5
time step continuity errors : sum local = 1.56011e-06, global = 2.27227e-07, cumulative = -8.21821e-07
DICPCG: Solving for p_rgh, Initial residual = 0.161567, Final residual = 9.91333e-08, No Iterations 465
time step continuity errors : sum local = 1.33674e-11, global = -9.29279e-14, cumulative = -8.21821e-07
ExecutionTime = 3476.99 s ClockTime = 4294 s

Courant Number mean: 0.000106596 max: 9.31549
Interface Courant Number mean: 5.9444e-06 max: 3.21124
Time = 0.00023

smoothSolver: Solving for alpha.water, Initial residual = 0.174622, Final residual = 8.06469e-09, No Iterations 8
Phase-1 volume fraction = -1.36574e-13 Min(alpha1) = -1.08339 Max(alpha1) = 1
MULES: Correcting alpha.water
MULES: Correcting alpha.water
Phase-1 volume fraction = -1.36574e-13 Min(alpha1) = -1.08339 Max(alpha1) = 1
DICPCG: Solving for p_rgh, Initial residual = 0.563562, Final residual = 0.0271184, No Iterations 4
time step continuity errors : sum local = 3.22933e-06, global = -3.09184e-07, cumulative = -1.13101e-06
DICPCG: Solving for p_rgh, Initial residual = 0.325179, Final residual = 0.0159427, No Iterations 5
time step continuity errors : sum local = 2.12216e-06, global = -2.7194e-07, cumulative = -1.40295e-06
DICPCG: Solving for p_rgh, Initial residual = 0.218524, Final residual = 9.34715e-08, No Iterations 480
time step continuity errors : sum local = 1.2633e-11, global = 8.28896e-14, cumulative = -1.40295e-06
ExecutionTime = 3557.34 s ClockTime = 4382 s

Courant Number mean: 0.000124486 max: 9.14801
Interface Courant Number mean: 5.45008e-06 max: 1.54779
Time = 0.000235

smoothSolver: Solving for alpha.water, Initial residual = 0.203736, Final residual = 9.52402e-09, No Iterations 17
Phase-1 volume fraction = -3.94801e-13 Min(alpha1) = -0.606969 Max(alpha1) = 1
MULES: Correcting alpha.water
MULES: Correcting alpha.water
Phase-1 volume fraction = -3.94801e-13 Min(alpha1) = -0.606969 Max(alpha1) = 1
DICPCG: Solving for p_rgh, Initial residual = 0.110379, Final residual = 0.00435067, No Iterations 2
time step continuity errors : sum local = 9.18565e-06, global = -8.93057e-08, cumulative = -1.49225e-06
DICPCG: Solving for p_rgh, Initial residual = 0.0295617, Final residual = 0.00142974, No Iterations 5
time step continuity errors : sum local = 3.09834e-06, global = 3.46288e-07, cumulative = -1.14596e-06
DICPCG: Solving for p_rgh, Initial residual = 0.0228198, Final residual = 9.75055e-08, No Iterations 453
time step continuity errors : sum local = 2.164e-10, global = -9.17758e-13, cumulative = -1.14596e-06
ExecutionTime = 3635.92 s ClockTime = 4469 s

Courant Number mean: 0.000156587 max: 22.8963
Interface Courant Number mean: 7.49421e-06 max: 2.03706
Time = 0.00024

smoothSolver: Solving for alpha.water, Initial residual = 0.20387, Final residual = 3.9583e-09, No Iterations 13
Phase-1 volume fraction = 6.13117e-13 Min(alpha1) = -4.09164 Max(alpha1) = 1
MULES: Correcting alpha.water
MULES: Correcting alpha.water
Phase-1 volume fraction = 6.13117e-13 Min(alpha1) = -4.09164 Max(alpha1) = 1
DICPCG: Solving for p_rgh, Initial residual = 0.749905, Final residual = 0.0333727, No Iterations 9
time step continuity errors : sum local = 9.46227e-06, global = -3.61406e-06, cumulative = -4.76002e-06
DICPCG: Solving for p_rgh, Initial residual = 0.307627, Final residual = 0.01456, No Iterations 6
time step continuity errors : sum local = 6.64208e-06, global = -1.50695e-06, cumulative = -6.26697e-06
DICPCG: Solving for p_rgh, Initial residual = 0.160218, Final residual = 9.90744e-08, No Iterations 489
time step continuity errors : sum local = 4.83966e-11, global = 2.85499e-13, cumulative = -6.26697e-06
ExecutionTime = 3718.94 s ClockTime = 4560 s

Courant Number mean: 0.000414007 max: 145.401
Interface Courant Number mean: 9.92862e-06 max: 5.30545
Time = 0.000245

smoothSolver: Solving for alpha.water, Initial residual = 0.426234, Final residual = 8.67918e-09, No Iterations 50
Phase-1 volume fraction = -6.7424e-14 Min(alpha1) = -5.62255 Max(alpha1) = 1
MULES: Correcting alpha.water
MULES: Correcting alpha.water
Phase-1 volume fraction = -6.7424e-14 Min(alpha1) = -5.54044 Max(alpha1) = 1.9061
DICPCG: Solving for p_rgh, Initial residual = 0.801868, Final residual = 0.0396942, No Iterations 4
time step continuity errors : sum local = 2.10043e-05, global = -7.37201e-06, cumulative = -1.3639e-05
DICPCG: Solving for p_rgh, Initial residual = 0.166809, Final residual = 0.00802116, No Iterations 6
time step continuity errors : sum local = 2.94754e-05, global = -1.06916e-05, cumulative = -2.43305e-05
exit
DICPCG: Solving for p_rgh, Initial residual = 0.330884, Final residual = 9.89421e-08, No Iterations 501
time step continuity errors : sum local = 3.14305e-10, global = 6.02658e-13, cumulative = -2.43305e-05
ExecutionTime = 3811.48 s ClockTime = 4667 s

Courant Number mean: 0.00181847 max: 479.069
Interface Courant Number mean: 0.000605703 max: 479.069
Time = 0.00025

smoothSolver: Solving for alpha.water, Initial residual = 0.702312, Final residual = 9.28023e-09, No Iterations 66
Phase-1 volume fraction = -3.41965e-12 Min(alpha1) = -18.9554 Max(alpha1) = 1
MULES: Correcting alpha.water
MULES: Correcting alpha.water
Phase-1 volume fraction = -3.41965e-12 Min(alpha1) = -15.4267 Max(alpha1) = 6.79324
DICPCG: Solving for p_rgh, Initial residual = 0.563373, Final residual = 0.0229745, No Iterations 5
time step continuity errors : sum local = 4.96062e-05, global = -1.45167e-05, cumulative = -3.88473e-05

really confused with what to do?
Thanks in advance.