Negative absolute pressure for material model

avb

I am trying to simulate a model similar to Ideal Gas Compression in an Actuating Piston   . My velocity value is higher than what is being run in the example.

When i run the model for 2.5 m/sec velocity ,i get the error  *** ERROR: Negative absolute pressure for material model <air> .  However on reducing the velocity to 0.025m/sec, the model runs.   I am confused why this happening. 

PS: I am using ideal gas for air.   

acupro

Typically these negative pressure and/or negative temperature errors happen when the boundary condition or initial condition values are not consistent with the ideal gas density being a function of absolute temperature and absolute pressure.  For example, typically the outflow condition is pressure = 0.  But for ideal gas density, you may need to use pressure = 101325 instead.  Etc.

Or sometimes the initial conditions may not be close enough to a physical state that the pressure goes negative and causes failure.  You may need to run first with constant properties and correct boundary conditions to establish a reasonable flowfield - then do a restart with ideal gas density.

If you can attach the .inp, please do so.