# Why is there reverse flow in Fluent?

I am simulating a axial turbine and number of cell are about 3000000.

Under relaxation factors are as follows:

Pressure: 0.1

momentum:0.1

Turbulent kinetic energy: 0.5

Turbulent dissipation rate: 0.5

Velocity formulation is relative.

Turbulence model is K-E relizable. The convergence of solution is monitored by checking the residuals of the numerically solved governing equations. Moreover, in order to judge the convergence, the behaviour of other quantities, such as the total pressure at the inlet and outlet boundaries, and torque coefficient generated by the rotor, are also monitored. Here, the default convergence criterion of each residual is reduced in order to allow the monitored quantities to stagnate at consistent values. It seems that convergence is ok but there is reverse flow!! why?

residuals :

torque coefficient:

total pressure at the inlet and outlet boundaries:

Mass flow rate:

I continued this run and is as follows:

Residuals are almost constant. What is the reason?

Is convergence OK?

• I cannot cite any professional sources that say how much reverse flow is acceptable, however I can say from personal experience that many of my Fluent simulations, both steady and transient, contain warnings about reverse flow yet still produce correct results. I would not worry about reverse flow too much; the residuals of mass/momentum/energy/etc. are much more important for gauging solution convergence. To suppress reverse flow warnnigs, type into the text user interface (TUI): solve set flow-warnings? no – Carlton Nov 10 '15 at 18:33