"Outflow" boundary in premixed sphere flames

[Alex-jian522]

Hello, I'm using PeleLMeX for a 2D premixed sphere flame. And I set the boudary conditions as follow (all four boundary conditions to be "outflow"):
#----------------------DOMAIN DEFINITION------------------------
geometry.is_periodic = 0 0 # For each dir, 0: non-perio, 1: periodic
geometry.coord_sys = 0 # 0 => cart, 1 => RZ
geometry.prob_lo = 0.0 0.0 0.0 # x_lo y_lo (z_lo)
geometry.prob_hi = 0.01 0.01 0.016 # x_hi y_hi (z_hi)

#>>>>>>>>>>>>> BC FLAGS <<<<<<<<<<<<<<<<
peleLM.lo_bc = Outflow Outflow
peleLM.hi_bc = Outflow Outflow

But from the velocity (and ave_pressure) contours, I found that the velocity at the four corners of the two-dimensional computational domain is almost 0, which is quite strange.

Is there something wrong with my boundary condition settings? Are there more suitable boundary conditions in PeleLMeX? Thank you very much for any reply.

[baperry2]

Relevant discussion from PeleC for reference: AMReX-Combustion/PeleC#753 (reply in thread)