hello,

i'm trying to simulate an airfoil in heaving motion, with a standard inlet velocity of u=1 and heaving amplitude equal to its chord.

at a low frequency of 0.5 or 1, the ans converge and i get a cyclic curve for both lift/darg coefficient.

however, when i increase f to 4, the max velocity reaches u~50. the cl reaches 1000+ and cd~400+, although it is still of a sinusodal shape. The time step also becomes very small, due to CFL condition.

my initial time step at f=4 is 1e-3 which means there's 250 time step per cycle. i even reduce time step to 2.5e-4 but worse... the ans explodes after a while.

btw, i'm using the ALE formulation and the whole grid simply moves as a whole, no deformation.

i don't think this is correct and i wonder what else can be done...

btw, Re=100 and increasing the grid size actually made matters worse....