I am working on Heart valve design. B.C for my model is pressure based. I provided inlet as pressure_inlet and outlet as pressure_outlet using udf. Total time of cardiac cycle is the analysis time i;e 0.86 s. For the first 0.2 s inlet pressure is more and for rest of time outlet pressure is more. But in my analysis backflow starts from the vary first step. How to deal with this?

thanking you!